2012 Vol. 30, No. 1
Display Method:
2012, 30(1): 1-19.
Abstract:
The hydrocarbone genernation is controlled by the source rocks and the heat. The source rock is the essential factor of the hydrocarbone formation and the heat is the subsidiary. The both are necessary factors. The interactional factors result in the hydrocarbon generation and distribution pattern. In China offshore, the sedimentary basins are of the stretch or extend slip depressions which formed in Tertiary. The synrift occurred in Paleogene. The thermal subsidence formed sequently in the earlymiddle Miocene. From late Miocene, the Neotectonic movement happened actively in a great number of basins. The source rocks formed mainly during the period of the paleogene synrifting. According to the characters of the sediments, the basins are divided into two groups, namely, the continental/terrestrial rift and the superimposed rift. The continental rift are the sags that the synrifting stratum are absolutely composed of the terrestrial sediments. The superimposed rift are the sags filled with the marine sediments or the onshoreoffshore sediments besides the terrestrial sediments. Bohai bay basin, Yellow Sea Basin, the northern of the pearl mouth basin and Beibuwan Basin are parts of the continental rifts. Those basins, located in the inner of the craton or the continental shelf, are assigned into the inside belt. The outside belt , consisted of the East China Sea Basin, Taixi basin, Taixinan basin and the southern of the pearl mouth basin, is situated in the active continental margin or the continental slope which is subjected to the passive continental margin. In the inside belt,the main source rocks are the middledeep lake facies mud which formed in the Paleocene, the Eocene and the Oligocene. The Eocene source rocks are dominated. In the outside belt, the source rocks are composed of the lake facies, the onshoreoffshore facies and the marine facies sediments and the onshoreoffshore facies is the main source rocks. The geologic age of the source rocks is similar with that of the inside belt but the EoceneOligocene is dominated. The source rocks of the lake facies are oilprone in the inside belt. The source rocks of the onshoreoffshore facies are gasprone in outside belt. The heat flow values are low or slight higer in the inside belt, but these are high or superhigher in the outside belt. Because of the coupling interaction of the source rocks and the geothermal field, the oilprone source rocks produce the oil in inside belt and the gasprone source rocks bring out the gas in the outside belt. The inside belt are the main oilproduced area and the exploration would focus on the liquid hydrocarbone. Whereas the outside belt would be the nature gas exploration. The oil exploration should be in Bohai bay basin, the northern of the south China sea and the Yellow sea basin, moreover, the nature gas exploration would be emphasized in the north continental slope of the South China sea and East China Sea basin.
The hydrocarbone genernation is controlled by the source rocks and the heat. The source rock is the essential factor of the hydrocarbone formation and the heat is the subsidiary. The both are necessary factors. The interactional factors result in the hydrocarbon generation and distribution pattern. In China offshore, the sedimentary basins are of the stretch or extend slip depressions which formed in Tertiary. The synrift occurred in Paleogene. The thermal subsidence formed sequently in the earlymiddle Miocene. From late Miocene, the Neotectonic movement happened actively in a great number of basins. The source rocks formed mainly during the period of the paleogene synrifting. According to the characters of the sediments, the basins are divided into two groups, namely, the continental/terrestrial rift and the superimposed rift. The continental rift are the sags that the synrifting stratum are absolutely composed of the terrestrial sediments. The superimposed rift are the sags filled with the marine sediments or the onshoreoffshore sediments besides the terrestrial sediments. Bohai bay basin, Yellow Sea Basin, the northern of the pearl mouth basin and Beibuwan Basin are parts of the continental rifts. Those basins, located in the inner of the craton or the continental shelf, are assigned into the inside belt. The outside belt , consisted of the East China Sea Basin, Taixi basin, Taixinan basin and the southern of the pearl mouth basin, is situated in the active continental margin or the continental slope which is subjected to the passive continental margin. In the inside belt,the main source rocks are the middledeep lake facies mud which formed in the Paleocene, the Eocene and the Oligocene. The Eocene source rocks are dominated. In the outside belt, the source rocks are composed of the lake facies, the onshoreoffshore facies and the marine facies sediments and the onshoreoffshore facies is the main source rocks. The geologic age of the source rocks is similar with that of the inside belt but the EoceneOligocene is dominated. The source rocks of the lake facies are oilprone in the inside belt. The source rocks of the onshoreoffshore facies are gasprone in outside belt. The heat flow values are low or slight higer in the inside belt, but these are high or superhigher in the outside belt. Because of the coupling interaction of the source rocks and the geothermal field, the oilprone source rocks produce the oil in inside belt and the gasprone source rocks bring out the gas in the outside belt. The inside belt are the main oilproduced area and the exploration would focus on the liquid hydrocarbone. Whereas the outside belt would be the nature gas exploration. The oil exploration should be in Bohai bay basin, the northern of the south China sea and the Yellow sea basin, moreover, the nature gas exploration would be emphasized in the north continental slope of the South China sea and East China Sea basin.
2012, 30(1): 20-32.
Abstract:
The origin of ooids represents a sedimentogical problem like an enigma. On the basis of experiment studies, Brehm et al. (2006) concluded that the ooid can be analogical to the stromatolite, i.e. the ooid is the product resulted from the activities of a special spherical microbial mat. Recently, studies on modern ooids in Bahamian Archipelago by Duguid et al. (2010) indicate that microbes do not play a role in ooid formation; thus, a new chemical model for the ooid formation has been proposed, i.e. whereby a veneer of ACC precipitates on an ooid while it is at the sediment water interface (the active phase) and this veneer of ACC later recrystallizes to aragonite needles and a new cortex layer is formed (the stationary phase). Two different views represent the new advances on studies of the ooid origin. Whereas, the particular microscopic fabrics for both the giant ooids of the lower Triassic in south China and the ooids of the Cambrian in north China provide more supporting evidence for the microbial origin of the ooid formation.
The origin of ooids represents a sedimentogical problem like an enigma. On the basis of experiment studies, Brehm et al. (2006) concluded that the ooid can be analogical to the stromatolite, i.e. the ooid is the product resulted from the activities of a special spherical microbial mat. Recently, studies on modern ooids in Bahamian Archipelago by Duguid et al. (2010) indicate that microbes do not play a role in ooid formation; thus, a new chemical model for the ooid formation has been proposed, i.e. whereby a veneer of ACC precipitates on an ooid while it is at the sediment water interface (the active phase) and this veneer of ACC later recrystallizes to aragonite needles and a new cortex layer is formed (the stationary phase). Two different views represent the new advances on studies of the ooid origin. Whereas, the particular microscopic fabrics for both the giant ooids of the lower Triassic in south China and the ooids of the Cambrian in north China provide more supporting evidence for the microbial origin of the ooid formation.
2012, 30(1): 33-42.
Abstract:
Jiantianba of Lichuan, western Hubei, is located in platform margin facies between carbonate platform facies in the eastern Sichuan and Western Hubei Trough. In the study area, the water gradually shallowed from the bottom to up in the stage of Changxing Formation of Late Permian, and developed a huge scale platform marginal reef deposition in aggradation progradation. Based on the multidisciplinary analysis of measured profiles, the authors discussed the reef composition and forming model of Changxing Formation reef in Jiantianba section. The study demonstrated that the study area developed two thirdorder sequences in Changxing depositional stage of late Permian and the body of reef in the Jiantianba of Lichuan was located in HST of sequence 1of Changxing Formation. And its internal constituted by the four parasequence sets. Pss1 mainly composed by dark grey lamellar or lamellar middle bedded cryptite, clastizoic cryptite, middle bedded bioclastic cryptite, the internal could be further divided into three parasequences namely PS2, PS3 and PS4. PS2 and PS3 were located in PSS1 lowermiddle part which are composed by a set of slope facies of lamellar dark gray mudstone deposit, and PS4 was located at the top of PSS1 and developed a set of gray middle lamellar bioclastic limestone with the shoal facies deposition and the reef of Jiantianba was developed on the basis of the above bioclastic bank. PSS2 was a platform edge bioherm deposition, developed a set of grey massive algae bonding, algal bondingbaffle and baffle bioconstructed limestone, this parasequence set internal developed three parasequences, and PS5 mainly was algae bondstone, the lower part of PS6 and PS7 mainly were algae bondstone, the upper part of PS6 and PS7 was algae bondbafflestone, which reflects the water shallow gradually, hydrodynamic stronger and bioherm prosperous gradually. PSS3 is mainly composed by a set of gray massive baffleframework reef limestone, sponge organic framework reef and partly limestone breccia, the internal can be further divided into three parasequences namely PS8 PS9 and PS10; With relative sea level further drops, frame builders extremely flouring and mainly are Sphinctozoa, Inozoa and little Sclerospongiae, Hydrozoa and Bryozoan, this period was flourishing period of reefs, this parasequence set constitutes the main deposition of platform margin reefs. PSS4 constituted by a mediumbedded and light gray bioclastic limestone with dolomite and remains of bioclastic dolomite, and belonged to platform edge and restricted platform deposition. As the relative sea level fell gradually and hydrodynamic force strengthening progressively, the reef in the Jiantianba of Lichuan experienced four stages of evolution, including a foundation, the initial flourishing, prosperous, and the largest decline of organic reef. Reefs in Jiantianba of Lichuan reservoir system mainly distributed at the top of the HST, the environment for the formation include platform edge bioherm, platform edge reef and restricted platform dolomite deposition at the top of reef, high quality reservoir is closely related to the reef composition and deposition conditions.
Jiantianba of Lichuan, western Hubei, is located in platform margin facies between carbonate platform facies in the eastern Sichuan and Western Hubei Trough. In the study area, the water gradually shallowed from the bottom to up in the stage of Changxing Formation of Late Permian, and developed a huge scale platform marginal reef deposition in aggradation progradation. Based on the multidisciplinary analysis of measured profiles, the authors discussed the reef composition and forming model of Changxing Formation reef in Jiantianba section. The study demonstrated that the study area developed two thirdorder sequences in Changxing depositional stage of late Permian and the body of reef in the Jiantianba of Lichuan was located in HST of sequence 1of Changxing Formation. And its internal constituted by the four parasequence sets. Pss1 mainly composed by dark grey lamellar or lamellar middle bedded cryptite, clastizoic cryptite, middle bedded bioclastic cryptite, the internal could be further divided into three parasequences namely PS2, PS3 and PS4. PS2 and PS3 were located in PSS1 lowermiddle part which are composed by a set of slope facies of lamellar dark gray mudstone deposit, and PS4 was located at the top of PSS1 and developed a set of gray middle lamellar bioclastic limestone with the shoal facies deposition and the reef of Jiantianba was developed on the basis of the above bioclastic bank. PSS2 was a platform edge bioherm deposition, developed a set of grey massive algae bonding, algal bondingbaffle and baffle bioconstructed limestone, this parasequence set internal developed three parasequences, and PS5 mainly was algae bondstone, the lower part of PS6 and PS7 mainly were algae bondstone, the upper part of PS6 and PS7 was algae bondbafflestone, which reflects the water shallow gradually, hydrodynamic stronger and bioherm prosperous gradually. PSS3 is mainly composed by a set of gray massive baffleframework reef limestone, sponge organic framework reef and partly limestone breccia, the internal can be further divided into three parasequences namely PS8 PS9 and PS10; With relative sea level further drops, frame builders extremely flouring and mainly are Sphinctozoa, Inozoa and little Sclerospongiae, Hydrozoa and Bryozoan, this period was flourishing period of reefs, this parasequence set constitutes the main deposition of platform margin reefs. PSS4 constituted by a mediumbedded and light gray bioclastic limestone with dolomite and remains of bioclastic dolomite, and belonged to platform edge and restricted platform deposition. As the relative sea level fell gradually and hydrodynamic force strengthening progressively, the reef in the Jiantianba of Lichuan experienced four stages of evolution, including a foundation, the initial flourishing, prosperous, and the largest decline of organic reef. Reefs in Jiantianba of Lichuan reservoir system mainly distributed at the top of the HST, the environment for the formation include platform edge bioherm, platform edge reef and restricted platform dolomite deposition at the top of reef, high quality reservoir is closely related to the reef composition and deposition conditions.
2012, 30(1): 43-53.
Abstract:
The upper Carboniferous phylloid algal reef and circumjacent limestone has undergone intensive diagenesis in the Bianping Village of Houchang Town, Ziyun County, the cements，signs of the effect of the diagenesis, are prominent and representative in the region of Houchang Town. The diagenesis of phylloid algal reef limestone are studied in detail by means of rock outcrop and slab and thin section analysis and observation using polarising microscope, alizarin red and potassium ferricyanide staining, cathodoluminescence. Diagenetic environments in the reef limestone are recognized, paragenetic sequences determined, diagenetic stages divided, and the diagenetic history reconstructed . The main types of the diagenesis include micritization, cementation, neomorphism, physical compaction, dissolution, shear or hightemperature recrystallization, fracturing, etc. Among the processes, cementation, neomorphism, dissolution affect rock over a long time, intensively, having various appearances. During syndiagenetic stage, sediment rich in the fragments of phylloid algal thalli had high porosity and largely preserved shelter porosity, micritization and cementation occurs extensively, marine botryoidal cement and acicular cement grew in pores; whereas bioclastic wackestone and packstone sediment poor in the fragments of phylloid algal thalli generally had low porosity and permeability, micrite cement grew in pores. There were light compaction and dissolution, and cementation that play a key role in the diagenetic process of the reef limestone, during early diagenetic stage. Cementation supplied a great deal cements, including blocky calcite spar and calcite microspar precipitated in small pores, and radiating cement fans grew in big pores. Cementation constructed rock framework, and consequently decided the features of the limestone rock. During epidiagenetic stag, vuggy or channel porosity was created by intense meteoric dissolution in the recharge area; meteoric phreatic cements precipitated in downflow areas, including isopachous columnar cement, and equant and blocky calcite cement, isopachous columnar cement is volumetrically more abundant. So far the porosity of the reef limestone bad been reduced dramatically through earlystage cementation, so the reef limestone could prevent mechanical compaction. During middle and late diagenetic stage, nearly occluded porosity was filled with isopachous bladed cement and coarse drusy or blocky calcite spar because of low rates of fluid influx and efflux, making total porosity in the reef limestone reduce to approximately zero. Preexisting cements were altered on the hydrocarbon composition and color, but the crystal fabrics unaltered. The color of isopachous bladed to columnar calcite cement changed from gray to white, and the color of botryoidal cement became more blackish due to hydrocarbon infiltration. A little isopachous bladed to columnar calcite cement were dissolved, leaving mouldic pores filled subsequently. Construction fracturing is one of the main types of diagenesis that took place during catagenesis stage. Rusty microcrystalline layers containing Fe2O3 lining the wall of some fractures, and vadose pisoids and ferrugineous crystal silt containing Fe2O3 deposited at the bottom of the cavities formed in the tectonic fractures, indicate that they formed in oxidizing vadose environments. Most fractures are filled with white or green bladed cement and clear coarse sparry calcite cement, the middle part of some fractures is filled with bitumen block. Nearly all twins in calcite filling fractures are thicker than 1μm, therefore it can be derived that the thick twins deformed at the temperature above 200℃. So the phylloid algal reef limestone was again buried deeper than 2.8km during catagenesis stage. This indicates that the Nanpanjiang Basin has undergone frequent elevationsubsidence. It might be a reason for that the phylloid algal reef limestone did not become oil and gas reservoirs that the pores of the phylloid algal reef limestone were occluded by burial cement. Only limestone that has large interconnected secondary pores generated during catagenesis stage could become oil and gas reservoirs in the Nanpanjiang Basin.
The upper Carboniferous phylloid algal reef and circumjacent limestone has undergone intensive diagenesis in the Bianping Village of Houchang Town, Ziyun County, the cements，signs of the effect of the diagenesis, are prominent and representative in the region of Houchang Town. The diagenesis of phylloid algal reef limestone are studied in detail by means of rock outcrop and slab and thin section analysis and observation using polarising microscope, alizarin red and potassium ferricyanide staining, cathodoluminescence. Diagenetic environments in the reef limestone are recognized, paragenetic sequences determined, diagenetic stages divided, and the diagenetic history reconstructed . The main types of the diagenesis include micritization, cementation, neomorphism, physical compaction, dissolution, shear or hightemperature recrystallization, fracturing, etc. Among the processes, cementation, neomorphism, dissolution affect rock over a long time, intensively, having various appearances. During syndiagenetic stage, sediment rich in the fragments of phylloid algal thalli had high porosity and largely preserved shelter porosity, micritization and cementation occurs extensively, marine botryoidal cement and acicular cement grew in pores; whereas bioclastic wackestone and packstone sediment poor in the fragments of phylloid algal thalli generally had low porosity and permeability, micrite cement grew in pores. There were light compaction and dissolution, and cementation that play a key role in the diagenetic process of the reef limestone, during early diagenetic stage. Cementation supplied a great deal cements, including blocky calcite spar and calcite microspar precipitated in small pores, and radiating cement fans grew in big pores. Cementation constructed rock framework, and consequently decided the features of the limestone rock. During epidiagenetic stag, vuggy or channel porosity was created by intense meteoric dissolution in the recharge area; meteoric phreatic cements precipitated in downflow areas, including isopachous columnar cement, and equant and blocky calcite cement, isopachous columnar cement is volumetrically more abundant. So far the porosity of the reef limestone bad been reduced dramatically through earlystage cementation, so the reef limestone could prevent mechanical compaction. During middle and late diagenetic stage, nearly occluded porosity was filled with isopachous bladed cement and coarse drusy or blocky calcite spar because of low rates of fluid influx and efflux, making total porosity in the reef limestone reduce to approximately zero. Preexisting cements were altered on the hydrocarbon composition and color, but the crystal fabrics unaltered. The color of isopachous bladed to columnar calcite cement changed from gray to white, and the color of botryoidal cement became more blackish due to hydrocarbon infiltration. A little isopachous bladed to columnar calcite cement were dissolved, leaving mouldic pores filled subsequently. Construction fracturing is one of the main types of diagenesis that took place during catagenesis stage. Rusty microcrystalline layers containing Fe2O3 lining the wall of some fractures, and vadose pisoids and ferrugineous crystal silt containing Fe2O3 deposited at the bottom of the cavities formed in the tectonic fractures, indicate that they formed in oxidizing vadose environments. Most fractures are filled with white or green bladed cement and clear coarse sparry calcite cement, the middle part of some fractures is filled with bitumen block. Nearly all twins in calcite filling fractures are thicker than 1μm, therefore it can be derived that the thick twins deformed at the temperature above 200℃. So the phylloid algal reef limestone was again buried deeper than 2.8km during catagenesis stage. This indicates that the Nanpanjiang Basin has undergone frequent elevationsubsidence. It might be a reason for that the phylloid algal reef limestone did not become oil and gas reservoirs that the pores of the phylloid algal reef limestone were occluded by burial cement. Only limestone that has large interconnected secondary pores generated during catagenesis stage could become oil and gas reservoirs in the Nanpanjiang Basin.
2012, 30(1): 54-64.
Abstract:
The Bayan Har sedimentary basin has been a hotspot and key area in studying QinghaiTibet Plateau geotectonics and Tethys, which is located in the northeast of QinghaiTibet Plateau hinderland. The domination sedimention of Bayan Har basin which has some different sizes of limestone platforms or limestone mounds are composed of Triassic turbidite rocks. In this paper, we study the sedimentary environment of hummocky limestone by the way of sedimentary petrology and geochemistry. Samples of this paper were collected from four isolated carbonate mounds on Long Stone Mountain of Bayan Har Basin, Qinghai province, which was developed in the Permian Triassic Maerzheng Formation strata with Ammonoid that produced a dark gray thinbedded micritic limestone and grayblack slate. XRD analysis showed that the average calcite content of hummocky limestone from Permian Triassic strata of Long Stone Mountain of Bayan Har Basin is up to 97%. Major element analysis showed that the CaO average content of hummocky limestone is up to 53.38%, so the CaO content is close to the theoretical value of calcite 56.03%, while Al2O3, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, TiO2 and others content are below 5 ‰. Those indicate that the chemical and minerals composition of carbonate are very pure. The shalenormalized REE patterns of 5% HNO3 soluble phase of limestone (carbonate minerals) showed total rare earth elements (ΣREE) were low, negative Ce anomaly , Eu was normal or slightly positive anomalies, Pr /Pr* was from 1.17 to 1.63. It is consistent with those of Permian limestone, Permian sea water, and modern eastern Pacific sea water and illustrated that it formed in oxidation environment of the open sea. The correlation coefficient between total rare earth (ΣREE) and Al, Cu, Zn, K and Ti were from 0.81 to 0.90 and showed a positive correlation, and the correlation coefficient between total rare earth (ΣREE) and Ca, Mg, Mn were from 0 to 0.33 and illustrated there was no obvious relevance or relevance. It is said that rare earth elements of hummocky limestone mainly related to the background value of sedimentary environment and has no matter with carbonate minerals. Hummocky limestone δ13CPDB were from +4.30‰ to +5.93‰ and δ18OPDB were from 13.72‰ to 11.27‰. δ13CPDB is basically consistent with the normal marine carbonate scope and indicating δ13CPDB remained the original sedimentary characteristics of hummocky limestone. But δ18OPDB was significantly affected by diagenesis and did not represent the original sedimentary features. The V / Cr ratios of limestone are very low, *Uau values are only from 0.08 μg/g to 0.5 μg/g, and the contents of U, V, Mo, Cr, Co, Cu and Zn elements, that were enriched in anoxic environment, are low or absent. All instructed that limestone formed in oxygenrich environment. All above sedimentary rocks and geochemical characteristics show that the Permian Triassic hummocky limestone might be the product of rapid deposition in relatively oxic environment of open sea.
The Bayan Har sedimentary basin has been a hotspot and key area in studying QinghaiTibet Plateau geotectonics and Tethys, which is located in the northeast of QinghaiTibet Plateau hinderland. The domination sedimention of Bayan Har basin which has some different sizes of limestone platforms or limestone mounds are composed of Triassic turbidite rocks. In this paper, we study the sedimentary environment of hummocky limestone by the way of sedimentary petrology and geochemistry. Samples of this paper were collected from four isolated carbonate mounds on Long Stone Mountain of Bayan Har Basin, Qinghai province, which was developed in the Permian Triassic Maerzheng Formation strata with Ammonoid that produced a dark gray thinbedded micritic limestone and grayblack slate. XRD analysis showed that the average calcite content of hummocky limestone from Permian Triassic strata of Long Stone Mountain of Bayan Har Basin is up to 97%. Major element analysis showed that the CaO average content of hummocky limestone is up to 53.38%, so the CaO content is close to the theoretical value of calcite 56.03%, while Al2O3, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, TiO2 and others content are below 5 ‰. Those indicate that the chemical and minerals composition of carbonate are very pure. The shalenormalized REE patterns of 5% HNO3 soluble phase of limestone (carbonate minerals) showed total rare earth elements (ΣREE) were low, negative Ce anomaly , Eu was normal or slightly positive anomalies, Pr /Pr* was from 1.17 to 1.63. It is consistent with those of Permian limestone, Permian sea water, and modern eastern Pacific sea water and illustrated that it formed in oxidation environment of the open sea. The correlation coefficient between total rare earth (ΣREE) and Al, Cu, Zn, K and Ti were from 0.81 to 0.90 and showed a positive correlation, and the correlation coefficient between total rare earth (ΣREE) and Ca, Mg, Mn were from 0 to 0.33 and illustrated there was no obvious relevance or relevance. It is said that rare earth elements of hummocky limestone mainly related to the background value of sedimentary environment and has no matter with carbonate minerals. Hummocky limestone δ13CPDB were from +4.30‰ to +5.93‰ and δ18OPDB were from 13.72‰ to 11.27‰. δ13CPDB is basically consistent with the normal marine carbonate scope and indicating δ13CPDB remained the original sedimentary characteristics of hummocky limestone. But δ18OPDB was significantly affected by diagenesis and did not represent the original sedimentary features. The V / Cr ratios of limestone are very low, *Uau values are only from 0.08 μg/g to 0.5 μg/g, and the contents of U, V, Mo, Cr, Co, Cu and Zn elements, that were enriched in anoxic environment, are low or absent. All instructed that limestone formed in oxygenrich environment. All above sedimentary rocks and geochemical characteristics show that the Permian Triassic hummocky limestone might be the product of rapid deposition in relatively oxic environment of open sea.
2012, 30(1): 65-72.
Abstract:
The recognition of carbonate origin in lake facies of the second Member of Funing Formation, the west slope of Jinhu Sag existed different vuewoaubts, so the major part of this research was the sedimentary facies of the carbonate rock. The main components of the carbonate rock were intraclast and bioclast, and other components were few ooide and crumb, the grain content of the rock were different, the content of different area were different, and the content of different formation were alike different; the matrix of the rock was micrite matrix, and cementing material of the rock was calcsparit cementing material. After the analysis of the components of carbonate rock, the conservation of fossil, the distributed law of the stratum thickness and cryptite, the conservation of fossil in the workarea was unbroken, the distributed law of the stratum thickness was obvious, the change of the stratum thickness was little; and the cryptite was distributed in all the area. So a kind sedimentary facies was established which was the carbonate terrace, the carbonate terrace was a kind of depositional system made up by the bioclastic limestone and cryptite, and it was a kind of standard carbonate formation formed in the strongweak hydrodynamic force environment. This facies can be classified into carbonate sheet, carbonate dam, and carbonate strand and corcass. In the plane, the water was shallow in the west part of the study area, and hydrodynamic force was powerful, so the carbonate dam and strand was developed; in the east, the water was deep, and hydrodynamic force was weak, so the carbonate terrace was developed, in longitudinal direction, the carbonate formation deposited from the E1f232 sublayer, the fastigium of the deposition was E1f222 sublayer, and declined in the E1f212 sublayer, the deposition formed a entire carbonate sedimentary system. Finally, the sedimentary model of the carbonate rock in Lake Facies was established.
The recognition of carbonate origin in lake facies of the second Member of Funing Formation, the west slope of Jinhu Sag existed different vuewoaubts, so the major part of this research was the sedimentary facies of the carbonate rock. The main components of the carbonate rock were intraclast and bioclast, and other components were few ooide and crumb, the grain content of the rock were different, the content of different area were different, and the content of different formation were alike different; the matrix of the rock was micrite matrix, and cementing material of the rock was calcsparit cementing material. After the analysis of the components of carbonate rock, the conservation of fossil, the distributed law of the stratum thickness and cryptite, the conservation of fossil in the workarea was unbroken, the distributed law of the stratum thickness was obvious, the change of the stratum thickness was little; and the cryptite was distributed in all the area. So a kind sedimentary facies was established which was the carbonate terrace, the carbonate terrace was a kind of depositional system made up by the bioclastic limestone and cryptite, and it was a kind of standard carbonate formation formed in the strongweak hydrodynamic force environment. This facies can be classified into carbonate sheet, carbonate dam, and carbonate strand and corcass. In the plane, the water was shallow in the west part of the study area, and hydrodynamic force was powerful, so the carbonate dam and strand was developed; in the east, the water was deep, and hydrodynamic force was weak, so the carbonate terrace was developed, in longitudinal direction, the carbonate formation deposited from the E1f232 sublayer, the fastigium of the deposition was E1f222 sublayer, and declined in the E1f212 sublayer, the deposition formed a entire carbonate sedimentary system. Finally, the sedimentary model of the carbonate rock in Lake Facies was established.
Analysis on Controlling Factors of Marine Sequence Stratigraphy Evolution in Pearl River Mouth Basin
2012, 30(1): 73-83.
Abstract:
The Pearl River Mouth basin transformed to a kind of quasipassive continental margin basin from a continental rifted lake basin after Nanhai movement, and then a set of continentaloceanic transitional facies formations and marine formations which are now the main oilproduction formation formed in Pearl River Mouth basin. The analysis on controlling factors of these sets of formations is useful to the thirdorder sequence stratigraphy division and correlation, and helpful to understand the type and structure of each sequence. Based on the analysis of marine sequence type and developing models of Zhuhai Formation to Yuehai Formation, the controlling factors of marine sequence stratigraphy evolution in Pearl River Mouth Basin are analyzed according to its configuration. It is considered that the tectonic movement, paleogeographic framework, relative sealevel change and sediment supply are the main controlling factors of marine sequence stratigraphy evolution. But these four factors have different effects at different times. The tectonic movement and paleogeographic framework play an important role to the development of sequence stratigraphy from late Oligocene to early Miocene when the basin framework made a great adjustment. Three important movements happened during the period of marine formation forming: the Nanhai movement and the Baiyun movement made the basin framework changed, and controlled the early depositional filling in the basin; The Dongsha movement made parts of basin serious uplift and denudation. These three movements all formed regional unconformities which make up of the secondorder sequence boundaries. The influence of paleogeographic framework on the sequence stratigraphy happened in the early period of marine sequence forming, which include the influence of palaeouplift topography, depression topography during the faultdepression stage and shelf breaks. During the peaceful period without tectonic movement, relative sealevel change and sediment supply become the main controlling factors. There is relative wide and smooth continental shelf in Pearl River Mouth Basin, and different types of sequence formed due to the degree of relative sea level fall. When there is a significantly large fall in sea level, reaching to shelf break, a type 1 unconformity develops, such as sequence boundary SB21、SB13.8 and SB10.5 in Pearl River Mouth Basin. When the sea level falling is of lesser magnitude,not reaching to shelf break, a type 2 unconformity develops, such as sequence boundary SB11.7, SB8.5 and SB6.3.In the early period of marine sequence forming, there are three kinds of sediment supply which are PaleoPearl River delta,Hanjiang delta and Dongsha uplift; but from late stage of Zhujiang Formation, the sediment supply of Paleopearl River delta become the main resources. Whereas the influence area of PaleoPearl River delta and other sediment supplies made the same sequence present different characters at different places.
The Pearl River Mouth basin transformed to a kind of quasipassive continental margin basin from a continental rifted lake basin after Nanhai movement, and then a set of continentaloceanic transitional facies formations and marine formations which are now the main oilproduction formation formed in Pearl River Mouth basin. The analysis on controlling factors of these sets of formations is useful to the thirdorder sequence stratigraphy division and correlation, and helpful to understand the type and structure of each sequence. Based on the analysis of marine sequence type and developing models of Zhuhai Formation to Yuehai Formation, the controlling factors of marine sequence stratigraphy evolution in Pearl River Mouth Basin are analyzed according to its configuration. It is considered that the tectonic movement, paleogeographic framework, relative sealevel change and sediment supply are the main controlling factors of marine sequence stratigraphy evolution. But these four factors have different effects at different times. The tectonic movement and paleogeographic framework play an important role to the development of sequence stratigraphy from late Oligocene to early Miocene when the basin framework made a great adjustment. Three important movements happened during the period of marine formation forming: the Nanhai movement and the Baiyun movement made the basin framework changed, and controlled the early depositional filling in the basin; The Dongsha movement made parts of basin serious uplift and denudation. These three movements all formed regional unconformities which make up of the secondorder sequence boundaries. The influence of paleogeographic framework on the sequence stratigraphy happened in the early period of marine sequence forming, which include the influence of palaeouplift topography, depression topography during the faultdepression stage and shelf breaks. During the peaceful period without tectonic movement, relative sealevel change and sediment supply become the main controlling factors. There is relative wide and smooth continental shelf in Pearl River Mouth Basin, and different types of sequence formed due to the degree of relative sea level fall. When there is a significantly large fall in sea level, reaching to shelf break, a type 1 unconformity develops, such as sequence boundary SB21、SB13.8 and SB10.5 in Pearl River Mouth Basin. When the sea level falling is of lesser magnitude,not reaching to shelf break, a type 2 unconformity develops, such as sequence boundary SB11.7, SB8.5 and SB6.3.In the early period of marine sequence forming, there are three kinds of sediment supply which are PaleoPearl River delta,Hanjiang delta and Dongsha uplift; but from late stage of Zhujiang Formation, the sediment supply of Paleopearl River delta become the main resources. Whereas the influence area of PaleoPearl River delta and other sediment supplies made the same sequence present different characters at different places.
2012, 30(1): 84-91.
Abstract:
Like Amaon fan and Mississippi fan, Bengal fan is a favorable field for investigating sedimentary process in deepwater. Considering lacking coring and well data, highresolution 3D seismic data from the study area was analyzed to study the architecture and evolution of sedimentary elements on the upper Bengal Fan. the area of interest belonged to deepwater region, and stratigraphy was formed in marine deposition. Six typical seismic facies have been identified, which were incised channel fill facies, gull wingshaped facies, wedgeshaped divergent facies, transparent facies, highamplitude parallel facies and lowamplitude parallel facies. Seismic Facies 1 was interpreted as coarsegrained deposits of abandoned channels. Seismic Facies 2 represented channellevee complex. Seismic Facies 3 was interpreted as finegrained levee sediments. Seismic Facies 4 represented mass transport deposits. Seismic Facies 5 was interpreted as lobes，which was different from sheet sand interpreted by predecessors. Seismic Facies 6 represented hemipelagic drapes and fills. On seismic profile lobex and channels display high amplitude, which means coarse lithology deposition, and may be good reservoirs. Through analysis of SN and EW seismic profiles reflection charateristics, seismic attribute planeform, we revealed the sedimentary evolution: during the period of SQ1, lobes were deposited, and turbidute flow tansported sediments far into basin; main deepwater elements of SQ2 were channels and levees, with channel migrating from SE to NW; Sedimentary elements of SQ3 were lobes, locally MTDs originated from slides, slumps and debris flow; channelleveed complex mainly dominated the stratigraphy of SQ4.
Like Amaon fan and Mississippi fan, Bengal fan is a favorable field for investigating sedimentary process in deepwater. Considering lacking coring and well data, highresolution 3D seismic data from the study area was analyzed to study the architecture and evolution of sedimentary elements on the upper Bengal Fan. the area of interest belonged to deepwater region, and stratigraphy was formed in marine deposition. Six typical seismic facies have been identified, which were incised channel fill facies, gull wingshaped facies, wedgeshaped divergent facies, transparent facies, highamplitude parallel facies and lowamplitude parallel facies. Seismic Facies 1 was interpreted as coarsegrained deposits of abandoned channels. Seismic Facies 2 represented channellevee complex. Seismic Facies 3 was interpreted as finegrained levee sediments. Seismic Facies 4 represented mass transport deposits. Seismic Facies 5 was interpreted as lobes，which was different from sheet sand interpreted by predecessors. Seismic Facies 6 represented hemipelagic drapes and fills. On seismic profile lobex and channels display high amplitude, which means coarse lithology deposition, and may be good reservoirs. Through analysis of SN and EW seismic profiles reflection charateristics, seismic attribute planeform, we revealed the sedimentary evolution: during the period of SQ1, lobes were deposited, and turbidute flow tansported sediments far into basin; main deepwater elements of SQ2 were channels and levees, with channel migrating from SE to NW; Sedimentary elements of SQ3 were lobes, locally MTDs originated from slides, slumps and debris flow; channelleveed complex mainly dominated the stratigraphy of SQ4.
2012, 30(1): 92-100.
Abstract:
In recent years, much more tightgas of the late Triassic Xujiahe Formation are discovered in Yuanba which is located in the northeastern Sichuan foreland basin in China, Sichuan Basin is about 1.9×106 km2 that evolved into foreland basin from Paleozoic platform in late Triassic. The basin is surrounded by the Longmen thrust belt(west), Jiangnan uplift(east),MichangDaba thrust belt(north) and Kangdian uplift(south). The provenance of Yuanba sedimentary rock come from Michang thrust belt, and the main sedimentary types are nonmarine braided delta and shallow lake Facies in Xujiahe Formation that can be divided into 5 rock section, Tx1, Tx3, Tx5 is shallow lake mudsiltstone and lateral continues, Tx2,Tx4 are sandstones deposited by braided river delta. Braided channels sandstones are developed extremely and overlap each other in vertical and continuous distribution. These characters are similar to the other areas of Sichuan basin. But quartz sandstones are found first in the upper Triassic Xujiahe Formation in Sichuan basin. Quartz sandstones are distributed at the bottom of Tx1 and interlayer Tx2 of Xujiahe in Yuanba, these quartz sandstones occurrence is particular that occur in unconformable surface of Tx1 and on the top of two layers lithic arenites of Tx2 that are composed of three rock section(Tx12 sandstone, Tx12 mudsiltstone and Tx32 sandstone). Results of our study point out that quartz sandstones are different depositional environment from lithic sandstones below which belong to deltaic deposits widely in highstand and early regressive systems tracts, whereas quartz sandstones are deposited in beach or tidal environment when the sea level rise rapidly, our analysis shows that quartz sandstones beach are long and narrow parallel to shoreline, and may be controlled by Michang Mount foredeep belt, but lithic sandstones braided delta below extend from north to south perpendicular to shoreline. Quartz arenites are easily recognized with lower GR log than other sandstones, and mainly very fine sands(Tx1) to fine sands(Tx2) with little clay or matrix grains, and have mature compositional and textural maturity. Quartz sandstones thickness is about 10 to 15 m in the study area. Because of strong digenesis process(Mesogenesis to Telogenesis), Xujiahe sandstones are tightgas reservoir with porosity ranging from 5.0%~11.0% and average permeability 1.9×10-3μm2. According to much more casting thinsection, the primary pores little occur in all kinds of sandstones. The secondary pores are major pore types that come from dissolution of minerals and fragments. Generally there are a few quartz sandstones reservoirs developed in Xujiahe Fm. but they have better reservoir conditions in Yuanba area because high density protogenetic fissure are developed in quartz grains of quartz sandstones, and these protogenetic fissure may be closed in diagenetic processes after deposition. When tectonic extrusion stress occur, new much fissures are produced and old reopened in quartz sandstones because quartz sandstones with cracks are easily broken, and immensely increase cracks density. Meanwhile, these fissures also induce a lot of dissolution process that improve porosity and connectivity of quartz sandstones reservoirs. According to casting thinsections, the main pore types of quartz sandstones are fissures that include long newborn cracks and short protogenetic cracks, and the secondly pore types are corrosion pores that distributed along fractures. Our analysis shows quartz sandstones as reservoirs related to provenance come from Michang thrust belt, quartz grains with cracks are not only in quartz sandstones, but also other kinds of sandstones for example lithic sandstones have quartz mineral with cracks in Yuanba area, so crack quartz maybe come from ancient source rocks.
In recent years, much more tightgas of the late Triassic Xujiahe Formation are discovered in Yuanba which is located in the northeastern Sichuan foreland basin in China, Sichuan Basin is about 1.9×106 km2 that evolved into foreland basin from Paleozoic platform in late Triassic. The basin is surrounded by the Longmen thrust belt(west), Jiangnan uplift(east),MichangDaba thrust belt(north) and Kangdian uplift(south). The provenance of Yuanba sedimentary rock come from Michang thrust belt, and the main sedimentary types are nonmarine braided delta and shallow lake Facies in Xujiahe Formation that can be divided into 5 rock section, Tx1, Tx3, Tx5 is shallow lake mudsiltstone and lateral continues, Tx2,Tx4 are sandstones deposited by braided river delta. Braided channels sandstones are developed extremely and overlap each other in vertical and continuous distribution. These characters are similar to the other areas of Sichuan basin. But quartz sandstones are found first in the upper Triassic Xujiahe Formation in Sichuan basin. Quartz sandstones are distributed at the bottom of Tx1 and interlayer Tx2 of Xujiahe in Yuanba, these quartz sandstones occurrence is particular that occur in unconformable surface of Tx1 and on the top of two layers lithic arenites of Tx2 that are composed of three rock section(Tx12 sandstone, Tx12 mudsiltstone and Tx32 sandstone). Results of our study point out that quartz sandstones are different depositional environment from lithic sandstones below which belong to deltaic deposits widely in highstand and early regressive systems tracts, whereas quartz sandstones are deposited in beach or tidal environment when the sea level rise rapidly, our analysis shows that quartz sandstones beach are long and narrow parallel to shoreline, and may be controlled by Michang Mount foredeep belt, but lithic sandstones braided delta below extend from north to south perpendicular to shoreline. Quartz arenites are easily recognized with lower GR log than other sandstones, and mainly very fine sands(Tx1) to fine sands(Tx2) with little clay or matrix grains, and have mature compositional and textural maturity. Quartz sandstones thickness is about 10 to 15 m in the study area. Because of strong digenesis process(Mesogenesis to Telogenesis), Xujiahe sandstones are tightgas reservoir with porosity ranging from 5.0%~11.0% and average permeability 1.9×10-3μm2. According to much more casting thinsection, the primary pores little occur in all kinds of sandstones. The secondary pores are major pore types that come from dissolution of minerals and fragments. Generally there are a few quartz sandstones reservoirs developed in Xujiahe Fm. but they have better reservoir conditions in Yuanba area because high density protogenetic fissure are developed in quartz grains of quartz sandstones, and these protogenetic fissure may be closed in diagenetic processes after deposition. When tectonic extrusion stress occur, new much fissures are produced and old reopened in quartz sandstones because quartz sandstones with cracks are easily broken, and immensely increase cracks density. Meanwhile, these fissures also induce a lot of dissolution process that improve porosity and connectivity of quartz sandstones reservoirs. According to casting thinsections, the main pore types of quartz sandstones are fissures that include long newborn cracks and short protogenetic cracks, and the secondly pore types are corrosion pores that distributed along fractures. Our analysis shows quartz sandstones as reservoirs related to provenance come from Michang thrust belt, quartz grains with cracks are not only in quartz sandstones, but also other kinds of sandstones for example lithic sandstones have quartz mineral with cracks in Yuanba area, so crack quartz maybe come from ancient source rocks.
2012, 30(1): 101-110.
Abstract:
The widespread sandstone in Xujiahe Fomation of the Upper Triassic, Sichuan Foreland Basin, is one of the most important exploration strata. With the exploration development of the gasfield, it needs to clarify the predominant factors that control the widespread sandstone developing to guide the further exploration and production. To elucidate the depositional mechanism and spacial arrangement of the the widespread sandstone, the sedimentary physical simulation method was adopted to transform the original geological conditions into physical model, on base of investigating the evolution of tectonic, ancient landform and sedimentary system, and so on. And the simulation parameters were taken into consideration and designed to study the mechanism of widespread sandstone through the simulation of flume experiment technology. Three provenances were designed in the experiment to incarnate the characteristics of sedimentary systems during different stages and at different locations under the multisource conditions. Six intervals were simulated to playback the sedimentary characteristics, by conducting the experiment which was designed referring to principle of simulation and natrural model method. The main controlling factors of widespread sandstone were concluded, by designed such as simulation parameters,such as flow, sediment flux,gradient,subsidence and lake level et al. Some preliminary conclusions are obtained as follows: 1.Under the gradual slope conditions, it is in the shallow areaat the depth of 2.3 cm, slope of 4 that distributary channels migrated frequently, where the area water passed became larger gradually. And so did the area where sandbody deposited and was retransformd, which was benefit for widespread sandstone developing. The sandbodies were universally thin and homogeneous. And the widththickness ratio of the deltas is grater than 98∶〖KG-*2〗1. 2.In the experiment, when the flux was 4.35 l/s and sediment content was 9.5 g/s, the channels branched and sandbodies moved forward. While was 0.49 l/s and 0.4 g/s, single channel developed and sandbodies were eroded. So the flux and sediment content of different water consociation helped widespread sandstone development. 3.With tectonic subsidence and accommodation extending, the sand sediment developed to sandbodies of certain scale. 4. With frequent changes of the lake level, sandbodies of each stage expanded to different directions in the plane and overriding in vertical. Besides, the lobes combinated laterally, widespread sandstone was easily developed. 5. In the experiment, convergence of 3 sources showed explain of the development of widespread sandstone. During 6th depositional stage, the lake level rised in ascending order: 10cm12cm14cm16 cm18cm,when the sandbodies deposited continuously towards the source regions.When the lake level dropped from 18cm to 12cm, the accommodation decreased,the sediment carried by rivers deposited in lowlying location and former sandbodies were reformed obviously,which was benefit to widespread sandstone. In the depositional process, the channels bifurcated into distributary channels and lateral migrated continuously. The sandbody prograted and retrogradated vertically by fluctuation of lake level and assembled in horizontal and vertical direction. Then widespread sandstone developed.
The widespread sandstone in Xujiahe Fomation of the Upper Triassic, Sichuan Foreland Basin, is one of the most important exploration strata. With the exploration development of the gasfield, it needs to clarify the predominant factors that control the widespread sandstone developing to guide the further exploration and production. To elucidate the depositional mechanism and spacial arrangement of the the widespread sandstone, the sedimentary physical simulation method was adopted to transform the original geological conditions into physical model, on base of investigating the evolution of tectonic, ancient landform and sedimentary system, and so on. And the simulation parameters were taken into consideration and designed to study the mechanism of widespread sandstone through the simulation of flume experiment technology. Three provenances were designed in the experiment to incarnate the characteristics of sedimentary systems during different stages and at different locations under the multisource conditions. Six intervals were simulated to playback the sedimentary characteristics, by conducting the experiment which was designed referring to principle of simulation and natrural model method. The main controlling factors of widespread sandstone were concluded, by designed such as simulation parameters,such as flow, sediment flux,gradient,subsidence and lake level et al. Some preliminary conclusions are obtained as follows: 1.Under the gradual slope conditions, it is in the shallow areaat the depth of 2.3 cm, slope of 4 that distributary channels migrated frequently, where the area water passed became larger gradually. And so did the area where sandbody deposited and was retransformd, which was benefit for widespread sandstone developing. The sandbodies were universally thin and homogeneous. And the widththickness ratio of the deltas is grater than 98∶〖KG-*2〗1. 2.In the experiment, when the flux was 4.35 l/s and sediment content was 9.5 g/s, the channels branched and sandbodies moved forward. While was 0.49 l/s and 0.4 g/s, single channel developed and sandbodies were eroded. So the flux and sediment content of different water consociation helped widespread sandstone development. 3.With tectonic subsidence and accommodation extending, the sand sediment developed to sandbodies of certain scale. 4. With frequent changes of the lake level, sandbodies of each stage expanded to different directions in the plane and overriding in vertical. Besides, the lobes combinated laterally, widespread sandstone was easily developed. 5. In the experiment, convergence of 3 sources showed explain of the development of widespread sandstone. During 6th depositional stage, the lake level rised in ascending order: 10cm12cm14cm16 cm18cm,when the sandbodies deposited continuously towards the source regions.When the lake level dropped from 18cm to 12cm, the accommodation decreased,the sediment carried by rivers deposited in lowlying location and former sandbodies were reformed obviously,which was benefit to widespread sandstone. In the depositional process, the channels bifurcated into distributary channels and lateral migrated continuously. The sandbody prograted and retrogradated vertically by fluctuation of lake level and assembled in horizontal and vertical direction. Then widespread sandstone developed.
2012, 30(1): 111-119.
Abstract:
Based on the experimental methods of slice identification, casting slice, scan electron microscope and X-ray diffractions, characteristics of petrology and diagenesis on reservoir in Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation of Permian system in the east Ⅱ part of Sulige gas field were studied. The result shows that the main lithology of sandstone in this area is dominated by lithic sandstone and lithic silicarenite with low grade of maturity. Diagenesis of sandstone in this area mainly include compaction, cementation, corrosion and alteration. Diagenetic minerals mainly include siliceous mineral (chalcedony, quartz secondary overgrowth, and authigenic quartz small crystal), clay minerals (chlorite, illitesmectite formation, kaolinite, illite) and carbonate minerals (calcite, ferrocalcite, ankerite) etc. The highest diagenetic stage reach to period B of middle diagenetic stage on the basis of maturity of organic matter, diagentic minerals, homogenisation temperature of fluid inclusion etc. diagenetic symbols. Diagenesis of sandstone in the east Ⅱ part of Sulige gas field underwent syndiagenetic stage, early diagenetic stage and middle diagenetic stage. Diagenetic environment succession went through faintly acidic environment in period A of early diagenetic stage, relative highly acidic environment in period B of early diagenetic stage, highly acidic environment in period A of middle diagenetic stage, and faintly alkaline environment in period B of middle diagenetic stage. Fast decreasing of porosity could be seen in evolution curve of porosity caused by cementation from period B of early diagenetic stage to period A of middle diagenetic stage. The early diagenetic compaction is one of main factors to decreasing porosity of Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation by means of quantitative calculation. Cementation is the most important factor to decreasing porosity in the studied area. Cementation in period B of middle diagenetic stage is the most important factor leading to poor physical property of sandstone reservoirs especially. The secondary pore formed by corrosion in acidity medium condition in period A of middle diagenetic stage can distinctly ameliorate poor reservoir capability of sandstone. Consequently, erosion play a key role in promoting of physical property of sandstone reservoirs in the east Ⅱ part of Sulige gas field. Secondary pore formed by corrosion of calc-alkali volcanics rock, feldspar and calcite cements in acidity medium condition in period A of middle diagenetic stage is main reserving space in the studied area. Corrosion of quartz particle was discovered in this area for the first time, which implies properties of fluid medium transferred gradually from acidity to alkaline since period B of middle diagenetic stage.
Based on the experimental methods of slice identification, casting slice, scan electron microscope and X-ray diffractions, characteristics of petrology and diagenesis on reservoir in Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation of Permian system in the east Ⅱ part of Sulige gas field were studied. The result shows that the main lithology of sandstone in this area is dominated by lithic sandstone and lithic silicarenite with low grade of maturity. Diagenesis of sandstone in this area mainly include compaction, cementation, corrosion and alteration. Diagenetic minerals mainly include siliceous mineral (chalcedony, quartz secondary overgrowth, and authigenic quartz small crystal), clay minerals (chlorite, illitesmectite formation, kaolinite, illite) and carbonate minerals (calcite, ferrocalcite, ankerite) etc. The highest diagenetic stage reach to period B of middle diagenetic stage on the basis of maturity of organic matter, diagentic minerals, homogenisation temperature of fluid inclusion etc. diagenetic symbols. Diagenesis of sandstone in the east Ⅱ part of Sulige gas field underwent syndiagenetic stage, early diagenetic stage and middle diagenetic stage. Diagenetic environment succession went through faintly acidic environment in period A of early diagenetic stage, relative highly acidic environment in period B of early diagenetic stage, highly acidic environment in period A of middle diagenetic stage, and faintly alkaline environment in period B of middle diagenetic stage. Fast decreasing of porosity could be seen in evolution curve of porosity caused by cementation from period B of early diagenetic stage to period A of middle diagenetic stage. The early diagenetic compaction is one of main factors to decreasing porosity of Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation by means of quantitative calculation. Cementation is the most important factor to decreasing porosity in the studied area. Cementation in period B of middle diagenetic stage is the most important factor leading to poor physical property of sandstone reservoirs especially. The secondary pore formed by corrosion in acidity medium condition in period A of middle diagenetic stage can distinctly ameliorate poor reservoir capability of sandstone. Consequently, erosion play a key role in promoting of physical property of sandstone reservoirs in the east Ⅱ part of Sulige gas field. Secondary pore formed by corrosion of calc-alkali volcanics rock, feldspar and calcite cements in acidity medium condition in period A of middle diagenetic stage is main reserving space in the studied area. Corrosion of quartz particle was discovered in this area for the first time, which implies properties of fluid medium transferred gradually from acidity to alkaline since period B of middle diagenetic stage.
2012, 30(1): 120-127.
Abstract:
Components of the clay mineral illite, smectite, kaolinite, and chlorite were measured and analyzed at eleven horizons from eleven observed sections to interpret the EarlyMid Cretaceous paleoclimate in western Zhejiang and Fujian provinces, SE China. The results show that in total the relative content of illite is over 80% in average in most of the LowerMid Cretaceous; abundant smectite is presented in the Bantou Formation of western Fujian and the upper Shouchang Formation, lower Hengshan Formation, middle Jinhua Formation, and upper Quxian Formation of west Zhejiang, in which the highest value is 49%; kaolinite is few, only high values (up to 38%) ocurring in the middle Quxian Formation in western Zhejiang and upper Shouchang Formation. It is proposed that it was aridsemiarid climate of tropicsubtropic in the EarlyMid Cretaceous in SE China, corresponded to the whole greenhouse (continental) climate in the world; there could be an interruption of hothumid climate in the earlyAptian and early Cenomanian in western Zhejiang that could be attributed to relatively developed vegetation and larger lacustrine area; and short durations of drycold climate could have happened in the Valanginian in western Fujian and in the early Aptian, late Albian, middle Cenomanian in western Zhejiang, which is corresponding to those of the Cretaceous oceanic anoxic events, and is supposed to be caused by regional tectonic uplifts in SE China.
Components of the clay mineral illite, smectite, kaolinite, and chlorite were measured and analyzed at eleven horizons from eleven observed sections to interpret the EarlyMid Cretaceous paleoclimate in western Zhejiang and Fujian provinces, SE China. The results show that in total the relative content of illite is over 80% in average in most of the LowerMid Cretaceous; abundant smectite is presented in the Bantou Formation of western Fujian and the upper Shouchang Formation, lower Hengshan Formation, middle Jinhua Formation, and upper Quxian Formation of west Zhejiang, in which the highest value is 49%; kaolinite is few, only high values (up to 38%) ocurring in the middle Quxian Formation in western Zhejiang and upper Shouchang Formation. It is proposed that it was aridsemiarid climate of tropicsubtropic in the EarlyMid Cretaceous in SE China, corresponded to the whole greenhouse (continental) climate in the world; there could be an interruption of hothumid climate in the earlyAptian and early Cenomanian in western Zhejiang that could be attributed to relatively developed vegetation and larger lacustrine area; and short durations of drycold climate could have happened in the Valanginian in western Fujian and in the early Aptian, late Albian, middle Cenomanian in western Zhejiang, which is corresponding to those of the Cretaceous oceanic anoxic events, and is supposed to be caused by regional tectonic uplifts in SE China.
2012, 30(1): 128-136.
Abstract:
Two transects (Transect I, Transect II) were selected in areas with Spartina alterniflora, and native vegetation, respectively, for investigation of both distribution and mineralization of soil organic matter (SOM) in the Chongmingdongtan salt marsh of the Yangtze Estuary, China. This study is based the on content of particulate organic carbon (POC), δ13C value of POC, molar ratio of C/N, and grain size characteristics of drilling cores in high tidal flat (core DT012, core DT081), middle tidal flat (core DT021, core DT082) and bare flat (core DT032, core DT083). Cores with the same altitude at the two transects contrast in variations of both POC content and δ13C value with depth, and are different in average values of δ13C and POC content, respectively. The average content of POC of core DT012 (0.8%) is markedly greater than that of POC of core DT081 (0.47%). The average content of POC of core DT021 (0.38%) is greater than that of POC of core DT082 (0.11%). δ13C values of core DT081 average 24.52‰, and the average value of δ13C of core DT012 is 19.73‰. The average value of δ13C of core DT082 (22.06‰) is close to that of δ13C of core DT021 (22.92‰). Therefore, the variation trend of SOM composition from high tidal flat (core DT012) to middle tidal flat (core DT021) of Transect I is not consistent with that of SOM composition from high tidal flat to middle tidal flat of Transect II. This may be due to differences in SOM composition between the two transects. Transect I was located in the area with invasive Spartina alterniflora that is of C4 type plant. POC content is positively correlated with δ13C value for core DT012, suggesting that organic components from Spartina alterniflora are predominant in SOM at the drilling site. Core DT012 contrasts markedly with core DT081 in correlation between δ13C value and POC content. This is due to the difference in vegetation type between the sites of the two cores, with C3 type plant at the site of core DT081 and C4 type plant at the site of core DT012. The average content of POC of core DT012 is the greatest among those of POC of the studied cores, which may correlate to the high primary production of Spartina alterniflora. Core DT021 is different with core DT012 in correlation between δ13C value and POC content, and is similar to core DT081 that is located in the area with native vegetation. This suggests that SOM at the site of core DT021 are mainly composed of organic components from primary sediments that are transported by the Yangtze River. The correlation between δ13C value and POC content of core DT021 has not been changed thoroughly by the organic components from Spartina alterniflora, which may correlate to the weaker mineralization of SOM, due to the limited time period for the development of middle tidal flat. Spartina alterniflora has produced marked impacts on both content and composition of SOM in the high tidal flat, and discernable impacts on composition of SOM in the middle tidal flat. Native vegetation has exerted marked influence on composition of SOM in the high tidal flat. Salt marsh vegetations have therefore made remarkable impacts on distribution and mineralization of SOM. Organic components of different stages of mineralization are mixed in the SOM of the high tidal flat. SOM composition is relatively simple in the middle tidal flat, indicating that SOM mineralization is less complicated there. Both clay content and water content vary markedly with depth, suggesting that sedimentary sequences have initial constraints on distribution of materials with depth in the salt marsh. Cores with different altitudes contrast markedly in both vertical distribution and mineralization of SOM. Soil carbon dynamics are constrained by the characteristic sedimentary processes on the salt marsh of the Yangtze Estuary.
Two transects (Transect I, Transect II) were selected in areas with Spartina alterniflora, and native vegetation, respectively, for investigation of both distribution and mineralization of soil organic matter (SOM) in the Chongmingdongtan salt marsh of the Yangtze Estuary, China. This study is based the on content of particulate organic carbon (POC), δ13C value of POC, molar ratio of C/N, and grain size characteristics of drilling cores in high tidal flat (core DT012, core DT081), middle tidal flat (core DT021, core DT082) and bare flat (core DT032, core DT083). Cores with the same altitude at the two transects contrast in variations of both POC content and δ13C value with depth, and are different in average values of δ13C and POC content, respectively. The average content of POC of core DT012 (0.8%) is markedly greater than that of POC of core DT081 (0.47%). The average content of POC of core DT021 (0.38%) is greater than that of POC of core DT082 (0.11%). δ13C values of core DT081 average 24.52‰, and the average value of δ13C of core DT012 is 19.73‰. The average value of δ13C of core DT082 (22.06‰) is close to that of δ13C of core DT021 (22.92‰). Therefore, the variation trend of SOM composition from high tidal flat (core DT012) to middle tidal flat (core DT021) of Transect I is not consistent with that of SOM composition from high tidal flat to middle tidal flat of Transect II. This may be due to differences in SOM composition between the two transects. Transect I was located in the area with invasive Spartina alterniflora that is of C4 type plant. POC content is positively correlated with δ13C value for core DT012, suggesting that organic components from Spartina alterniflora are predominant in SOM at the drilling site. Core DT012 contrasts markedly with core DT081 in correlation between δ13C value and POC content. This is due to the difference in vegetation type between the sites of the two cores, with C3 type plant at the site of core DT081 and C4 type plant at the site of core DT012. The average content of POC of core DT012 is the greatest among those of POC of the studied cores, which may correlate to the high primary production of Spartina alterniflora. Core DT021 is different with core DT012 in correlation between δ13C value and POC content, and is similar to core DT081 that is located in the area with native vegetation. This suggests that SOM at the site of core DT021 are mainly composed of organic components from primary sediments that are transported by the Yangtze River. The correlation between δ13C value and POC content of core DT021 has not been changed thoroughly by the organic components from Spartina alterniflora, which may correlate to the weaker mineralization of SOM, due to the limited time period for the development of middle tidal flat. Spartina alterniflora has produced marked impacts on both content and composition of SOM in the high tidal flat, and discernable impacts on composition of SOM in the middle tidal flat. Native vegetation has exerted marked influence on composition of SOM in the high tidal flat. Salt marsh vegetations have therefore made remarkable impacts on distribution and mineralization of SOM. Organic components of different stages of mineralization are mixed in the SOM of the high tidal flat. SOM composition is relatively simple in the middle tidal flat, indicating that SOM mineralization is less complicated there. Both clay content and water content vary markedly with depth, suggesting that sedimentary sequences have initial constraints on distribution of materials with depth in the salt marsh. Cores with different altitudes contrast markedly in both vertical distribution and mineralization of SOM. Soil carbon dynamics are constrained by the characteristic sedimentary processes on the salt marsh of the Yangtze Estuary.
2012, 30(1): 137-147.
Abstract:
Grain size of sediment in littoral area of estuaries is vulnerable to humaninduced changes in riverine sediment supply and coastal hydrodynamics. In recent years, sediment from the Yangtze River to the sea has drastically decreased, which has resulted in erosion in the subaqueous delta. Meanwhile, many coastal engineering structures have been built at the mouth of the Hangzhou Bay. Less has been known of the sedimentary impacts in the inshore area adjacent to the Yangtze Estuary and Hangzhou Bay. To examine the spatial pattern of and recent changes in sediment grain size in the littoral area off the Yangtze Estuary and Hangzhou Bay, we obtained 33 surface sediment samples using a box sampler and 7 sediment cores (1.4 to 4.8 m in length) using a vibro piston corer in April 2008. These samples were analyzed for grain size parameters in the laboratory using a laser particle size analyzer. Comparison of grain size was made between the present result and results of historical periods. The results include: 1) In agreement with the results of historical periods, the present study showed an overall spatial pattern of coarse sediment in the east (sand) and finegrained sediment in the west (mud). Nevertheless, in contrast to the historical results, the borderline between the sand and mud areas has retreated landward (or westward) for 10 to 30 km in the northern portion (off the Yangtze Estuary and the main Hangzhou Bay) whereas it has advanced seaward (or eastward) for up to 50 km in the southern area (south of the Zhoushan Archipelago). 2) In comparison with the results of historical periods that the longshore distributed mud (clay) zone was disconnected at the east of the Zhoushan Archipelago, the spatial pattern of surface sediment grain size in the present study indicated a consecutive longshore mud zone, which suggests the historical disconnection of the longshore mud (clay) zone at the east of the Zhoushan Archipelago has disappeared at least for surface sediment. This change was mainly attributed to the construction of large bridges across the channels between the islands of the Zhoushan Archipelago. The piers of these bridges were considered to have reduced the water and sediment exchange between the Hangzhou Bay and the East China Sea and weakened the currents at the previous disconnecting area of the longshore mud (clay) zone. 3) The results of grain size trend analysis of surface sediment along the longshore mud zone support the hypothesis that the sediments derived from the Yangtze River have been mainly transported southward and southeastward.4) The core sediments, sampled successfully in the mud zone (we failed to sample core sediment in the sand zone), are mainly composed of silt and clay. Most of the cores show significant vertical fluctuations of grain size. These vertical fluctuations seem to reflect historical events of climate changes which have resulted in longterm changes in riverine sediment supply and ocean hydrodynamics. The surface sediment of the cores sampled in the recent erosion area (recognized by other authors based on bathymetric comparison) indicates a coarsening trend, which is considered to have resulted from the recent drastic decrease in riverine sediment supply. We conclude that the sediments in the littoral area of the Yangtze Estuary and Hangzhou Bay are susceptible to anthropogenic and climate impacts both from the catchment and the coastal region.
Grain size of sediment in littoral area of estuaries is vulnerable to humaninduced changes in riverine sediment supply and coastal hydrodynamics. In recent years, sediment from the Yangtze River to the sea has drastically decreased, which has resulted in erosion in the subaqueous delta. Meanwhile, many coastal engineering structures have been built at the mouth of the Hangzhou Bay. Less has been known of the sedimentary impacts in the inshore area adjacent to the Yangtze Estuary and Hangzhou Bay. To examine the spatial pattern of and recent changes in sediment grain size in the littoral area off the Yangtze Estuary and Hangzhou Bay, we obtained 33 surface sediment samples using a box sampler and 7 sediment cores (1.4 to 4.8 m in length) using a vibro piston corer in April 2008. These samples were analyzed for grain size parameters in the laboratory using a laser particle size analyzer. Comparison of grain size was made between the present result and results of historical periods. The results include: 1) In agreement with the results of historical periods, the present study showed an overall spatial pattern of coarse sediment in the east (sand) and finegrained sediment in the west (mud). Nevertheless, in contrast to the historical results, the borderline between the sand and mud areas has retreated landward (or westward) for 10 to 30 km in the northern portion (off the Yangtze Estuary and the main Hangzhou Bay) whereas it has advanced seaward (or eastward) for up to 50 km in the southern area (south of the Zhoushan Archipelago). 2) In comparison with the results of historical periods that the longshore distributed mud (clay) zone was disconnected at the east of the Zhoushan Archipelago, the spatial pattern of surface sediment grain size in the present study indicated a consecutive longshore mud zone, which suggests the historical disconnection of the longshore mud (clay) zone at the east of the Zhoushan Archipelago has disappeared at least for surface sediment. This change was mainly attributed to the construction of large bridges across the channels between the islands of the Zhoushan Archipelago. The piers of these bridges were considered to have reduced the water and sediment exchange between the Hangzhou Bay and the East China Sea and weakened the currents at the previous disconnecting area of the longshore mud (clay) zone. 3) The results of grain size trend analysis of surface sediment along the longshore mud zone support the hypothesis that the sediments derived from the Yangtze River have been mainly transported southward and southeastward.4) The core sediments, sampled successfully in the mud zone (we failed to sample core sediment in the sand zone), are mainly composed of silt and clay. Most of the cores show significant vertical fluctuations of grain size. These vertical fluctuations seem to reflect historical events of climate changes which have resulted in longterm changes in riverine sediment supply and ocean hydrodynamics. The surface sediment of the cores sampled in the recent erosion area (recognized by other authors based on bathymetric comparison) indicates a coarsening trend, which is considered to have resulted from the recent drastic decrease in riverine sediment supply. We conclude that the sediments in the littoral area of the Yangtze Estuary and Hangzhou Bay are susceptible to anthropogenic and climate impacts both from the catchment and the coastal region.
2012, 30(1): 148-157.
Abstract:
Based on the major and trace elements and grainsize analysis，as well as the 210Pb isotope data, the sedimentary history within a hundred year of the Core ZM11 was reconstructed and the impacting factors were discussed. It was shown that the sedimentation rate is about 2.5 cm/a starting from 1950. Because the sediment was dredged during the construction of the Twin JettyGroyne Complex in the North Passage of the South Channel and was eroded from delta front, the sedimentation rate of the Core ZM11 within the last ten years was above 3 cm/a, while the Changjiang sediment was declining during the same period. The thickness of sediment deposited during 19981999 was about 20 cm, possibly induced by the 1998 major flood event that is recognized by the 0.3 cm finesand layer at ~ 46 cm depth. The variation of the sediment grain size in Core ZM11, presumably controlled by the complexity of subaqueous delta, is not consistent with the sediment grain size variations of the Datong gauging station. The geochemical element analysis results showed that sediment of Core ZM11 mainly come from the Changjiang River. Grain size，terrigenous material input，biological sedimentation and human activity are the major factors that resulted the element content variations of the Core ZM11.
Based on the major and trace elements and grainsize analysis，as well as the 210Pb isotope data, the sedimentary history within a hundred year of the Core ZM11 was reconstructed and the impacting factors were discussed. It was shown that the sedimentation rate is about 2.5 cm/a starting from 1950. Because the sediment was dredged during the construction of the Twin JettyGroyne Complex in the North Passage of the South Channel and was eroded from delta front, the sedimentation rate of the Core ZM11 within the last ten years was above 3 cm/a, while the Changjiang sediment was declining during the same period. The thickness of sediment deposited during 19981999 was about 20 cm, possibly induced by the 1998 major flood event that is recognized by the 0.3 cm finesand layer at ~ 46 cm depth. The variation of the sediment grain size in Core ZM11, presumably controlled by the complexity of subaqueous delta, is not consistent with the sediment grain size variations of the Datong gauging station. The geochemical element analysis results showed that sediment of Core ZM11 mainly come from the Changjiang River. Grain size，terrigenous material input，biological sedimentation and human activity are the major factors that resulted the element content variations of the Core ZM11.
2012, 30(1): 158-165.
Abstract:
Taihu Lake is the third largest freshwater lake in China. East Taihu Lake with an area of 131 km2 and water depth of 0.9 m, dominated by macrophyte, is important drinking water source of Suzhou and Shanghai City. Sedimentary cores named DJZ and DQG were collected from East Taihu Lake in 2009 using gravity corer. The length of DJZ and DQG is 59 and 33 cm, respectively. Radio nuclides including 210Pb and 137Cs were also analyzed for dating the sediments at both cores. Sediment accumulation rate (SAR) of DQG was averaged to be 0.15 g/cm2/a based on 1963 dating marker of 137Cs. At DJZ core, SAR was higher relative to DQG core showing variation between 1.0~2.0 g/cm2/a. Elements including copper, lead, zinc, chromium, nickel, ferrum and others were analyzed for the purpose of understanding metal accumulation and human impact at East Taihu Lake combined with dating results. Between bottom to 30 cm, Cu, Pb, Zn, Cr and Ni in DJZ core showed increase trend. In the upper 30 cm sediments of DJZ core, the profiles of Pb, Cr and Ni showed relatively constant value while Cu and Zn demonstated upward increase in these sections. The average contents of Cu, Pb, Zn, Cr and Ni in DQG core were 22.34, 50.83, 98.35, 66.19, 26.74 mg/kg respectively for sediments between 0 and 9 cm, while 13.18, 26.25, 46.33, 58.95, 20.45 mg/kg for 9~33 cm sediments. In this paper Fe element as a proxy of grain size was selected for normalization and calculation of metal enrichment factor (EF) and anthropogenic heavy metal fluxes. The results showed that, except the cores surface sediment, Pb, Zn, Cu, Cr and Ni enrichment factors did not exceed 2, and EF of Cr and Ni was nearly 1. It was revealed that the heavy metals including lead, copper, zinc were continuously enriched in recent decades, especially since the 1970s at East Taihu Lake. From 1970s to 1990s anthropogenic fluxes of Pb, Zn, Cu changed slightly, and then increased corresponding to development of industry in catchment. Since early 2000s, the total and anthropogenic Pb fluxes declined, which may be due to forbidden use of leaded petrol in China and adjustment of industrial structure in basin in the period.
Taihu Lake is the third largest freshwater lake in China. East Taihu Lake with an area of 131 km2 and water depth of 0.9 m, dominated by macrophyte, is important drinking water source of Suzhou and Shanghai City. Sedimentary cores named DJZ and DQG were collected from East Taihu Lake in 2009 using gravity corer. The length of DJZ and DQG is 59 and 33 cm, respectively. Radio nuclides including 210Pb and 137Cs were also analyzed for dating the sediments at both cores. Sediment accumulation rate (SAR) of DQG was averaged to be 0.15 g/cm2/a based on 1963 dating marker of 137Cs. At DJZ core, SAR was higher relative to DQG core showing variation between 1.0~2.0 g/cm2/a. Elements including copper, lead, zinc, chromium, nickel, ferrum and others were analyzed for the purpose of understanding metal accumulation and human impact at East Taihu Lake combined with dating results. Between bottom to 30 cm, Cu, Pb, Zn, Cr and Ni in DJZ core showed increase trend. In the upper 30 cm sediments of DJZ core, the profiles of Pb, Cr and Ni showed relatively constant value while Cu and Zn demonstated upward increase in these sections. The average contents of Cu, Pb, Zn, Cr and Ni in DQG core were 22.34, 50.83, 98.35, 66.19, 26.74 mg/kg respectively for sediments between 0 and 9 cm, while 13.18, 26.25, 46.33, 58.95, 20.45 mg/kg for 9~33 cm sediments. In this paper Fe element as a proxy of grain size was selected for normalization and calculation of metal enrichment factor (EF) and anthropogenic heavy metal fluxes. The results showed that, except the cores surface sediment, Pb, Zn, Cu, Cr and Ni enrichment factors did not exceed 2, and EF of Cr and Ni was nearly 1. It was revealed that the heavy metals including lead, copper, zinc were continuously enriched in recent decades, especially since the 1970s at East Taihu Lake. From 1970s to 1990s anthropogenic fluxes of Pb, Zn, Cu changed slightly, and then increased corresponding to development of industry in catchment. Since early 2000s, the total and anthropogenic Pb fluxes declined, which may be due to forbidden use of leaded petrol in China and adjustment of industrial structure in basin in the period.
2012, 30(1): 166-178.
Abstract:
By comparing the large and mediumsized oil and gas fields, it is discovered that reservoirs in superimposed basins are most of multistage formation process, and the late accumulation is favorable for largescale preservation. Based on summary of accumulation progress, characteristic and model of the vorious oilgas pool, combined with features of the tectonic evolution of the study area, it composes the hydrocarbon accumulation pattern classification, and divides oil and gas multiphase accumulation model into 5 types according to the criteria: continuous oilgas filled, early strong reformation, strongly reworked in mediumterm, late strongly reworked and alternation of multistage filling and reworked. Strength of structural changes and occurring period are taken into account to construct the pattern classification criteria, and the two parameters are all relative. The characteristic of continuous oilgas filled is that the oil and gas transportation capability is strong and it can not only form the normal reservoir, but also the pyrolysis gas reservoir. The early strong reformation means the strength of structure is more stronger and the range is larger during the early period, it makes the hydrocarbon expelled from resource can not be assemble in the suitable trap, in contrast the later oil and gas can form the reservoir. Strongly reworked in mediumterm mode indicates that much of tectonic movements strongly happened after the reservoir accumulated, oil and gas reservoirs will be reformed or lost to some extent each time, so the late contribution is the main result of this type. The late strongly reworked type means that the hydrocarbon formed and expelled from source all accumulated in the relatively stable environment, and in the late, there happens the strong and largescale tectonic movements, these movements change the existed reservoirs in the aspect of quality and quantity. The last one is multistage filling and reworked type, which most occurs in the region happened strong and frequent extremely tectonic movements. Although the reservoirs formed early, strong tectonic movements destroy or change them all, after several times, it basically, can not form a large reservoir. Among the model of the multistage of oilgas formation listed above, the first type can form the typical reservoir under normal circumstance, moreover, the condensate gas reservoir is more. The second one is similar to the forth type, but because the time of destroy is different, the corresponding results are very different. Early strong reformation type can destroy the reservoir accumulated in the early stage seriously, and because of the later stable tectonic movements, it can preserve the hydrocarbon formed in the later period, such as the distribution of Silurian bituminous sandstone in Tazhong region and much of reservoir existed in Carboniferous and Thriassic. The third one can preserve the earlier reservoir to some extent, and meanwhile, it also can accumulate the late hydrocarbon because the strength of the tectonic movements become weaker. The characteristic of the forth type is the strength of tectonic is very strong, and it can be destructive. To the maximum extent, it can completely destroy the former reservoirs, the remaining is very little. The last type is a model without exploration effectiveness, and the result of structural damage is highly visible, So the resource accumulated under this condition is restricted extremely. In the context of late accumulation is favorable for exploration, it determine that the region with the model of continuous oilgas filled and surrounding areas is most likely to accumulate large scale and many types of oilgas reservoirs because there have little tectonic movements and the damage. However, the model of alternation of multistage filling and reworking have little exploration effectiveness because of many tectonic movements and damages. Consequently, the exploration for oilgas should try to avoid these areas.
By comparing the large and mediumsized oil and gas fields, it is discovered that reservoirs in superimposed basins are most of multistage formation process, and the late accumulation is favorable for largescale preservation. Based on summary of accumulation progress, characteristic and model of the vorious oilgas pool, combined with features of the tectonic evolution of the study area, it composes the hydrocarbon accumulation pattern classification, and divides oil and gas multiphase accumulation model into 5 types according to the criteria: continuous oilgas filled, early strong reformation, strongly reworked in mediumterm, late strongly reworked and alternation of multistage filling and reworked. Strength of structural changes and occurring period are taken into account to construct the pattern classification criteria, and the two parameters are all relative. The characteristic of continuous oilgas filled is that the oil and gas transportation capability is strong and it can not only form the normal reservoir, but also the pyrolysis gas reservoir. The early strong reformation means the strength of structure is more stronger and the range is larger during the early period, it makes the hydrocarbon expelled from resource can not be assemble in the suitable trap, in contrast the later oil and gas can form the reservoir. Strongly reworked in mediumterm mode indicates that much of tectonic movements strongly happened after the reservoir accumulated, oil and gas reservoirs will be reformed or lost to some extent each time, so the late contribution is the main result of this type. The late strongly reworked type means that the hydrocarbon formed and expelled from source all accumulated in the relatively stable environment, and in the late, there happens the strong and largescale tectonic movements, these movements change the existed reservoirs in the aspect of quality and quantity. The last one is multistage filling and reworked type, which most occurs in the region happened strong and frequent extremely tectonic movements. Although the reservoirs formed early, strong tectonic movements destroy or change them all, after several times, it basically, can not form a large reservoir. Among the model of the multistage of oilgas formation listed above, the first type can form the typical reservoir under normal circumstance, moreover, the condensate gas reservoir is more. The second one is similar to the forth type, but because the time of destroy is different, the corresponding results are very different. Early strong reformation type can destroy the reservoir accumulated in the early stage seriously, and because of the later stable tectonic movements, it can preserve the hydrocarbon formed in the later period, such as the distribution of Silurian bituminous sandstone in Tazhong region and much of reservoir existed in Carboniferous and Thriassic. The third one can preserve the earlier reservoir to some extent, and meanwhile, it also can accumulate the late hydrocarbon because the strength of the tectonic movements become weaker. The characteristic of the forth type is the strength of tectonic is very strong, and it can be destructive. To the maximum extent, it can completely destroy the former reservoirs, the remaining is very little. The last type is a model without exploration effectiveness, and the result of structural damage is highly visible, So the resource accumulated under this condition is restricted extremely. In the context of late accumulation is favorable for exploration, it determine that the region with the model of continuous oilgas filled and surrounding areas is most likely to accumulate large scale and many types of oilgas reservoirs because there have little tectonic movements and the damage. However, the model of alternation of multistage filling and reworking have little exploration effectiveness because of many tectonic movements and damages. Consequently, the exploration for oilgas should try to avoid these areas.
2012, 30(1): 179-188.
Abstract:
Controlled by the multicycle superposition and reverse evolution of basin, the source rocks of CarboniferousPermian coalbearing strata has experienced secondary hydrocarbon generation in the eastern Liqing Depression, which shows a strong deviation in the space. The simulation results of hydrocarbon generating history of these source rocks show that, the CarboniferousPermian source rocks entered the hydrocarbon generation window in the EarlyMiddle Triassic, then the hydrocarbon generation suspended in the whole region due to the Indosinian movement, after that the source rocks buried again in the MesoCenozoic and secondary hydrocarbon generation function occurred. The secondary hydrocarbon generation varies with different well blocks in the time and space. There are three secondary hydrocarbon generation stages in sags, first stage was in the Cretaceous period, second stage was in the Paleogene period, and third stage was in the Neogene period, the peak amount of hydrocarbon generating stage was in the Cenozoic period. Hydrocarbon contribution at the three secondary hydrocarbon generation stages was equivalent to about thirty percent in sags that the Paleogene was relatively thin. While sags that the Paleogene was relatively thick, hydrocarbon contribution in the Paleogene period was the most, which was more than fifty percent, then followed by the Cretaceous period, and hydrocarbon contribution in the Neogene period was the least. There are two secondary hydrocarbon generation stages in prominence, peak amount of hydrocarbon generating stage was in the Mesozoic period. Hydrocarbon contribution in the Cretaceous period was more than ninety percent. There are none secondary hydrocarbon generation stages in uplift. Most of the hydrocarbon that generated early period has been destroyed, while the hydrocarbon which generated late period is available on the geological conditions of hydrocarbon accumulation, this is a main target of oil and gas exploration. Differential subsidence is the main controlling factor of the differentiation of secondary hydrocarbon generation, which results from the three cycle superposition and reverse evolution of the basin. The uplift that formed at the last stage of the Indo Chinese epoch did not accept formation deposition unit Neogene period. The prominence that formed at the early stage of the Himalayan epoch absented Paleogene deposition. Formation deposition was continued in the sags, but formation deposition in the Paleogene period was differential. Source rocks in sag have entered in the mature to highmature stage and can be the gas kitchen of the late coalgas reservoir at the present.
Controlled by the multicycle superposition and reverse evolution of basin, the source rocks of CarboniferousPermian coalbearing strata has experienced secondary hydrocarbon generation in the eastern Liqing Depression, which shows a strong deviation in the space. The simulation results of hydrocarbon generating history of these source rocks show that, the CarboniferousPermian source rocks entered the hydrocarbon generation window in the EarlyMiddle Triassic, then the hydrocarbon generation suspended in the whole region due to the Indosinian movement, after that the source rocks buried again in the MesoCenozoic and secondary hydrocarbon generation function occurred. The secondary hydrocarbon generation varies with different well blocks in the time and space. There are three secondary hydrocarbon generation stages in sags, first stage was in the Cretaceous period, second stage was in the Paleogene period, and third stage was in the Neogene period, the peak amount of hydrocarbon generating stage was in the Cenozoic period. Hydrocarbon contribution at the three secondary hydrocarbon generation stages was equivalent to about thirty percent in sags that the Paleogene was relatively thin. While sags that the Paleogene was relatively thick, hydrocarbon contribution in the Paleogene period was the most, which was more than fifty percent, then followed by the Cretaceous period, and hydrocarbon contribution in the Neogene period was the least. There are two secondary hydrocarbon generation stages in prominence, peak amount of hydrocarbon generating stage was in the Mesozoic period. Hydrocarbon contribution in the Cretaceous period was more than ninety percent. There are none secondary hydrocarbon generation stages in uplift. Most of the hydrocarbon that generated early period has been destroyed, while the hydrocarbon which generated late period is available on the geological conditions of hydrocarbon accumulation, this is a main target of oil and gas exploration. Differential subsidence is the main controlling factor of the differentiation of secondary hydrocarbon generation, which results from the three cycle superposition and reverse evolution of the basin. The uplift that formed at the last stage of the Indo Chinese epoch did not accept formation deposition unit Neogene period. The prominence that formed at the early stage of the Himalayan epoch absented Paleogene deposition. Formation deposition was continued in the sags, but formation deposition in the Paleogene period was differential. Source rocks in sag have entered in the mature to highmature stage and can be the gas kitchen of the late coalgas reservoir at the present.
2012, 30(1): 189-196.
Abstract:
The fluid inclusion of reservoir is one of important means to reveal the time of oil and natural gas charging. In present study the time of oil and natural gas charging in Yacheng and Lingshui Formation in Yacheng area of the Qiongdongnan Basin, southern China have been investigated by the analysis of type, distribution, fluorescence and homogenization temperature of fluid inclusions in samples of 5 Wells. The results indicated that the oil and natural gas bearing hydrothermal fluids have been charged twice into the sandstone reservoirs in the Paleogene reservoir. The first charge stage was characterized by condensategas with buffyellow fluorescent light, its hydrocarbon fluid inclusions are dominated by liquid hydrocarbon inclusions and gasliquid hydrocarbon inclusions, and the homogenization temperature (Th) of coeval aqueous inclusions ranges from 130℃ to 160℃. The time of first condensategas charging had been estimated at late Miocene to early Pliocene based on the regional burial thermal evolution history. The second charged stage was characterized by oil and natural gas with light blue fluorescence. Their hydrocarbon fluid inclusions were dominanted by gas hydrocarbon inclusions, gasliquid hydrocarbon inclusions and threephase hydrocarbon inclusions, the Th of coeval aqueous inclusions showed higher range from 160℃ to 190℃ than the 1st charged stage, and the charging time was estimated as Quaternary.
The fluid inclusion of reservoir is one of important means to reveal the time of oil and natural gas charging. In present study the time of oil and natural gas charging in Yacheng and Lingshui Formation in Yacheng area of the Qiongdongnan Basin, southern China have been investigated by the analysis of type, distribution, fluorescence and homogenization temperature of fluid inclusions in samples of 5 Wells. The results indicated that the oil and natural gas bearing hydrothermal fluids have been charged twice into the sandstone reservoirs in the Paleogene reservoir. The first charge stage was characterized by condensategas with buffyellow fluorescent light, its hydrocarbon fluid inclusions are dominated by liquid hydrocarbon inclusions and gasliquid hydrocarbon inclusions, and the homogenization temperature (Th) of coeval aqueous inclusions ranges from 130℃ to 160℃. The time of first condensategas charging had been estimated at late Miocene to early Pliocene based on the regional burial thermal evolution history. The second charged stage was characterized by oil and natural gas with light blue fluorescence. Their hydrocarbon fluid inclusions were dominanted by gas hydrocarbon inclusions, gasliquid hydrocarbon inclusions and threephase hydrocarbon inclusions, the Th of coeval aqueous inclusions showed higher range from 160℃ to 190℃ than the 1st charged stage, and the charging time was estimated as Quaternary.
2012, 30(1): 197-204.
Abstract:
After the paleopressure buildup by means of measured pressure, mudstone sonic log interval and fluid inclusions, the pressure evolution model of the fourth member of the Shahejie Formation is analyzed in Minfeng area, Dongying depression. The results show that, different periods of reservoir formation correspond to different pressure system in Es4 reservoir, Minfeng area: the hydrocarbon accumulation of Sha 2last stage of Dongying was accomplished in a higher pressure system; the hydrocarbon accumulation environment of the last stage of Ng was normal pressure; and after the middle and late period of Nm the cracking gas in the central area of sub sag was formed in a high pressure system. The dynamic evolution process of formation pressure is the results of integrated effect of multiple factors, the first high pressure was due to uncompaction of the highrate deposition of the formation, and the hydrocarbongeneration made a little contribution; a large amount of hydrocarbon played an important part in the form of the second high pressure, in addition, the sedimentation acted as the auxiliary role. Under the influence of the decrease of geothermal gradient, fracture, sand bodypressure discharge and the deepburial of gas reservoir, the gas reservoir founded in Sha 4 reservoir, Minfeng area is mainly normal pressure.
After the paleopressure buildup by means of measured pressure, mudstone sonic log interval and fluid inclusions, the pressure evolution model of the fourth member of the Shahejie Formation is analyzed in Minfeng area, Dongying depression. The results show that, different periods of reservoir formation correspond to different pressure system in Es4 reservoir, Minfeng area: the hydrocarbon accumulation of Sha 2last stage of Dongying was accomplished in a higher pressure system; the hydrocarbon accumulation environment of the last stage of Ng was normal pressure; and after the middle and late period of Nm the cracking gas in the central area of sub sag was formed in a high pressure system. The dynamic evolution process of formation pressure is the results of integrated effect of multiple factors, the first high pressure was due to uncompaction of the highrate deposition of the formation, and the hydrocarbongeneration made a little contribution; a large amount of hydrocarbon played an important part in the form of the second high pressure, in addition, the sedimentation acted as the auxiliary role. Under the influence of the decrease of geothermal gradient, fracture, sand bodypressure discharge and the deepburial of gas reservoir, the gas reservoir founded in Sha 4 reservoir, Minfeng area is mainly normal pressure.
