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煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例

宋磊 王淑萍 赵妍菲 孙沛沛 盛凯

宋磊, 王淑萍, 赵妍菲, 孙沛沛, 盛凯. 煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例[J]. 沉积学报, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
引用本文: 宋磊, 王淑萍, 赵妍菲, 孙沛沛, 盛凯. 煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例[J]. 沉积学报, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
SONG Lei, WANG ShuPing, ZHAO YanFei, SUN PeiPei, SHENG Kai. Characteristics and Genetic Model of High-quality Reservoir of Clastic Rocks in Coal-bearing Strata: A case of the Carboniferous Taiyuan Formation in the Dawangzhuang area, Jiyang Depression[J]. Acta Sedimentologica Sinica, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
Citation: SONG Lei, WANG ShuPing, ZHAO YanFei, SUN PeiPei, SHENG Kai. Characteristics and Genetic Model of High-quality Reservoir of Clastic Rocks in Coal-bearing Strata: A case of the Carboniferous Taiyuan Formation in the Dawangzhuang area, Jiyang Depression[J]. Acta Sedimentologica Sinica, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138

煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例

doi: 10.14027/j.issn.1000-0550.2023.138
基金项目: 

国家自然科学基金项目 42272165

详细信息
    作者简介:

    宋磊,男,1997年出生,硕士研究生,油气储层地质学,E-mail: 1244501248@qq.com

    通讯作者:

    王淑萍,女,讲师,油气储层评价,E-mail: wshp0619@163.com

Characteristics and Genetic Model of High-quality Reservoir of Clastic Rocks in Coal-bearing Strata: A case of the Carboniferous Taiyuan Formation in the Dawangzhuang area, Jiyang Depression

  • 摘要: 目的 济阳坳陷大王庄地区石炭系太原组煤系地层分布广泛,煤系地层中的优质储层控制因素对油气勘探有重要影响,但是其储层特征及成因模式尚不明确。 方法 综合利用薄片鉴定、阴极发光、扫描电镜、流体包裹体、C-O同位素、原位激光剥蚀等技术方法,结合埋藏史和构造演化史研究,对济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩优质储层特征及成因模式进行了研究。 结果 济阳坳陷大王庄地区太原组煤系地层碎屑岩储层以岩屑质石英砂岩为主,优质储层储集空间以次生孔隙为主,主要为大气淡水以及有机酸溶蚀形成的填隙物溶蚀孔和长石溶蚀孔。胶结物为两期石英次生加大边和两期碳酸盐胶结物,以碳酸盐胶结物为主。两期石英加大边分别来源于石英颗粒的压溶作用和长石溶解供源。菱铁矿为同沉积—早成岩阶段由孔隙水沉淀形成的成岩碳酸盐岩,铁白云石主要与有机酸脱羧作用形成的CO2有关。 结论 沉积相控制了现今优质储层岩相的分布位置,优质储层主要受控于晚期抬升的大气淡水淋滤作用以及埋藏有机酸溶蚀作用;受构造活动控制,优质储层与对接断层的距离较远,避免了脱羧作用产生的CO2进一步沉淀形成铁白云石破坏储层物性。
  • 图  1  济阳坳陷大王庄地区地质概况

    (a) tectonic location map; (b) north⁃south structural section; (c) stratigraphic histogram of well Da 675

    Figure  1.  Structural location, strata, and north⁃south structural section of the Dawangzhuang area, Jiyang Depression

    Fig.1

    图  2  济阳坳陷大王庄地区石炭系太原组储层砂岩分类三角图

    Q. quartz; F. felspar; L. lithic

    Figure  2.  QFL triangular diagram of reservoir sandstones from the Carboniferous Taiyuan Formation (C3t) in the Dawangzhuang area, Jiyang Depression

    Fig.2

    图  3  济阳坳陷大王庄地区石炭系太原组碎屑岩储层储集空间类型

    (a) well Dagu 41, 2 717.1 m, secondary pores were formed by the dissolution of interstitial materials and cuttings, in which red arrows refer to the dissolution pores of debris, yellow arrows refer to the dissolution pores of interstitial materials, blue cast thin sections, plane⁃polarized light (PPL); (b) well Dagu 41, 2 717.8 m, feldspar dissolution pores, blue cast thin section, PPL; (c) well Dagu 82, 2 546.7 m, residual intergranular pores, surrounding quartz overgrowth edge development, blue cast thin section, PPL

    Figure  3.  Reservoir storage⁃space types of clastic reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area,Jiyang Depression

    Fig.3

    图  4  济阳坳陷大王庄地区石炭系太原组砂岩储层物性特征

    Figure  4.  Physical properties of sandstone reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    图  5  济阳坳陷大王庄地区石炭系太原组砂岩储层孔隙度与渗透率关系

    Figure  5.  Relationship between porosity and permeability of sandstone reservoirs for the Carboniferous Taiyuan Formation,Dawangzhuang area, Jiyang Depression

    图  6  济阳坳陷大王庄地区石炭系太原组砂岩储层成岩作用类型及特征

    (a) well Dagu 82, 2 550.4 m, the particles are mainly point⁃line contact, PPL; (b) well Da 675, 3 101.6 m, mica plastic deformation, PPL; (c) well Da 675, 3 101.6 m, feldspar dissolution along the cleavage, PPL; (d) well Dagu 82, 2 717.1 m, particle dissolution forms mold hole, PPL; (e) well Dagu 82, 2 557.4 m, with internal dissolution of cuttings and blue cast thin sections, PPL; (f) well Dagu 82, 2 550.4 m, interstitial dissolution, PPL; (g) well Dagu 82, 2 546.5 m, quartz overgrowth edge development, PPL; (h) well Dagu 82, 2 550.0 m, two stages of quartz secondary overgrowth edge, visible two stages of dust trace line, PPL; (i) well Dagu 82, 2 550.0 m, with the same horizon as figure b, the first quartz secondary overgrowth edge is brown, and the second quartz secondary overgrowth edge is black, cathodoluminescence (CL); (j) well Dagu 82, 2 550.0 m, ankerite was dyed blue by alizarin red solution, filled in intergranular pores in its shape, PPL; (k) well Da 675, 3 101.6 m, siderite is not dyed with alizarin red solution, it is yellowish brown, self⁃shaped, diamond⁃shaped and distributed at the edge of the pore. The blue iron dolomite dyed by alizarin red solution is filled in the remaining space of siderite in its shape, PPL; (l) well Da 675, 3 101.6 m, siderite is black⁃brown, good self⁃shaped, CL; (m) well Dagu 82, 2 550.0 m, ankerite is black, visible bright red rim, CL; (n) well Da 675, 3 101.6 m, siderite is in the form of self⁃shaped independent rhombohedral, scanning electron microscope (SEM); (o) well Dagu 82, 2 550.4 m, ankerite is a collection of multiple rhombohedral morphology, filled in the intergranular, SEM; (p) well Dagu 82, 2 546.5 m, vermicular kaolinite filled in intergranular and throat, PPL; (q) well Da 675, 3 101.6 m, worm⁃like, book⁃like kaolinite, pseudo⁃hexagonal plate⁃like crystal, SEM; (r) well Dagu 82, 2 550.0 m, with massive pyrite filling in the intergranular, with strong metallic luster, reflected light (RL); figures a⁃h and j⁃k are blue cast section; Ank. iron dolomite; Sd. siderite; XTP. X diffraction analysis test points

    Figure  6.  Types and characteristics of diagenesis in sandstone reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    Fig.6

    图  7  石英颗粒和石英次生加大边微量元素含量关系

    Figure  7.  Correlation of trace elements content between quartz grains and quartz overgrowth edge

    图  8  长石颗粒和第二期石英次生加大边微量元素分布特征图

    Figure  8.  Characteristics of trace elements in the feldspar and the second phase of quartz overgrowth

    图  9  济阳坳陷大王庄地区石炭系太原组碳酸盐胶结物稀土元素分布特征

    (a) siderite; (b) ankerite

    Figure  9.  Distribution characteristics of rare earth elements in carbonate cements from the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    Fig.9

    图  10  济阳坳陷大王庄地区石炭系太原组砂岩中碳酸盐胶结物C⁃O同位素特征

    Figure  10.  Diagram showing carbon and oxygen isotopic characteristics of various carbonate cements in the sandstone from the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    图  11  石英颗粒破裂愈合缝中油包裹体与气液两相盐水包裹体组合

    (a) well Dagu 82, 2 546.7 m, single liquid phase and gas⁃liquid two⁃phase hydrocarbon inclusions are community⁃like development, mostly oval and irregular shape, PPL; (b) well Dagu 82, 2 546.7 m, blue fluorescent gas⁃liquid two⁃phase and single liquid hydrocarbon inclusions are widely developed, and yellow fluorescent gas⁃liquid two⁃phase hydrocarbon inclusions can be seen, ultraviolet fluorescence (UV); (c) well Da 675, 3 101.6 m, triangular and oval yellowish⁃brown gas⁃liquid two⁃phase oil inclusions and their associated triangular and oval colorless gas⁃liquid two⁃phase brine inclusions, PPL; (d) well Da 675, 3 101.6 m, yellow fluorescent gas⁃liquid two⁃phase hydrocarbon inclusions and non⁃fluorescent gas⁃liquid two⁃phase brine inclusions in the same FIA, with the same field of view as figure c, UV; (e) well Dagu 82, 2 550.4 m, triangular and elliptical colorless gas⁃liquid two⁃phase oil inclusions and their associated transparent triangular and elliptical gas⁃liquid two⁃phase brine inclusions, PPL; (f) well Dagu 82, 2 550.4 m, blue fluorescent gas⁃liquid two⁃phase hydrocarbon inclusions and non⁃fluorescent gas⁃liquid two⁃phase brine inclusions in the same FIA, with the same field of view as figure (e), UV; Red dotted line: quartz fracture healing seam development direction; AI. gas⁃liquid two⁃phase brine inclusions; HI. hydrocarbon inclusions

    Figure  11.  Combination of gas⁃liquid two⁃phase hydrocarbon inclusions and gas⁃liquid two⁃phase brine inclusions in the healed fractures of quartz grains

    Fig.11

    图  12  石英颗粒破裂愈合缝中与气液两相烃类包裹体同期的气液两相盐水包裹体均一温度分布直方图

    Figure  12.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions coeval with the gas⁃liquid two⁃phase hydrocarbon inclusions in the healed fractures of the quartz grains

    图  13  石英次生加大边中的气液两相盐水包裹体组合

    (a) well Dagu 82, 2 550 m, the first phase of brown quartz secondary overgrowth edge in the oval, circular gas⁃liquid two⁃phase brine inclusion combination, PPL; (b) well Dagu 82, 2 550.0 m, the red box is the quartz secondary overgrowth edge position of the inclusion combination in figure (a), PPL; (c) well Dagu 82, 2 550.0 m, with the same field of view as figure (b), brown quartz secondary overgrowth edge, CL; (d) well Da 675, 3 101.6 m, the second phase of black quartz secondary overgrowth edge in the oval gas⁃liquid two⁃phase brine inclusion combination, PPL; (e) well Da 675, 3 101.6 m, the red box is the quartz secondary overgrowth edge position of the inclusion combination in figure (a), PPL; (f) well Da 675, 3 101.6 m, with the same field of view as figure (b), brown quartz secondary overgrowth edge, CL

    Figure  13.  Assemblage of the gas⁃liquid two⁃phase brine inclusions in quartz overgrowth edge

    Fig.13

    图  14  石英次生加大边中气液两相盐水包裹体均一温度分布直方图

    Figure  14.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions in the quartz overgrowth edges

    图  15  碳酸盐胶结物中的气液两相盐水包裹体组合

    (a) well Da 675, 3 101.6 m, rhombic and rectangular gas⁃liquid two⁃phase brine inclusions in siderite, PPL; (b) well Da 675, 3 101.6 m, the siderite position where the inclusion combination is located in figure a has good self⁃shape, PPL; (c) well Dagu 82, 2 550.0 m, oval gas⁃liquid two⁃phase brine inclusions in ankerite, PPL; (d) well Dagu 82, 2 550.0 m, the position of ankerite where the inclusion combination is located in figure (c), the surface is dirty, PPL

    Figure  15.  Combination of gas⁃liquid two⁃phase brine inclusions in carbonate cements

    Fig.15

    图  16  碳酸盐胶结物中气液两相盐水包裹体均一温度分布直方图

    Figure  16.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions in the carbonate cements

    图  17  济阳坳陷大王庄地区石炭系太原组储层成岩—成藏演化序列

    Figure  17.  Diagenetic⁃accumulation evolution sequence reservoir for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    图  18  济阳坳陷大王庄地区构造演化剖面

    (a) Middle Triassic; (b) Late Triassic; (c) the end of the Early Cretaceous; (d) Kongdian period; (e) Fourth member of Shahejie Formation; (f) present day

    Figure  18.  Structural evolution of the Dawangzhuang area in the Jiyang Depression

    Fig.18

    图  19  济阳坳陷大王庄地区石炭系太原组岩屑类型及结构特征

    (a) well Da 675, 3 100.1 m, basalt debris, with obvious coarse basalt structure, cross⁃polarized light (XPL); (b) well Da 675, 3 100.1 m, basalt debris, containing a large number of dark iron⁃rich dark minerals, PPL; (c) well Dagu 82, 2 550.0 m, the interior of the amygdaloid structure of the cuttings was filled with quartz in the later stage, XPL

    Figure  19.  Rock debris types and structural characteristics of the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

    Fig.19

    图  20  济阳坳陷大王庄地区南北向地震剖面(测线位于图1a,AB)

    Figure  20.  North⁃south seismic profile of the Dawangzhuang area in the Jiyang Depression (survey line located on the Fig.1a, AB)

    图  21  济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩优质储层成因模式

    Figure  21.  High⁃quality reservoir genesis model for the Carboniferous Taiyuan Formation Dawangzhuang area, Jiyang Depression

    表  1  济阳坳陷大王庄地区石炭系太原组储层中菱铁矿和铁白云石胶结物微量元素含量(10-6)及地球化学参数

    Table  1.   Trace element contents (10-6) and geochemical parameters of siderite and ankerite from C3t in the Dawangzhuang area, Jiyang Depression

    井号深度/m矿物类型LiTiVCrCoNiRbSrBaV/CrV/(V+Ni)Sr/Ba
    大6753 101.6Sd0.351.466.720.771.410.0125.992.978.698.74
    大6753 101.6Sd0.661.764.450.920.920.0837.682.544.8114.83
    大6753 101.6Sd0.502.1715.382.990.941.520.0128.043.565.140.917.87
    大6753 101.6Sd0.382.1414.452.033.431.190.0428.344.567.140.926.22
    大6753 101.6Sd0.601.124.651.091.724.850.0023.061.544.260.4914.96
    大6753 101.6Sd0.541.737.441.170.900.450.0734.163.406.340.9410.05
    大6753 101.6Sd1.132.4124.346.552.989.372.4827.2614.953.710.721.82
    大6753 101.6Sd0.583.5417.041.490.991.3718.745.3111.400.933.53
    大6753 101.6Sd0.482.197.232.500.671.000.0122.991.492.890.8815.40
    大6753 101.6Sd0.524.7019.524.014.190.7330.702.714.870.9611.35
    大6753 101.6Sd0.421.785.970.778.535.0629.353.377.740.548.72
    大6753 101.6Sd0.390.804.150.850.751.090.0629.451.464.900.7920.13
    大6753 101.6Sd0.481.8310.811.781.580.9732.051.976.070.9216.29
    大古822 546.5Sd1.690.031.600.4656.3887.059.850.383.520.0226.02
    大古822 546.5Sd1.320.0832.933.5152.8986.920.027.580.239.380.2733.16
    大古822 546.5Sd1.050.2665.193.3643.6764.240.006.560.1519.410.5043.18
    大古822 546.5Sd1.023.0772.458.9113.324.310.2515.821.808.130.948.79
    大古822 546.5Sd0.391.795.301.030.380.0317.282.025.158.56
    大古412 717.8Ank0.122.7741.796.4367.8229.1398.930.726.500.59136.95
    大古412 717.8Ank0.243.3346.215.7844.3220.000.8094.741.158.000.7082.12
    大6753 101.6Ank0.059.3081.0019.810.750.300.02193.830.324.091.00603.90
    大6753 101.6Ank0.082.5840.648.190.190.0180.930.234.96354.28
    大6753 101.6Ank0.908.510.623.132.380.02136.650.0713.820.782 026.10
    大6753 101.6Ank0.052.2267.939.271.013.720.04123.981.257.330.9598.98
    大6753 101.6Ank0.053.18116.717.300.621.050.01135.170.426.750.99319.11
    大古822 546.7Ank0.031.0141.577.453.443.64104.262.185.580.9247.80
    大古822 546.7Ank0.020.8238.157.713.704.73221.1943.084.950.895.13
    大古822 546.7Ank0.141.0935.806.153.814.100.14237.7832.505.830.907.32
    大古822 546.7Ank0.101.2029.913.082.010.570.02281.0937.449.700.987.51
    大古822 546.7Ank0.060.3626.862.132.040.69241.7818.2012.630.9713.28
    大古822 546.7Ank0.7436.007.593.885.380.03147.061.084.740.87136.08
    大古822 546.7Ank0.091.4716.044.173.873.590.18171.832.073.850.8283.03
    大古822 546.7Ank0.7217.3225.495.444.332.891.36328.9418.774.680.9017.53
    大古822 546.7Ank0.091.4314.564.944.345.200.02107.650.492.950.74221.80
    大古822 546.7Ank0.2011.8014.396.162.523.520.79271.474.982.330.8054.49
    大古822 546.7Ank0.152.7941.1215.893.052.040.14234.552.652.590.9588.43
    大古822 546.7Ank0.550.4714.122.613.764.150.06186.218.395.420.7722.18
    大古822 550.4Ank0.133.7439.8310.126.356.23600.620.383.940.861592.05
    大古822 550.4Ank1.2694.9525.334.8111.294.780.72300.4351.005.270.845.89
    大古822 550.4Ank0.1979.4417.573.752.772.200.97253.0613.234.680.8919.13
    下载: 导出CSV

    表  2  济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩储层分类评价

    Table  2.   Classification and evaluation of clastic rock reservoirs in coal⁃bearing strata from the Carboniferous Taiyuan Formation Dawangzhuang area, Jiyang Depression

    储层类型岩相成岩相与对接断层距离储集空间孔隙度/%渗透率/×10-3μm2
    中、粗砂岩溶蚀增孔主控型次生孔>8>5
    中砂岩压实和溶蚀共控型较远次生孔、残余粒间孔5~81~5
    中砂岩压实—胶结主控型微量次生孔2~50.1~1.0
    细砂岩压实主控型几乎不发育<2<0.1
    下载: 导出CSV
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出版历程
  • 收稿日期:  2023-11-02
  • 修回日期:  2023-12-19
  • 录用日期:  2024-01-10
  • 网络出版日期:  2024-01-10
  • 刊出日期:  2025-12-10

目录

    煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例

    doi: 10.14027/j.issn.1000-0550.2023.138
      基金项目:

      国家自然科学基金项目 42272165

      作者简介:

      宋磊,男,1997年出生,硕士研究生,油气储层地质学,E-mail: 1244501248@qq.com

      通讯作者: 王淑萍,女,讲师,油气储层评价,E-mail: wshp0619@163.com

    摘要: 目的 济阳坳陷大王庄地区石炭系太原组煤系地层分布广泛,煤系地层中的优质储层控制因素对油气勘探有重要影响,但是其储层特征及成因模式尚不明确。 方法 综合利用薄片鉴定、阴极发光、扫描电镜、流体包裹体、C-O同位素、原位激光剥蚀等技术方法,结合埋藏史和构造演化史研究,对济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩优质储层特征及成因模式进行了研究。 结果 济阳坳陷大王庄地区太原组煤系地层碎屑岩储层以岩屑质石英砂岩为主,优质储层储集空间以次生孔隙为主,主要为大气淡水以及有机酸溶蚀形成的填隙物溶蚀孔和长石溶蚀孔。胶结物为两期石英次生加大边和两期碳酸盐胶结物,以碳酸盐胶结物为主。两期石英加大边分别来源于石英颗粒的压溶作用和长石溶解供源。菱铁矿为同沉积—早成岩阶段由孔隙水沉淀形成的成岩碳酸盐岩,铁白云石主要与有机酸脱羧作用形成的CO2有关。 结论 沉积相控制了现今优质储层岩相的分布位置,优质储层主要受控于晚期抬升的大气淡水淋滤作用以及埋藏有机酸溶蚀作用;受构造活动控制,优质储层与对接断层的距离较远,避免了脱羧作用产生的CO2进一步沉淀形成铁白云石破坏储层物性。

    English Abstract

    宋磊, 王淑萍, 赵妍菲, 孙沛沛, 盛凯. 煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例[J]. 沉积学报, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
    引用本文: 宋磊, 王淑萍, 赵妍菲, 孙沛沛, 盛凯. 煤系地层优质储层特征及成因模式——以济阳坳陷大王庄地区石炭系太原组为例[J]. 沉积学报, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
    SONG Lei, WANG ShuPing, ZHAO YanFei, SUN PeiPei, SHENG Kai. Characteristics and Genetic Model of High-quality Reservoir of Clastic Rocks in Coal-bearing Strata: A case of the Carboniferous Taiyuan Formation in the Dawangzhuang area, Jiyang Depression[J]. Acta Sedimentologica Sinica, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
    Citation: SONG Lei, WANG ShuPing, ZHAO YanFei, SUN PeiPei, SHENG Kai. Characteristics and Genetic Model of High-quality Reservoir of Clastic Rocks in Coal-bearing Strata: A case of the Carboniferous Taiyuan Formation in the Dawangzhuang area, Jiyang Depression[J]. Acta Sedimentologica Sinica, 2025, 43(6): 2114-2134. doi: 10.14027/j.issn.1000-0550.2023.138
      • 石炭系—二叠系是全球主要的聚煤期之一[12],煤系地层广泛分布于我国的含油气盆地中,蕴含丰富的油气资源,具有良好的勘探前景[3]。煤系地层指含煤层的地层,煤系地层中的储集层,称之为煤系储层,一般为低孔低渗或中孔低渗型储层,储集空间以次生孔隙为主[4]。煤系地层优质储层一般受有利沉积相带、沉积早期的酸性水介质、成岩作用类型及强度、晚期有机酸溶蚀作用等因素的控制[35]。煤系储层和常规储层的一个显著区别是煤系储层在早成岩阶段一般以酸性水介质为主,极少沉淀碳酸盐、硫酸盐以及大部分硅酸盐矿物来提高储层的抗压实能力,导致原生孔隙大大减少,在中成岩早期因煤系烃源岩生烃作用产生大量有机酸,造成长石等铝硅酸盐类矿物颗粒溶解,形成以次生孔隙为主的优质储层[45]。但是,对于沉淀了大量碳酸盐胶结物的煤系储层,其碳酸盐胶结物的形成环境、形成时间及对优质储层的影响缺乏细致的分期次研究,优质储层的次生孔隙成因与构造背景、成岩演化和煤系烃源岩生烃及晚期有机酸脱羧之间的关系缺乏系统研究[47]

        煤系地层的优质储层特征及控制因素研究是煤系储层油气勘探的关键[35],渤海湾盆地济阳坳陷煤系地层分布于各次级凹陷中[67]。大王庄地区石炭系太原组主要由煤系地层组成,储层非均质性较强,其中大675井在太原组产出工业油气,但是,目前的研究主要集中在烃源岩评价[8]、岩相古地理[6,9]、生烃史[10]等方面,缺乏对大王庄地区石炭系太原组煤系储层的系统研究,是该区油气勘探虽然取得了突破但勘探成功率较低的主要原因。因此,本文旨在恢复大王庄地区石炭系太原组煤系储层的成岩演化序列,分析其优质储层的主控因素,尤其是次生孔隙的成因以及碳酸盐胶结物对储层的影响,以大王庄地区石炭系太原组为例建立煤系地层优质储层成因的一般模式。研究成果可对济阳坳陷煤系地层优质储层的研究及油气勘探提供参考,并有助于寻找煤系地层分布地区的有利储层。

      • 济阳坳陷位于渤海湾盆地东南隅,是渤海湾盆地的次一级负向构造单元,面积约2.6×104 km2,坳陷内包括车镇、沾化、惠民和东营四个凹陷[11]。车镇凹陷为济阳坳陷西北部的一个次级凹陷,北部和西部与埕宁隆起以断层相隔、南部过渡至无棣凸起和义和庄凸起,东部与沾化凹陷相邻,呈狭长的“S”型展布(图1a),是一个北断南超的“箕状”断陷盆地[1213],现今位于斜坡带的上古生界与洼陷带的沙河街组通过断层对接(图1b)。大王庄地区位于车镇凹陷东北部,处于盆地的缓坡构造带。该区在早古生代奥陶纪晚期因加里东运动而整体上升为陆地,缺失了上奥陶统、志留系、泥盆系和下石炭统(图1c),从晚石炭世开始因海西运动而沉降接受沉积形成上古生界,自下而上依次发育本溪组、太原组、山西组、下石盒子组。其中,太原组为一套海陆过渡相沉积的煤系地层,潟湖泥炭坪相和障壁岛岛后泥坪相为太原组主要成煤环境[6,14],发育三套煤层,单层厚度介于3.5~8.5 m(图1c),砂岩储层主要为障壁岛相[6,9],太原组现今埋深介于2 500~3 200 m。上古生界发育两套煤系烃源岩——本溪组和太原组,生成的油气以煤成气为主[15],但根据油气勘探实践现今储层产出以石油为主。

        图  1  济阳坳陷大王庄地区地质概况

        Figure 1.  Structural location, strata, and north⁃south structural section of the Dawangzhuang area, Jiyang Depression

      • 为了分析储层储集空间、成岩作用以及成岩演化序列,从胜利油田勘探开发研究院采集了济阳坳陷大王庄地区太原组2 550.0~3 101.6 m范围内12块岩心样品。在中国石油大学(华东)深层油气全国重点实验室,使用蔡司Axioscope A1 APOL数字透射显微镜观察了12个铸体薄片;在配备CL8200-MKSCL仪器的蔡司Axioscope A1 APOL光学显微镜下对硅质胶结物和碳酸盐胶结物进行了阴极发光分析;制备了15片厚度约为0.05 mm的双面抛光薄片,利用蔡司Imager A1m多功能显微镜对烃类流体包裹体岩相学特征进行显微观察,包括流体包裹体尺寸、产状、相态、气液比、宿主矿物以及烃类包裹体的荧光颜色,依据同一石英破裂愈合缝或交叉石英破裂愈合缝为同一期包裹体组合的原则划分出不同的烃类包裹体组合。对硅质胶结物和碳酸盐胶结物中包裹体组合进行研究,硅质胶结物包裹体组合首先在偏光显微镜下观察并寻找胶结物中的包裹体,为避免阴极发光分析中测试仓温度对气液两相盐水包裹体稳定态的影响,需要在测温之后在阴极发光显微镜下观察包裹体组合所在碳酸盐胶结物和硅质胶结物的阴极发光特征。选取了12块包裹体发育且适合测温的薄片,依据循环测温流程[16],使用配备50倍物镜、10倍目镜和校准的Linkam THMSG600型冷热台进行气液两相盐水包裹体的均一温度测定,该仪器的温度测量范围为-196 ℃至600 ℃,测定误差在±1 ℃。利用50 μm、100 μm的微钻系统,对14个薄片样品进行了菱铁矿和铁白云石胶结物的微钻取样,利用MAT253稳定同位素质谱仪测定了菱铁矿和铁白云石胶结物粉末的C-O同位素值,δ13C和δ18O的测量精度小于0.6‰和0.8‰。

        在中国科学院地球化学研究所矿床地球化学国家重点实验室,通过激光剥蚀电感耦合等离子质谱仪分析,测试了厚度约为0.1 mm的9个薄片中长石、硅质胶结物、碳酸盐胶结物以及高岭石中的微量元素和稀土元素含量,数据处理使用CPMSDataCal 10.7软件,采用多外标、单内标的元素含量分析处理方法[17],稀土元素含量分析采用澳大利亚后太古宙页岩(PASS)和北美页岩(N)进行标准化[1819]

      • 济阳坳陷大王庄地区太原组储层岩石类型有粗砂岩、中砂岩、细砂岩、粉砂岩,以中、粗砂岩为主。储层以岩屑质石英砂岩为主,其次为岩屑质长石砂岩和长石岩屑砂岩,成分成熟度较低,石英面积含量介于13%~86%(平均56.9%),岩屑(主要为喷出岩岩屑)面积含量介于14%~75%(平均28.1%),长石面积含量介于0~35%(平均15.1%)(图2);杂基含量较低,一般介于3%~23%;胶结物主要为硅质胶结物、高岭石和铁白云石,平均含量分别为5.3%、2.6%和6.8%;颗粒分选较好,磨圆为次圆—次棱角状。

        图  2  济阳坳陷大王庄地区石炭系太原组储层砂岩分类三角图

        Figure 2.  QFL triangular diagram of reservoir sandstones from the Carboniferous Taiyuan Formation (C3t) in the Dawangzhuang area, Jiyang Depression

      • 济阳坳陷大王庄地区太原组碎屑岩储层孔隙整体上发育较好,以溶蚀孔隙为主,主要类型为填隙物溶蚀孔、长石溶蚀孔隙,此类孔隙大小不均,极不规则,但连通性较好(图3a,b);原生孔隙保存相对较少,主要为分布在石英颗粒间的原生孔隙,边缘平直,通常表现为三角形或多边形,孔隙直径较小,形状规则,但平面连通性差(图3c)。储层孔隙度介于0.5%~12.2%,平均值为8.0%,85%以上的孔隙度介于0~10.0%(图4);渗透率介于(0.012~134.32)×10-3 μm2,平均值为4.54×10-3 μm2,90%以上的渗透率小于10×10-3 μm2图4),孔隙度与渗透率交会图显示物性相关性较差(R2=0.252 5)(图5),整体为低孔低渗的砂岩储层。

        图  3  济阳坳陷大王庄地区石炭系太原组碎屑岩储层储集空间类型

        Figure 3.  Reservoir storage⁃space types of clastic reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area,Jiyang Depression

        图  4  济阳坳陷大王庄地区石炭系太原组砂岩储层物性特征

        Figure 4.  Physical properties of sandstone reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

        图  5  济阳坳陷大王庄地区石炭系太原组砂岩储层孔隙度与渗透率关系

        Figure 5.  Relationship between porosity and permeability of sandstone reservoirs for the Carboniferous Taiyuan Formation,Dawangzhuang area, Jiyang Depression

      • 济阳坳陷大王庄地区太原组碎屑岩储层压实作用中等,颗粒以点—线接触、线接触为主(图6a),可见云母等塑性颗粒压弯变形(图6b);胶结作用在研究区广泛发育,主要为硅质胶结物、碳酸盐胶结物以及少量的高岭石和黄铁矿。其中,碳酸盐胶结物最为发育,主要为菱铁矿和铁白云石胶结,硅质胶结物主要为石英次生加大边。

        图  6  济阳坳陷大王庄地区石炭系太原组砂岩储层成岩作用类型及特征

        Figure 6.  Types and characteristics of diagenesis in sandstone reservoirs for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

      • 济阳坳陷大王庄地区太原组碎屑岩储层经历了强烈的溶蚀作用,主要表现为长石、岩屑和填隙物的溶蚀(图6c~f)。其中,长石颗粒一般沿解理缝溶蚀破碎,或者经历强烈的溶蚀作用后只剩残余部分,或者颗粒完全消失形成铸模孔(图6c,d),岩屑一般发生粒内溶蚀形成蜂窝状的溶孔(图6e),填隙物受溶蚀作用影响使得之前在孔隙中的矿物颗粒呈漂浮状(图6f)。其中,主要为长石颗粒和填隙物的强烈溶蚀,形成了以次生孔隙为主的砂岩储层。

      • 研究区太原组储层硅质胶结物较为发育(图6g),主要为石英次生加大边,在偏光显微镜下可见明显的两期尘迹线(图6h)。阴极发光显微镜下第一期石英次生加大边呈棕色(图6i),环绕石英颗粒边缘生长,宽度介于10~90 μm(图6i),微量元素Li、Na、Sc、Ti、Ge、Sr与微量元素Al的含量分布关系图中显示,第一期石英次生加大边与石英颗粒的分布范围大部分一致,少量在石英颗粒的分布范围之外,两者的Al含量主要分布在小于500×10-6的范围(图7)。第二期石英次生加大边在阴极发光显微镜下呈黑色(图6i),其在第一期石英次生加大边的基础上呈锯齿状继续向外生长,宽度介于10~120 μm(图6i),是研究区硅质胶结物的主要形式。其微量元素的分布范围与石英颗粒相差较大,第二期石英次生加大Al的含量主要分布在大于500×10-6的范围(图7)。微量元素分析表明长石颗粒与第二期石英次生加大边的微量元素分布特征一致,表现为明显的Ti、Fe、Rb、Ba元素富集,Sc、V、Co元素贫乏,而第一期石英次生加大边的微量元素分布特征与长石颗粒相差较大,主要表现在Sc、Sr、Ba元素(图8)。

        图  7  石英颗粒和石英次生加大边微量元素含量关系

        Figure 7.  Correlation of trace elements content between quartz grains and quartz overgrowth edge

        图  8  长石颗粒和第二期石英次生加大边微量元素分布特征图

        Figure 8.  Characteristics of trace elements in the feldspar and the second phase of quartz overgrowth

      • 碳酸盐胶结物在研究区最为发育,以铁白云石和菱铁矿为主,填充在粒间孔隙中(图6j,k),菱铁矿主要分布在大675井,深度在3 100 m左右,大古41井几乎不发育菱铁矿,大古82井发育少量菱铁矿,深度在2 546 m左右,铁白云石则在各个井段均有分布。铁白云石呈他形填充于粒间孔隙或菱铁矿的剩余空间,表面光洁(图6j),菱铁矿在单偏光下呈黄褐色,自形较好,常分布于孔隙边缘,向孔隙内部生长(图6k)。阴极发光下铁白云石呈黑色,常发育亮红色环边(图6l),菱铁矿呈黑棕色(图6m)。扫描电镜下可见菱铁矿具有完整的菱面体形态(图6n),铁白云石呈多个菱面结合体形态填充于粒间孔隙(图6o)。菱铁矿和铁白云石的微量元素含量及相关比值(V/Cr、V/(V+Ni)、Sr/Ba)见表1,菱铁矿的V/Cr介于2.89~19.41,平均值为6.86,V/(V+Ni)介于0.02~0.96,平均值为0.71,Sr/Ba介于1.82~43.18,平均值为14.42;铁白云石的V/Cr介于2.33~13.82,平均值为5.94,V/(V+Ni)介于0.02~0.96,平均值为0.91,Sr/Ba介于5.13~2 026.1,平均值为270.1。菱铁矿稀土元素分布呈“平坦型”,铁白云石轻稀土和重稀土元素贫乏,呈典型的“帽型结构”(图9),两者的Gd/Gd*N(Gd*N=(EuN+TbN))均大于1,菱铁矿和铁白云石的Gd/Gd*N分别介于3.78~6.86和4.18~10.95(表1)。C-O同位素分析表明菱铁矿的δ13CPDB值介于-5.3‰~-1.7‰,δ13OPDB值介于-9.8‰~-6.8‰,铁白云石的δ13CPDB值介于-6.3‰~-3.5‰,δ13OPDB值介于-17.2‰~-14.6‰(图10)。

        表 1  济阳坳陷大王庄地区石炭系太原组储层中菱铁矿和铁白云石胶结物微量元素含量(10-6)及地球化学参数

        Table 1.  Trace element contents (10-6) and geochemical parameters of siderite and ankerite from C3t in the Dawangzhuang area, Jiyang Depression

        井号深度/m矿物类型LiTiVCrCoNiRbSrBaV/CrV/(V+Ni)Sr/Ba
        大6753 101.6Sd0.351.466.720.771.410.0125.992.978.698.74
        大6753 101.6Sd0.661.764.450.920.920.0837.682.544.8114.83
        大6753 101.6Sd0.502.1715.382.990.941.520.0128.043.565.140.917.87
        大6753 101.6Sd0.382.1414.452.033.431.190.0428.344.567.140.926.22
        大6753 101.6Sd0.601.124.651.091.724.850.0023.061.544.260.4914.96
        大6753 101.6Sd0.541.737.441.170.900.450.0734.163.406.340.9410.05
        大6753 101.6Sd1.132.4124.346.552.989.372.4827.2614.953.710.721.82
        大6753 101.6Sd0.583.5417.041.490.991.3718.745.3111.400.933.53
        大6753 101.6Sd0.482.197.232.500.671.000.0122.991.492.890.8815.40
        大6753 101.6Sd0.524.7019.524.014.190.7330.702.714.870.9611.35
        大6753 101.6Sd0.421.785.970.778.535.0629.353.377.740.548.72
        大6753 101.6Sd0.390.804.150.850.751.090.0629.451.464.900.7920.13
        大6753 101.6Sd0.481.8310.811.781.580.9732.051.976.070.9216.29
        大古822 546.5Sd1.690.031.600.4656.3887.059.850.383.520.0226.02
        大古822 546.5Sd1.320.0832.933.5152.8986.920.027.580.239.380.2733.16
        大古822 546.5Sd1.050.2665.193.3643.6764.240.006.560.1519.410.5043.18
        大古822 546.5Sd1.023.0772.458.9113.324.310.2515.821.808.130.948.79
        大古822 546.5Sd0.391.795.301.030.380.0317.282.025.158.56
        大古412 717.8Ank0.122.7741.796.4367.8229.1398.930.726.500.59136.95
        大古412 717.8Ank0.243.3346.215.7844.3220.000.8094.741.158.000.7082.12
        大6753 101.6Ank0.059.3081.0019.810.750.300.02193.830.324.091.00603.90
        大6753 101.6Ank0.082.5840.648.190.190.0180.930.234.96354.28
        大6753 101.6Ank0.908.510.623.132.380.02136.650.0713.820.782 026.10
        大6753 101.6Ank0.052.2267.939.271.013.720.04123.981.257.330.9598.98
        大6753 101.6Ank0.053.18116.717.300.621.050.01135.170.426.750.99319.11
        大古822 546.7Ank0.031.0141.577.453.443.64104.262.185.580.9247.80
        大古822 546.7Ank0.020.8238.157.713.704.73221.1943.084.950.895.13
        大古822 546.7Ank0.141.0935.806.153.814.100.14237.7832.505.830.907.32
        大古822 546.7Ank0.101.2029.913.082.010.570.02281.0937.449.700.987.51
        大古822 546.7Ank0.060.3626.862.132.040.69241.7818.2012.630.9713.28
        大古822 546.7Ank0.7436.007.593.885.380.03147.061.084.740.87136.08
        大古822 546.7Ank0.091.4716.044.173.873.590.18171.832.073.850.8283.03
        大古822 546.7Ank0.7217.3225.495.444.332.891.36328.9418.774.680.9017.53
        大古822 546.7Ank0.091.4314.564.944.345.200.02107.650.492.950.74221.80
        大古822 546.7Ank0.2011.8014.396.162.523.520.79271.474.982.330.8054.49
        大古822 546.7Ank0.152.7941.1215.893.052.040.14234.552.652.590.9588.43
        大古822 546.7Ank0.550.4714.122.613.764.150.06186.218.395.420.7722.18
        大古822 550.4Ank0.133.7439.8310.126.356.23600.620.383.940.861592.05
        大古822 550.4Ank1.2694.9525.334.8111.294.780.72300.4351.005.270.845.89
        大古822 550.4Ank0.1979.4417.573.752.772.200.97253.0613.234.680.8919.13

        图  9  济阳坳陷大王庄地区石炭系太原组碳酸盐胶结物稀土元素分布特征

        Figure 9.  Distribution characteristics of rare earth elements in carbonate cements from the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

        图  10  济阳坳陷大王庄地区石炭系太原组砂岩中碳酸盐胶结物C⁃O同位素特征

        Figure 10.  Diagram showing carbon and oxygen isotopic characteristics of various carbonate cements in the sandstone from the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

      • 济阳坳陷大王庄地区太原组煤系地层碎屑岩储层除了发育硅质胶结和碳酸盐胶结物之外,高岭石和黄铁矿胶结也较为发育。高岭石呈蠕虫状充填于粒间孔隙和喉道(图6p),晶体呈假六方板状(图6q)。黄铁矿呈规则四边形或不规则状充填于粒间孔隙中,具有强烈的金属光泽,呈团块状填充于粒间孔隙,较为发育(图6r)。

      • 济阳坳陷大王庄地区太原组砂岩储层发育3类流体包裹体组合类型:石英颗粒破裂愈合缝中的气液两相烃类包裹体与气液两相盐水包裹体组合、石英次生加大边中的气液两相盐水包裹体组合以及菱铁矿、铁白云石中的气液两相盐水包裹体组合。

        气液两相烃类包裹体在荧光下分别呈黄色和蓝色,主要发育于石英颗粒破裂愈合缝中,呈群落状或串珠状分布,以蓝色荧光油包裹体为主(图11a,b)。荧光下呈黄色的气液两相油包裹体单偏光下为黄褐色,直径介于2~8 μm,形态从近圆形、三角形到不规则多边形均有发育(图11c,d);荧光下呈蓝色的气液两相油包裹体单偏光下多呈透明无色状,有的呈黄褐色,其直径变化较大,介于3~18 μm,形态多为椭圆形(图11e,f)。两种荧光的气液两相油包裹体气泡体积约占包裹体体积的2%~5%,与气液两相油包裹体同期的气液两相盐水包裹体呈串珠或群落状沿石英颗粒破裂愈合缝发育,透明无色,直径介于3~7 μm,形态多为三角形和椭圆形,不发荧光(图11c~f)。与气液两相黄色荧光油包裹体同期的气液两相盐水包裹体均一温度主峰分布在90 ℃~100 ℃(图12),与气液两相蓝色荧光油包裹体同期的气液两相盐水包裹体均一温度主峰分布在100 ℃~110 ℃(图12);阴极发光下呈棕色的第一期石英次生加大边中气液两相盐水包裹体呈孤立状或串珠状发育,形态多呈椭圆形到近圆形,直径介于3~6 μm(图13a~c),均一温度主峰分布在90 ℃~100 ℃(图14);阴极发光下呈黑色的第二期石英次生加大边中气液两相盐水包裹体多呈串珠状分布,形态呈椭圆形,直径介于2~4 μm,发育较多(图13d~f),均一温度主峰分布在110 ℃~120 ℃(图14)。

        图  11  石英颗粒破裂愈合缝中油包裹体与气液两相盐水包裹体组合

        Figure 11.  Combination of gas⁃liquid two⁃phase hydrocarbon inclusions and gas⁃liquid two⁃phase brine inclusions in the healed fractures of quartz grains

        图  12  石英颗粒破裂愈合缝中与气液两相烃类包裹体同期的气液两相盐水包裹体均一温度分布直方图

        Figure 12.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions coeval with the gas⁃liquid two⁃phase hydrocarbon inclusions in the healed fractures of the quartz grains

        图  13  石英次生加大边中的气液两相盐水包裹体组合

        Figure 13.  Assemblage of the gas⁃liquid two⁃phase brine inclusions in quartz overgrowth edge

        图  14  石英次生加大边中气液两相盐水包裹体均一温度分布直方图

        Figure 14.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions in the quartz overgrowth edges

        菱铁矿因自身呈黄褐色,表面较脏,其中的气液两相盐水包裹体在单偏光下边缘较为模糊,多呈孤立状发育,偶见群落状发育,形态多呈菱形或矩形,直径介于3~12 μm(图15a,b);铁白云石中气液两相盐水包裹体呈孤立状分布,形态多呈椭圆形,直径介于2~11 μm(图15c,d)。菱铁矿中的气液两相盐水包裹体均一温度介于60 ℃~90 ℃,主峰介于80 ℃~90 ℃(图16),冰点温度介于-6.3 ℃~-8.6 ℃,根据冰点温度推算盐度介于9.60%~12.39%[20];铁白云石中的气液两相盐水包裹体均一温度主峰介于100 ℃~130 ℃(图16),主峰介于100 ℃~110 ℃,冰点温度介于-3.1 ℃~-4.5 ℃,根据冰点温度推算盐度介于5.11%~7.17%[20]

        图  15  碳酸盐胶结物中的气液两相盐水包裹体组合

        Figure 15.  Combination of gas⁃liquid two⁃phase brine inclusions in carbonate cements

        图  16  碳酸盐胶结物中气液两相盐水包裹体均一温度分布直方图

        Figure 16.  Histogram showing homogenization temperature distribution of the gas⁃liquid two⁃phase brine inclusions in the carbonate cements

      • 在济阳坳陷大王庄地区太原组煤系地层碎屑岩储层岩石学及储集特征、成岩作用类型及特征、流体包裹体岩相学和均一温度研究的基础上,将硅质胶结物、碳酸盐胶结物中的气液两相盐水包裹体,与气液两相黄色荧光油包裹体、气液两相蓝色荧光油包裹体同期的气液两相盐水包裹体的均一温度,投点到埋藏史图(以大675井为例),确定了硅质胶结物和碳酸盐胶结物形成以及油气充注的时间,结合微量元素、稀土元素及C-O同位素分析、盆地构造演化[21]和现今油气勘探实践,建立了大王庄地区太原组煤系储层的成岩—成藏演化序列和盆地构造演化史(图1718)。

        图  17  济阳坳陷大王庄地区石炭系太原组储层成岩—成藏演化序列

        Figure 17.  Diagenetic⁃accumulation evolution sequence reservoir for the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

        图  18  济阳坳陷大王庄地区构造演化剖面

        Figure 18.  Structural evolution of the Dawangzhuang area in the Jiyang Depression

        晚石炭世,大王庄地区太原组沉积了一套海陆过渡相的地层,泥坪相为太原组主要的成煤环境,障壁岛相为砂岩储层的主要发育环境,而潮坪相、泥坪相形成了主要的分隔层[22]。济阳坳陷北部阴山造山带东部的富铁质玄武岩可能为研究区主要的沉积物源之一[2324],因为在薄片中发现了大量的玄武岩岩屑以及保留杏仁体结构的喷出岩岩屑(图19),母岩在风化过程中形成的铁质随频繁的海进海退进入沉积盆地,为菱铁矿的沉积提供铁的物质来源。一般认为,V/Cr>4.25、V/(V+Ni)>0.77为厌氧的还原沉积环境,2<V/Cr<4.25、0.60<V/(V+Ni)<0.77为弱氧化—弱还原环境,V/Cr<2、V/(V+Ni)<0.60为氧化环境[2526];Sr/Ba>1.0为海相环境,0.6<Sr/Ba<1.0为海陆过渡相环境,Sr/Ba<0.6为陆相沉积[27];Gd/Gd*正异常(大于1)表示海相还原环境[28]。菱铁矿的V/Cr介于2.89~19.41,平均值为6.86,V/(V+Ni)介于0.02~0.96,平均值为0.71,Sr/Ba介于1.82~43.18,平均值为14.42,表明其形成于还原的咸水海相环境,菱铁矿较低的冰点温度对应其较高的盐度[29],也佐证了这一点。

        图  19  济阳坳陷大王庄地区石炭系太原组岩屑类型及结构特征

        Figure 19.  Rock debris types and structural characteristics of the Carboniferous Taiyuan Formation, Dawangzhuang area, Jiyang Depression

        碳酸盐胶结物的δ13C值与其C来源有关,受有机碳影响则偏负值,与无机碳有关则偏正值[30];碳酸盐胶结物的δ18O值与其形成温度有关,温度高则偏负值,反之偏正值[31]。从碳酸盐胶结物C-O同位素成岩模板投点可看出(图10[3034],本区菱铁矿主要为成岩碳酸盐,并且O同位素的值较高,同期的气液两相盐水包裹体介于80 ℃~90 ℃,也说明其形成于较低的温度下,平坦的稀土元素配分型式也表明其一般形成于早成岩阶段的氧化—还原带[35]。因此,在持续的海平面上升背景下,早期沉积在孔隙水中的Fe3+被还原成Fe2+,孔隙水逐渐由早期的酸性变为微弱碱性,Fe2+与海水中的CO32-才能结合形成菱铁矿充填于粒间孔隙,形成于232~227 Ma(图17);而在频繁海进海退(沉积环境不稳定,少量沉淀),尤其海平面下降(酸性氧化环境)的沉积条件下很难发育菱铁矿,因为菱铁矿一般形成于弱还原—还原的微弱碱性环境[36],现今菱铁矿分布在有限的井段和深度也说明了这一点。中三叠世末期,本溪组和太原组煤系烃源岩埋深介于1 600~1 900 m,Ro刚达到0.5(图17),处于早期生烃阶段,由于地层很快抬升(图18a),推测生烃量较少或未达到生烃门限,并且未找到此时形成的烃类包裹体。

        晚三叠世,受印支运动影响,地层抬升,早期沉积的二叠系顶部地层遭受剥蚀,但大气淡水由于顶部的上、下石盒子组泥岩遮挡并未下渗到太原组(图17图18b)。

        早侏罗世到早白垩世末期,受燕山运动影响,盆地发生负反转,接受沉积(图18c)。在地层持续埋深的背景下,距今125~98 Ma,石英颗粒发生压溶作用形成第一期石英次生加大边,同期气液两相盐水包裹体介于100 ℃~110 ℃(图14),因为第一期石英次生加大边的微量元素大部分与石英颗粒相似[37]图8),同时有少量长石溶解供源,其微量元素分布与自身石英颗粒分布相差较大(图7)。晚侏罗世,本溪组和太原组煤系烃源岩埋深介于1 650~ 2 150 m,地层温度介于85 ℃~105 ℃,Ro大于0.5,二次生烃(图17);距今148~142 Ma,太原组储层发生一期黄色荧光油充注(图17),同期的气液两相盐水包裹体均一温度介于90 ℃~100 ℃(图12)。

        晚白垩世到孔店期,受喜山运动的挤压抬升,受埕南大断层的影响,盆地“北断南超”,古生界南段抬至近地表,本溪组和太原组煤系烃源岩生烃停滞,大气淡水顺层淋滤形成淋滤带、过渡带和沉淀带(图18d),长石遭到溶蚀形成高岭石,充填在粒间孔隙中,并在靠南端形成大量的次生孔隙(图6p)。

        沙四期到第四纪以后,研究区处于断陷湖盆阶段,地层快速埋深,并且埋藏深度大于第二期(图17图18e,f)。封闭体系下煤系烃源岩生烃,有机质热演化,0.95 Ma至今,形成一期铁白云石胶结物(图17),因为铁白云石的稀土元素分布特征具有MREE富集的“帽型结构”,常为孔隙水中沉淀,成因可能为颗粒有机碳中的MREE释放到孔隙水中导致MREE富集[38]。同时,铁白云石的HREE也相对富集,在还原环境下,颗粒有机质分解之后,孔隙水中的HREE会形成碳酸盐络合物,导致孔隙水中的HREE富集[35,39],C-O同位素分析也说明铁白云石的形成与有机酸脱羧作用有关,O同位素的低值说明其形成于较高的温度下,铁白云石中的气液两相盐水包裹体均一温度介于110 ℃~120 ℃也说明了这一点。综上认为,烃源岩在第三期埋深阶段中产生的大量有机酸进入砂岩储层中,使砂岩中的长石、岩屑发生溶蚀形成了大量的次生孔隙,同时为孔隙流体提供了Ca2+、Fe2+;另一方面,底部太原组煤系烃源岩中有机酸热脱羧作用产生的CO2也可与Ca2+、Fe2+相结合,沉淀出铁白云石,但是由于新近纪太原组下伏的烃源岩埋藏深度较浅(图17),而有机酸脱羧反应的最佳温度在140 ℃~150 ℃及以上[4041],所以煤系烃源岩有机酸脱羧作用提供的CO2有限;而新近纪到第四纪受盆地北断南超的构造格局影响,大王庄地区南部斜坡带发育较多的正断层,使沙三下亚段烃源岩与太原组储层侧向对接(图20)。沙三下亚段为富有机质烃源岩,其中由有机酸脱羧作用产生的CO2流体可通过断层充注至太原组,并且埋藏较深,位于洼陷带(图18f),结合济阳坳陷沙三下亚段有机质成熟阶段热解脱羧作用产生CO2δ13CPDB值介于-4‰~-35‰[42],而伴随有机质的成熟和成岩作用的不断进行,形成碳酸盐胶结物的δ13CPDB值应多数低于0[43],研究区铁白云石的δ13CPDB值介于-6.3‰~-3.5‰,也符合这一点,并且形成于有机酸脱羧区的碳酸盐胶结物一般δ13CPDB呈负值[44],因此,铁白云石沉淀可能还受控于与对接断层的距离,对比大古82井与大675井的铁白云石平均含量(面积含量分别为4.9%和8.6%),结合地震剖面,明显距离对接断层远的大古82井铁白云石含量更少。在0.6 Ma至今,长石颗粒受有机酸溶蚀形成第二期石英次生加大边及高岭石(图17),因为第二期石英次生加大边富含Al(图7),而且其微量元素分布与长石相似(图8),同期的气液两相盐水包裹体均一温度介于100 ℃~110 ℃(图14)。渐新世至今,本溪组和太原组煤系烃源岩埋深介于2 500~3 300 m,地层温度介于100 ℃~130 ℃,Ro介于0.6~0.8。0.65 Ma至今,太原组储层发生一期蓝色荧光油充注(图17),同期的气液两相盐水包裹体均一温度介于100 ℃~110 ℃(图12),推测此次油气充注为沙三下亚段和石炭系—二叠系煤系烃源岩的混源充注,以沙三下亚段烃源岩生成的石油为主,因为济阳坳陷古近系烃源岩与太原组储层侧向近距离对接、断—砂疏导体系有利于形成新生古储型油气藏[45],并且济阳坳陷石炭系—二叠系的煤系烃源岩多以生气为主,大675井太原组储层的勘探实践也表明太原组储层以石油产出为主。烃类充注时一般会带来H2S等还原性气体,易与孔隙水中的Fe2+结合生成团块状黄铁矿胶结物(图6r)。

        图  20  济阳坳陷大王庄地区南北向地震剖面(测线位于图1a,AB)

        Figure 20.  North⁃south seismic profile of the Dawangzhuang area in the Jiyang Depression (survey line located on the Fig.1a, AB)

      • 沉积相控制优质储层的有利相带以及砂泥岩的分布特征,对于济阳坳陷大王庄地区石炭系太原组沉积相类型、分布和相模式,前人已开展了大量的研究[6,9,14]。太原组沉积时期北部阴山造山带物源供给能力逐渐增强,海水由东向西覆盖整个研究区,发育潟湖相、障壁岛相、潮坪相[6,9]。障壁岛相主要分布在大王庄地区的南部缓坡带,沉积中心位于大王庄地区的大古82井附近,以沉积岩屑砂岩为主,砂地比大于0.5,在障壁岛外侧发育小范围潮坪沉积,潟湖相广泛发育,主要沉积细砂岩及泥岩[23]。结合前人的研究和地震剖面,推测现今优质储层分布在大王庄地区中部的障壁岛相。另外,同生期成煤的酸性环境对早期成岩作用具有重要影响,不易沉淀碳酸盐岩,降低了储层的抗压实能力。

        成岩作用是研究区优质储层发育的最重要因素,主要表现为对储集空间发育及演化的影响,经过成岩演化分析,认为对济阳坳陷大王庄地区石炭系太原组碎屑岩优质储层具有明显控制作用的成岩作用类型主要有压实作用、胶结作用以及溶蚀作用三种。压实作用是造成济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩储层原生孔隙大量减少的最主要成因。煤系地层在同生期阶段,地层水一般以酸性为主,不沉淀碳酸盐岩,硅质胶结物等。碎屑颗粒紧密堆积,颗粒之间多呈线接触,因此储层的抗压实能力弱。在地层持续埋深的条件下,受上覆地层压力的影响,沉积物被不断压实,云母等塑性颗粒发生扭曲及变形,使储层原生孔隙大量减少、孔隙连通性和孔喉结构变差,进而降低了储层的物性。研究区储层经历三次埋藏演化,并且埋藏深度依次增大,使储层的原生孔隙以及早期形成的次生孔隙均遭到破坏。研究区砂岩分选较好,分选系数S0介于1.0~1.2。按照砂岩的初始孔隙度计算公式(Φ1=20.91+22.90/S0[46],得出太原组储层的初始孔隙度在40.0%左右,实测孔隙度平均值为8.0%。通过镜下圈定硅质胶结物、碳酸盐胶结物以及次生孔隙的面积,得到胶结作用损失孔隙度(胶结物含量)平均值为9.9%,得到溶蚀作用增加的孔隙度(次生孔隙含量)平均值为7.5%。由于构造抬升阶段与深埋藏阶段的溶蚀孔隙特征区分难度大,综合盆地构造演化认为太原组受大气淡水的影响可能更大。因为开放体系下长期的风化淋滤更有助于形成次生孔隙,封闭体系下有机酸流体的活动受限,可能只会影响局部的次生孔隙形成,并且新生代快速埋藏以后太原组地层温度不大于120℃,生成的有机酸含量有限,因为有机酸大量生成的温度区间为80 ℃~140 ℃[47]。压实作用损失孔隙度(=初始孔隙度-胶结物损失孔隙度-实测孔隙度+溶蚀增加孔隙度)为29.6%[48],实际压实作用损失孔隙度可能偏大,因为黄铁矿和高岭石胶结物含量较少,在计算时并未统计在内。从压实率的计算结果来看,太原组储层由压实作用造成的孔隙损失率达到74.1%左右,处于中等压实强度。

        构造作用主要控制了济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩储层的埋藏、抬升以及对接断层的发育,构造的埋藏与抬升控制了相应的埋藏及表生成岩作用,最重要的是使洼陷区的沙三下亚段烃源岩地层与太原组储层发生对接,烃类、有机酸的输入以及后期有机酸脱羧作用对太原组煤系地层碎屑岩储层产生了重要影响,5.1小节已做了详细的分析,此处不再赘述。

      • 综合考虑储层的控制因素,包括沉积相、成岩作用、构造作用。沉积相是优质储层发育的基础,控制了不同粒度砂岩以及砂泥岩(储层及隔夹层)的分布,促进储层物性的分异,溶蚀作用对储层物性具有明显的改善作用,晚期铁白云石胶结物和第二期石英次生加大边胶结了原生孔隙和部分次生孔隙,与对接断层的距离控制着晚期铁白云石胶结物的发育程度。结合这些有利和不利的控制因素,将研究区储层分为较好、中等、较差和差储层4类(表2)。其中将 Ⅰ 类储层定义为优质储层,属于溶蚀增孔主控型且远离对接断层的粗砂岩和中砂岩储层,发育少量的菱铁矿(含量小于5%)和微量的铁白云石胶结物(含量小于5%)和硅质胶结物为主(含量小于4%),以次生孔隙为主,孔隙度大于8%,渗透率大于5×10-3 μm2;Ⅱ类储层主要为压实和溶蚀共控型、距离对接断层较远的中砂岩储层,发育少量的菱铁矿(含量小于10%)和铁白云石胶结物(含量小于10%)和硅质胶结物为主(含量小于8%),孔隙度介于5%~8%,渗透率介于(1~5)×10-3 μm2,次生孔隙较为发育,同时可见少量残余粒间孔;Ⅲ类储层属于压实—胶结主控型、距离对接断层近的中砂岩储层,孔隙度介于2%~5%,渗透率介于(0.1~1)×10-3 μm2,以大量菱铁矿和铁白云石胶结物(含量在15%~20%)为主,同时第二期次生加大边异常发育(含量在5%~10%),次生孔隙几乎被胶结物所充填;Ⅳ类储层主要为压实主控型的细砂岩,孔隙度小于2%,渗透率小于0.1×10-3 μm2,主要受压实作用影响,几乎不发生其他成岩作用,为差储层。

        表 2  济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩储层分类评价

        Table 2.  Classification and evaluation of clastic rock reservoirs in coal⁃bearing strata from the Carboniferous Taiyuan Formation Dawangzhuang area, Jiyang Depression

        储层类型岩相成岩相与对接断层距离储集空间孔隙度/%渗透率/×10-3μm2
        中、粗砂岩溶蚀增孔主控型次生孔>8>5
        中砂岩压实和溶蚀共控型较远次生孔、残余粒间孔5~81~5
        中砂岩压实—胶结主控型微量次生孔2~50.1~1.0
        细砂岩压实主控型几乎不发育<2<0.1
      • 结合研究区的构造发育史,建立了济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩优质储层的成因模式(图21)。

        图  21  济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩优质储层成因模式

        Figure 21.  High⁃quality reservoir genesis model for the Carboniferous Taiyuan Formation Dawangzhuang area, Jiyang Depression

        晚石炭纪,对于障壁岛相沉积的砂岩,同生期由于煤系地层的酸性条件,碳酸盐极少沉淀。但是由于研究区处于海陆过渡相,早成岩阶段,海平面持续下降条件下,地层水继续保持酸性,此时菱铁矿极少沉淀,保存了一定数量的原生孔隙;海平面持续上升条件下,地层孔隙水逐渐由酸性转变为弱碱性,大量的菱铁矿胶结物占据原生孔隙并堵塞喉道,并且未观察到菱铁矿后期发生溶蚀;频繁海进海退条件下,地层孔隙水在酸性与弱碱性之间变换,菱铁矿胶结物沉积条件不稳定,仅少量进行沉淀。

        晚三叠—早侏罗时期虽然地层经历了构造抬升,但由于顶部二叠系(主要为泥岩和砂岩)的遮挡,太原组未受到大气淡水淋滤作用。

        早侏罗—早白垩世末期主要由压溶作用形成的第一期石英次生加大边由于含量较低,所以不但没有破坏储层孔隙,反而提高了储层的抗压实能力,保护了少量的原生孔隙。但是,后期古近纪以来形成的第二期石英次生加大边由于占据的储集空间较大,使得储层部分粒间孔隙和喉道被堵塞,从而破坏了储层的物性。总体上说,硅质胶结物降低了储层的物性。

        晚白垩世到沙四期太原组抬升至近地表,受到大气淡水淋滤,储层遭受第一期溶蚀作用,形成大量的长石、岩屑以及填隙物溶蚀孔,此次溶蚀作用形成了现今以次生孔隙为主的优质储层。新近纪以后,受烃源岩生烃作用影响,有机酸进入太原组储层,使得储层的长石、岩屑及填隙物进一步溶蚀,形成一部分次生孔隙。随着烃源岩的进一步埋深,太原组和沙三下亚段烃源岩内有机酸发生脱羧作用形成的CO2进入太原组储层,形成铁白云石胶结物,他形充填在原生孔隙内菱铁矿占据的剩余空间。

        海平面持续下降条件下,菱铁矿的极少沉淀以及晚期的大气淡水和有机酸溶蚀作用,距离对接断层远的位置形成Ⅰ类储层;频繁海进海退条件下,菱铁矿少量沉淀,距离对接断层中等的位置后期形成 Ⅱ类储层;海平面持续上升条件下,早期菱铁矿大量沉淀堵塞原生孔隙和喉道,后期溶蚀有限,并且距离对接断层较近的位置形成Ⅲ类储层。对于潮坪相沉积的细砂岩,由于压实作用,岩石致密,几乎不发生其他成岩作用,形成Ⅳ类储层。

      • (1) 济阳坳陷大王庄地区太原组碎屑岩储层以岩屑质石英砂岩为主,储集空间以次生孔隙为主,溶蚀作用强烈,主要类型为有机酸溶蚀形成的填隙物和长石溶蚀孔隙,孔隙整体发育较好,储层孔隙度平均为8.0%,渗透率平均为4.54×10-3 μm2。发育两期硅质胶结物和两期碳酸盐胶结物。硅质胶结物主要为石英次生加大边,两期石英次生加大边分别来源于石英颗粒压溶作用以及有机酸溶蚀长石颗粒。碳酸盐胶结物为菱铁矿和铁白云石,菱铁矿主要为海平面上升背景下同沉积时期—早成岩阶段由岩屑溶蚀的Fe2+和海水中的CO32-结合在孔隙水中沉淀,铁白云石由早期有机酸溶蚀长石、岩屑和填隙物形成的Ca2+、Fe2+、Mg2+,结合晚期烃源岩有机酸脱羧作用提供的CO2所形成。

        (2) 济阳坳陷大王庄地区石炭系太原组煤系地层碎屑岩储层成岩—成藏演化序列为:菱铁矿→第一期石英次生加大边→第一期黄色荧光油充注→高岭石→铁白云石→第二期石英次生加大边→第二期蓝色荧光油充注→高岭石→黄铁矿。

        (3) 优质储层受沉积相、成岩作用和构造作用综合控制,沉积相控制了优质储层的原始分布,压实作用及胶结作用整体对储层起破坏性作用,同时与对接断层的距离控制着晚期铁白云石胶结物的沉淀,大气淡水下渗和有机酸溶蚀对优质储层的发育起积极的建设性作用。现今优质储层主要分布在大王庄中心地区的障壁岛相,距离对接断层较远的位置。

        (4) 煤系地层优质储层主要受控于碳酸盐胶结物的沉淀,同生期持续的酸性条件下,不利于早期沉淀碳酸盐胶结物提高储层抗压实能力,原生孔隙遭到破坏。对于经历多期埋藏—抬升的煤系储层,早成岩阶段弱碱—弱还原条件下形成的菱铁矿进一步损失了大量的原生孔隙,晚期抬升大气淡水淋滤或埋藏有机酸溶蚀作用有效改善了储层的物性,形成了以次生孔隙为主的优质储层,同时优质储层应远离有机酸脱羧区,避免脱羧作用产生的CO2使得碳酸盐矿物沉淀堵塞孔隙。

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