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Dec.  2021
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TANG Yu, ZHANG YunFeng, HU LinHui, TANG HongMing, XU Liang, CHEN SiQi, LIU DongXi, ZHONG PingQiang. Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough[J]. Acta Sedimentologica Sinica, 2021, 39(6): 1593-1608. doi: 10.14027/j.issn.1000-0550.2021.096
Citation: TANG Yu, ZHANG YunFeng, HU LinHui, TANG HongMing, XU Liang, CHEN SiQi, LIU DongXi, ZHONG PingQiang. Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough[J]. Acta Sedimentologica Sinica, 2021, 39(6): 1593-1608. doi: 10.14027/j.issn.1000-0550.2021.096

Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough

doi: 10.14027/j.issn.1000-0550.2021.096
Funds:

National Natural Science Foundation of China 41702122

  • Received Date: 2020-12-17
  • Rev Recd Date: 2021-07-02
  • Publish Date: 2021-12-10
  • In this study, the margin platform in the central eastern region to the west of the Kaijiang-Liangping Trough was divided into two areas: (1) the main central Longgang area, and (2) the eastern Longgang area, to determine the properties, genesis, patterns and differences of the reservoir. The main Longgang area is a steep-slope platform margin type. The reef⁃shoal complex growth close to the outer edge of the platform margin has a ridgeline shape, with multiple stages apparent in the vertical direction. The eastern part of the Longgang area is a gently sloping platform margin; the reef⁃shoal complex is the product of broad horizontal and vertical development. The former type of reservoir space contains constitutively selective intragrain dissolution pores, intergrain dissolution pores and non-constitutively selective dissolution fractures and structural fractures, producing low porosity and low permeability. The latter type consists mainly of intercrystal pores, intercrystal dissolved pores, intergrain dissolved pores and structural dissolution joints, resulting in a fracture-type reservoir possessing extremely low porosity and low permeability. Development of the reef⁃shoal complex reservoir was completely controlled by atmospheric freshwater dissolution, reflux infiltration and dolomitization, together with early diagenetic near-surface karstification, burial dissolution and buried dolomitization. The water body in the eastern Longgang area was relatively deep, resulting in weak atmospheric freshwater dissolution in the syngenetic stage, and weak near-surface dissolution in the early diagenetic stage. The high-quality reservoir is influenced by fractures and buried dissolution.
  • [1] 聂明龙,赵星林,程木伟,等. 阿姆河右岸区块卡洛夫—牛津阶礁滩型储集层特征[J]. 新疆石油地质,2016,37(5):615-619.

    Nie Minglong, Zhao Xinglin, Cheng Muwei, et al. Characteristics of reef-flat reservoirs of Callovian-Oxfordian stage in right bank area, Amu-Darya Basin[J]. Xinjiang Petroleum Geology, 2016, 37(5): 615-619.
    [2] 王大鹏,白国平,徐艳,等. 全球古生界海相碳酸盐岩大油气田特征及油气分布[J]. 古地理学报,2016,18(1):80-92.

    Wang Dapeng, Bai Guoping, Xu Yan, et al. Characteristics and hydrocarbon distribution of the Paleozoic giant marine carbonate rock oil-gas fields in the world[J]. Journal of Palaeogeography, 2016, 18(1): 80-92.
    [3] 焦养泉,荣辉,王瑞,等. 塔里木盆地西部一间房露头区奥陶系台缘储层沉积体系分析[J]. 岩石学报,2010,27(1):285-296.

    Jiao Yangquan, Rong Hui, Wang Rui, et al. Reservoir depositional system analysis of Ordovician carbonate platform margin in Yijianfang outcrops of western Tarim Basin[J]. Acta Petrologica Sinica, 2011, 27(1): 285-296.
    [4] 周新源,王招明,杨海军,等. 中国海相油气田勘探实例之五塔中奥陶系大型凝析气田的勘探和发现[J]. 海相油气地质,2006,11(1):45-51.

    Zhou Xinyuan, Wang Zhaoming, Yang Haijun, et al. Cases of discovery and exploration of marine fields in China (Part 5): Tazhong Ordovician condensate field in Tarim Basin[J]. Marine Origin Petroleum Geology, 2006, 11(1): 45-51.
    [5] Büyükutku A G, Eseller G. The reservoir potential of the Upper Eocene carbonates of the northern Thrace Basin, Turkey[J]. Energy Sources, 2008, 31(1): 25-30.
    [6] 郑荣才,陈浩如,王强,等. 土库曼斯坦阿姆河盆地卡洛夫—牛津阶储层特征及控制因素分析[J]. 岩石学报,2014,30(3):779-788.

    Zheng Rongcai, Chen Haoru, Wang Qiang, et al. The reservoir characteristics and their controlling factors of Callovian-Oxfordian carbonates in Amu Darya Basin[J]. Acta Petrologica Sinica, 2014, 30(3): 779-788.
    [7] Carozzi A V. Depositional models and reservoir properties of Miocene reefs, Visayan islands, Philippines[J]. Journal of Petroleum Geology, 1995, 18(1): 29-48.
    [8] 屈海洲,孙尧斌,张云峰,等. 碳酸盐岩层序地层格架内组构选择性孔隙分布特征:以塔里木盆地塔中地区上奥陶统良里塔格组台地边缘相为例[J]. 古地理学报,2017,19(5):879-891.

    Qu Haizhou, Sun Yaobin, Zhang Yunfeng, et al. Characteristics of fabric selective pore distribution in carbonate sequence stratigraphy framework: A case study from platform margin facies of the Upper Ordovician Lianglitage Formation in Tazhong area, Tarim Basin[J]. Journal of Palaeogeography, 2017, 19(5): 879-891.
    [9] 赵文智,沈安江,周进高,等. 礁滩储集层类型、特征、成因及勘探意义:以塔里木和四川盆地为例[J]. 石油勘探与开发,2014,41(3):257-267.

    Zhao Wenzhi, Shen Anjiang, Zhou Jingao, et al. Types, characteristics, origin and exploration significance of reef-shoal reservoirs: A case study of Tarim Basin, NW China and Sichuan Basin, SW China[J]. Petroleum Exploration and Development, 2014, 41(3): 257-267.
    [10] Zhou X Y, Wang Z M, Yang H J, et al. Large-scale Tazhong Ordovician reef-flat oil-gas field in the Tarim Basin of China[J]. Acta Geologica Sinica, 2009, 83(1): 179-188.
    [11] 段金宝. 普光与元坝礁滩气田天然气成藏特征对比[J]. 西南石油大学学报(自然科学版),2016,38(4):9-18.

    Duan Jinbao. The comparative study of natural gas accumulation characteristics between Puguang and Yuanba reef-bank gas field[J]. Journal of Southwest Petroleum University (Science & Technology Edition), 2016, 38(4): 9-18.
    [12] Hao F, Guo T L, Du C G, et al. Accumulation mechanisms and evolution history of the giant Puguang gas field, Sichuan Basin, China[J]. Acta Geologica Sinica, 2009, 83(1): 136-145.
    [13] Ma Y S, Guo T L, Zhao X F, et al. The Formation mechanism of high-quality dolomite reservoir in the deep of Puguang gas field[J]. Science China (Seri. D): Earth Sciences, 2008, 51(1): 53-64.
    [14] Liu J Q, Li Z, Huang J C, et al. Distinct sedimentary environments and their influences on carbonate reservoir evolution of the Lianglitag Formation in the Tarim Basin, northwest China[J]. Science China (Seri. D): Earth Sciences, 2012, 55(10): 1641-1655.
    [15] 韩剑发,孙崇浩,于红枫,等. 塔中Ⅰ号坡折带奥陶系礁滩复合体发育动力学及其控储机制[J]. 岩石学报,2011,27(3):845-856.

    Han Jianfa, Sun Chonghao, Yu Hongfeng, et al. Kinetics of reef-shoal complexes and its restriction to reservoir in Ordovician from Tazhong I fault belt[J]. Acta Petrologica Sinica, 2011, 27(3): 845-856.
    [16] 徐安娜,汪泽成,江兴福,等. 四川盆地开江—梁平海槽两侧台地边缘形态及其对储层发育的影响[J]. 天然气工业,2014,34(4):37-43.

    Xu Anna, Wang Zecheng, Jiang Xingfu, et al. Morphological characteristics of platform margins along the Kaijiang-Liangping Trough and their influences on reservoir development in the Sichuan Basin[J]. Natural Gas Industry, 2014, 34(4): 37-43.
    [17] Zheng J, Wang Z Y, Zhong Z Q, et al. Development pattern and reservoir-Formation mechanism of reef-bank complex in Late Ordovician Lianglitage Formation, Tazhong area, Tarim Basin, China[J]. Indian Journal of Geo Marine Sciences, 2018, 47(2): 269-280.
    [18] Guo C, Chen D Z, Qin H R. Multiple dolomitization and later hydrothermal alteration on the Upper Cambrian-Lower Ordovician carbonates in the northern Tarim Basin, China[J]. Marine and Petroleum Geology, 2016, 72: 295-316.
    [19] 范兴燕,张研,肖高杰,等. 轮深地区寒武系台缘礁滩相储层预测[J]. 石油与天然气地质,2015,36(5):793-803.

    Fan Xingyan, Zhang Yan, Xiao Gaojie, et al. Reservoir prediction of the Cambrian reef flat facies of platform margin in Lunshen area[J]. Oil & Gas Geology, 2015, 36(5): 793-803.
    [20] 严张磊,邢凤存,段金宝,等. 川东北地区长兴组台缘礁滩带沉积结构及储集层分布[J]. 新疆石油地质,2018,39(3):311-317.

    Yan Zhanglei, Xing Fengcun, Duan Jinbao, et al. Sedimentary texture and reservoir distribution of platform margin reef-flat zone in Changxing Formation of northeastern Sichuan Basin[J]. Xinjiang Petroleum Geology, 2018, 39(3): 311-317.
    [21] Zhang Y F, Tan F, Sun Y B, et al. Differences between reservoirs in the intra-platform and platform margin reef-shoal complexes of the Upper Ordovician Lianglitag Formation in the Tazhong oil field, NW China, and corresponding exploration strategies[J]. Marine and Petroleum Geology, 2018, 98: 66-78.
    [22] 郭旭升,黄仁春,付孝悦,等. 四川盆地二叠系和三叠系礁滩天然气富集规律与勘探方向[J]. 石油与天然气地质,2014,35(3):295-302.

    Guo Xusheng, Huang Renchun, Fu Xiaoyue, et al. Gas accumulation and exploration direction of the Permian and Triassic reservois of reef-bank facies in Sichuan Basin[J]. Oil & Gas Geology, 2014, 35(3): 295-302.
    [23] 郑志红,李登华,白森舒,等. 四川盆地天然气资源潜力[J]. 中国石油勘探,2017,22(3):12-20.

    Zheng Zhihong, Li Denghua, Bai Senshu, et al. Resource potentials of natural gas in Sichuan Basin[J]. China Petroleum Exploration, 2017, 22(3): 12-20.
    [24] 赵学钦,杨海军,马青,等. 塔北西部一间房组碳酸盐岩礁滩体同生期暴露溶蚀作用模式[J]. 中国地质,2015,42(6):1811-1821.

    Zhao Xueqin, Yang Haijun, Ma Qing, et al. Syn-sedimentary corrosion mode of carbonate reef-banks in the Middle Ordovician Yijianfang Formation within the western Tabei uplift of Tarim Basin[J]. Geology in China, 2015, 42(6): 1811-1821.
    [25] 文华国,周刚,郑荣才,等. 四川盆地开江—梁平台棚东侧长兴组礁白云岩沉积—成岩—成藏系统[J]. 岩石学报,2017,33(4):1115-1134.

    Wen Huaguo, Zhou Gang, Zheng Rongcai, et al. The sedimentation-diagenesis-reservoir formation system of reef dolomites from Changxing Formation in the eastern of Kaijiang-Liangping platform-shelf, Sichuan Basin[J]. Acta Petrologica Sinica, 2017, 33(4): 1115-1134.
    [26] 张单明,刘波,秦善,等. 川东北二叠系长兴组碳酸盐岩深埋成岩过程及其意义[J]. 岩石学报,2017,33(4):1295-1304.

    Zhang Shanming, Liu Bo, Qin Shan, et al. Deeply buried diagenetic process and its significance for the carbonate of Changxing Formation in the northeastern Sichuan Basin[J]. Acta Petrologica Sinica, 2017, 33(4): 1295-1304.
    [27] 罗韵. 元坝地区长兴组生物礁生长发育模式及储层特征研究[D]. 成都:成都理工大学,2015.

    Luo Yun. The research of reefs growth pattern and reservoir characteristics of Changxing Formation in Yuanba area[D]. Chengdu: Chengdu University of Technology, 2015.
    [28] 唐洪,吴斌,张婷,等. 川东北铁山—龙会地区长兴组礁滩相储层特征及主控因素[J]. 现代地质,2013,27(3):644-652.

    Tang Hong, Wu Bin, Zhang Ting, et al. Reef-beach reservoir features of Changxing Formation and its controlling factors in Tieshan-Longhui of northeastern Sichuan[J]. Geoscience, 2013, 27(3): 644-652.
    [29] 秦鹏,胡忠贵,吴嗣跃,等. 川东长兴组台缘礁滩相储层纵向非均质性特征及形成机制:以川东宣汉盘龙洞长兴组剖面为例[J]. 岩石矿物学杂志,2018,37(1):61-74.

    Qin Peng, Hu Zhonggui, Wu Siyue, et al. Vertical heterogeneity and formation mechanism of the platform edge reef and bank reservoir in Changxing Formation of eastern Sichuan Basin[J]. Acta Petrologica et Mineralogica, 2018, 37(1): 61-74.
    [30] Zhao W Z, Xu C C, Wang T S, et al. Comparative study of gas accumulations in the Permian Changxing reefs and Triassic Feixianguan oolitic reservoirs between Longgang and Luojiazhai-Puguang in the Sichuan Basin[J]. Chinese Science Bulletin, 2011, 56(31): 3310-3320.
    [31] 尹正武,凡睿,陈祖庆,等. 生物礁滩岩性气藏含气面积的圈定方法:以元坝气田长兴组气藏为例[J]. 石油实验地质,2012,34(5):499-505.

    Yin Zhengwu, Fan Rui, Chen Zuqing. Delineation of gas-bearing area of lithologic gas reservoir in organic beach reef: A case study in Changxing Formation, Yuanba gas field[J]. Petroleum Geology and Experiment, 2012, 34(5): 499-505.
    [32] 国家经济贸易委员会. SY/T 5478—2003碳酸盐岩成岩阶段划分[S]. 北京: 石油工业出版社, 2003.[State Economic and Trade Commission. SY/T 5478—2003 Division of diagenetic stages of carbonate rocks[S]. Beijing: Petroleum Industry Press, 2003.]
    [33] Eren M, Kaplan M Y, Kadir S. Petrography, geochemistry and origin of Lower Liassic dolomites in the Aydıncık area, Mersin, southern Turkey[J]. Turkish Journal of Earth Sciences, 2007, 16(3): 339-362.
    [34] Bosence D. Carbonate reservoirs porosity evolution and diagenesis in a sequence stratigraphic framework: Developments in Sedimentology, Vol. 55; Clyde H. Moore; Elsevier, Amsterdam, hardbound, ISBN 0-444-50838-4 (€158.8, $172.5); softbound, ISBN 0-444-50850-3 (€72.6, $79)[J]. Marine and Petroleum Geology, 2002, 19(10): 1295-1296.
    [35] Scholle P A, Ulmer-Scholle D S. A color guide to the petrography of carbonate rocks: Grains, textures, porosity, diagenesis[M]. Tulsa: American Association of Petroleum Geologists, 2003.
    [36] Keith M L, Weber J N. Carbon and oxygen isotopic composition of selected limestones and fossils[J]. Geochimica et Cosmochimica Acta, 1964, 28(10/11): 1787-1816.
    [37] Vasconcelos C, McKenzie J A, Warthmann R, et al. Calibration of the δ18O Paleothermometer for dolomite precipitated in microbial cultures and natural environments[J]. Geology, 2005, 33(4): 317-320.
    [38] Veizer J, Ala D, Azmy K, et al. 87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater[J]. Chemical Geology, 1999, 161(1/2/3): 59-88.
    [39] 王一刚,余晓锋,杨雨,等. 流体包裹体在建立四川盆地古地温剖面研究中的应用[J]. 地球科学:中国地质大学学报,1998,23(3):285-288.

    Wang Yigang, Yu Xiaofeng, Yang Yu, et al. Applications of fluid inclusions in the study of paleo-geotemperature in Sichuan Basin[J]. Earth Science: Journal of China University of Geosciences, 1998, 23(3): 285-288.
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  • Received:  2020-12-17
  • Revised:  2021-07-02
  • Published:  2021-12-10

Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough

doi: 10.14027/j.issn.1000-0550.2021.096
Funds:

National Natural Science Foundation of China 41702122

Abstract: In this study, the margin platform in the central eastern region to the west of the Kaijiang-Liangping Trough was divided into two areas: (1) the main central Longgang area, and (2) the eastern Longgang area, to determine the properties, genesis, patterns and differences of the reservoir. The main Longgang area is a steep-slope platform margin type. The reef⁃shoal complex growth close to the outer edge of the platform margin has a ridgeline shape, with multiple stages apparent in the vertical direction. The eastern part of the Longgang area is a gently sloping platform margin; the reef⁃shoal complex is the product of broad horizontal and vertical development. The former type of reservoir space contains constitutively selective intragrain dissolution pores, intergrain dissolution pores and non-constitutively selective dissolution fractures and structural fractures, producing low porosity and low permeability. The latter type consists mainly of intercrystal pores, intercrystal dissolved pores, intergrain dissolved pores and structural dissolution joints, resulting in a fracture-type reservoir possessing extremely low porosity and low permeability. Development of the reef⁃shoal complex reservoir was completely controlled by atmospheric freshwater dissolution, reflux infiltration and dolomitization, together with early diagenetic near-surface karstification, burial dissolution and buried dolomitization. The water body in the eastern Longgang area was relatively deep, resulting in weak atmospheric freshwater dissolution in the syngenetic stage, and weak near-surface dissolution in the early diagenetic stage. The high-quality reservoir is influenced by fractures and buried dissolution.

TANG Yu, ZHANG YunFeng, HU LinHui, TANG HongMing, XU Liang, CHEN SiQi, LIU DongXi, ZHONG PingQiang. Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough[J]. Acta Sedimentologica Sinica, 2021, 39(6): 1593-1608. doi: 10.14027/j.issn.1000-0550.2021.096
Citation: TANG Yu, ZHANG YunFeng, HU LinHui, TANG HongMing, XU Liang, CHEN SiQi, LIU DongXi, ZHONG PingQiang. Characteristics and Differences of the Platform Margin Reservoir, Changxing Formation, Central Eastern Region, West of the Kaijiang-Liangping Trough[J]. Acta Sedimentologica Sinica, 2021, 39(6): 1593-1608. doi: 10.14027/j.issn.1000-0550.2021.096
  • 台缘礁滩复合体因沉积厚度大、期次多、横向连续性好、易受溶蚀、白云岩化等成岩作用改造而形成规模性储集层,是全球海相油气勘探最为重要的领域之一[1-5]。近年来,世界范围内诸如阿姆达里亚盆地卡洛温—牛津阶[6]、菲律宾威萨洋岛中新世礁群储层[7],中国塔里木盆地塔中地区上奥陶统[8-10]、四川盆地普光地区上二叠统台缘礁滩型储层[11-13]相继获得重要油气发现,并在礁滩型储层形成的沉积学背景、动力学机制、非均质性等方面取得了诸多研究成果[9,14-15]。与此同时,台缘礁滩体作为一种易溶体,其储层形成机制较为复杂,常受到沉积微相、多期溶蚀/岩溶作用、白云岩化作用、构造破裂作用等的综合控制[16-21],给有利储层预测带来诸多困难。

    目前,四川盆地东部二叠系乐平统长兴组勘探已经取得了丰硕成果,发现了礁滩体气藏10余个,储量约2 065.78×108 m3,尤其是台缘礁滩体,占了天然气产量的80%以上[22-23]。但是,对台缘礁滩体储层的成因研究多集中在某一、两个方面,如沉积环境[14]、准同生期大气淡水溶蚀[24]、白云岩化[25-26]、热液溶蚀[27]等,缺乏对台缘礁滩体储层成因的多因素综合分析,这影响了油气高效勘探。本文以钻井较多的(或勘探程度较高的)四川盆地东部开江—梁平海槽西侧中东段二叠系乐平统长兴组台缘礁滩复合体为例,综合应用岩心、薄片、阴极发光、碳氧同位素、包裹体均一温度、有序度等数据,从礁滩复合体类型及规模、储集空间类型、多期岩溶、白云岩化等方面系统分析储层特征,明确其成因,建立其演化模式,以期为本区及类似地质条件下的礁滩体油气勘探提供指导,为后期开发做准备。

  • 研究区处于四川省的仪陇县—重庆市梁平县一带,呈北西—南东向展布。二叠系乐平统长兴组台地边缘的形成及分布与开江—梁平海槽的形成及演化密切相关:受晚二叠世长兴期早期峨眉“地裂运动”拉张影响,先期存在的碳酸盐岩台地演化为台—盆相间的沉积格局,开江—梁平海槽形成,呈北西—南东向展布[25]。研究区受此及生物建造影响,逐渐演化为台地边缘相,发育了多世代的礁滩复合体,亦呈北西—南东向展布[20,28]图1);至早三叠世飞仙关期晚期,开江—梁平海槽由于沉积物的填平补齐作用而消失,研究区亦由台地边缘相演化为蒸发台地相。研究区长兴组地层自下而上划分为长一段—长三段三个岩性段,地层厚度92~240 m,由台缘外带向内带逐渐减薄[29-30]

    Figure 1.  Structural location and sedimentary characteristics in the Late Permian Changxing Formation in the study area (red outline)

  • 研究区长兴组台缘碳酸盐岩结构组分包括生物格架、颗粒、泥、晶粒、胶结物等。生物类型丰富,包括海绵、苔藓虫、珊瑚、藻、层孔虫等造礁生物及有孔虫、介形虫、海百合、腕足、双壳、腹足等附礁生物(图2a,c,d);颗粒包括生物碎屑、内碎屑、鲕粒、藻团块等(图2b,e~j)。晶粒存在于白云岩中,类型包括泥晶—粉晶、细晶等(图2k,i)。碳酸盐岩生物、颗粒间多碳酸盐泥、胶结物充填,泥以云泥为主,胶结物多为亮晶方解石(图2)。

    Figure 2.  Sedimentary microfacies properties

  • 对四川盆地晚二叠世开江—梁平海槽西侧的LG001-1、LG001-10、LG001-28、LG84、TS4、TS5等井的长兴组取心井段的岩心和薄片观察描述及测井资料进行分析,依据岩石类型、沉积构造、生物组合等相标志,将研究区内长兴组沉积相划分为台地边缘相,进一步划分为颗粒滩和生物礁亚相,和生屑滩、砂屑滩、礁翼、礁核、礁间等微相。颗粒滩主要发育于长兴组长二、长三段地层,厚度一般小于50 m;生物礁垂向上表现为多期旋回特征,单个生物礁厚度一般小于20 m,造礁生物呈树枝状、柱状、丘状等;它们通常以复合体形式存在,垂向上具多期加积的特征,礁顶部常发育颗粒滩,并常发生白云化作用(图3)。

    Figure 3.  Sedimentary microfacies profile and migration pattern of reef⁃shoal complex on the platform margin of Changxing Formation, Late Permian, well LG001⁃28

  • 将开江—梁平海槽西侧中东段台地边缘形态划分为陡坡型台地边缘和缓坡型台地边缘2种类型,前者分布于龙岗主体地区,后者分布于龙岗东地区,二者在生物礁滩的平面组合特征、礁滩体大小、白云岩化程度以及空间迁移上具有一定的差异性。从地貌上来看,龙岗主体地区和龙岗东地区存在明显的地貌差异,龙岗主体地区台缘带地貌相对较陡,而到龙岗东地区台缘带斜坡坡度变缓[20]。从生物礁的形态结构来看,长兴组生物礁的形态结构也具明显的分异:地貌相对更缓的龙岗东地区其台缘带礁滩体表现为宽缓的低丘,平行台缘带呈带状分布,发育规模略小,总厚度为20~100 m,礁滩体内部次级礁滩体叠置方式以侧积为主,可见垂向加积,单个礁滩复合体厚度介于30~50 m,其中礁体厚度介于5~10 m,颗粒滩厚度介于5~30 m;而地貌较陡的龙岗主体地区其台缘带礁滩体外形呈山脊线状,紧靠台地较陡一侧生长,总体单排分布且迁移弱,分布较集中,礁滩以复合体形式存在,总体累计厚度大(80~400 m),横向宽度窄(0.5~2 km),礁滩体内部多期次级礁滩体垂向加积,侧积作用不明显,单个礁滩体内的生物礁厚度一般小于20 m,颗粒滩厚度一般小于50 m(图4[16,31]。龙岗主体地区礁滩白云化程度高于龙岗东地区。

    Figure 4.  Sedimentary facies pattern of the Late Permian Changxing Formation in the central Longgang area and edge of Longgang area to the west of the Kaijiang⁃Liangping Trough

  • 龙岗主体地区和龙岗东地区长兴组均发育台缘礁滩储层,但在储层岩性、储集性能、礁滩体白云岩化程度等方面存在差异。龙岗主体地区地处陡坡型台地边缘,其礁滩体暴露时间较长,白云化和溶蚀作用时间较强,在礁滩体顶部可见溶蚀孔隙更为发育,而龙岗东地区地处缓坡型台地边缘,其礁滩暴露时间短且频繁,其礁滩体白云化程度不高,储集岩类发育的厚度薄但期次多,横向分布广。总体上龙岗主体地区的礁滩储层优于龙岗东地区。

  • 龙岗主体地区与龙岗东地区长兴组储层岩石类型相似,均以礁云岩、颗粒云岩及细—粉晶白云岩为主。龙岗东地区含有少量的礁灰岩储层。其中颗粒云岩主要包括生屑、砂屑和砾屑云岩,以生屑云岩为主。礁云岩中造礁生物主要为串管海绵、纤维状海绵、硬海绵及水螅等,局部达90%,附礁生物有孔虫、介形虫、苔藓、藻类等。颗粒云岩、晶粒云岩中发育粒内孔、串珠状溶孔、粒间孔、晶间孔、溶蚀缝等。礁云岩中则发育大量的生物格架孔、体腔孔等。礁灰岩中未云化或弱云化,储集空间以生物体腔溶蚀孔、粒内微孔为主,局部见压溶缝和构造缝,具有一定的储集能力(图25)。

    Figure 5.  Pore and fracture features in study area

  • 龙岗主体地区与龙岗东地区长兴组台缘礁滩储层储集空间类型几乎全为次生孔隙类型,包含组构选择性的粒内溶孔、粒间溶孔、晶间溶孔、体腔孔、格架孔和非组构选择性的溶洞、粒间溶孔、构造缝和缝合线、溶蚀缝等。两地区储集空间的发育有一定差异性,前者以组构选择性的粒内溶孔、粒间溶孔、晶间孔、晶间溶孔与非组构选择性的溶蚀缝洞和构造裂缝并存为特征,后者以晶间孔、晶间溶孔、非组构选择性粒间溶孔、构造缝、构造溶蚀缝等为主(图5)。储集空间类型含量上亦有较大差异性,区内龙岗主体长兴组储层最主要类型为粒间溶孔、粒内溶孔,在统计385张薄片中其各占储集空间频率22.3%和30.1%。龙岗东长兴组储层主要类型为晶间孔、裂缝等,在统计的324张薄片中其各占储集空间频率为23.2%和15.3%。(图6)。

    Figure 6.  Histogram of frequency of main reservoir pore types in the platform margin reef⁃shoal reservoirs west of Kaijiang⁃Liangping Trough

  • 对龙岗主体地区台缘礁滩储层20余口井、近400张铸体薄片、1 245个孔隙度数据、620个渗透率数据和龙岗东地区台缘礁滩储层4口井、200张薄片、1 050个孔隙度数据、620个渗透率数据统计分析可得,两地区长兴组储层孔隙度和渗透率具有一定的可比性。

    据龙岗主体地区物性统计资料显示,各样品孔隙度大小差别很大,大部份样品具有低孔低渗的特征,其中孔隙度大于或等于2%的样品数(即储层样品)占总样品数的50.4%,大于5%的样品占总样品数的7.3%,表明虽然储层整体不是特别发育,但总体仍有高孔层存在;渗透率级差较大,其中(0.001~0.1)×10-3 μm2的样品数占总样品数的36.3%;(0.1~10)×10-3 μm2之间的样品数占总样品数的58.8%,大于10×10-3 μm2的样品数占总样品数的4.9%,区内储层虽然整体不是很发育,但局部地区仍有高渗层的存在(图7)。

    Figure 7.  Histograms of physical properties of platform margin reef⁃shoal reservoirs west of the Kaijiang⁃Liangping Trough

    据龙岗东地区物性统计资料显示,大部份样品具有特低孔隙度和低渗透率的特征,其中低值孔隙度占比高,孔隙度小于2%的占76.6%,但也存在较高值(7.62%);渗透率小于0.1×10-3 μm2的样品占82.1%,但渗透率较高值的样品亦占一定比例(17.9%),显示了裂缝发育的特征(图7)。

  • 海槽两侧台地边缘形态不仅控制礁滩体的沉积模式和成岩作用,并最终影响礁滩体储层的分布。龙岗主体地区礁滩体储层主要集中分布在台缘陡坡一侧的每期礁滩体旋回的顶部,累计厚度介于30~60 m,横向分布窄,储层类型多属于低孔隙度、低渗透率的孔隙型储层。龙岗东地区其礁滩体储层主要位于大型缓坡附近,分布在每期礁滩体旋回的顶部,其厚度薄,但期次多,累计厚度约为20 m,横向分布较广,储层类型多属于特低孔隙度和低渗透率的裂缝—孔隙型储层[16]

  • 室内磨制薄片812片并鉴定,应用设备为Zeiss AXIO SCOPE. A1偏光显微镜;阴极发光观察共完成LG001-1、LG001-28、LG84、TS4等井150张薄片,应用设备为CL8200 MK5阴极发光仪;δ 13C、δ 18O测定共完成211个样点,应用设备为Isoprime100同位素质谱仪;微量元素测试共完成156个样点,应用设备为JXA-8230型电子探针—波谱仪;包裹体温度测试共完成86个样点,应用设备为THMSG 600地质冷热台;白云石有序度测试共完成80个样点,应用设备理学DMAX-3C衍射仪。实验分析均在西南石油大学油气藏地质及开发工程国家重点实验室完成。

  • 龙岗主体地区和龙岗东地区台缘礁滩均发生胶结、白云化、溶蚀、压实、破裂等作用,但两地区胶结以及溶蚀、白云化作用规模有所不同。通过成岩作用类型及相互作用关系,结合碳酸盐岩成岩阶段划分标准[32]建立龙岗主体地区和龙岗东地区台缘礁滩成岩序列(图8)。研究区海底成岩环境时形成了第一期纤状方解石胶结物。进入到准同生期后,局部礁滩地貌高部位被准同生期大气淡水溶蚀,选择性地溶蚀第一期方解石胶结物,并与随后的粒状方解石呈胶结不整合接触的情况。溶蚀形成了选择性溶蚀的粒内溶孔、骨架孔、体腔孔。部分礁滩未受大气淡水的影响,未发生溶蚀作用;随后,由于高Mg的流体密度较大,将在重力作用下向下回流渗透进入生物礁、颗粒滩、滩间沉积物中,交代改造礁滩体高陡部位及胶结物,导致生物礁发育段自上而下白云石含量逐渐减弱,白云化程度逐渐减小。龙岗主体地区礁滩体位于台缘带较陡区域,更易于受到波浪改造,准同生期容易暴露水面,高陡部位生物礁发育较好且礁盖易于白云岩化;龙岗东地区礁滩体位于在台缘带坡度较缓区域,由于水动力条件较弱,生物礁发育较小,且未经历或者很少经历,白云岩化弱甚至不发育。

    Figure 8.  Diagenetic sequence of the platform margin reef⁃shoal complex

    随着上覆沉积物堆积加厚,礁滩复合体进入到浅埋藏环境(即成岩早期),在上升的岩溶成岩环境中,经历较短的海平面下降和上升时期侧向挤压和构造抬升,因台地边缘古地形相对较高,暴露范围大,进行抬升岩溶作用,以原生及准同生期大气水溶蚀形成的孔隙作为重要的先期通道基础,发生早成岩近地表岩溶作用,形成了非选择性的溶缝、洞,呈现花斑状。龙岗东地区台缘礁滩古地形相对较缓,早成岩近地表溶蚀较弱。浅埋藏环境时,受地层中封存的高盐度海水的影响,再次发生白云化,这一次白云化对前期形成的白云石改造较为强烈,同时,交代部分方解石,形成粉—细晶自形白云石。埋藏期溶蚀、胶结作用溶蚀早期的粒状方解石胶结物并被单晶方解石所胶结(图9)。中—深埋藏环境后,构造拉张以及热液活动强烈,发育大量的低角度斜交缝或网状缝,流体沿断层下盘及裂缝带上涌,对早期大气成岩透镜体中的孔隙层等储集层进行多期埋藏溶蚀改造,形成规模可观的非选择性溶蚀缝洞系统。

    Figure 9.  Dissolution characteristics of dolostone during burial period

  • 开江—梁平海槽西侧上二叠统长兴组台缘带礁滩体主要经历了准同生期大气淡水溶蚀、回流渗透白云化、早成岩近地表岩溶及埋藏溶蚀4个阶段。

  • 准同生期,沉积物处于半固结成岩状态,受次级沉积旋回和海平面变化的控制,台缘礁滩沉积体,短暂出露海面或处于大气淡水透镜体内,遭受富含CO2的大气淡水溶蚀作用,并有具明显的垂向分带特征。在大气渗流带和潜水面附近,沉积物中多发生组构选择性溶蚀,常形成粒内溶孔、铸模孔、粒间溶孔等溶蚀孔缝 并可见渗流粉砂(图10)。

    Figure 10.  Identification mark of the meteoric water dissolution in penecontemporaneous stage

    龙岗主体地区和龙岗东地区台缘礁滩体沿台地边缘分布,海平面下降时,地势较高的龙岗主体地区暴露时间较长,地貌高点受大气淡水淋滤作用改造较强,选择性地溶蚀由准稳定矿物组成的颗粒或第一期方解石胶结物,形成生物碎屑以及非生物碎屑的粒内溶孔和铸模孔以及出现海底纤状环边方解石被溶蚀,并与随后的粒状方解石呈胶结不整合接触的情况。龙岗东地区因地势较缓,礁滩体暴露时间短,大气淡水淋滤作用改造弱,粒内溶孔等储集空间发育较龙岗主体地区弱。潜流带中下部形成的第二期叶片状、等轴细粒状及共轴增生的方解石胶结物比正常海水胶结物具较少的Sr、Mg和Na,阴极发光为昏暗光,反映了来自大气淡水的稀释作用,为典型的大气淡水胶结物特性,溶蚀在胶结之前发生(图11表1)。

    Figure 11.  Cathodoluminescence of calcite cements

    井号 位置 胶结物类型 阴极发光特征 微量元素/×10-6
    Mn Fe Sr Mg Na Ba K
    TS4 1 纤状 不发光 0 120 870 204 800 4 810 240 860
    TS4 2 纤状 不发光 120 0 920 173 200 630 0 220
    TS4 3 叶片状 昏暗光 0 310 0 210 100 930 100 330
    TS4 4 粒状 昏暗光 100 150 220 212 000 290 0 200
    TS4 5 粒状 不发光 80 130 364 6 330 20 0 330
    TS4 6 粒状 不发光 280 30 650 5 280 530 0 180
    LG001-1 1 纤状 不发光 0 0 824 209 200 390 0 320
    LG001-1 2 纤状 不发光 160 30 860 207 900 570 0 150
    LG001-1 3 叶片状 昏暗光 0 90 0 2 360 0 0 140
    LG001-1 4 粒状 昏暗光 0 20 540 4 230 240 0 130
    LG001-1 5 粒状 昏暗光 330 460 680 3 520 300 0 260
    LG001-1 6 粒状 昏暗光 190 40 100 196 100 560 0 430

    Table 1.  Electron probe microanalysis (EPMA) of calcite cements

  • 研究区内长兴组台缘礁滩白云岩分为两类,具残余结构的云岩和颗粒云岩。白云石晶型大小、自形程度大致能够反映白云岩的成因。粉晶、细晶云岩大多呈半自形白云石残余结构生屑,反映了快速白云岩化导致的晶型较差,主要形成于准同生期的回流渗透白云岩化。部分以自形细晶白云石形式存在,主要形成于浅埋成岩环境中较缓慢结晶生长环境[33-35]。总体来说,龙岗主体地区及龙岗东地区礁滩白云岩特征具有一定的相似性也存在差异(表2)。

    地区 白云石晶粒粒径/μm 白云石晶粒 白云石晶体形态 白云石含量变化 白云石有序度
    龙岗主体地区 40~250 粉晶、细晶级均可识别 自形程度较好,多呈半自形—自形 自上而下逐渐减少 0.59~0.94
    龙岗东地区 10~200 泥晶、粉晶、细晶级均可识别 自形程度中等,他形—半自形—自形均有分布 自上而下逐渐减少 0.54~0.76

    Table 2.  Petrological properties of reef⁃shoal dolostones

    龙岗主体地区和龙岗东地区长兴组生物礁滩白云岩均具有高Fe、低Mn、δ 13C(PDB)值为正低值,δ 18O(PDB)值为中等负值特征,含量有所区别[36-37]表3)。其中龙岗主体地区δ 13C(2.23‰~2.71‰),且向礁顶部位变轻,δ 18O(-5.94‰~-5.00‰);龙岗东地区δ 13C(2.13‰~2.63‰),δ 18O(-6.94‰~-5.55‰),均分布在同时期全球古海水δ 13C、δ 18O变化范围内[38],并与全球典型埋藏白云岩δ 13C、δ 18O分布区间一致,表明白云化作用发生于埋藏成岩环境中;研究区内长兴组白云化流体的古盐度指数Z全部大于120,均值为128(表3[36],反映了其成岩流体盐度较高,根据白云岩的δ 18O值与其形成温度之间的经验关系式,计算白云岩形成的温度56 ℃~70 ℃[37]表3);据前人研究,川东地区上二叠统古地温梯度为3.5 ℃/100 m[39],取古地表温度为25 ℃,得出白云岩的成岩深度区间:885~1 285 m,属于浅埋藏环境。综上,推测白云化作用发生在浅埋藏环境,白云化流体为地层中封存的高盐度海水。

    井号 深度/m 岩性 产状 δ 13C /(‰,VPDB) δ 18O /(‰,VPDB) Fe/×10-6 Mn/×10-6 Sr/×10-6 Z值 T/℃
    LG001-28 4 712.35 残余砂屑细晶云岩 砂屑内部的半自形— 自形细晶白云石充填 2.23 -5.00 922.661 40.706 424.812 127.3 56
    LG001-28 4 944.64 棘屑细晶云岩 粒间半自形—自形细晶白云石充填 2.71 -5.89 1 384.580 64.712 117.133 128.901 62
    LG84 4 513.17 生屑细晶云岩 棘屑内部半自形—自形细晶白云石充填 2.87 -5.94 812.344 71.929 75.935 129.377 62
    LG84 4 514.7 含生屑细晶云岩 粒间半自形细晶白云石充填 2.71 -5.55 538.959 64.020 74.416 129.043 59
    TS4 3 214 亮晶砾屑鲕粒灰岩 鲕粒内部半自形粉晶白云石充填 2.60 -6.94 1 088.190 74.382 278.858 130.219 69
    TS4 3 219 含生屑粉晶云岩 粒间半自形粉晶白云石充填 2.63 -6.66 925.122 100.905 603.332 129.916 67
    TS4 3 255 亮晶鲕粒灰岩 鲕粒内部半自形粉—细晶白云充填 2.13 -6.29 846.584 105.567 188.301 130.086 65
    TS4 3 268 含生屑泥晶灰岩 生屑内部半自形—自形细晶白云石充填 2.06 -6.97 675.705 87.593 448.712 127.3 70
    TS4 3 279 粉晶云岩 粒间半自形粉晶白云石充填 2.21 -6.96 1 041.324 96.756 163.685 127.3 69
    TS4 3 308 粉晶云岩 粒间半自形粉晶白云石充填 2.24 -6.50 1 312.890 109.846 188.548 124.720 66

    Table 3.  Electron probe microanalysis (EPMA) of reef⁃shoal dolostones

    根据Fe、Mn含量及Fe/Mn值,阴极发光强度中等,并且在白云岩的晶间孔、晶间溶孔的孔壁发育有沥青斑点及薄膜,再次印证龙岗—龙岗东地区长兴组白云岩形成于油气充注之前的浅埋藏环境(图12)。通过以上对白云石特征的分析,认为龙岗主体以及龙岗东地区内白云石化作用包括准同生期的回流渗透白云石化及浅埋藏期的白云石化。

    Figure 12.  Cathodoluminescence characteristics of reef⁃shoal dolostones

  • 早成岩近地表溶蚀在沉积岩未经中深埋藏抬升暴露即成岩早期发生,此时岩石矿物未经过完全稳定化转变便抬升剥蚀,以原生及准同生期大气水溶蚀形成的孔隙作为重要的先期通道基础,形成的储集空间包括溶蚀孔洞、缝、小型洞穴等,充填物有碳酸盐岩砂、泥,呈花斑状、蜂窝状等特征。通过龙岗主体地区、龙岗东地区等井的早成岩近地表岩溶发育层段的统计,发现LG001-28、LG84等井以及TS4井等井均有不同程度的早成岩近地表岩溶发育。LG001-28井发育3套早成岩近地表岩溶,发育深度为4 698.22~4 701.54 m、4 710.5~4 718.28 m、4 784.91~4 788.53 m,厚度分别为3.32 m、7.78 m、3.62 m;LG84井发育1套早成岩近地表岩溶,深度为4 515.3~4 515.6 m;TS4井发育一套厚约2.6 m的早成岩近地表岩溶(图13)。说明该期岩溶作用发育普遍,长兴组末期应存在区域性的暴露面。龙岗主体地区发育厚度更大,厚度较大的井一般也是礁滩体较发育的井,其原生、准同期溶蚀形成的孔隙是该期岩溶作用的发育重要基础。

    Figure 13.  Features of early diagenetic near⁃surface karstification

  • 中—深埋藏环境后,埋藏溶蚀作用不仅期次多,而且分布较普遍,规模也较大,伴随着下伏地层烃源岩热演化过程中形成的酸性流体及岩浆期后热液的进入断层、裂缝及先期存在的孔洞层,对台缘近断层孔洞层进行溶蚀,形成了孤立状溶蚀小型洞穴、沿裂缝、缝合线扩溶形成的串珠状溶孔、以及埋藏期白云石被溶蚀,形成晶间溶孔、不规则孔,这都使得优质储层更加发育。通过对龙岗、龙岗东地区礁滩云岩中裂缝中方解石均一温度的测试,发现龙岗主体地区多分布在120 ℃~128 ℃之间,龙岗东地区多分布在105 ℃~108 ℃之间,均为埋藏成因(图1415)。

    Figure 14.  Frequency histogram of homogeneous temperature of calcite in fractures

    Figure 15.  Homogeneous temperature of calcite in fractures

  • 在对四川盆地东部开江—梁平海槽西侧中东段上二叠统长兴组进行地层及沉积相等分析的基础上,结合研究区实际油气勘探成果,建立了四川盆地东部开江—梁平海槽西侧中东段二叠系乐平统长兴组龙岗主体—龙岗东地区台缘礁滩复合体储层演化模式(图16)。区内二叠系乐平统长兴组储层主要发育在开江一梁平海槽西侧中东段台地边缘相中,储层发育分布受礁体制约,受控于晩二叠世长兴期沉积环境变迁。在准同生期,礁滩处于海平面以下,未被溶蚀;海平面下降,龙岗主体地貌较陡,大多数台缘礁滩复合体暴露在大气中,接受淡水淋滤,在礁滩顶部形成淡水透镜体,礁滩地貌高部位被准同生期大气淡水溶蚀,以选择性溶蚀的粒内溶孔为主,局部礁滩未受大气淡水的影响,未发生溶蚀作用;而龙岗东地区地貌较缓,大多数台缘礁滩未暴露在大气中,未发生溶蚀作用,局部礁滩地貌高部位被溶蚀;随后,由于高Mg的流体密度较大,将在重力作用下向下回流渗透进入生物礁、颗粒滩、滩间沉积物中,交代改造礁滩体高陡部位及胶结物,导致生物礁发育段自上而下白云石含量逐渐减弱,白云化程度逐渐减小,在礁顶部位多形成选择性溶蚀孔为主。同理,龙岗东地区台缘礁滩白云化程度较低,选择性溶蚀孔洞发育较龙岗主体差。在上升的岩溶成岩环境中,经历较短的海平面下降和上升时期侧向挤压和构造抬升后,台地边缘古地形相对较高,暴露范围大,形成抬升岩溶作用,以原生及准同生期大气水溶蚀形成的孔隙作为重要的先期基础通道,发生早成岩近地表岩溶作用,形成了非选择性的岩溶缝、洞。

    Figure 16.  Reservoir evolution patterns of the Late Permian Changxing Formation in the center and edge of Longgang area west of the Kaijiang⁃Liangping Trough

    在浅埋藏时期,由于上覆地层的压实作用,地层中封存的高盐度海水在弱固结的沉积物中运动而发生白云石化,由于Mg2+供给相对不足,白云石结晶缓慢,形成自形程度较好的白云石晶体。中—深埋藏环境后,下伏地层烃源岩热演化过程中形成的酸性流体及岩浆期后热液沿着断层、裂缝及先期存在的孔洞层,对台缘近断层礁滩体进行溶蚀,使得礁滩体优质储层更加发育。

  • (1) 研究区内长兴组沉积相划分为台地边缘相,将台地边缘相带按其沉积特征进一步划分为颗粒滩亚相、生物礁亚相,这些亚相又可进一步划分为砂屑滩、生屑滩、砾屑滩、滩间海、礁间、礁核等微相。长兴组不同地区生物礁差异性明显,相比之下,台缘礁发育规模较大,分布稳定。

    (2) 开江—梁平海槽西侧中东段台地边缘根据台地边缘形态划分为龙岗主体的陡坡型台地边缘和龙岗东的缓坡型台地边缘2种类型;前者礁滩体呈山脊线状、紧靠台缘外带生长、累计厚度大,北西—南东向单排分布,垂向呈多期次加积、横向宽度窄;后者礁滩体宽缓、平行于台缘呈带状分布、累计厚度薄,垂向侧积为主、横向宽度大。

    (3) 储集空间类型前者以组构选择性的粒内溶孔、粒间溶孔、晶间孔、晶间溶孔和非组构选择性的溶蚀缝洞和构造裂缝并存为特征,后者以晶间孔、晶间溶孔、非组构选择性粒间溶孔、构造缝、构造溶蚀缝等为主;储集类型前者为低孔低渗的孔隙型,后者为特低孔特低渗的裂缝型—孔隙型储层。

    (4) 龙岗主体台缘礁滩储层受准同生期大气淡水溶蚀、回流渗透白云化、早成岩近地表岩溶及埋藏溶蚀、埋藏白云化等的综合控制;龙岗东地区水体相对较深,同生阶段的大气淡水溶蚀和早成岩期近地表溶蚀较弱,优质储层受裂缝及埋藏溶蚀作用控制。

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