石油与天然气地质 ›› 2023, Vol. 44 ›› Issue (1): 55-74.doi: 10.11743/ogg20230105

• 油气地质 • 上一篇    下一篇

深埋条件下微生物碳酸盐岩成岩作用与孔隙演化——以四川盆地西部中三叠统雷口坡组为例

钱一雄1(), 武恒志2, 周凌方1, 董少峰3, 王琼仙4, 宋晓波4, 邓美洲4, 李勇4   

  1. 1.中国石化 石油勘探开发研究院 无锡石油地质研究所，江苏 无锡 214151
    2.中国石化 国际石油勘探开发有限公司，北京 100029
    3.西南石油大学 油气藏地质及开发工程国家重点实验室，四川 成都 610500
    4.中国石化 西南分公司 石油勘探开发研究院，四川 成都 610081
  • 收稿日期:2022-05-11 修回日期:2022-08-15 出版日期:2023-02-01 发布日期:2023-01-13
  • 第一作者简介:钱一雄（1962—），男，博士、教授级高级工程师，碳酸盐岩沉积与储层。E-mail： qyx9167@vip.sina.com。
  • 基金项目:
    国家重点基础研发项目(2017YFC0603103);中国科学院A类战略性先导科技专项(XDAXX010201-3)

Diagenesis and porosity evolution of microbial carbonate rocks undergone a deep burial history： Taking the Leikoupo Formation of Middle Triassic in western Sichuan Basin as an example

Yixiong QIAN1(), Hengzhi WU2, Lingfang ZHOU1, Shaofeng DONG3, Qiongxian WANG4, Xiaobo SONG4, Meizhou DENG4, Yong LI4   

  1. 1.Wuxi Branch，Petroleum Exploration and Production Research Institute，SINOPEC，Wuxi，Jiangsu 214126，China
    2.International Petroleum Exploration and Production Corporation，SINOPEC，Beijing 100029，China
    3.State Key Laboratory of Oil and Gas Reservoir Geology and Exploration，Southwest Petroelum University，Chengdu，Sichuan 610500，China
    4.Institute of Exploration and Development，Southwest Oil and Gas Company，SINOPEC，Chengdu，Sichuan 610081，China
  • Received:2022-05-11 Revised:2022-08-15 Online:2023-02-01 Published:2023-01-13

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摘要：

四川盆地西部（简称川西）中三叠统雷口坡组白云岩是埋深超过5 000 m的油气勘探目的层之一。通过对10余口钻井以及多条实测露头剖面的研究，采用了包括薄片、铸体片、阴极发光、环境扫描电镜及能谱分析（SEM-EDS）、流体包裹体、微区碳-氧同位素、碳酸盐岩△47团簇同位素温度计、方解石U-Pb定年以及FIB-CT等技术方法，探讨了深埋条件下微生物碳酸盐岩成岩流体与孔隙演化的机理。研究表明，研究区存在开放、封闭和半开放等3种早期成岩体系，分别对应于潮湿气候条件下的潮间带-潮下浅水带的藻（灰）云岩中的强大气淡水作用（带），干旱条件下的潮上-潮间带膏盐岩-含藻纹层泥晶云岩的弱大气淡水作用以及早期表生-浅埋藏下的细菌微生物-灰泥相互作用。大规模白云岩化作用，以及埋藏-构造期的去云化作用分别发生于晚三叠世的卡尼阶（226.50 Ma ± 9.68 Ma）与诺利阶（211.50 Ma ± 1.50 Ma），地层温度分别为43 ~ 54 ℃和50 ℃。在白云石（δ18O水=-0.83 ‰ ~ 9.70 ‰）与方解石（δ18O水=-1.16 ‰ ~ 12.94 ‰）的胶结过程中，随着胶结物晶体增大，δ18O水总体逐渐降低，指示了温度升高与盐度升降变化。统计结果表明，微生物碳酸盐岩的主要孔隙类型包括格架孔（占比32.38 %）、扩溶缝洞（占比43.69 %）和微孔隙。微孔隙连通性好，富有机酸的孔隙流体抑止了规模性的胶结作用，导致部分孔隙得以保存。向上变浅的浅水潮下带-潮间带 “米氏（级）微生物岩沉积旋回”，以及开放-半开放早期成岩体系是孔隙发育的基础。埋藏成岩流体迭加改造作用导致了储层孔隙度在一定程度上减少。

关键词: 孔隙演化, 成岩流体, 微生物碳酸盐岩, 雷口坡组, 中三叠统, 四川盆地西部

Abstract:

The microbial dolomite reservoir in the Middle Triassic Leikoupo Formation， western Sichuan Basin， has been one of the exploration targets with a buried depth excessing 5 000 m and it serves as an excellent object of study for diagenetic fluids and pore evolution that are probably accountable for the formation of deeply-buried microbial carbonate reservoirs. Samples and data from more than 10 wells and several outcrops and seismic sections were studied with multi-technical methods， such as cast thin section observation， cathodoluminescence microscopy （CL）， scanning electron microscopy+energy-dispersive X-ray spectroscopy （SEM-EDS）， fluid inclusion microthermometry， carbon and oxygen isotope analysis via microsampling， carbonate clumped isotopes thermometer （△47）， U-Pb dating of calcite， FIB-SEM and so on. The results show that there are three early diagenetic subsystems： open， closed and semi-open （transition）， which respectively correspond to the intensive meteoric water influx in algal dolostone in intertidal-subtidal zones under humid climate， the weak meteoric water influx in evaporate rock-algal lamellated micritic dolostone in supratidal-intertidal zones under arid climate and the interaction between bacteria & microbial and carbonate mud druing an early supergene-shallow burial period. Large-scale dolomitzation and de-dolomitization during the burial-tectonic epochs are believed to take place repecitvely in the Carnian（226.50 ± 9.68 Ma）and Norian（211.50 ± 1.50 Ma）stages of Late Triassic， with temperatures of 43 ℃ to 54 ℃ and 50 ℃， respectively. Four to five successive dolomitization and calcite cementation stages have been identified， showing that the δ18Owater （PDB‰） of parent fluids varies between -0.83 ‰ and 9.70 ‰ for dolomite， and between -1.16 ‰ and 12.94 ‰ for calcites， while with the enlargement of cement crystalline， the overall δ18Owater slowly reduces， indicating an increase in temperature and fluctuationg salinity. Statistics reveal that vugs and solution-enlarged fractures （43.69 %）， framework pores （32.38 %） and micro-poros are the major pore types of microbial carbonate rocks. The micropores are well connected as organic acid-rich pore fluid inhibiting large-scale cementation and result in the partial preservion of pores with a good connectivity. Thereby， the shallow subtidal to supratidal zones with a development of shallow-up Mirokovich sedimentary cycle for microbial carbonate rocks， combined with the open to semi-open early diagenetic system， are the basis of reservoir porosity development and preservation， and the superposition and transformation of burial diagenetic fluids leads to the overall reduction of porosity.

Key words: pore evolution, diagenetic fluid, microbial carbonate rocks, Leikoupo Formation, Middle Triassic, western Sichuan Basin

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