124 / 2023-07-14 09:20:01

四川盆地五峰组－龙马溪组页岩储层演化机制

五峰组－龙马溪组页岩储层演化机制

摘要：依依据矿物岩石学、有机地球化学、储集空间、物性及含气性特征等特征，系统分析并探讨了上奥陶统五峰组-下志留统龙马溪组页岩储层特征、演化机制及其对页岩气勘探开发的影响，提出“生物硅钙控格架、协同演化促生孔、压力演化控保存”的页岩储层演化机制。研究结果表明：①岩相、有机孔载体类型及其赋存方式对有机孔的发育具有重要控制作用，硅质页岩大尺度有机质充填粒间孔（3~5 µm）发育程度高，最利于有机质大孔发育；粘土质页岩受TOC含量和有机质-粘土复合体结构影响，有机孔的孔径分布范围广、平均孔径大，但有机孔总量较小。②同生-早成岩阶段早期形成的生物石英、微生物白云石和黄铁矿等构成的刚性支撑格架利于原生孔隙的保存。中成岩阶段早期，有机酸的产生和消耗、不稳定矿物溶蚀/蚀变、粘土矿物转化和干酪根生油具有同步性，为生油期液态烃的充注与滞留提供了有利空间。中成岩晚期至晚成岩阶段，干酪根和滞留烃裂解生气、成孔和增压促进了有机孔与微裂缝的发育。③超压对压实作用的缓解利于有机孔形态与页岩物性的保持，对高应力敏感性粘土质页岩物性的保持影响显著，对底部高脆性矿物页岩段影响较低。盆内至盆缘构造的改造与泄压强度逐渐增大，底部硅质页岩物性变化不显著，上部粘土质页岩物性降低显著，封盖作用增强。未来研究重点应聚焦于不同类型（深层、常压等）页岩储层构造-压力与生烃-成岩演化耦合关系及其对页岩储集类型、页岩气富集与保存机制等方面。

关键词：页岩气；储层；演化；岩相；地层压力；五峰组－龙马溪组；四川盆地

Reservoir evolution mechanisms of the Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in the Sichuan Basin

Wang Ruyue¹, Hu Zongquan¹, Long Shengxiang¹, Du Wei¹, Zhao Jianhua⁴

(1. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China; 2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 102206, China; 3. SINOPEC Key Laboratory of Shale Gas/Oil Exploration & Production, Beijing 102206, China; 4. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, Shandong, China)

Abstract: Based on analysis of mineral petrology, organic geochemistry, storage space, physical properties and gas-bearing characteristics, evolution mechanism and their influence on shale gas exploration and development in the Upper Ordovician Wufeng and Lower Silurian Longmaxi shales are scrutinized and discussed. The shale reservoir evolution mechanism of "biological silicon-calcium controls rigid mineral frameworks, co-evolution promotes pore generation, and pressure evolution controls preservation" is proposed. Results show that: (1) lithofacies along with the type and occurrence of organic matter (organic pore carrier) play an important role in controlling the development of organic pores. The interparticle pores (>3~5 µm) filled with organic matter in the siliceous shale are highly developed, which is most conducive to the development of organic macropores. The development of organic pores in argillaceous shale is affected by the TOC content and the structure of the organo-clay composites. Pore size of the organic pores in argillaceous shale shows great variances with a relatively large average, but the total number of organic pores is small. (2) The rigid mineral framework composed of bio-quartz, microbial dolomite and pyrite formed in the syngenesis to the early diagenesis stage contributes to the preservation of original pores. In the early stage of the middle diagenesis, the production and consumption of organic acids, unstable mineral dissolution/alteration, clay mineral transformation and kerogen oil generation are synchronized, which provides favorable spaces for the charging and retention of liquid hydrocarbons during the oil generation period. From the late mid-diagenesis stage to the late diagenetic stage, shale gas/organic pore generation and pressure increase of kerogen as well as retained hydrocarbon cracking promote the development of organic pores and micro-fractures. (3) The mitigation against compaction by overpressure allows the maintenance of organic pore morphology and shale physical properties. Its influence on high stress-sensitive argillaceous shale at upper section is obvious, which is on the other hand unapparent on siliceous shale at the bottom. With the tectonic deformation and pressure relief intensity increasing from the basin to the edge areas, the physical properties of the siliceous shale at the bottom largely remains the same, while the physical properties of the upper argillaceous shale become poor resulting in an enhanced sealing capacity. Future research should focus on the coupling relationship between structure-pressure and hydrocarbon generation-diagenesis evolution of different types (deep, normal pressure, etc.) shale reservoirs and their effects on shale reservoir types, shale gas enrichment and preservation mechanisms, etc.

Key words: shale gas; reservoir; evolution; lithofacies; formation pressure; Wufeng-Longmaxi Formations; Sichuan Basin