四川盆地上奥陶统五峰组-下志留统龙马溪组页岩储层特征与演化机制

Reservoir characteristics and evolution mechanisms of the Upper Ordovician Wufeng-Lower Silurian Longmaxi shale， Sichuan Basin

王濡岳 胡宗全 龙胜祥 杜伟 吴靖 邬忠虎 聂海宽 王鹏威 孙川翔 赵建华

Ruyue Wang Zongquan Hu Shengxiang Long Wei Du Jing Wu Zhonghu Wu Haikuan Nie Pengwei Wang Chuanxiang Sun Jianhua Zhao

依据矿物岩石学、有机地球化学、储集空间、物性及含气性等特征，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—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。

The characterization of the Upper Ordovician Wufeng - Lower Silurian Longmaxi shale in terms of mineralogy， organic geochemistry， storage space， physical properties and gas-bearing potential， is applied to discuss the evolutionary mechanisms and their influence on shale gas exploration and development， proposing a shale reservoir evolution mechanism of “framework development as controlled by biogenetic silica-calcite， pore generation as promoted by co-evolution， and pore preservation as controlled by pressure evolution”. The results show that： （1） lithofacies along with the type and occurrence of organic matters （organic pore carrier） plays an important role in controlling the development of organic pores. The intergranular pores （with a size of greater than 3-5 μm） filled with organic matters in the siliceous shales are highly developed， the most conducive to the development of organic macropores. The development of organic pores in argillaceous shales is affected by the content and the structure of organo-clay complexes， and the organic pores are characterized by a wide range of distribution， large pore size on average， and small total number.（2） The rigid framework composed of bio-quartz， microbial dolomite and pyrite formed in the early of contemporaneous-early diagenetic 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， clay mineral transformation and oil generation from kerogens are synchronized， serving to provide spaces favorable for the charging and retention of liquid hydrocarbons during the oil generation period. From the late mesogenetic stage to the late diagenetic stage， gas generation， organic pore formation and pressure increase from cracking of kerogen and retained hydrocarbon jointly promote the development of organic pores and micro-fractures.（3） The compaction mitigation by overpressure allows the maintenance of organic pore morphology and shale physical properties. Its influence on highly stress-sensitive argillaceous shale at upper interval is obvious， while on the other hand， unapparent on highly brittle shale intervals at the bottom. With the tectonic modification and pressure relief intensity getting enhanced from the basinal center to edges， the physical properties of siliceous shale at the bottom largely remain the same， while the physical properties of the upper argillaceous shale become poor resulting in an enhanced sealing capacity.

10.11743/ogg20220209