渝东南武隆向斜常压页岩气形成与演化

为了研究渝东南武隆地区常压页岩气的形成与演化，利用研究区页岩气钻井数据，综合运用岩石薄片观察、氩离子抛光扫描电镜分析、构造平衡剖面及埋藏史分析等多种实验方法与分析技术，并基于“动态保存”四要素（沉积-埋藏-生烃-抬升）对常压页岩气富集主控因素进行了分析。研究表明：武隆地区常压页岩气形成与演化受控于3个关键因素。①五峰组-龙马溪组沉积岩性组合为页岩气形成供烃供储供保，深水陆棚相形成区域上分布稳定的优质页岩，是良好的烃源基础，上部厚层页岩封盖使生成的烃类有效保存。②有机质孔为页岩气提供了储集空间，内部复杂的孔隙形态改善了页岩的渗透性，与有机质伴生的脆性矿物一定程度上减弱了压实作用对有机质孔的影响。③构造作用直接影响页岩气规模。构造作用导致页岩中气体运移散失，武隆向斜五峰-龙马溪组沉积后经历了持续深埋并达到生烃高峰，之后发生了大规模的抬升，生成的烃类部分散失，使储层压力降低，形成常压（地层压力系数0.8~1.2）页岩气。

Formation and evolution of normal pressure shale gas reservoir in Wulong Syncline,Southeast Chongqing,China

In order to understand the formation and evolution of the normal pressure shale gas reservoirs in Wulong Syncline in Southwest Chonqing,China the major controlling factors of shale gas accumulation were studied through drilling data analysis,thin section observation,Ar-SEM,tectonic balanced section and burial history analyses,in combination with analysis of four dynamic preservation factors (sedimentation,burial evolution,hydrocarbon generation,and tectonic uplifting).Results show that there are 3 key elements controlling the formation and evolution of the typical normal pressure shale gas reservoirs in Wulong syncline.The first one is the favorable lithological association of the Wufeng and Longmaxi Formations.The quality shales of deep shelf facies are stable in lateral distribution and have high potential of hydrocarbon generation,while the overlying thick shale has good sealing capacity,thus is favorable for the preservation of shale gas.The second one is the favorable reservoir conditions.The organic nanopores provide high porosity for gas storage and the complex pore geometries improve the permeability of the shale reservoirs.In addition,the brittle minerals associated with the organic maters acted as skeleton and protected to some extent the organic nanopores from compaction during diagenesis.The third one is tectonic evolution which determines the reservoir scale.After the continuous deep burial and main period of hydrocarbon generation,the target reservoirs experienced reformation during tectonic uplift,which led to the partial gas migration and dispersion,and the formation of normal-pressure shale gas reservoir with a pressure coefficient in the range from 0.8 to 1.2.