渝东南地区常压页岩气富集主控因素分析

Analysis of major factors controlling the accumulation in normal pressure shale gas in the southeast of Chongqing

中国志留系页岩气勘探主要集中在四川盆地及其周缘,近年来不断取得新成果,盆内焦石坝等地区的勘探取得重大突破,页岩气藏以超压为主要特征,盆外构造改造作用较强,页岩气藏以常压为主要特征。在勘探实践基础上,开展页岩层序地层、沉积微相、地球化学、储层特征、构造作用等综合地质研究,明确了渝东南地区常压页岩气富集三大主控因素。一是深水陆棚相优质页岩是页岩气富集的基础,渝东南地区五峰组—龙马溪组优质页岩厚20~40m,TOC含量为2%~4%,RO值为2%~3%,页岩气富集静态评价指标优越;二是保存条件是页岩气富集高产的关键因素,通过PY1、NY1、RY1等井钻探效果与断层、埋深、距剥蚀区远近等相关性分析,指出构造改造较弱、距离断层远近、离剥蚀区距离、埋深适中为页岩气富集的必要条件;三是有机孔隙发育是页岩气高产的重要因素,运用氩离子抛光扫描电镜、比表面积及孔径分析、纳米CT、热模拟等实验手段,研究认为有机孔隙是页岩气赋存的主要储集空间,有机质热演化、压实作用、地层压力是影响有机孔隙的主要因素;在此基础上建立了渝东南地区常压页岩气甜点区优选标准。

Exploration of shale gas in Silurian in China mainly concentrates in the Sichuan Basin and around,new achievements are acquired constantly in recent years,i.e.,explorations in Jiaoshiba and other regions in Sichuan Basin have made major breakthroughs.Shale-gas reservoirs in those areas are characterized by overpressure.Shale gas reservoirs out of the Sichuan Basin are characterized by normal pressure because of strong tectonization.Based on practices of exploration,this study researched comprehensive geology,including the shale sequence stratigraphy,sedimentary microfacies,geochemistry,reservoir characteristics,tectonization,etc.Three major factors controlling the accumulation of shale gas with normal pressure in the southeast of Chongqing was established.Firstly,development of high quality shale in deep continental shelf is the base of enrichment of shale gas.The shale gas accumulation static evaluation index of Wufeng-Longmaxi Formations in the research area are superior.The high-quality shale is 20-40 meters thick,the TOC is 2%-4%,and RO is 2%-3%.Secondly,preservation condition is the key factor to the shale gas accumulation and high yield.Through the comparative analysis between drilling results of Wells PY1,NY1,RY1 and faults,burial depth,distance from the denudation area,etc.,it indicates that the intension of tectonic reworking,the distance to the fault and outcrop,moderate burial depth are the key conditions of shale gas enrichment.Thirdly,development of organic pore is important to the high yield of shale gas.Using SEM,specific surface area and pore size analysis,nano CT,thermal simulation experiment method,etc.,it demonstrates that the organic pore is the primary reservoir space of shale gas occurrence,thermal evolution of organic matters,compaction,and formation pressure are key element to influence organic pore.Standards for dessert optimization of normal pressure shale gas in the southeast of Chongqing were established.