鄂西地区上二叠统海相页岩气富集条件差异与控制因素——以红星区块吴家坪组二段和恩施地区大隆组为例

Gas differential enrichment characteristics and controlling factors of Upper Permian marine shale in western Hubei area:Case study of Wujiaping Formation II in Hongxing block and Dalong Formation in Enshi area

鄂西地区上二叠统海相页岩气资源潜力大,近年来在恩施、红星等地区获得诸多勘探发现,但不同地域页岩气勘探效果不同,储集性能、含气性等富集条件存在诸多差异。以红星区块吴家坪组二段和恩施地区大隆组为研究对象,综合利用钻井、测井、地震和实验室分析测试等资料,开展页岩气富集差异特征精细刻画和控制因素分析。研究发现:①吴家坪组二段与大隆组原始品质较为相似,富有机质页岩厚度略有差异;②吴家坪组二段储集性能、“源—储耦合”性和含气性均优于大隆组,有机质孔保存带来的储集性能差异是造成含气性差异的主要原因;③扬子周缘中—新生代强烈的构造挤压导致恩施地区大隆组初始抬升时间更早、上覆地层剥蚀量更大,页岩气保存条件相对较差;④埋深和构造样式可以有效指示现今保存条件,红星区块吴家坪组二段埋深大、发育在宽缓背斜内,较恩施地区复向斜浅埋藏的大隆组更有利于页岩气富集。综合提出勘探建议,认为两套页岩具有不同的勘探开发难点,应加强对比研究,分类施策。

The western Hubei area,which is adjacent to the Sichuan Basin,have great shale gas resources potential in the Upper Permian marine shales,and have achieved a series of exploration discoveries in recent years,such as Enshi,Hongxing and other areas.However,there are many differences in reservoir performance,gas-bearing property and other enrichment conditions,hence the shale gas display effect in different regions are diverse.Taking the Wujiaping Formation II in Hongxing block and Dalong Formation in Enshi area as the research objects,the detailed characterization of shale gas enrichment differences and analysis of controlling factors have been carried out by comprehensive use of drilling,logging,seismic and laboratory analysis and testing data.The results show that:(1)The original quality of the Wujiaping Formation II is relatively similar to that of the Dalong Formation,with a slight difference in the thickness of organic shale;(2)The reservoir performance,source-reservoir coupling and gas-bearing property of the Wujiaping Formation II are better than that of the Dalong Formation;(3)The strong Meso-Cenozoic tectonic compression around the Yangtze led to earlier initial uplift of the Dalong Formation in Enshi area,resulting in greater denudation of the overlying strata,and relatively poor shale gas preservation conditions;(4)The burial depth and structural style can effectively indicate the current preservation conditions.The Wujiaping Formation II in Hongxing block that was deeply buried and developed in a wide-gentle anticline,is more conducive to shale gas enrichment than the Dalong Formation,which is shallowly buried in the complex syncline in Enshi area.There have different structural styles and preservation conditions for two sets of shale in the two areas,which bring different difficulties in exploration and development.Therefore,comparative research should be strengthened and classified practical methods should be taken from the perspective of accelerating exploration and development.