中扬子地区五峰组—龙马溪组页岩气成藏关键地质因素

中国南方中扬子地区上奥陶统五峰组—下志留统龙马溪组具有较好的页岩气勘探前景,但目前对于该区复杂的地质条件及页岩气勘探开发潜力的认识尚不够全面,制约了其勘探成效。为了揭示该区五峰组—龙马溪组页岩气富集的主控因素,以单井储层综合评价为基础,结合钻井、测井、岩心、露头及分析测试数据,对五峰组—龙马溪组黑色页岩的沉积环境、储层发育特征及保存条件等页岩气关键富集条件进行研究,并与四川盆地焦石坝和长宁等页岩气主产区块进行对比。研究结果表明:①该区富有机质页岩段形成于五峰组—龙一3亚段沉积期,为深水陆棚沉积,厚度介于15～39 m,由南至北逐渐增厚;②优质页岩段储层岩石相类型以硅质页岩相为主,孔隙度介于1.60%～7.44%,储集空间以有机孔为主、连通性较好,总有机碳含量高,有机质类型为腐泥型—偏腐泥混合型,热演化程度高,含气性较好,可压裂性好;③当阳复向斜内地层保存较好、产状平缓、断裂发育少、顶底板厚度大且分布稳定,页岩气保存条件较好;④较之于长宁、焦石坝等区块,中扬子地区具有埋藏深、两向应力差较大和地层压力系数较低的特点。结论认为,该区五峰组—龙马溪组具有较好的页岩气富集条件,具备进一步开展勘探...

Key geological factors for shale gas accumulation inthe Wufeng–Longmaxi Fms in the central Yangtze area

The Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the central Yangtze area of southern China has a good prospect of shale gas exploration. So far, however, its complicated geological conditions and shale gas exploration and development potentials have not been understood completely, which affects its exploration achievements. In order to determine the main factors controlling shale gas enrichment in the Wufeng–Longmaxi Fms in this area, this paper studied the key shale gas enrichment conditions in the black shale there (e.g. sedimentary environments, reservoir development characteristics and preservation conditions) based on single-well comprehensive reservoir evaluation, combined with drilling, logging, core, outcrop and test data. In addition, it was compared with the main shale gas blocks in the Sichuan Basin, such as Jiaoshiba and Changning. And the following research results are obtained. First, the organic-rich shale section in this area was formed during the sedimentation from Wufeng Formation to the third submember of the first Member of Longmaxi Formation. It is the deposit of deepwater continental facies, and its thickness is in a range of 15–39 m, presenting a trend of increasing from south to north. Second, the reservoir rocks in the high-quality shale sections are dominated by siliceous shale, and the reservoir porosity is in a range of 1.60–7.44%. The reservoir spaces are dominated by organic pores with good connectivity and high total organic carbon (TOC) content. The organic matter is of a sapropel–sapropel prone hybrid type, with a high thermal evolution degree, better gas bearing property and good fracability. Third, the Dangyang synclinorium is characterized by better strata preservation, rock occurrence flat, less developed faults and thick and stable roofs and floors, so its shale gas preservation conditions are better. Fourth, different from the Changning and Jiaoshiba Blocks, the central Yangtze area is characterized by great burial depth, large bidirectional stress difference, and low formation pressure coefficient. In conclusion, the Wufeng–Longmaxi Fms is better in shale gas enrichment conditions and has a potential of further exploration. However, its commercial shale gas development and scale production increase in the future face challenges due to its large stress difference, great burial depth, and lower pressure coefficient.