鄂西宜昌地区下古生界五峰组-龙马溪组页岩气储层发育特征与勘探潜力

近年来,鄂西宜昌地区上奥陶统五峰组-下志留统龙马溪组页岩气勘探取得了一系列重要发现和突破。为进一步明确该区五峰组-龙马溪组页岩气勘探潜力,文章在前人研究的基础上,利用钻井及野外露头资料,结合地震、测井和分析测试数据,对宜昌地区五峰组-龙马溪组页岩气储层发育特征、优质储层分布及勘探潜力等进行了深入研究。结果表明,宜昌地区五峰组-龙马溪组下部黑色富有机质页岩储层岩石类型丰富,普遍具有高硅(石英平均含量>50%)、高碳(TOC平均为2.47%)、高成熟度(R_o普遍大于2%)、低孔(普遍低于5%)和特低渗(平均为0.19×10^-3μm²)特征,储层含气性较好,平均含气量超过2.0 m³/t。优质储层主要集中在五峰组和龙马溪组黑色页岩下部,对应于凯迪阶WF2-WF3笔石带和鲁丹阶LM2-LM3笔石带,厚度约11 m,与四川焦石坝和长宁地区相比,该区优质储层厚度偏薄。最后通过保存条件和经济性评价分析,认为鄂西宜昌东部斜坡区五峰组-龙马溪组页岩气保存条件相对较好,埋藏较浅,地质资源量超过1 200×10

Characteristics and exploration potential of the Wufeng-Longmaxi shale gas reservoirs of Lower Paleozoic in Yichang area,western Hubei Province,China

During the past few years,several shale gas discoveries were made in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in Yichang of western Hubei Province,China.The shale gas potential of the formations was then explored by combining the previous studies with updated analyses of drilling data and outcrops,geophysical information and testing results.A summary of the development characteristics,reservoir distribution and resource potential of the formations shows that the targeted dark,organic-rich rocks at the lower part of the formations have high quartz content(more than 50% on average)and TOC(2.47% on average),and high maturity(R o of more than 2% in general),low porosity(less than 5% in general),extra-low permeability(0.19×10^-3μm^2 on average),and relatively high gas content(2.0 m^3/t on average).Quality reservoirs are mostly distributed in the lower part(about 11 m thick)of the black rocks and can be corresponded to the WF2-WF3 Katian graptolite zone and LM2-LM3 Rhuddanian graptolite zone.The reservoirs are thinner than high-quality reservoirs in Jiaoshiba and Changning areas,Sichuan Province.However,judging by their preservation conditions and economy,we propose that the rocks in the slope of eastern Yichang with their shallower burial depth,relatively better preservation conditions as well as a geological reserve of over 1200×10^8 m^3,are worthy of further exploration.