黔西地区下石炭统旧司组页岩气聚集条件及含气性分析

为研究旧司组页岩气聚集条件和含气性特征,以黔西地区下石炭统旧司组页岩为研究对象,采用薄片鉴定、X-射线衍射分析、覆压孔渗、扫描电镜、低温氮吸附、有机地球化学、含气量现场解析、等温吸附等测试方法开展研究。结果表明:黔西地区旧司组富有机质页岩广泛发育,厚度主体上介于30~100 m之间,有机碳含量高,有机质类型主要为Ⅱ型,处于过成熟生干气阶段;矿物成分主要为石英和黏土矿物,脆性指数均大于50%,为超低孔、超低渗,孔隙类型多样,孔径介于2~4 nm之间,以中孔为主,比表面积和总孔体积较大,具备良好的页岩气聚集条件;页岩微观孔隙的分形维数(D₁、D₂)较大,平均值分别为2.804 1、2.753 8,页岩孔隙结构较为复杂、非均质性较强;现场解析总含气量主体介于1.5~3.0 m³/t之间,等温吸附气量介于1.58~4.52 m³/t之间,含气性能较好,旧司组显示出具有良好的页岩气勘探潜力。

Shale Gas Accumulation Conditions and Gas-bearing Properties of the Lower Carboniferous Jiusi Formation in Western Guizhou

In order to study the shale gas accumulation conditions and gas-bearing characteristics of the Jiusi Formation,we conducted thin-section microscopic identification,X-ray diffraction(XRD)analysis,overburden porosity and permeability,scanning electron microscopy(SEM),low-temperature nitrogen adsorption,organic geochemistry,in-situ gas content,and isothermal adsorption analyses.The results show that the organic-rich Jiusi Formation(Fm.)shale is widely developed(mainly 30 to 100m thick)and has high TOC.It is mainly of type II and in the stage of over-mature dry gas generation.The shale contains mainly quartz and clay mineral,and with high brittleness index(>50%),ultra-low porosity and permeability.The rocks have also various pore types,medium pore size,large specific surface area and total pore volume,and good shale gas accumulation conditions.The fractal dimension of micro-pores is large,with average D1 and D2 of 2.804,1 and 2.753,8 respectively,reflecting complex pore structure and strong heterogeneity.The gas and adsorbed gas contents are of 1.5 to 3.0 m³/t and 1.58 to 4.52m³/t,respectively.The results indicate good gas-bearing performance,suggesting that the Jiusi Formation has good shale gas exploration potential.