柴达木盆地北缘中侏罗统大煤沟组泥页岩吸附特征及其影响因素

Adsorption Characteristics and Influence Factors of Middle Jurassic Dameigou Formation Shale in Northern Qaidam Basin

页岩中吸附气含量是页岩总含气量中的重要组成部分。页岩吸附特性及其影响因素研究对于预测页岩总含气量及评价页岩气资源潜力具有重要的意义。柴达木盆地北缘侏罗系大煤沟组为一套湖相暗色泥页岩,分布广泛,有机碳含量高,已钻探获得页岩气发现。为研究这套泥页岩的吸附特征和影响因素,选取包括柴页1井岩心在内的40件泥页岩样品进行了有机地球化学、储层性能、岩石矿物学和含气量等一系列实验测试,分析了泥页岩有机碳含量等参数对吸附能力的影响。结果表明研究区大煤沟组泥页岩最大甲吸附气含量随压力增大而吸附能力逐渐增强,至一定程度达到饱和后不再增加;泥页岩中的有机碳、氯仿沥青"A"和黏土矿物可有效吸附和溶解甲烷,对吸附能力产生积极影响;在页岩热演化程度总体偏低的情况下,液态烃和可溶有机质大量存在并占据孔隙空间从而降低了泥页岩的比表面积,对其吸附能力产生消极影响。

The adsorption gas content is a key component of shale gas.Shale in different areas has various adsorption characteristics,whose influence factors are also diverse.A set of lacustrine dark mudstone and shale are developed in Jurassic Dameigou Formation of northern Qaidam Basin,whose total organic content is really high.The discovery of shale gas has been proved by drilling over there.In order to research the adsorption characteristics of shale mentioned above,40 samples of shale and mudstone,selected from Well CY1,have been measured on TOC,thermal maturity,rock pyrolysis,X-ray analysis,isothermal adsorption and nitrogen adsorption.The adsorption capacity and influence factors of terrestrial rich organic matter shale in Dameigou Formation have been analysed.The methane volume of shale in Dameigou Formation in the research area is from 0.4 to 7.1 m^3/t,and adsorption capacity increases gradually with increasing pressure until reaching saturation.The adsorption capacity of shale has positive correlation with several factors such as TOC,chloroform bitumen " A" content and clay mineral content.It also has negative correlation with several factors such as specific surface area and thermal maturity.The adsorption characteristics and influence factors of terrestrial shale is not completely the same as those of the marine shale,which is caused by a number of factors including high total organic content,low level of thermal maturity and different types of clay mineral.