黔北地区下古生界页岩气储层孔隙结构特征

Pore structure characteristics of the Lower Paleozoic formation shale gas reservoir in northern Guizhou

页岩孔隙结构是影响页岩气储层储集能力和页岩气开采效果的重要因素.以下寒武统牛蹄塘组和下志留统龙马溪组页岩样品为研究对象,综合运用扫描电子显微镜、高压压汞、CO2和N2气体吸附等实验方法,对黔北地区下古生界页岩气储层孔隙度、孔隙类型与特征、孔径分布进行了研究,认为该区下古生界页岩发育多种成因类型的微米-纳米级孔隙,为页岩气赋存提供了储集空间.研究结果表明：1）黔北地区下古生界页岩孔隙度为1.30%～13.37%,平均4.56%;2）下古生界页岩微观孔隙类型多样,以粒间孔、有机质孔和粒内孔最为常见;3）微孔（〈2nm）和介孔（2～50nm）为黔北地区下古生界页岩气储集的主要载体,两者比表面积之和占总比表面积的94.3%,两者孔容之和占总孔容的59.1%,孔径主要分布于0.4～0.7nm,3～10nm和0.05～200.00μm这3个区间段,为狭缝状孔、管状孔和墨水瓶状孔;4）龙马溪组页岩孔隙度、孔径与牛蹄塘组页岩存在一定的差异,龙马溪组页岩孔隙度平均为6.4%,孔径均值为4.71nm,牛蹄塘组页岩孔隙度平均为5.3%,孔径均值为4.23nm;5）下古生界页岩气储层孔隙结构受页岩有机碳、有机质成熟度及矿物成分的影响：随着有机碳、石英含量的增加,页岩孔隙度和微孔孔容呈增加趋势;随着成熟度R_o、黏土矿物含量的增加,页岩孔隙度和孔容呈降低趋势.

Pore structure of shale is an important factor influencing the storage capacity of a shale gas reservoir and the effect of shale gas development.Taking shale samples from Lower Cambrian Niutitang formation and Lower Silurian Longmaxi formation in northern Guizhou as the research object,combined with scanning electron microscope（SEM）,high pressure mercury injection,CO_2 and N_2 gas adsorption experiments,the porosity,types and characteristics of microscopic pore,pore size distribution of the Lower Paleozoic formation shale gas reservoir in northern Guizhou were studied in this paper.It is suggested that there are various genetic types of micro-nano pores developed in the Lower Paleozoic formation shale in northern Guizhou,which provide the main reservoir spaces for shale gas.The results show that：1）The porosity of the Lower Paleozoic formation shale in northern Guizhou is 1.30%—13.37%in range,and the average is 4.56%.2）Various types of microscopic pores exist in the Lower Paleozoic formation shale.The intergranular pore,organic matter pore and intraparticle pore are the most common.3）Micropore（2nm）and mesopore（2—50nm）are the main reservoir storage space for shale gas.The surface area of micropore plus mesopore accounts for 94.3% of the total surface area.Their pore volume accounts for 59.1% of the total pore volume.Their poresize distribution mainly falls in 0.4—0.7nm,3—10nm and 0.05—200.00μm.The pore structure is the parallel-plate pore with slit shape,two ends opened tube pore and ink-bottle pore.4）There are some differences in the porosity and pore size between the Longmaxi formation shale and the Niutitang formation shale.The average porosity and pore size of the Longmaxi formation shale is 6.4% and 4.71 nm,while the average porosity and pore size of the Niutitang formation shale is 5.3% and 4.23 nm,respectively.5）The pore structure of the Lower Paleozoic formation shale gas reservoir is mainly influenced by total organic carbon content,organic matter maturity,and mineral composition of shale.The porosity and micropore volume of shale show a growing trend with the increase of total organic carbon content and quartz content,but present a down trend with the increase of maturity Roand clay minerals content.