鄂尔多斯盆地延长探区延长组页岩气储层孔隙结构特征

摘要

In order to evaluate the space and the gas storage capacity of terrestrial shale gas reservoirs,many shale samples were taken from the Chang 7 and Chang 9 members of the Upper Triassic Yanchang Formation in Yanchang exploration area of Ordos basin,and the pore type and pore structure of these samples and their influ ence factors were studied by the use of scanning electron microscope (SEM),high pressure mercury injection and low-temperature gas adsorption experiments with CO2 and N2.The results reveal the following aspects:(1)There are many types of microscopic pores in these shale samples,mainly including intergranular pores and intragranular pores,and a small amount of crystal particle pores and dissolution pores exists,and organic matter pores are less development.These pores provide the main storage spaces for the shale gasreservoir.(2)Mesopores (2-50 nm) contribute to the main pore volume and specific surface area of Yanchang Formation,accounting for 74.34％ of the total pore volume and 64.40％ of the total surface area.The shale samples from the Chang 9 Member have a greater total pore volume and total specific surface area than those from the Chang 7 Member.(3)The pore structure is dominated by slit type pores and plate pores,and the pore size distribution mainly falls in 0.4-0.9 nm,3-25 nm and 5-200 μm.The average pore size of Yanchang Formation shale is 8.53 nm,and the Chang 7 Member shale has a greater average pore size than the Chang 7 Member shale.(4) The organic carbon content,organic matter maturity and mineral composition content affect the pore development of the Yanchang Formation shale.The mineral composition content is the main controlling factor of the pore development of Yanchang Formation shale which is predominated by the mesopore.The increase of the organic carbon content and maturity of shales mainly play a positive role in the development of the micropore in Yanchang Formation shale.%为了评价陆相页岩气储层的储集空间和储气能力,以鄂尔多斯盆地延长探区上三叠统延长组长7段、长9段页岩为研究对象,运用电子扫描显微镜、高压压汞、低温CO2和N2气体吸附等实验方法,对陆相页岩气储层孔隙类型特征、孔隙结构及其影响因素进行研究.结果表明:(1)延长探区上三叠统延长组陆相页岩发育多种类型微观孔隙,以粒间孔和粒内孔为主,少量晶间孔和溶蚀孔,有机质孔发育较少,为陆相页岩气赋存提供了储集空间;(2)延长组页岩中介孑孔(2～50 nm)贡献了其主要的孑孔容和比表面积,占总孑孔容的74.37％,占总比表面积的64.40％,且长9段页岩的总孔容和总比表面积均大于长7段页岩;(3)延长组页岩孔隙结构以狭缝型孑孔和板状孔为主,孑孔径主要分布在0.4～0.9 nm、3～ 25 nm和5～200 μm区间段内,延长组页岩平均孔径为8.53 nm,且长7段页岩平均孔径大于长9段页岩;(4)页岩有机碳含量、有机质成熟度及矿物成分含量共同影响着延长组页岩孔隙的发育,其中矿物成分含量是以介孔孔隙为主的延长组页岩孔隙发育的主控因素,有机碳含量及成熟度的增加主要对页岩中微孔孔隙的发育起到积极作用.