陆相页岩气的储集空间特征及赋存过程——以鄂尔多斯盆地陕北斜坡构造带延长探区延长组长7段为例

Reservoir space characteristics and charging process of Lacustrine shale gas—a case study of the Chang 7 member in Yanchang Block in Shanbei slope of Erdos Basin

页岩的储集空间不但影响页岩气的储量,还影响页岩气井的产能。研究页岩气的赋存空间及赋存过程有助于确定勘探靶位。综合利用野外露头、岩心观察、薄片分析及扫描电镜等多种手段,研究了鄂尔多斯盆地陕北斜坡构造带延长探区延长组长7段页岩的储集空间类型及其特征。在此基础上,通过解吸模拟实验进行页岩气气体特征分析,最终重建页岩气的赋存过程。结果表明,延长探区长7段页岩发育原生粒间孔、次生溶蚀孔、有机质生烃孔、构造张裂缝及层间页理缝等多种孔、缝类型。在解吸过程中,分子直径较小的甲烷气最容易解吸,含13C的甲烷分子则相对解吸困难。在生气初期,长7段页岩生成的少量重烃气主要吸附于有机质表面及微孔中;在生气期,页岩优先吸附重烃气和具13C的甲烷气;当满足页岩的吸附和溶解等残留需要后,气体以游离态赋存。

Reservoir spaces in shale controls not only the shale gas reserves,but also the production capacity of shale gas wells ,thus the study of reservoir space characteristics and charging process of lacustrine shale gas helps greatly to determine exploration targets.This paper integrates various technologies,such as field outcrops,core observation,thin section and SEM Pore Imaging,to study the reservoir space types and their features of Chang 7 shale of the Yanchang Fm in Yanchang Block of Shanbei slope zone,Erdos Basin.Combined with the experimental results of shale gas components,this paper simulates the shale gas charging process.The results show that,the reservoir spaces of Chang 7 shale are dominated by primary intergranular pores,secondary dissolved pores,organic pores,structural fractures and lamellation fractures.In the desorption process,the methane gas with relatively small molecule size is the first to be released from shale.However,the methane gas containing 13 C is relatively more difficult to be released from the shale.In the early gas generating stage,the small portion of heavy gas gener-ated from Chang 7 shale mainly adsorbed on the organic surface and micropores.In the main gas generating stage,heavy gas and 13 CCH4-containing methane had priority over other gas components to be absorbed in the shale reservoir.Only when the adsorption capacity and dissolution capacity of shale were met,could the free gas exist in the shale reservoir.