新疆阜康地区八道湾组煤系页岩气储层孔隙结构特征

Pore structure characteristics of a shale gas reservoir from coal measures in the Badaowan Formation, Fukang area of the Xinjiang Uygur Autonomous Region

为了评价煤系页岩气的储层性质,运用扫描电子显微镜、高压压汞、低压N2和CO2气体吸附等实验方法,对新疆阜康地区侏罗系八道湾组煤系页岩气储层孔隙的发育情况、结构特征进行了研究,并分析了八道湾组页岩孔隙发育的主要影响因素。结果表明,八道湾组页岩发育多种类型孔隙,以粒内孔、粒间孔为主,有机质孔次之,溶蚀孔发育较少,为煤系页岩气赋存提供储集空间。八道湾组页岩纳米级孔隙以微孔和介孔为主,占孔隙总孔容的77.30%,占总比表面积的89.80%,是页岩气赋存的主要载体;页岩孔隙结构类型以狭缝型孔和板状孔为主,孔隙主要分布在0.4~1.3 nm、3~30 nm和50~200 nm之间。八道湾组页岩孔隙的发育受页岩有机碳含量、成熟度和矿物成分含量影响较大,其中有机碳含量对微孔发育的促进作用明显,成熟度的增加主要对页岩中介孔和宏孔的发育产生重要影响,黏土矿物含量与页岩的介孔孔容及总孔容呈一定的正相关关系,脆性矿物则相反。

To evaluate the shale-gas reservoir in coal measures, the morphologic development and structural characteristics of pores in a coal-measures shale-gas reservoir in the Jurassic Badaowan Formation in the Fukang area of the Xinjiang Uygur Autonomous Region, China were studied. The major factors influencing the shale pores were analyzed using scanning electron microscopy, high-pressure mercury intrusion, low-pressure nitrogen and carbon dioxide gas adsorption. The results show that the Badaowan shale develops many types of pores, including mainly intragranular and intergranular pores, followed by organic pores and a small number of dissolution pores, which provide reservoir space for shale gas in coal measures. The nano-scale pores in the Badaowan shale are mainly micropores and mesopores, accounting for 77.30% of the total pore volume and 89.80% of the total specific surface area. These conditions are favorable for shale-gas accumulation. The pore structure types of shale are mainly slit pores and plate pores, and the pore diameter distribution can be described mainly by 0.4 –1.3 nm, 3–30 nm, and 50–200 nm. The development of the Badaowan shale pores is greatly influenced by the organic carbon content, maturity, and mineral composition. The organic carbon content is the main factor controlling the development of the micropores. Increase in maturity mainly affects the development of mesopores and macropores in shale. Clay minerals are positively correlated with the mesoporous volume and total pore volume in shale, but negatively correlated in brittle minerals.