陆相页岩气储层孔隙发育特征及其主控因素分析:以鄂尔多斯盆地长7段为例

鄂尔多斯盆地延长组是目前最具页岩气潜力的研究层段之一。本文以该盆地东部长7段为研究对象，运用氮气吸附法及氩离子剖光扫描电镜分析对页岩气储层孔隙结构及孔隙类型进行分析和测定，并结合岩石矿物组分、有机质成熟度以及总有机碳（TOC）质量分数，讨论了孔隙结构和影响因素。结果表明，长7段页岩气储层孔隙结构复杂，根据吸附回线形态可分为2类：Ⅰ类回线主要对应孔径为2.6~4.2 nm的狭缝结构或楔形结构的平行板状孔或微裂缝，具体可分为黏土矿物矿片间孔隙、有机质内狭缝状孔隙及基质微裂隙等类型；Ⅱ类回线主要为分布于2.3~3.1、3.5~3.8、4.3~5.2 nm等多个孔径段的开放型圆筒状孔，包括有机质孔和残余粒间孔。中孔和微孔是总孔体积和比表面积的主要贡献者。w（TOC）是延长组页岩总孔体积及比表面积的主要控制因素，与总孔体积及比表面积均呈正相关关系；镜质体反射率及矿物含量对孔隙发育的控制作用不明显，但黏土矿物对微孔孔容贡献较大，其中伊利石质量分数与BET比表面积及孔容有较好的相关性。

Characteristics of Pore Development and Its Main Controlling Factors of Continental Shale Gas Reservoirs:A Case Study of Chang 7 Member in Ordos Basin

The Yanchang Formation is one of the most promising area for shale gas exploration in the Ordos basin.The Chang 7 Member of the Yanchang Formation in the eastern Ordos basin was selected as the research object.Based on the nitrogen isothermal adsorption,field emission scanning electron microscopy (FESEM) in combination with the laboratory tests on mineralogy,maturity and TOC,the pore types,structures as well as their controlling factors were analyzed respectively.As shown in the results,the pore structure of Chang 7 Member shale gas reservoir is complex,and can be divided into 2 types according to the adsorption loop morphology.Type Ⅰ loops mainly correspond to the parallel platelike holes or micro-cracks witha pore structure of 2.6 4.2 nm in diameter or in a wedge structure,and can be classified into clay-mineral intergranular pores,organic-matrix like pores,and matrix microcracks;typeⅡ loops are mainly open-ended cylindrical boreholes in 2.3 3.1 nm,3.5 3.8 nm,and 4.3 5.2 nm,including organic pores and residual intergranular pores.Mesopores and micropores are major contributors to total volume and specific surface area,which is controlled mainly by TOC with a positive correlation with both total volume and specific surface area.Neither Ro nor mineral contents show any influences on the pore structure;however,clay minerals contribute a lot to the volume of micropores,which is supported by the relatively positive correlation between illite contents and the total volume and specific surface area.