武乡区块山西组泥页岩孔隙结构及分形特征研究

沁水盆地东部煤系伴生泥页岩广泛发育,页岩气资源潜力大,开展该区泥页岩孔隙结构特征的研究对页岩含气性评价及实现煤层气、页岩气合探共采具有重要意义。本文以盆地内武乡区块Y井二叠系山西组泥页岩为研究对象,通过XRD、高压压汞和低温液氮吸附等实验手段对泥页岩孔隙结构特征及分形特征进行了研究。结果表明,Y井山西组泥页岩的矿物组成以黏土矿物和石英为主;泥页岩中小于50 nm的孔隙大量发育,结构形态上以狭缝平板型孔隙和"细瓶颈"孔隙为主;泥页岩样品吸附曲线呈倒S型,属于Brunauer分类方案中的Ⅱ型曲线,其脱附曲线属于IUPAC分类方案中的H2型(兼具H1型及H3型),属De Boer分类方案中的B型(兼具E型及C型); Y井山西组泥页岩分形维数接近3,非均质性较强,矿物成分、总孔体积、平均孔径和TOC含量是影响泥页岩分形维数的重要因素。

Pore structure and fractal characteristics of mud shale in Shanxi Formation of Wuxiang block

The coal-associated mud shale is widely developed in the east of the Qinshui Basin and has great potential for shale gas resources. Research on the pore structure characteristics of mud shale in this area is of great significance for the evaluation of shale gas-bearing properties and the realization of joint exploration and co-production of coalbed methane and shale gas. In this paper, the mud shale of the Permian Shanxi Formation from Well Y in the Wuxiang block of the basin was taken as the research object. The pore structure characteristics and fractal characteristics of the mud shale were studied by means of XRD, high-pressure mercury intrusion, and low-temperature liquid nitrogen adsorption. The results show that the mineral composition of the mud shale of the Shanxi Formation in the Y-well is dominated by clay minerals and quartz. There are a large number of pores smaller than 50 nm, and the pore structure is mainly composed of crack pores and "thin bottleneck" pores. The mud shale adsorption curve is of inverted S-type, suggesting type Ⅱ curve of Brunauer classification scheme. The desorption line belongs to the H2 type( both H1 type and H3 type) in the IUPAC classification scheme, and belongs to the B type( both E type and C type) in the De Boer classification scheme. The fractal dimension of mud shale in Shanxi Formation of Well Y is close to 3, and the heterogeneity is strong. Mineral composition, total pore volume, average pore size and TOC content are important factors affecting the fractal dimension of mud shale.