沁水盆地东部武乡区块泥页岩孔隙结构特征研究

Study on pore structure characteristics of mud shale in Wuxiang Block of eastern Qinshui Basin

沁水盆地东部武乡区块煤系伴生泥页岩广泛发育,页岩气资源潜力大,加强该区泥页岩孔隙结构特征的研究对页岩含气性评价以及实现煤层气、页岩气合探共采具有重要意义。为此,以武乡区块X井二叠系山西组泥页岩为主要研究对象,通过高压压汞和低温液氮试验手段对沁水盆地东部武乡地区X井泥页岩孔隙结构进行了研究。研究结果表明:沁水盆地武乡区块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。其脱附回线属于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)。主要发育裂缝型孔,墨水瓶型孔次之,分选性好,开放型孔较少,连通性较差;目标层属于页岩气较差的储层段,不利于储层的吸附、扩散和渗透,但经压裂改造可改善;压汞试验测得泥页岩主要大量发育孔径在5~7 nm及15 nm左右的孔隙,液氮试验测得沁水盆地武乡区块泥页岩孔隙孔径集中分布在1.18 nm左右;BET比表面积为10.022~15.454 m2/g,平均值约为13.342 m2/g,其中微孔是泥页岩比表面积的主要贡献者;孔隙直径分布在5.56~6.50 nm,平均值为5.75 nm,平均孔径在中孔范围内。总孔隙体积在0.008 12~0.012 54 cm3/g,平均孔体积为0.01 cm3/g。综合液氮压汞的试验分析结果可知,武乡地区X井山西组泥页岩孔隙中主要发育<50 nm的孔,其中2~50 nm的孔是总孔体积的主要贡献者。

Coal-bearing associated shale in Wuxiang Block of eastern Qinshui Basin is widely developed and has great potential for shale gas resources.Strengthening the study of pore structure characteristics of shale is of great significance to the evaluation of shale gas-bearing property and the realization of co-exploration and co-exploitation of coalbed gas and shale gas.Therefore,the pore structure of the shale of the Permian Shanxi Formation of Well X in Wuxiang Block is studied by means of high pressure mercury injection and low temperature liquid nitrogen experiments.The results show that the adsorption curve of mudstone samples in Wuxiang Block of Qinshui Basin is inverted Sshaped,which belongs to Type II curve of Brunauer classification scheme.The desorption line belongs to the H2 type( both Type H1 and Type H3) in the IUPAC classification scheme,and belongs to the Type B( both Type E and Type C) in the De Boer classification scheme.Fractured holes are mainly developed,followed by ink bottle holes,with good sorting,fewer open holes and poor connectivity.Target layer belongs to the reservoir with poor shale gas,which is not conducive to the adsorption,diffusion and permeability of reservoir,but can be improved by fracturing.The pore size of shale is mainly about 5 ~ 7 nm and 15 nm by mercury injection test. The pore size of mudstone in Wuxiang Block of Qinshui Basin is concentrated at about 1.18 nm measured by liquid nitrogen experiment.BET specific surface area ranges from 10.022 to 15.454 m2/g,with an average of 13.342 m2/g.Micropore is the main contributor to shale specific surface area.The average pore diameter ranges from 5.56 to 6.50 nm,with an average of 5.75 nm.The average pore size is in the range of mesoporous.The total pore volume is between 0.008 12 and 0.012 54 cm3/g,and the average pore volume is 0.01 cm3/g.According to the experimental results of liquid nitrogen mercury injection,the pore size of shale in Shanxi Formation of Well X in Wuxiang Area is less than 50 nm,and the pore size of 2 ~ 50 nm is the main contributor to the total pore volume.