沁水盆地中东部海陆过渡相页岩孔隙结构及分形特征

Investigation of pore structure and fractal characteristics of marine-continental transitional shale in the east-central of Qinshui Basin

为研究海陆过渡相页岩的孔隙结构及分形特征,对采自沁水盆地的12块样品进行了低温氮气吸附、扫描电镜、X-射线衍射和有机质含量等系列分析测试。结果表明,研究区页岩黏土矿物最为富集,石英含量次之,有机质含量平均为2.98%,干酪根类型以Ⅲ型为主。中孔是研究区页岩的主体孔隙,对孔隙体积和比表面积贡献最大。研究区页岩孔隙具有明显的分形特征,利用FHH模型计算得到2种分形维数(D1、D2)。黏土矿物含量与D1、D2具有较好的正相关性,有机质含量与分形维数无明显相关关系。D1和D2具有一定的正相关性,可以共同定量表征页岩孔隙结构的复杂程度和孔隙表面的粗糙程度。分形维数D1、D2越大,页岩孔隙体积和比表面积越大,越有利于气体的富集,但是D2越大孔隙结构越趋于复杂,不利于气体的渗流。分形维数D1越大而D2适中的页岩储集能力较强,且有利于页岩气的开发。

To better understand the pore structure and fractal characteristics of marine-continental transitional shale in the east-central of Qinshui Basin,we collected 12 shale samples and performed a series of parallel experiments,including low-temperature nitrogen adsorption,scanning electron microscopy,total organic carbon content and X-ray diffraction analyses.The results show that the dominant minerals in the shale were clay minerals,followed by quartz.The average value of total organic carbon was 2.98%and kerogen in the shale samples is characterized by typeⅢ.According to the N2 physisorption analysis,mesopores which significantly contribute to the pore volume and specific surface area were dominant in the marinecontinental transitional shale samples.The pore in shale is fractal and the fractal dimensions were obtained from using the FHH model,named D1 and D2.There is a positive relationship between D1,D2 and clay minerals,in contrast,the impact of TOC on the fractal dimensions is relatively weak.There is a positive correlation between D1 and D2,indicating that both fractal dimensions can be used to characterize the pore structure and pore surface of the marine-continental transitional shale.More pore volume and specific surface area are always developed in shale with higher D1 and D2.However,the higher the D2,the more complicated of pore structure which is favorable for gas adsorption rather than gas transportation.Therefore,the higher the D1,the moderate the D2,the shale is favorable for gas storing-accumulating and exploitation.