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鄂尔多斯盆地三叠系延长组张家滩陆相页岩层系中发育大量粉砂质纹层,与相邻纯页岩呈薄互层状产出。为了更全面地研究页岩层系的孔隙结构发育特征,采用物理方法分离页岩岩心中的粉砂质纹层和纯页岩层,综合采用二氧化碳吸附法、氮气吸附法和压汞法获得全孔径范围内的孔隙结构特征。结果表明:粉砂质纹层孔径分布特征呈多峰分布,发育微米级孔隙,孔径较大,总孔体积平均为2.02mL/g,孔隙度平均为5.40%,大孔(>50nm)是其孔体积的主要贡献者;纯页岩孔径分布特征呈双峰分布,主要分布在100nm以下孔径区间,孔径较小,总孔体积平均为1.41mL/g,孔隙度平均为3.67%,中孔(2~50nm)是其孔体积的主要贡献者。粉砂质纹层的实测孔隙度是纯页岩孔隙度的1.2~1.8倍,估算渗透率比纯页岩大2~4个数量级。因此,页岩层系中的粉砂质纹层相对纯页岩具有较大的孔径和孔体积,有利于提高页岩层系整体的储渗能力。
In the Ordos Basin, a large amount of silty textured layers are developed in the Zhangjiatan continental shale strata of the Triassic Yanchang Formation and are thinly interbedded with adjacent pure shale. In order to study the pore structure development characteristics of shale strata in a more comprehensive way, silt texture and shale layers in shale cores were separated by physical methods. Carbon dioxide adsorption, nitrogen adsorption and mercury intrusion were used to obtain the full aperture range Within the pore structure features. The results showed that the pore size distribution of silty textured layer showed multimodal distribution, with micropores developed. The average pore volume was 2.02mL / g, the average pore volume was 5.40%, and macropore (> 50nm) The main contribution of pore volume; pure shale pore size distribution showed a bimodal distribution, mainly in the pore size range below 100nm, a smaller pore size, the average pore volume of 1.41mL / g, an average porosity of 3.67%, mesoporous 2 ~ 50nm) is the main contributor to its pore volume. The measured porosity of silty textured layer is 1.2 ~ 1.8 times that of pure shale, and permeability is estimated to be 2 ~ 4 orders of magnitude larger than pure shale. Therefore, the silt layer in shale system has larger pore size and pore volume than pure shale, which is beneficial to improve the overall permeability and storage capacity of shale system.