济阳坳陷缓坡带页岩油储层微观孔隙结构及分形特征

Micropore structure and fractal characteristics of shale oil reservoir in gentle slope zone of Jiyang Depression

页岩孔隙主要为微—纳米级孔,其微观孔隙结构及分形特征对页岩油储层评价至关重要。通过岩心和薄片观察、X衍射全岩矿物分析和低温氮气吸附-脱附实验等方法,定量表征了济阳坳陷缓坡带陆相页岩油储层的微观孔隙结构和分形特征。结果表明:济阳坳陷缓坡带主要发育碳酸盐质页岩、混合碳酸盐质页岩、含硅灰质页岩、含灰(硅)混合质页岩等4种岩相类型。低温氮气吸附-脱附曲线主要呈现为Ⅳ类,发育4种迟滞回线类型。选取多层吸附区域氮气吸附数据,计算分形维数,页岩样品分形维数介于2.4106~2.6160,平均为2.5275,页岩样品孔隙结构整体复杂,粗糙程度中等偏高,非均质性较强。页岩的有机质丰度变化主要受陆源碎屑质量分数的影响。分形维数与比表面积和平均孔径关系密切,页岩比表面积和平均孔径越小,分形维数越大。页岩孔隙结构特征多与页岩层理的发育程度密切相关,纹层状页岩具有更大的平均孔径、更好的孔隙结构及更弱的非均质性。

The pores of shale are mainly micro-nano pores,and their micropore structure and fractal characteristics are crucial to the evaluation of shale oil reservoirs.Through core and thin section observation,X diffraction analysis and low-temperature nitrogen adsorption-desorption experiment,the micropore structure and fractal characteristics of continental shale oil reservoirs in gentle slope zone of Jiyang Depression were quantitatively characterized.The results indicate that the gentle slope zone in Jiyang Depression mainly develops four types of lithofacies:carbonate shale,mixed carbonate shale,siliceous limestone shale,and limestone(siliceous)mixed shale.The adsorption-desorption curve of low-temperature nitrogen mainly presents as Class IV,with four types of hysteresis loops developed.The fractal dimension of shale samples was calculated from the nitrogen adsorption data in the multi-layer adsorption area.The fractal dimension of shale samples was between 2.4106-2.6160,with an average of 2.5275.The pore structure of shale samples was generally complex,with medium to high roughness and strong heterogeneity.The abundance of organic matter in shale was mainly affected by the content of terrigenous detritus.The fractal dimension was closely related to the specific surface area and average pore diameter.The smaller the specific surface area and average pore diameter of shale,the greater the fractal dimension.The pore structure of shale was closely related to the development degree of shale bedding.Laminated shale had larger average pore diameter,better pore structure and weaker heterogeneity.