为明确四川盆地长宁地区龙马溪组低电阻页岩储层孔隙发育差异性,采用低阻页岩与常规页岩相对比的研究手段,开展了有机碳分析、氮气吸附实验、XRD矿物组分分析和扫描电镜等一系列实验,阐明了长宁低阻页岩储层孔隙结构及其分形特征,并明确了它们的控制因素.结果显示,长宁地区大多数低阻页岩孔隙发育程度明显差于常规页岩,其中,孔体积发育的差异主要体现在2~20 nm孔径范围内,比表面积差异则主要集中在小于1.5 nm和大于1.8 nm段.页岩储层孔隙结构随电阻率的降低有变差的趋势,对低电阻页岩储集能力影响更明显的是有机质含量和成熟度.相较于常规电阻页岩,低电阻页岩在小孔隙段具有更加复杂的孔径及孔壁发育.黏土矿物和黄铁矿对分形维数的影响在不同电阻率页岩中是一致的,而有机质对2类页岩分形维数的影响相反.有机质对分形维数的影响与过演化页岩石墨化后的有机孔变化密切相关.
For the study of pore development characteristics of low-resistivity shales in Changing area,Sichuan Basin,a series of experiments,such as organic carbon analysis,nitrogen adsorption,XRD mineral composition analysis,and scanning electron microscopy were carried out,and differences between low-resistivity shale and conventional shale in Changning area were studied through comparative method.The pore structures and fractal characteristics of the low-resistivity shale reservoirs were Clarified,and their controlling factors were revealed.The results show that the pore development degree of most low-resistivity shales in Changning area is significantly worse than that of con-ventional shales.Among them,the difference in pore volume is mainly reflected in the pore size range of 2~20 nm,and the difference in specific surface area is primarily concentrated in the segments less than 1.5 nm and more than 1.8 nm.The pore structure of the shale reservoirs tends to worsen with the decrease in resistivity.The organic matter content and maturity have a more obvious influence on the reservoir capacity of low-resistance shales.Compared with conventional resistance shales,small pores of low-resistance shales develop more complex pore sizes and pore walls.The effects of clay minerals and pyrite on the fractal dimension of shales with different resistivity are consistent.In contrast,the effect of organic matter on the fractal dimension of shales with different resistivity are opposite.The effect of organic matter on fractal dimension is closely related to the change of organic pores of over-evolutional shales after graphitization.