四川盆地长宁地区龙马溪组上、下段页岩储层差异研究

On the differences of reservoir characteristics of the upper and the lower Longmaxi Formation shale in the Changning Region of Sichuan Basin

以四川盆地宜宾长宁地区露头页岩为研究对象,综合利用矿物组成测试、有机碳含量测试、阳离子交换容量测试、低压氮气吸附测试、分形理论等方法,对比分析龙马溪组页岩上段和下段的矿物组成分布、有机碳含量分布及孔隙结构的差异,并讨论这种差异对龙马溪组页岩储层特征的影响。研究结果表明,四川盆地长宁地区龙马溪组页岩上段和下段的矿物组成主要以石英和黏土矿物为主,其中上段石英含量低于下段石英含量,上段黏土矿物含量高于下段黏土矿物含量,下段有机碳含量高于上段有机碳含量;相比龙马溪组页岩上段,龙马溪组页岩下段有较低的黏土矿物含量和较高的石英含量,使其水化膨胀能力较低及其有较高的脆性特征;相比龙马溪组页岩上段,龙马溪组页岩下段富含更多的有机质,使其比表面积和总孔容较高,分形维数较大,孔隙结构复杂,吸附气体能力强。

Presented a study on outcrop shale of Longmaxi Formation of Lower Silurianin the Changning region of Sichuan Basin. Using the X ray diffraction （XRD） analysis, total organic carbon （TOC） content analysis, N2 absorption/desorption analysis, cation exchange capacity analysis and fractal analysis, the differences of the mineralogical, TOC contents and pore structure between the upper part of Longmaxi Formation shale and lower part of Longmaxi Formation shale were comparatively analyzed. And the influences of the differences on the reservoir characteristics of Longmaxi Formation shale were discussed. The result shows that the major min- eralogical compositions of the upper part of Longmaxi Formation shale and lower part of Longmaxi Formation shale are quartz and clay mineral, the quart contents of the upper part are lower than that of the lower part and the clay mineral contents of the upper part are higher than that of the lower part. Meanwhile, the TOC contents of the upper part are lower than that of the lower part. Compared with the upper part of Longmaxi Formation shale, there are lower in clay mineral and higher in quartz in the upper part of Longmaxi Formation shale, re- sulting in a lower hydration swelling capacity and a higher brittleness. Compared with the upper part of Longmaxi Formation shale, the lower part of Longmaxi Formation shale are rich in TOC, resulting in a higher specif- ic surface area and total pore volumes, and the fractal dimensions are larger, and the pore structures are more complicated, resulting in a higher adsorption capacity.