渝东南武隆地区龙马溪组页岩孔裂隙特征研究

Shale Pore Characteristics of Longmaxi Formation in Wulong Area, Southeastern Chongqing

张颖 张海涛 何希鹏 高玉巧 张培先

ZHANG Ying ZHANG Haitao HE Xipeng GAO Yuqiao ZHANG Peixian

中国石化华东油气分公司, 江苏 南京 210000

East China Company, SINOPEC, Nanjing, Jiangsu 210000, China

为明确渝东南武隆地区龙马溪组页岩孔裂隙发育特征，利用岩芯观察、氩离子抛光扫描电镜分析、低温氮气吸附脱附实验等方法，结合图像分析技术和分形几何理论，对LY-1井龙马溪组页岩孔隙结构及分形特征进行了研究。结果表明，武隆地区龙马溪组页岩宏观裂隙以层间页理缝和成岩收缩缝为主，扫描电镜下可见粒内孔、粒间孔及有机质孔，有机质孔最为发育，孔径几纳米到几十纳米；低温N吸附实验结果显示龙马溪组页岩存在3类优势孔径，I类优势孔径分布在1.0~1.5 nm，表明微孔是该区主要的孔隙之一，Ⅱ、Ⅲ类优势孔径分别分布在2.5~3.5 nm、5.0~18.0 nm，孔径>4.0 nm时曲线分维值与TOC、脆性矿物含量及含气量呈负相关性，与黏土矿物呈正相关性。研究认为，有机质孔为页岩气富集提供了最主要的空间，黏土矿物发育复杂结构的孔隙对气体赋存具有一定贡献。

Core observation, argon-ion polishing scanning electron microscopy, and low temperature nitrogen adsorption and desorption methods were used to study the pore characteristics of shale in the Longmaxi Formation, Wulong area, southeastern Chongqing. The shale pore structures and fractal features of the LY-1 Well, Longmaxi Formation, were investigated using image analysis technology and the fractal geometry theory. The results show that the macro shale fractures in the area are mainly interlayer lamellation cracks and diagenetic shrink micro-cracks. The intragranular pores, intergranular pores, and organic matter (OM) holes can be observed by the scanning electron microscope. The OM holes, with dimensions from several to dozens of nanometers, develop well, and the low-temperature N adsorption results show that the shale in the Longmaxi Formation has three significant pore sizes. The pore size of type I ranges from 1.0 to 1.5 nm, indicating that micropores are the most developed pores in the area. The types Ⅱ and Ⅲ pore sizes are from 2.5 to 3.5 nm and from 5.0 to 18.0 nm. When the pore size >4.0 nm, the curve fractal dimension value has a negative relationship with TOC, brittle mineral and gas contents, and has a positive relationship with clay minerals. The study shows that OM pores provide major reservoir spaces for shale gas, and pores with complex structures in clay minerals make a certain contribution to the shale gas reservoir.

10.11885/j.issn.1674-5086.2016.08.08.01