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

doi:10.11885/j.issn.1674-5086.2016.08.08.01

Abstract

Abstract: 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 N₂ 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.

Key words: Longmaxi Formation, pore structure, image analyze, fractal theory, Wulong Area

CLC Number:

TE122

ZHANG Ying, ZHANG Haitao, HE Xipeng, GAO Yuqiao, ZHANG Peixian. Shale Pore Characteristics of Longmaxi Formation in Wulong Area, Southeastern Chongqing[J]. 西南石油大学学报(自然科学版), 2018, 40(4): 29-39.

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