Abstract
This paper tries to determine the key evaluation parameters of shale reservoirs in the complex tectonic provinces outside the Sichuan Basin in South China, and also to target the sweet spots of shale reservoirs accurately. The pore-structure characteristics of the Lower Silurian Longmaxi shale gas reservoirs in Well LD1 of the Laifeng–Xianfeng Block, Upper Yangtze region, were evaluated. N2 adsorption and helium ion microscope (HIM) were used to investigate the pore features including pore volume, pore surface area, and pore size distribution. The calculated results show good hydrocarbon storage capacity and development potential of the shale samples. Meanwhile, the reservoir space and migration pathways may be affected by the small pore size. As the main carrier of pores in shale, organic matter contributes significantly to the pore volume and surface area. Samples with higher total organic carbon (TOC) content generally have higher porosity. Based on the Frenkel–Halsey–Hill equation (FHH model), two different fractal dimensions, D1 and D2, were observed through the N2 adsorption experiment. By analyzing the data, we found that large pores usually have large values of fractal dimension, owing to their complex pore structure and rough surface. In addition, there exists a good positive correlation between fractal dimension and pore volume as well as pore surface area. The fractal dimension can be taken as a visual indicator that represents the degree of development of the pore structure in shale.
Highlights
According to the trends of the global petroleum industry, hydrocarbon exploration is mainly focused on marine deep water, onshore deep layer, and unconventional oil and gas [1]
The helium ion microscope (HIM) images of L-1 show a large volume of micropores and fine mesopores developing with associated organic matters, which are usually mixed with clay minerals
Are there larger pores, but many cracks caused undeveloped pore structures based on analysis of N2 adsorption
Summary
According to the trends of the global petroleum industry, hydrocarbon exploration is mainly focused on marine deep water, onshore deep layer, and unconventional oil and gas [1]. There are few researches about Longmaxi shale in the western Hubei Province [22], which is outside the eastern margin of the Sichuan Basin, though a series of shale gas exploration wells were drilled in recent years. The study of this region can provide experience and guidance for the exploration and exploitation of complex tectonic deformation areas of marine shale in south China. The fractal characteristics of shale and coal collected from China have been calculated and analyzed through some experiments like mercury porosimetry, N2 gas adsorption, NMR, small-angle X-ray scattering (SAXS), and SEM digital images [35,36,37,38,39,40]
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