Characterization Method for Full-Size Pore Radius Distribution in Lianggaoshan Formation, Sichuan Basin

doi:10.7657/XJPG20250207

Abstract

Abstract:

The shale reservoirs of Lower Jurassic Lianggaoshan formation in the Sichuan Basin are well-developed, with nanoscale pores. These reservoirs are characterized by low porosity, low permeability, diverse pore types, complex pore structures, and a wide range of pore radius distribution. Therefore, accurately evaluating pore structure of shale reservoirs is of great significance for reservoir evaluation and sweet spot prediction. Using the data from scanning electron microscopy (SEM), gas adsorption experiments, and nuclear magnetic resonance (NMR) experiments, the pore structures of different lithofacies in the Lianggaoshan formation were characterized. The calculation models for pore radius distribution based on N₂ and CO₂ adsorption were defined，and the surface relaxation rate, a conversion parameter between pore radius and transverse relaxation time, was determined to enable the characterization of full-size pore radius across lithofacies. And the relationship between surface relaxation rate and mineral contents was investigated. The results show that the surface relaxation rate is inversely proportional to the contents of quartz, plagioclase, and calcite, and directly proportional to the contents of potassium feldspar, siderite, and clay minerals. Chlorite, pyrite, and siderite are paramagnetic materials; as the concentration of paramagnetic ions increases, the magnetic susceptibility of these minerals increases, thereby enhancing the surface relaxation rate.

Key words: Sichuan Basin, Lianggaoshan formation, pore structure, NMR logging, gas adsorption, pore radius distribution, surface relaxation rate

CLC Number:

P631

ZHAO Ji’er, RAN Qi, XIE Bing, LAI Qiang, BAI Li, ZHU Xun. Characterization Method for Full-Size Pore Radius Distribution in Lianggaoshan Formation, Sichuan Basin[J]. Xinjiang Petroleum Geology, 2025, 46(2): 181-191.

Figures/Tables 11

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Table 1.

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岩相	总孔体积/ （cm³·g^-1）	BET比表面积/ （m²·g^-1）	孔隙半径/ nm
粉砂岩相	0.003 3~0.011 7 （0.007 2）	1.32~6.39 （4.04）	6.01~9.97 （7.68）
泥质粉砂岩相	0.004 7~0.009 0 （0.006 7）	2.24~5.13 （3.38）	7.01~8.80 （8.06）
页岩相	0.004 5~0.009 7 （0.007 0）	1.20~4.10 （2.57）	8.41~17.48 （11.29）

岩相	吸附量/ （cm³·g^-1）	比表面积/ （m²·g^-1）	孔隙半径/ nm
粉砂岩相	0.33~0.88 （0.60）	2.49~6.73 （4.30）	0.31~0.42 （0.39）
泥质粉砂岩相	0.47~0.85 （0.65）	3.41~6.44 （4.87）	0.35~0.50 （0.40）
页岩相	0.63~1.01 （0.81）	4.71~7.72 （6.28）	0.42~0.51 （0.46）

岩相	孔隙半径为2 nm时对应T₂/ms	微孔表面弛豫速率/ （μm·ms^-1）	孔隙半径为50 nm时对应T₂/ms	介孔表面弛豫速率/ （μm·ms^-1）
粉砂岩相	0.16	0.013	0.80	0.021
泥质粉砂岩相	0.28	0.007	1.20	0.014
页岩相	0.23	0.009	1.20	0.014