Nano-Scale Pore Structure and Fractal Dimension of Longmaxi Shale in the Upper Yangtze Region, South China: A Case Study of the Laifeng–Xianfeng Block Using HIM and N2 Adsorption

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.

The Genetic Mechanism and Evolution Process of Overpressure in the Upper Ordovician–Lower Silurian Black Shale Formation in the Southern Sichuan Basin

“…(2) In the Late Hercynian, a series of marine carbonate deposition and marine-continental transitional coal-sedimentation layers were formed with an average thickness of 500 m. (3) During the Indosinian period, the Sichuan Basin experienced a transition from marine to continental sedimentation and the thickness of Triassic strata was approximately 1200 m. (4) During the Yanshanian period, approximately 2900 m of continental deposits were formed spanning from the Jurassic to the Cretaceous. (5) During the Himalayan period, the sedimentary caprock in the area was fully folded and fractured, forming the current tectonic features.…”

“…The black shales from the Wufeng Group (O 3 w) and the Longmaxi Group (S 1 l) are considered to be the most developed shale strata in China [1][2][3][4][5]. It has been proven by reservoir exploration and development that reservoir overpressure is an important indicator dominating the shale gas enrichment and production in southern China [6][7][8].…”

Pore Properties of the Lacustrine Shale in the Upper Part of the Sha-4 Member of the Paleogene Shahejie Formation in the Dongying Depression in East China

“…Among the techniques for quantitative analysis of shale pore systems [4,[12][13][14], low-pressure gas adsorption (LPGA) is important in the measurement of pore properties over a wide range of pore sizes. Low-pressure N 2 adsorption is frequently used to analyze mesopore characteristics in shale reservoirs [15]. One of reasons is that mesopores are usually much more than micropores and macropores in shale reservoirs [16].…”

Editorial for Special Issue “Nanomineralogy”

“…Several papers [22][23][24][25][26][27] in this special issue focus on energy geology, addressing the structure and composition of coal and shale nanominerals as well as changes in nanopores and their fractal dimensions. They also describe structural characteristics such as the size, shape, and connectivity of nanopores in unconventional oil and gas reservoirs, along with their evolutionary laws and control factors.…”

“…The findings indicated that the composition content porosimetry porosity generally increases with increasing OM and clay content and decreases with increasing quartz and feldspar content. Huang and coauthors [23] evaluated the pore structure characteristics of Lower Silurian Longmaxi shale gas reservoirs in Well LD1 of the Laifeng-Xianfeng Block, Upper Yangtze region in South China. N 2 adsorption and helium ion microscope (HIM) were used to investigate various pore features, including pore volume, pore surface area, and pore size distribution.…”