Influence of reservoir properties on the methane adsorption capacity and fractal features of coal and shale in the upper Permian coal measures of the South Sichuan coalfield, China

Abstract

Pore structure plays an essential role in the reservoir heterogeneity and methane adsorption capacity. Significant progress has been made in the pore structure classification of porous materials (such as coal and shale). Considering the pore structure characterization of the coal measures and the measuring range of high-pressure mercury intrusion porosimetry and low-pressure N2/CO2 gas adsorption, an integrated classification for coal and shale is provided. They are micropore (<2 nm), mesopore (2–100 nm), macropore A (100 nm–1 µm), macropore B (1–10 µm), and micro-fracture (>10 µm). For coal and shale samples from Guxu mining area, the micropores and mesopores largely control the gas adsorption while micro-fractures and macropore B are significant for the storage and flow of free gas. The fractal dimensions calculated from limited N2 adsorption data are not suitable for the coal samples which are not developed in mesopore and macropore A; these samples are precisely corresponding to the N2 adsorption/desorption isotherms of group B (reversible isotherm). Furthermore, the main factors influencing the methane adsorption capacity of coal and shale in the coal measures are micropore frequency, micro-fracture width, clay mineral composition, and total organic carbon content.

Hydrogeochemical Characteristics and Water–Rock Interactions of Coalbed-Produced Water Derived from the Dafosi Biogenic Gas Field in the Southern Margin of Ordos Basin, China

“…The lowest HCO 3 concentration was 285.5 mg/L, and the highest was 4092.2 mg/L, accounting for 3-40% of all anions. The difference in the HCO 3 concentrations reflected the different well locations and may be related to the dissolution of CO 2 in CBM. The water type of the coalbed-produced was mainly Na-Cl in the study area, containing a small Na-Cl-HCO 3 -type (Table 1 and Figure 2).…”

“…Coalbed methane (CBM), as a cleaner unconventional natural gas resource [1][2][3], has been widely prioritized development in major coal-producing countries (e.g., China, the United States, Canada, and Australia) [4][5][6]. The United States was the first to begin commercially developing CBM; China, Canada, and Australia are also entering the initial industrial CBM development stages [7].…”

Spatiotemporal Evolution and Genesis of the Late Ordovician—Early Silurian Marine Euxinia in Northeastern Upper Yangtze Basin, South China

“…In general, the transformation of anoxic water between ferruginous and euxinic conditions is mainly controlled by the input of OM, Fe and sulfate in the sedimentary system (Johnston et al, 2010;Raiswell and Canfield, 2012). Moreover, paleoproductivity is a direct factor in evaluating sedimentary OM, and OCAR is considered to be one of the most effective indicators for evaluating paleoproductivity (Shen et al, 2015;Bao et al, 2020). During the O-S period, the average values of OCAR were higher in Wc-1 well (1.85-124.80 mg/cm 2 /kyr, mean 32.81 mg/cm 2 /kyr) than those in Shaba section (0.85-58.10 mg/cm 2 /kyr, mean 21.01 mg/cm 2 /kyr) (Supplementary Table S1), consistent with the change in redox conditions, suggesting that the productivity level may be one of the main factors causing the change of redox conditions in the water column.…”

Advances on the Mechanism of Reservoir Forming and Gas Accumulation of the Longmaxi Formation Shale in Sichuan Basin, China

“…The preservation conditions of the Longmaxi Formation shale gas accumulated in the Sichuan Basin clearly exhibit regional variation. − The evaluation of shale gas using only static geological parameters produces unsatisfactory exploration results, which limit the exploration and development of shale gas. With increasing uplift amplitude, the vertical loss of shale gas and migration along the formation increase. , The free gas capacity of a shale reservoir depends on temperature, pressure, total organic carbon (TOC) content, and porosity. − The difference in gas abundance increases with increasing formation dip angle. From the interior of the Sichuan Basin to the region outside of the basin, the Longmaxi Formation strata exhibit earlier uplift, larger uplift amplitude, and shallower buried depth; consequently, the shale gas content outside the basin is generally lower than that in the basin .…”