Methane Adsorption Capacities of the Lower Paleozoic Marine Shales in the Yangtze Platform, South China

Abstract

The adsorption capacities of the Lower Silurian Longamxi and Lower Cambrian Niutitang marine shales in the Yangtze Platform in China were investigated through methane adsorption experiments. The correlations between the adsorption capacities and major factors, e.g., total organic carbon (TOC) contents, thermal maturity, mineral composition, moisture content, pressure, and temperature, were discussed. The isosteric adsorption heat was calculated according to the temperature dependency of the methane adsorption isotherms. The results show that, under the temperature of 30°C and pressure range of 0−12 MPa, the maximum adsorption capacity of the Longmaxi shales ranges between 0.47 and 3.08 m 3 /ton of rock and that of the Niutitang shales ranges between 1.59 and 7.43 m 3 /ton of rock. The Langmuir adsorption capacity varies from 0.54 to 3.84 m 3 /ton of rock for the Longmaxi shales and from 1.98 to 9.73 m 3 /ton of rock for the Niutitang shales. The TOC content shows a significantly positive correlation with the adsorption capacity, indicating that organic matter is responsible for adsorbing gas in the shales. For these high mature shales, the thermal maturity shows no effect on the adsorption capacity. The clay minerals show little contributions to the adsorption capacity in the shales because of the effect of the water content. For the studied shales, the moisture exhibits no distinct correlation with the adsorption capacity. The influence of the pressure on the adsorption capacity varies from sample to sample, while the temperature shows a generally negative effect on the adsorption capacity. The isosteric heat of adsorption ranges from 8.48 to 27.35 kJ/mol, with an average of 17.59 kJ/mol, indicating a dominant physical adsorption behavior of the methane molecule in the shales.

Quantitative characterization of micropore structure for organic-rich Lower Silurian shale in the Upper Yangtze Platform, South China: Implications for shale gas adsorption capacity

“…Such a pattern is quite analogous to previous studies (e.g. Ji et al, 2015;Wu et al, 2015) and is of great significance for understanding the changes in gas adsorption capacity of organic-rich shales.…”

“…Shale gas is stored in three different types of geological environment and they are (1) free gas in pores and fractures, (2) adsorbed gas in organic matters and clay minerals, (3) dissolved gas in residual oil and water (Zhang et al, 2012;Hao et al, 2013;Rexer et al, 2013;Ji et al, 2015;Wu et al, 2015;Chen et al, 2017a,b). Free gas and adsorbed gas are predominant in high-maturity shales (Hao et al, 2013).…”

“…Since shale gas can be stored in the form of adsorbed gas (Zhang et al, 2012;Rexer et al, 2013;Wu et al, 2015) and the adsorption behavior of gas in micropores is significantly different from that in mesopores or macropores Yang et al, 2016c), it is necessary to quantitatively evaluate the micropores in shales. This research focuses on the micropore structure characteristics of the Lower Silurian shale in the Upper Yangtze Platform, South China.…”

Lithofacies and cyclicity of the Lower Cambrian Niutitang shale in the Mayang Basin of western Hunan, South China

“…Because of the lack of vitrinite in these early Paleozoic marine shales, vitrinite reflectance (Ro) was calculated from the measured pyrobitumen reflectance (Rb) on the basis of their arithmetic relationship of Ro ¼ 0.3195 þ 0.6790Rb (Wu et al, 2015).…”

Determination of the absolute CH4 adsorption using simplified local density theory and comparison with the modified Langmuir adsorption model

“…In shale gas reservoirs, CH 4 is generally stored in three different states, which is claried as free-gas state in nanopores, absorbed-gas state in kerogen, and adsorbed-gas state on pore surface. [3][4][5] It has been found that the adsorbed CH 4 can take 20-85 vol% accounting for the total gas amount. 4 Recently, extensive studies are implemented to measure the CH 4adsorption on shale samples.…”