Adsorption Characteristics and Controlling Factors of CH4 on Coal-Measure Shale, Hedong Coalfield

Adsorbed gas is one of the crucial occurrences in shale gas reservoirs; thus, it is of great significance to ascertain the adsorption capacity of shale and the adsorption characteristics of CH4. In this investigation, the Taiyuan-Shanxi Formations' coal-measure shale gas reservoir of the Carboniferous-Permian era in the Hedong Coalfield was treated as the research target. Our results exhibit that the shale samples were characterized by a high total organic carbon (TOC) and over to high-over maturity, with an average TOC of 2.45% and average R-o of 2.59%. The mineral composition was dominated by clay (62% on average) and quartz (22.45% on average), and clay was mainly composed of kaolinite and illite. The Langmuir model showed a perfect fitting degree to the experimental data: V-L was in the range of 0.01 cm(3)/g to 0.77 cm(3)/g and P-L was in the range of 0.23-8.58 MPa. In addition, the fitting degree depicted a linear negative correlation versus TOC, while mineral composition did not exhibit a significant effect on the fitting degree, which was caused by the complex pore structure of organic matter, and the applicability of the monolayer adsorption theory was lower than that of CH4 adsorption on the mineral's pore surface. An apparent linear positive correlation of V-L versus the TOC value was recorded; furthermore, the normalized V-L increased with the growth of the total content of clay mineral (TCCM), decreased with the growth of the total content of brittle mineral (TCBM), while there was no obvious correlation of normalized V-L versus kaolinite, illite and quartz content. The huge amount of micropores and complex internal structure led to organic matter possessing a strong adsorption capacity for CH4, and clay minerals also promoted adsorption due to the development of interlayer pores and intergranular pores.

Automated summary

Adsorbed gas is crucial in shale gas reservoirs, and this study focused on the adsorption characteristics of coal-measure shale gas in the Taiyuan-Shanxi Formations. Results showed that organic matter and mineral composition influenced the adsorption characteristics, with organic matter possessing a strong adsorption capacity for CH4 due to its complex pore structure.