Migration of metamorphic CO₂ into a coal seam: a natural analog study to assess the long‐term fate of CO₂ in Coal Bed Carbon Capture, Utilization, and Storage Projects

Abstract

This study assesses the displacement of coalbed methane by CO 2 migration along a fault into the coal seam in the Yaojie coalfield. Coal and gas samples were collected continuously at various distances in NO.2 coal seam from F19 fault. Vitrinite reflectance, maceral, and pore distributions and proximate analysis of fourteen coal samples were performed. Gas components, concentrations, carbon isotopes of 28 gas samples were determined. We examined the coal-gas trace characteristics of coalbed methane displaced away from the fault by CO 2 injection after geological ages. From east to west, away from the F19 fault, the CO 2 concentration decreased, whereas the CH 4 concentration increased gradually. The d 13 C values for CO 2 varied between À9.94& and 1.12&, suggesting a metamorphic origin. A wider range of d 13 C CO2 values (from À9.94& to 20&) was associated with the mixing of microbial carbon dioxide, isotopic fractionation during CO 2 migration through the microporous structures of coals, and/or carbon isotope fractionation during gas-water exchange and dissolution of CO 2 . Away from the F19 fault, the volumes of micropores, mesopores and macropores decrease gradually. The Dubinin-Radushkevich (DR) micropore volume decreased from 0.0059 to 0.0037 cm 3 g -1 , and the mesopore and macropore volumes decreased from 0.066 to 0.026 cm 3 g -1 . The CO 2 injection can mobilize aromatic hydrocarbons and mineral matter from coal matrix, resulting in the decrease in the absorption peak intensity for coal samples after supercritical CO 2 treatment, which indicates that chemical reactions occur between coal and CO 2 , not only physical adsorption.

Time-Dependence of Mechanical Property Alterations on Anthracite Coals Treated by Supercritical Carbon Dioxide

“…Coal mass gets ductile as the coal becomes plasticized in the process of CO 2 adsorption, and this phenomenon is more notable under the condition of Sc-CO 2 adsorption. It has been put forward that physical and molecule microstructures of coal can be altered by the interaction between CO 2 and coal induced by sorption-induced swelling, pore size reset, hydrocarbon extraction, and macromolecular rearrangement [23][24][25][26][27]. However, the link between the weakening of coal strength and the microcosmic physical-chemical alterations of Sc-CO 2 -treated coal is still rarely reported.…”

Microscale Research on Effective Geosequestration of CO2 in Coal Reservoir: A Natural Analogue Study in Haishiwan Coalfield, China

“…It has been proven that CO 2 of Earth's crust derived from stratal carbonate pyrolysis generating inorganic CO 2 , which are influenced by contact metamorphism of carbonates and dynamic metamorphism of fault activities [24]. According to geological survey in Geological Institute (Gansu, China), magmatic intrusion has never happened in the region since the Paleozoic [25].…”

Addressing the CO 2 emissions of the world's largest coal producer and consumer: Lessons from the Haishiwan Coalfield, China

“…Thus large volumes of CO 2 have been naturally stored in the coal seams of the Haishiwan coalfield for >15 Ma. The process of CO 2 injection into the coal seam by dynamic metamorphism via faults and replacement of pre-existing CH 4 can be considered as a natural analogue of CO 2 -enhanced coalbed methane (ECBM) and CO 2 storage pilot projects [26,27].…”