CO2 utilization and sequestration potential in deep coal seams: A case study on Carboniferous coals from the Karaganda Basin, Kazakhstan

Kazakhstan is a major coal producer and emitter of carbon dioxide (CO 2 ), presenting both a challenge and an opportunity for CO₂ utilization and storage. The main goal of this work is to study the feasibility of CO 2 as a feedstock for enhanced coalbed methane recovery (CO 2 -ECBM), as well as the associated geological storage potential of the D6 coal seam in the Karaganda Basin. For this purpose, coal samples were investigated using elemental analysis, Rock-Eval pyrolysis (RE), organic petrography as well as low-pressure (LP: N 2 , CO 2 ), and high-pressure (HP: CO 2 , CH 4 ) sorption tests. Vitrinite reflectance values show that seam D6 reached the medium-volatile bituminous rank. Higher organic matter content significantly increases the LP CO 2 sorption capacity. The adsorption-desorption isotherms of CO 2 recorded under both LP and HP conditions show a hysteresis loop. This is probably due to interactions between CO 2 and functional groups leading to enhanced physisorption at LP and chemisorption and matrix swelling at HP conditions. This effect is favorable for storage purposes as it implies safe CO 2 trapping even at reduced reservoir pressure. The CBM potential of seam D6 is estimated at 9 billion m 3 initial gas and 360 million m 3 producible gas in place. Estimates of the adsorptive and total CO 2 storage capacity yielded 1.1 and 3.6 gigatons (Gt), respectively. With this considerable total storage capacity, Kazakhstan's current annual CO 2 emissions could be stored for 14 years. This study highlights how CO 2 can be effectively utilized as a feedstock to enhance methane recovery while achieving long-term CO 2 sequestration. • The Carboniferous D6 coal seam in the Karaganda Basin (central Kazakhstan) was studied by different analytical techniques. • The CBM potential of the seam was estimated at 9 billion m 3 initial gas and 360 million m 3 producible gas in place. • Estimates of the adsorptive and total CO 2 storage capacity yielded 1.1 and 3.6 gigatons (Gt), respectively.