Simulation-Based Evaluation of Concurrent CH4 Storage Potentials During CO2-ECBM in Karaganda Coal Basin

Abstract

Karaganda Basin contains the largest coalbed methane (CBM) reserve in Kazakhstan. We previously modelled the enhanced coalbed methane (ECBM) process by injecting CO2 into a typical well group which showed high production potential. With the global agreement on carbon neutrality, it is advantageous to explore the CO2 storage potential during CO2-ECBM in Karaganda Coal Basin. The CO2 storage potential of a given coal seam volume in the Karaganda Coal Basin is evaluated by setting up an extended 5-well pattern in a compositional reservoir simulator. The CO2-ECBM process is simulated by incorporating the reservoir parameters reported for the Karaganda Coal Basin, with variable CO2 injection rate and well pressures to optimize the injection strategy, such as the necessity of well stimulation. Simulation results showed that primary depletion followed by CO2 injection is a promising win-win strategy. Based on parameter sensitivity analysis, the CO2 injection rate should have an optimal value under pressure constraint, since higher injection rate does not contribute remarkably to the recovery. With the aid of CO2 injection, the methane recovery could be enhanced from 35.1×106 kg to 40.2×106 kg by 14.5% during the 4-year CO2 injection at constant rate of 60,000 m3/day with constraint pressure of 15,000 psi. Correspondingly over 99.98% of injected CO2 can be concurrently stored in the form of adsorbed and free gas in these case scenarios. Simulation results suggest that commercial CBM production could be established in the Karaganda Coal Basin, if properly implemented; meanwhile, the process entails enormous potential for CO2storage and represents a new opportunity for the Karaganda coal industry.