Measurement of CO 2 adsorption capacity with respect to different pressure and temperature in sub-bituminous: implication for CO 2 geological sequestration

CCUS (carbon capture, utilization, and storage) technology is regarded as a bottom method to achieve carbon neutrality globally. CO 2 storage in deep coal reservoirs serves as a feasible selection for CCUS, and its storage potential can be attributed to the CO 2 adsorption capacity of the coal. In this paper, a series of CO 2 adsorption isotherm experiments were performed at different pressures and temperatures in sub-bituminous coal from the southern Junggar Basin (reservoir temperature ∼25.9°C and pressure ∼3.91 MPa). In addition, the high-pressure CO 2 adsorption characteristics of the southern Junggar Basin coal were characterized using a supercritical D-R adsorption model. Finally, the CO 2 storage capacities in sub-bituminous coal under the in situ reservoir temperature and pressure were analyzed. Results indicated that the excess adsorption capacities increase gradually with increasing injection pressure before reaching an asymptotic maximum magnitude of ∼34.55 cm 3 /g. The supercritical D-R adsorption model is suitable for characterizing the excess/absolute CO 2 adsorption capacity, as shown by the high correlation coefficients > 0.99. The CO 2 adsorption capacity increases with declining temperature, indicating a negative effect of temperature on CO 2 geological sequestration. By analyzing the statistical relationships of the D-R adsorption fitting parameters with the reservoir temperature, a CO 2 adsorption capacity evolution model was established, which can be further used for predicting CO 2 sequestration potential at in situ reservoir conditions. CO 2 adsorption capacity slowly increases before reaching the critical CO 2 density, following a rapid decrease at depths greater than ∼800 m in the southern Junngar Basin. The research results presented in this paper can provide guidance for evaluating CO 2 storage potential in deep coal seams.