Dynamic Response of Gas Recovery Enhancement Efficiency in Coalbed Methane Displacement by Hot Flue Gas: From the Perspective of Thermo–Hydro–Mechanical–Chemical Coupling
Tong Liu, Tong Liu, Yu Shi, Ting Liu, Ting Liu, Baiquan Lin
Abstract
The displacement of coalbed methane (CBM) by hot flue gas is an effective method to enhance gas recovery, but the dynamic response mechanism of gas recovery enhancement efficiency under the influence of the main engineering control parameters (pressure, components, and temperature) of hot flue gas remains unclear. In this study, a thermo–hydro–mechanical–chemical (THMC) coupling model that takes into account the interaction between gas–liquid two-phase fluids, chemical reactions of minerals (dissolution and precipitation), and temperature variations of the reservoir in CBM displacement by hot flue gas was established first. Besides, the mechanism of gas recovery enhancement by hot flue gas was analyzed based on the validated parameters in the THMC coupling model, including gas–liquid two-phase effective pressure in fractures, gas concentration, gas content, calcite content, H + concentration, and spatiotemporal evolution laws of temperature. Furthermore, the variations of the effective breakthrough radius, gas recovery amount, and recovery enhancement efficiency under the influence of different pressures, components, and temperatures of the flue gas were analyzed. Finally, the dynamic response relationship between the main engineering control parameters and the recovery enhancement efficiency in CBM displacement by hot flue gas was further investigated. This study can provide theoretical guidance for the engineering control of recovery enhancement efficiency in CBM displacement by hot flue gas.