Investigation of the CO₂ Flooding Behavior and Its Collaborative Controlling Factors

Abstract

CO2 injection to enhance coalbed methane (CO2-ECBM) production is a promising technology for realizing the efficient exploitation of new energy resource, but its effect is cooperatively affected by miscellaneous influencing factors. To elucidate the mechanism and increase the efficiency of the displacement of CH4 by CO2, CO2 flooding experiments under the influence of the injection pressure, confining pressure, and temperature were conducted. The results show that an increase in the injection pressure enlarges the pore-fracture network of the coal matrix and promotes its gas adsorption ability and seepage capacity, while an increase in the confining pressure compresses the coal body and reduces the adsorption capacity and permeability. Increasing the temperature enhances kinetic energy and induces the thermal swelling effect, which disfavors the adsorption and seepage processes. The CO2 adsorption capacity is larger than the CH4 adsorption capacity due to the higher adsorption affinity of CO2, but the CO2 permeability is lower than the CH4 permeability due to the severe adsorption swelling effect. The CO2 flooding process is characterized by three parameters (equal percentage displacement time, displacement rate, and displacement efficiency) and can be divided into the CO2 driving stage, replacement and displacement stage, and equilibrium stage. The injection pressure and temperature decrease the displacement time and increase the displacement rate and displacement efficiency, while confining pressure shows the opposite trends. Multifactor interaction models of the displacement efficiency of coal seams at various buried depths were established and demonstrated to appropriately predict the displacement efficiency of CO2-ECBM in deep coal seams. The displacement efficiency is controlled by the reservoir performance, geological characteristics, and CO2 injection technology. The selection of a high-permeability coal reservoir and coal seams with an appropriate buried depth and the development of a reasonable injection plan are suggested for the implementation of CO2-ECBM extraction.

Coal Pores: Methods, Types, and Characteristics

“…In addition, it has been reported that carbon capture and sequestration technology can effectively reduce the CO 2 content in the atmosphere . By injecting CO 2 into deep unmineable coal seams, the geological sequestration of CO 2 and effective development of CBM can be achieved, which have environmental and energy benefits. , Pores are an important part of the coal matrix, as well as the main storage space and migration channels for gas in coal; their development directly affects the adsorption/desorption, diffusion, and seepage of gas , and thus the development of CBM and CO 2 sequestration. Different pore structure development characteristics correspond to the specific coal-forming environment and coal metamorphic degree.…”

CO2 Adsorption/Desorption, Induced Deformation Behavior, and Permeability Characteristics of Different Rank Coals: Application for CO2-Enhanced Coalbed Methane Recovery

“…Jessen et al also confirmed the stronger adsorption capacity of CO 2 than that of CH 4 and calculated that the adsorption capacity of CO 2 is three times that of CH 4 under the same conditions . Thus, the injected CO 2 molecules can occupy the adsorption sites that belong to CH 4 molecules and promote the desorption of CH 4 ; this working process has been affirmed and exhibited by numerical simulations and laboratory experiments. − However, the negative side is that the coal matrix will swell after being adsorbed by CO 2 , which can squeeze fractures existing in coal seams and weaken the seepage capacity of coal reservoirs; the CO 2 injectivity of coal seams is as a result reduced …”

Recent Advances and Perspectives of CO2-Enhanced Coalbed Methane: Experimental, Modeling, and Technological Development

“…The ultimate sorption-induced strain of CO 2 gas is greater than that of CH 4 and N 2 under the same conditions. Niu et al 33 conducted CO 2 adsorption experiments under the influence of multiple factors by the self-developed equipment, and results found that the increase of the injection pressure will promote the volume of adsorbed gas in coals, while the increase of the temperature, pressure, and water content will inhibit it. Liu et al 53 analyzed the change of coal permeability after CO 2 injection and found that it would decrease.…”