Meikuang Anquan (Mar 2022)
Influence of coal pore development characteristics on in-situ injecting CO2 to replace and drive CH4
Abstract
The mechanism of injecting CO2 to increase the production of CBM includes replacement, carrying, dilution and diffusion, etc, which are closely related to coal pores. In order to clarify the influence of coal pores on in-situ injecting CO2 to replace and drive CH4, the pore structure characteristics of three raw coal samples were analyzed, and then a self-made experiment platform was used to realize the injected gas replacement and driving CH4 in loaded coal. It is used to study the permeability and adsorption of raw coal under different conditions, and a step-by-step experiment of in-situ injecting CO2 to replace and drive CH4 is carried out, and the whole process of replacement and driving is deeply discussed. The experimental results show that the proportions of adsorption pores of YCW lignite, SL fat coal and YMY anthracite are 28.71%, 88.24%, and 89.24%, the development degree of seepage pores decreases sequentially. As the degree of coal metamorphism increases, the adsorption capacity of coal becomes larger and the permeability becomes smaller. The process of replacement and driving can be divided into three stages. In the early stage, injecting CO2 mainly plays the role of replacement. In the middle stage, injecting CO2 plays the role of replacement, carrying and dilution. In the later stage, injecting CO2 plays the role of carrying and dilution. For YCW lignite with adsorption pore and seepage pore, increasing gas injection pressure or reducing external load can effectively promote replacement, carrying and dilution, greatly improving the whole replacement and driving process, but little improving for SL fat coal and YMY anthracite with only adsorption pore. For example, when the gas injection pressure is 1 MPa and the external load is 6 MPa, the replacement and driving efficiency of YCW lignite, SL fat coal, and YMY anthracite is 62.4%, 48.4%, and 62.3%. When the gas injection pressure is 2 MPa and the external load is 4 MPa, the replacement and drive efficiency of three coal samples is 94.4%, 72.2%, and 71.0%, respectively.
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