Simulation Studies For Permeability Changes Caused By Supercritical CO₂ Injection Into Anthracite Coal Reservoir

The greenhouse effect has become increasingly serious, how to reduce emissions of CO₂ led all the attention, the CO₂-ECBM technology both can make use of coal reservoir seal CO₂ gas, and can improve coalbed methane（CBM） desorption, therefore its feasibility by wide attention and deep expectations. Taking Qinshui basin as study area, the geological conditions are relatively clear, south-central regions as the research focus that high degree of coal reservoir research, coal and CBM development projects focus, experimental samples gather convenient, and the anthracite coal reservoir No.3 of Shanxi Formation as target stratum. Based on the study area geology background, design experiments, using the self-developed "simulation of CO₂ injection coal reservoir permeability change experimental device", the simulation to study the different buried depth of coal seam ScCO₂-ECBM variation in coal and rock permeability of coal seam, and the study area ScCO₂-ECBM is simulated, finally the process feasibility is analyzed in the studied area.Through physical simulation experiment found that: As the temperature, confining pressure and axial compression pressure increase permeability all showed a trend of decline, and permeability more sensitive to confining pressure performance than the other two. Carbon dioxide directly in supercritical state injection of coal and normal pressure gas reservoir injected heats up at supercritical pressure will cause the coal and rock permeability attenuation, the latter coal and rock permeability attenuation slower, more conducive to seepage and diffusion of CO₂ in coal storage; Based on experiments then set up two permeability model between volume strain and permeability of coal rocks, and the models is verified, think more accord with the actual index model, with inflation decreases with the increase of strain, and the decline is the same, but the CO₂ gas state mutates, leads to the model poor adaptability when the change in gas state.This paper also designs the ScCO₂ with N2 alterning displacement experiment. Experiments found that the coal and rock of coal reservoir can approximate as elastomer, using displacement CH4, N2 injection coal can improve the permeability of coal seam, on free CH4 in reservoir displacement effect is better, for the adsorbed state CH4 displacement effect not as good as supercritical CO₂; While using ScCO₂-ECBM, each state of CH4 in coal reservoir displacement effects are better, but will cause permeability greatly attenuation, is not conducive to the coal reservoir fluid migration.This article with Shizhuang North CBM block SX007 well group in Qinshui basin as a study area for the ScCO₂-ECBM numerical simulation. Through simulation in the study area, obtained CH4 and CO₂ concentration change, well group bottom hole pressure change, the well group 20 annual amount of methane accumulation and geological sequestration of CO₂. And by comparing the injection solutions as a result, have chosen the optimal injection solution. The scheme for coal reservoir no damage, ScCO₂ injected can almost all sealed, and have uncommon facilitation for coalbed methane production rate, can also be appropriate to reduce the project cost.According to the result of simulating experiment and numerical simulation, combining with the geological characteristics of Qinshui basin, the feasibility of implementation of the project of ScCO₂-ECBM at area is analyzed. Analysis of Qinshui basin has rich coalbed methane resource and CO₂ sequestration ideal reservoir and cap rock, makes the ScCO₂-ECBM project in study area has important practical significance, and has theoretical feasibility. Poor but the basin anthracite coal reservoir permeability as a whole, is a key factor restricting process is feasible or not, and for this situation are proposed.