Experimental simulation on N₂ injection for enhancing supercritical CO₂ injectivity in anthracite reservoir

The injectivity of deep anthracite reservoir decreased significantly, which induced by supercritical CO2(ScCO2) injection. In this paper, we had an investigation on N-2 injection for improving ScCO2 injectivity in anthracite reservoir by the ScCO2 -ECBM experimental stimulation apparatus, and had a discussion on the mechanism of N-2 injection for enhancing ScCO2 infectivity in anthracite reservoir. The experimental data demonstrated that the anthracite original permeability was 3.10 x10(-5)mu m(2), the permeability decreased to 5.80 x10(-8)mu m(2 )after ScCO2 saturated adsorption. However, the permeability of anthracite increased to 2.73x 10(-5)mu m(2) as N-2 displaced the 99.6% volume of ScCO2 in anthracite. The permeability of anthracite decreased to 3.39 x10(-8)mu m(2) as the ScCO2 was injected to anthracite once again. The experimental results indicated that the N-2 injection was a method to improve the permeability of deep anthracite reservoir effectively, and the permeability of coal seam could recover to the order of original permeability. In addition, the experimental results also indicated that the coal seam permeability change induced by ScCO2 injection was recoverable. N-2 injection to the coal seam had a partial pressure effect, which could accelerate the ScCO2 desorption from coal matrix and flood the ScCO(2)migration.