Experimental Study On The Dynamic Permeability During The Injection Of CO₂ Into The Anthracitic Coal Reservoir

The existing research results show that effective stress and matrix swelling control the dynamic permeability when CO2 is injected into the coal reservoir. In order to understand how the minerals which are sensitive to CO2 in coals effect the dynamic permeability, a series of experiments including routine parameters testing, water-rock reaction and core flooding experiment were carried out on four samples (DY, RF, XL, QS) collected from Zhucang Syncline in the west Guizhou Province. On the basis of experiments, the mechanism of dynamic permeability during the injection of CO2 into anthracitic coal reservoir is revealed.Routine parameters indicate that the coal lithotypes of study area belong to semidurain-semiclarain; the Ro,max,max varies from 3.34% to 3.54%, belonging to anthracite coal; the volume content of vitrinite varies from 84.29% to 90.13% in the maceral analysis, and the mass content of fixed carbon in the promximate analysis varies from 70.73% to 83.72%; XL has the best pore structure while DY the worst, which is consistent with the adsorption capacity of samples. What's more, DY almost has the same adsorption capacity to CO2 compared with CH4.Observing from hand specimens, optical microscope and SEM indicates that most of the carbonate minerals and parts of the clay minerals are filled in the fractures of coals and most parts of pyrite and the rest clay minerals are filled in the pores. Water-rock reaction experiment indicates that the concentration of bicarbonate ion controls the corrosion of minerals, including calcite which is the most sensitive mineral to CO2, and gypsum and dolomite the secondary. Moreover, the clay minerals don't change their lattice structure but cationic exchange interaction occurs.The core flooding experiment results indicate that the liquid flow descends exponentially with time because of the swelling of matrix which can be tested by related models. Overburden pressure porosity-permeability testing indicates that the porosity and permeability get great improvement through core flooding experiment because of the corrosion of minerals in the fracture by testing the ions from the outlet liquid.Finally, some pieces of advice about injecting CO2 into the coal reservoir are put forward based on the experimental results.