Study On Theory And Experiment Of Permeability Changes Discipline In CBM Reservoir

Based on both experimental and theoretical investigations, the permeability of coalbed methane reservoir is studied and analyzed with reservoir depletion. Theoretically, a new analytical permeability model is proposed using MATCHSTICK geometry and constant volume theory. The new model incorporates primarily the changes in grain and cleat volumes and is, therefore, different from the other models that lay heavy on the pore volume and cleat compressibility. The model considers the effective stress and coal matrix shrinkage effect on the permeability changes. Experimentally, the uniaxial strain condition is successfully simulated in the laboratory. The flowrate/permeability is measured by using step-wise fashion for different methane pressures. The permeability trend is analyzed for methane depletion. Moreover, the constant volume theory is valid for the coalbed methane reservoir because the vertical strain does not change in the lab-scale experiment. The study provides the theoretical basis for further analysis and perdition of coalbed methane reservoir dynamical permeability changes. It is significantly important for the coalbed methane development. It also helps CBM production companies to make long-term planning.