A Study Of Coalbed Gas Reservoir Numerical Simulation

Coal seam geologic features and Coalbed gas flow characteristics through porosity media are so complex that conventionally classical percolation law are not suitable for coalbed gas reservoir. Large numbers of experimental studies and coalbed gas field applications have proved that three processes, coalbed gas adsorption, diffusion, percolation in the methane producing process, the changes in porosity and permeability are affected by coal matrix shrinkage and effective stress alteration.On the basis of the domestic and abroad literatures researches, the mechanisms of the storing, migrating and producing for coalbed gas and the complex exploiting procedure of coalbed gas are analyzed, a three-dimensional, dual-porosity, two-phase mathematical model for simulating methane producing process is developed; in model non-equilibrium, pseudo-steady sorption and the changes of reservoir parameters with the coal matrix shrinkage are taken considerate. In another hand, this complex mathematical model is approximated and solved by finite-difference and implicit pressure and explicit saturation method (IMPES). Coalbed Gas Reservoir Simulation software in 1.0 version (CBR-MS 1.0) with friendship interface of input and output is developed and the corresponding numerical and computer solution of mathematical model were set up. The productivity formulae of fractured horizontal well when calculate the production of coalbed gas well are derived, many factors effect the production of coalbed gas well are analyzed by the formulae; the simulator are applied to study the effect of coal matrix shrinkage on reservoir porosity, permeability and the well productivity, the sensibility of coal matrix shrinkage model are analyzed, the exploitation effect of fractured horizontal well and vertical well are compared.The acquired achievements are as follows: On the basis of the theories of solid deformation and solid surface energy, developing a coal matrix shrinkage model that indicates the effects of the deformation of coal matrix shrinkage on the porosity and permeability of fractures. The model avoids the reservoir porosity and permeability error that are brought by the inaccurate coal matrix coefficient and 1/ . On the basis of the theories of potential function principles and superposition principal, the horizontal well productivity formula is developed. Anisotropy of reservoir matrix, number of fractures and fractures of fully or partially penetrating in the formation and so on are considered in the formulae. A three-dimensional, dual-porosity, two-phase mathematical model developed,non-equilibrium, pseudo-steady sorption and the effects of the deformation of coal matrix shrinkage on the porosity and permeability of fracture are considered, and numerical solution is derived. Coalbed gas reservoir simulator in 1.0 version is developed by modifying source code of Black Oil Simulation procedure BOAST II, the simulator breaks through the limitation of others coalbed gas reservoir simulation software that don't take coal matrix shrinkage into account. The main procedure and the friendship interface of the simulator are programmed by Visual Basic in 6.0 version and Compaq Visual Fortran in 6.5 version, the calculated results are dealt with by corresponding software.