A Study Of Coalbed Methane Numerical Simulation Based On Low Permeability Coal Seam

Coalbed methane (CBM) is a hot topic recent years. It is a highly effective and clean energy resource that can substitute natural gas. Rational development and utilization of coalbed methane can effectively alleviate the harm of the gas to mine, reduce the amount of the released during the mining process and the damage of greenhouse. In addition, it can fill the shortage of natural gas and oil to provide clean energy. Although China has very rich coalbed methane resources, classic percolation theory is not applicable to the complex flow pattern of Chinese coalbed methane because of the complexity of coalbed methane reservoir characteristics, low permeability and the slow seepage of coalbed methane.This thesis using the theories and methods of coalbed methane geology, permeability mechanics, oil and gas geology and other disciplines, based on the data of domestic and foreign literature to analyze the mechanism of coalbed methane reservoir, migration and output, to generalize out the coalbed methane geological reservoir model. It mainly makes the following conclusions:(1) Coalbed methane is mainly stored as two forms of adsorption state and free state in coal reservoir. Coalbed methane experiences three processes from the surface of the matrix to go into the mining well bore such as desorption, diffusion and seepage. The adsorption and desorption that coal matrix effect on gas is reversible, a balance of adsorption and desorption is existed, and it is consistent with Langmuir isothermal adsorption model; adsorbed coalbed methane is mainly involved in diffusion motion that is consistent with Fick's first diffusion law; while the coalbed methane in free state form is mainly involved in seepage motion that is consistent with Darcy's seepage law. The process of coalbed methane exploitation from the substrate surface into the wellbore experiences desorption, diffusion and percolation. Especially for Chinese coalbed methane low permeability case, joined the coal reservoir pressure gradient factors, established a coalbed methane reservoir simulation mathematical model to describe the two-dimensional, dual porosity, quasi steady state gas-water flow migration rule.(2)This paper use the large multi-field coupling software COMSOL Multiphysics to realize the numerical simulation of coalbed methane, the influence on coalbed methane and water movement which caused by sensitive parameters has been analyzed, and history matching and forecasting the coalbed methane and water production.(3) In addition, with the Matlab GUI developed a software of coalbed methane reservoir simulation in Chinese that is "The numerical simulation of Low permeability coalbed methane software v1.0", achieving the numerical solution of this complex mathematical model. Using this software, make the numerical simulation of coalbed methane in Qinshui Basin and history matching, verifying the accuracy of software reliability, practicality and maneuverability.