Productivity And Optimum Technique Of Coal-bed Gas Multilateral Well

Coal-bed methane (CBM) is a new type of clean energy. Exploration and utilization of CBM can not only alleviate the shortage of conventional oil and gas, but also protect atmospheric environment. Multilateral well is an efficient technology which can increase the output of CBM. Numerical simulation can be used as a means of quantitive forecast and analysis, which can provide necessary theory basis and guidance scheme for development of CBM.Based on the literature research, the reservoir character, migration and production mechanisms of CBM are studied. On this basis, the mathematical model and numerical model of vertical well for CBM recovery is established and solved. The influencing factors of coal-bed gas production are analyzed.On this basis, the mathematical model and numerical model of multilateral well for CBM recovery is established. Such factors as sensitivity of porosity and permeability to pressure, accelerational and frictional pressure drops in well bore are considered in this model. Multiple cycle iterative solution method and preconditioned conjugate gradient method are adopted in numerical solution of this model.General features of multilateral well for CBM recovery are analyzed based on calculation. It is indicated that branches of multilateral well widely distributing in stratum make the stratum pressure drop down uniformly and quickly in controlled area, which facilitates the desorption and diffusion of coal-bed gas. It is the fundamental factor that multilateral well can increase the output of CBM. The effects of such stratum parameters as adsorption time, Langmuir constant and permeability on the coal-bed gas production of multilateral well are analyzed.Based on calculation, the principle of optimizing well configuration variables are obtained. The principle is that with branch length, separate angle and branch number increasing, prodution of multilateral well also increases, but the increase contribute to prodution decreasing. So we can get the best branch length, separate angle and branch number from the respective of economy. Besides that, in the case that other variables are the same, development effect of the branches with mosaic distribution is better than branches with symmetric distribution.