| In this thesis, theory of fluid-solid coupling of coalbed methane development and enhanced recovery coalbed methane by CO2 injection in low permeability coal seam reservoir and its application are studied. The major study work of this thesis include:1. Coalbed is modeled as dual porosity-single permeability model base on reservoir itself properties and properties of fluid flow through them. In addition, mechanisms of the storage, transport and production for coalbed methane are researched.2. A low permeability, dual-porous medium, gas-water two phase flow, fluid-solid coupling mathematical model and multispecies, fluid-solid coupling mathematical model for enhanced coalbed methane recovery by CO2 injection are established, and these model include coalbed methane desorption, diffusion and seepage process.3. Numerical solution method of dual-porous medium, gas-water two phase flow, fluid-solid coupling mathematical model and diffusion resource term in matrix system and method of dealing with dual-porosity grid system are given in detail.4. A three-dimension, dual-porous medium, gas-water two phase flow, fluid-solid coupling software that can adapt to low permeability coalbed reservoir characteristics are developed.5. By comparison coal seam gas prediction production with trial well production in Xin Ji Coal Mine, Anhui province, the correction, reliability, and practicability of the software are verified. Then the software are applied to simulation for coalbed methane development and enhanced recovery coalbed methane by CO2 injection. The main works of simulation in the following sections :(1) Single well scheme, comparison of coupling and noncoupling condition, in the equal exploiting time, the former reservoir pressure drop smaller than the latter's reservoir pressure drop. The former gas-water production are smaller than the fetter's gas-water production. The former scope of drop funnel, water saturation and coalbed methane concentration are smaller than the latter's scope of drop funnel, water saturation and coalbed methane concentration. The former water saturation, coalbed methane concentration drop slower than the latter's water saturation, coalbed methane concentration.(2) Two wells scheme, comparison of coupling and noncoupling condition, the changing laws of reservoir pressure, water saturation and coalbed methane concentration consistent with single well scheme condition, but after extracting aperiod of time, reservoir pressure drop faster than single well scheme. Reservoir pressure and coalbed methane storage drop faster around Two wells, because of wells interference. At the same time, single well production are improved greatly.(3) The bigger fluid pressure gradient of well bottom neighborhood is formed Because the reservoir is depleted. The pressure gradient gradually developing from wells to reservoir boundary. Base on effective stress principle, stress and strain of porous medium are changed because of changing of fluid pressure gradient, and result in changing porous medium structure changing, an the same time, effective permeability and porosity become lower. And production are decreased because of coulping action. Therefore in the cause of coalbed gas exploiting, the disadvantageous influence on production must be overcame, and the reasonable production system, are established to guaranteeing to minimum damage to the reservoir permeability.(4) It is important to choice well spacing, when multiple wells scheme are arranged, well spacing affect the economic efficiency and recovery rate of coalbed gas resources. The size of well spacing is decided reservoir characteristic and economic gas production. Shows as the results of simulation, well spacing influence on production and reservoir pressure and also relevant to reservoir permeability. Higher permeability reservoir , at the beginning of exploiting time, appearing wells interference, and increasing influence scope of pressure drop funnel. If the methane quality of coalbed...
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