考虑渗透率变化的煤层气储层数值模拟及参数敏感性研究

Research on Coalbed Methane Numerical Simulation Considering Permeability Changes and Parameter Sensitivity Analysis

煤层气开采过程中储层渗透率的变化对产气量影响较大,通过引入S&D渗透率变化模型,建立了考虑渗透率变化的煤储层三维气水两相渗流数学模型,完成模型检验后应用所编制软件研究了煤储层参数、吸附参数及渗透率模型特征参数对开发效果的影响。结果表明,煤层气产量随着初始含气量、煤层有效厚度、裂缝渗透率和Langmuir压力的增大而增大,随储层原始压力、裂缝孔隙度和Langmuir体积的增大而减小,而解吸时间对产气量影响不大;裂缝渗透率随着杨氏模量和基质收缩/膨胀系数的增大而增大,随泊松比和裂缝压缩系数的增大而减小。引入S&D模型后计算的累积产气量要比常规模型低1.3%,因此不可忽视煤层气产出过程中渗透率的变化。

The fracture permeability will change during coalbed methane production.In this paper,with the introduction of SD permeability model,the mathematical model for three dimensional gas-water two phase flow considering permeability changes is established.Then tentative analysis of coal reservoir parameters,adsorption parameters and characteristic parameters of SD model is carried out with relative software after the model is verified.It turns out that the gas production will grow along with the increase of initial gas content,seam thickness,fracture permeability and Langmuir pressure,and will reduce along with the increase of initial pressure,fracture porosity and Langmuir volume,while having not got much to do with the desorption time.In addition,the fracture permeability will grow along with the increase of Young＇s modulus and matrix shrinkage/swelling coefficients,and will decrease along with the grow of Poisson ratio and cleat volume compressibility.In this paper,the cumulative gas production calculated with the model considering permeability change is less than the traditional results by 1.3%,therefore permeability change cannot be ignored during CBM production.