页岩气藏运移机制及数值模拟

基于双重连续介质,采用尘气模型(DGM)建立基岩和裂缝运动方程,基岩中考虑气体在基岩孔隙中黏性流、Knudsen扩散、分子扩散以及气体在基岩孔隙表面的吸附解吸,吸附采用Langmuir等温吸附方程；裂缝中考虑黏性流、Knudesen扩散和分子扩散机制,在此基础上建立基岩-裂缝双重介质数值模型并采用有限元方法对模型进行求解.根据数值模拟结果对影响页岩气藏产能的因素进行分析.结果表明:页岩气产出气是游离气和吸附气解吸共同采出的结果,在给定的页岩气藏条件下,游离气影响更大,吸附对页岩气产能有较大影响,忽略吸附会导致预测产能偏低；Knudsen扩散(或Klinkenberg效应)对基岩视渗透率影响较大,越靠近生产井,Knudsen扩散和Klinkenberg效应的影响越大,基岩视渗透率随生产时间延长变大；裂缝渗透率越大,页岩气产量越大,基岩渗透率对页岩气产能影响不大.

Transport mechanisms and numerical simulation of shale gas reservoirs

Based on dual porosity continuum media, the kinematic equations in matrix and fracture were built by using dusty gas model (DGM). Viscous flow, Knudsen diffusion, free molecular diffusion and gas adsorption-desorption in pore surface were considered in matrix, the Langmuir isotherm adsorption equation was used in the dual porosity model. Viscous flow, Knudsen diffusion and free molecular diffusion were considered in fractures. Matrix-fracture dual porosity numerical model was established and calculated by finite element method. The influence factors of shale gas production were analyzed based on the numerical simulation results. The results show that the produced gas comes from both free gas and desorbed gas. The influence of free gas on shale gas production is greater than that of desorbed gas, but the adsorption should be considered in prediction of shale gas production because the predicted shale gas rate is low without considering adsorption. The Knudsen diffusion and Klinkenberg effect have great impact on matrix apparent permeability especially near the production wells, and the matrix apparent permeability increases with production time prolonging. The shale gas production increases with the fracture permeability increasing, and the matrix permeability has little influence on shale gas production.