低渗透气藏耦合流动模拟

COUPLED FLOW SIMULATION OF LOW PERMEABLE GAS RESERVOIRS

在低渗透气藏开采过程中,气体渗流受制于非达西效应和介质形变因素的影响,这影响不可忽视.然而,很少有文献来调查介质变形对低渗气藏气井产能的影响.文章建立了低渗气藏耦合流动数学模型,该模型考虑了非达西效应和介质变形因素的影响.数学模型采用有限差分隐式数值求解,对以前的一个气水两相数值模拟器源代码进行了修改,发展了一个简单的低渗气藏耦合流动数值模拟器.模拟计算分两个单元,即流体流动计算以及孔隙度、渗透率参数变化计算.算例分析结果表明:低渗气藏中孔隙度、渗透率参数变化降低气井产能的幅度比非达西流动影响大得多;不考虑耦合比考虑耦合计算的日产气量高出27%～39%.而在绝大多数气藏模拟计算中,都假定了孔隙度、渗透率参数保持常数,以致模拟计算结果比实际偏高.

During exploitation of low permeable gas reservoirs, gas percolation is influenced by the factors of non-Darcy flow effect and medium deformation, etc. However, the effect of medium deformation on the productivity of low permeable gas reservoirs is described in few literatures. The mathematical model of coupled flow for low permeable gas reservoirs is set up in the article. The model considers the influence of non-Darcy flow effect and medium deformation. The mathematical model is numerically solved by finite difference and implicit format treatment method. And the source code of a previous numerical simulator for gas/water bi-phase flow is modified. A simple numerical simulator of low permeable gas reservoirs is developed for coupled flow. The simulation calculation includes 2 steps: i.e. the calculation of fluid flowing and the calculation of variation of porosity and permeability. The case-analyzing results show the effect on the productivity of gas wells caused by the variation of porosity and permeability is much bigger than that by non-Darcy flow for low permeable gas reservoirs. The gas production calculated without considering the coupled flow is 27%-39% higher than that with considering the coupled flow. However, in most simulation calculations of gas reservoirs the porosity and permeability is assumed as a constant so that the result of simulation calculation is higher than the real situation.