基于有限元方法的深层页岩气水运动规律分析

针对深层页岩气高温高压条件下等温吸附曲线出现先增高后降低的现象，修正了Langmuir吸附模型，建立了考虑超临界吸附和非线性流动机理的深层页岩气压裂水平井气水两相流动数学模型，并基于有限元方法对模型进行求解，利用该数学模型对比分析了基质渗透率、改造区面积和主裂缝渗透率等因素对气水运动规律的影响。研究结果表明:改造区面积并不是越大越好，当改造区面积增大到一定程度时再继续增大改造区面积对提高产量效果不明显；开采过程中，主裂缝内流体会先流入井筒，之后改造区流体流入主裂缝，最后再由基质内流体对改造区进行补充，因此前期主要受主裂缝渗透率影响，后期主要受基质渗透率影响。研究结果对于深层页岩气田开发具有一定的指导意义。

Investigation of gas-water flow in deep shale gas reservoirs based on the finite element method

Considering the first rising and then falling of the isotherm at high temperature and high pressure for deep shale gas reservoirs, the Langmuir isotherm was modified, and the mathematic model incorporating supercritical adsorption and nonlinear flow was developed for gas-water two-phase flow of fractured horizontal wells in deep shale gas reservoirs. Moreover, the developed model was solved in a finite element approach and then used to investigate the effects of the matrix permeability, the reconstruction zone area and main fracture permeability on the flow of gas and water. The research showed that a larger the reconstruction zone area is not always preferred—further expansion of the reconstruction zone area beyond a threshold brings about no considerable gain in production. Moreover, it is indicated that during the production, the fluids inside the main fracture first flow into the well, then the fluids in the reconstruction zone flow into the main fracture, and finally the matrix fluids recharge the reconstruction zone. Therefore, early production is mostly affected by the main fracture permeability, and late production is dominated by matrix permeability. The findings of this research provide guidance for the recovery of deep shale gas.