页岩气离散裂缝网络模型数值模拟方法研究

页岩气开发已经成为当今世界各国的焦点，然而关于页岩气的理论研究还处于起步阶段。目前关于页岩气数值模拟方法的应用大多局限于常规油气藏数值模拟所采用的连续介质模型，但页岩气藏天然裂缝发育，非均质性强，连续介质模型不能准确表征页岩气特有的渗流特征。基于离散裂缝网络模型(DFN)，从渗流理论出发，建立页岩气离散裂缝网络渗流数学模型，表征页岩气在干酪根中的扩散效应，孔壁的吸附—解吸附效应，纳米孔隙中的滑脱效应、Knudsen扩散效应以及裂缝内的非达西渗流规律。利用有限差分法求解渗流方程并进行敏感性分析。最终得出：①页岩气不同生产阶段，产气机理不同|②滑脱效应和Knudsen扩散效应对页岩气产能影响较大，而吸附—解吸附效应和干酪根中的扩散效应对延长页岩气稳产期起到关键作用。通过和现有页岩气数值模拟软件CMG(2012版)计算结果对比，该模型在模拟裂缝性页岩气藏时更符合实际情况，为页岩气数值模拟的研究奠定了基础。

Investigation of Shale Gas Numerical Simulation Method Based on Discrete Fracture Network Model

The theoretical study about the shale gas development is still in infancy although it has become a focus of the world today.Most shale gas numerical simulation methods based on the continuous medium model,which is used for conventional oil and gas reservoir,cannot accurately characterize the shale gas special percolation features.This article introduced a shale gas seepage flow model which is established based on the Discrete Fracture Network (DFN) and the flow mechanisms,which accurately characterizes the diffusion in kerogen,adsorption-desorption on pore wall,gas slippage and Knudsen diffusion in nonporous,and also the non-Darcy flow in fractures.Finite difference method is employed for numerical solution of nonlinear partial differential equations and the preliminary simulation results show that: the slippage and Knudsen diffusion have a great effect on the shale gas production,especially the diffusion in kerogen and adsorption play key roles in extending stable production time in shale gas reservoir|The comparison with the results of CMG (2012 Edition) shows that the DFN model is more consistent with the actual situation in the simulation of fractured shale gas reservoir.