压裂页岩气藏多尺度耦合流动数值模拟研究  

NUMERICAL SIMULATION OF MULTI-SCALE COUPLED FLOW IN AFTERFRACTURING SHALE GAS RESERVOIRS

作　　者：夏阳[1,2] 邓英豪 韦世明 金衍 Xia Yang;Deng Yinghao;Wei Shiming;Jin Yan(State Key Laboratory of Petroleum Resources and Prospecting,Beijing 102249,China;College of Petroleum Engineering,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]油气资源与探测国家重点实验室,北京102249 [2]中国石油大学(北京)石油工程学院,北京102249

出　　处：《力学学报》2023年第3期616-629,共14页Chinese Journal of Theoretical and Applied Mechanics

基　　金：国家自然科学基金企业创新发展联合项目(U19B6003-05)。

摘　　要：在碳达峰的国策背景之下,页岩气成为传统能源向绿色清洁低碳能源转型的重要过渡和能源支点.压后页岩气藏流体流动力学成为高效开发页岩气的关键力学问题.文章将小尺度低导流天然裂缝等效升级为连续介质,建立有机质-无机质-天然裂缝三重连续介质模型,同时对大尺度高导流裂缝采用离散裂缝模型刻画,嵌入天然裂缝连续介质中,构建多重连续/离散裂缝模型.综合考虑吸附气的非平衡非线性解吸附和表面扩散,自由气的黏性流和克努森扩散,给出页岩气在多尺度复杂介质中的非线性耦合流动数学模型.提出多尺度扩展有限单元法对离散裂缝进行显式求解,创新性构建三类加强形函数捕捉离散裂缝的局部流场特征,解决了压后页岩海量裂缝及多尺度流动通道的流动模拟难题.文章提出的模型和方法既能准确刻画高导流裂缝对渗流的影响,又克服了海量多尺度离散裂缝导致计算量增大的问题.通过算例展示了压后页岩各连续介质的压力衰减规律,发现裂缝中自由气、有机质中自由气、无机质中吸附气依次滞后的压力(浓度)扩散现象,重点分析了吸附气表面扩散系数、自由气克努森扩散系数、天然裂缝连续介质渗透率和吸附气解吸附速率对页岩气产量的影响.文章重点解决压后页岩多尺度流动通道的表征和复杂耦合流动机理的建模,并开发了高效的数值模拟算法,对于压后页岩的产能评价具有一定的意义.Under the national policy background of peak carbon dioxide emissions,shale gas becomes an important transition and energy fulcrum for the transition from traditional energy to green,clean and low-carbon energy.And the fluid flow mechanism of shale gas reservoirs after fracturing becomes a key mechanical problem for the efficient development of shale.In this paper,the small-scale low-conductivity natural fractures are equivalently upgraded to a continuous medium,and a triple organic-inorganic-natural fracture continuous medium model is established.The discrete fracture model is used to portray the large-scale high-conductivity fractures,which are embedded into the natural fracture continuous medium,and a multiple continuous/discrete fracture model(MC/DFM)is constructed.The non-equilibrium nonlinear desorption and surface diffusion of adsorbed gas,viscous flow,and Knudsen diffusion of free gas are integrated to give a nonlinear coupled flow mathematical model of shale gas in the multi-scale complex medium.The multi-scale extended finite element method(MXFEM)is proposed to solve the discrete fractures explicitly,and three types of enrichment functions are innovatively constructed to capture the local flow field characteristics of the discrete fractures,which solves the flow simulation problems of the massive fractures and multi-scale flow channels in the afterfracturing shale.The model and method proposed in this paper can not only accurately characterize the effect of high conductivity fractures on gas flow,but also overcome the problem of the dramatic increase in computational amount due to massive multi-scale discrete fractures.The pressure decay law of each continuous medium is demonstrated by a calculation example,and the pressure/concentration diffusion phenomena of free gas in fracture,free gas in organic medium,and adsorbed gas in the inorganic medium are found to lag in sequence.The analysis focuses on the effects of adsorbed gas surface diffusion coefficient,free gas Knudsen diffusion coefficient,natural

关 键 词：多尺度 多重连续介质 离散裂缝模型 页岩气流动 数值模拟 

分 类 号：TE371[石油与天然气工程—油气田开发工程]