页岩气藏的双重介质-离散裂缝模型

考虑页岩气藏开发中渗流的多尺度效应，提出了一个基于裂缝-孔隙双重介质的离散裂缝模型．在该模型中，基质、天然裂缝和人工压裂裂缝采用各自控制方程独立计算，不同介质之间通过流量交换相互关联．为分析模型可靠性，分别和基于渗透率粗化及压裂裂缝导流能力无穷大的模型对比．数值算例显示，伴随着网格细分，该模型与精确渗透率粗化模型具有相同计算精度，两者收敛速度均较快，但该模型易推广到多相流动问题，而等压模型对产量将有所高估．研究了地质参数和工艺参数对气井产量的影响规律．计算结果表明天然裂缝渗透率及基质孔隙扩散系数对产气速率有着重要影响，产气速率伴随着人工压裂裂缝导流能力、长度以及数目的增加而增加，但是增加幅度会逐步趋缓．

A Discrete Fracture-Dual Porosity Coupling Model for Shale Gas Reservoirs

Considering the multi-scale effects of the seepage flow in the shale gas reservoir, a specific discrete-fracture model based upon the fracture-matrix dual-porosity was proposed. In this model, matrix, natural fracture networks and artificial fractures were simulated from their own control equations, coupling each other with exchange flows. For analyzing the reliability, this model was compared with two typical dual-porosity models, which are independently based upon the permeability upscaling and infinite diverting capacity in artificial fractures. Numerical examples show that the proposed model and the dual porosity model with accurate upscaling permeability both have the same accuracy with good convergence. And moreover, the proposed model can be easily extended to the simulations for the multiphase flows, while the constant-pressure model overestimates the production rate. The effects of the geological parameters and the process parameters upon the gas well production were also investigated. It is shown that the natural fracture permeability and diffusion coefficient of matrix have significant influence on gas production rate. With the increasing of diverting capacity, the length and the number of artificial fractures, gas production rate is also on the increase. Nevertheless, the rate of increase slows down gradually.