水平压裂缝导流作用下的油藏数值模拟方法

A METHOD OF NUMERICAL SIMULATION FOR RESERVOIRS WITH HORIZONTAL HYDRAULIC FRACTURES

埋深浅、油层破裂压力高或EOR过程中垂向地应力减小的油层水力压裂后容易形成水平裂缝,为此基于模拟垂直裂缝的嵌入裂缝模型,提出了一种能够高效处理水平裂缝的油藏数值模拟方法,准确模拟了水平裂缝对油层开采状况的影响。采用规则网格单独剖分油藏基质,根据水平裂缝与油藏网格的多边形相交面划分非规则裂缝网格,通过定义非相邻网格连接记录裂缝网格与基质网格、井之间的连接关系。基质与裂缝耦合的流体流动方程离散后,建立了带有加边七对角稀疏系数矩阵的三维油藏基质与裂缝系统数值模拟模型。应用该模型模拟了含有水平裂缝的一注一采低渗油藏,并与局部网格加密模型、多段井模型以及等效渗透率模型的模拟结果进行对比,该模型的模拟结果与局部网格加密模型比较接近。最后以大注采压差两注一采水驱开发的低渗油藏为例,研究了不同裂缝穿透比和无量纲导流能力对油井生产动态的影响。

It is possible to create horizontal fractures in the shallow reservoirs with high fractured pressure or vertical stress decreasing after EOR. So an efficient numerical simulation method for reservoirs with horizontal hydraulic fractures was brought forward to simulate accurately the effect of horizontal fractures on development of reservoirs based on the embedded fracture model for simulating vertical fractures. Reservoir matrixes were divided by regular grids individually,and irregular fractures grids were divided based on the polygonal intersections between horizontal fractures and matrixes,and then the contact relations of fractures' grids and matrixes' grids and wells were recorded by nonneighboring grids connections. Multiphase flow equations coupled reservoir matrixes and fractures were dispersed,and the numerical simulation model of 3D reservoir matrix and fracture system with seven- diagonal sparse coefficient matrix was constructed. The model was applied to simulate low-permeability reservoir with horizontal fractures developed by one injection well and one production well,and the simulation results were compared with local grid refinement model,multi-segment well model and permeability equivalent model,and it's closer to the local grid refinement model. Finally,taking the case of low- permeability reservoir developed by two injection wells and one production well under high injection- production pressure difference as example,the influence of different fracture length / well space ratios and dimensionless flow conductivities on the production dynamic was studied.