煤层气藏数值模拟垂向网格优化

Vertical grid optimization of numerical simulation of coalbed methane reservoir

数值模拟是研究煤层气藏工程的一种常规方法,建立模型时人们常忽略垂向网格精细程度对模拟的影响,无法准确反映出垂向上流体流动规律、气水分异现象以及压降漏斗展布等,对模拟结果有很大影响。为了研究垂向网格划分精度对煤层气藏数值模拟过程的影响,采用不同模拟器对垂向网格的精细程度进行模拟计算,运用渗透率等效方法、局部网格加密方法和模拟器自带压裂方法模拟煤层压裂缝,总共模拟了3种方法 15套方案。结果表明,垂向网格划分精度对煤层气生产影响较大,当网格步长达到1.5m时计算结果较为精确,可以满足模拟需求。网格数量及网格步长的合理划分,能够更好地呈现煤层中气水分异现象,有助于分析气水流动状态,便于历史拟合和产量预测。

Numerical simulation is a common method for the research of coalbed methane(CBM)reservoir engineering.However,the effect of the vertical grid size for the simulation results are often ignored when modeling.So,the behavior of fluid-flow in vertical grids,the gravitational differentiation of gas and water,and the pressure drop funnel are not accurately reflected,which have great influence on the simulation results.In order to study the influence of vertical grid division on numerical simulation of CBM production process,different simulators are used to simulate different longitudinal grid sizes.Permeability equivalent method,local grid refinement(LGR)method and new fracturing method in simulator are used to simulate fracturing.15 schemes of 3 methods were simulated.The results show that the vertical grid division has great influence on the production,when the grid size is 1.5 m,the calculation results are more accurate,which can satisfy the simulation demand.The reasonable division of vertical grid can better show the phenomenon of gas and moisture difference in layers,and help to analyze the flow state of liquids,at the same time,is in favor of history matching and production prediction.