页岩气多尺度渗流数值模拟技术——以昭通国家级页岩气示范区为例

A numerical simulation technology for the multi-scale flow of shale gas and its application in Zhaotong National Shale Gas Demonstration Area

页岩气藏的渗流机理复杂,沿用传统的油藏数值模拟器表现出了不适应性。为了实现对页岩气藏的有效模拟,引入等效数学模型——气体状态方程、渗透率模型及气体吸附模型,并且建立嵌入式离散裂缝网格剖分方法,进而开发出流固耦合模型;在此基础上,基于昭通国家级页岩气示范区2口水平井的Petrel地质建模成果,利用所建立的流固耦合模型进行压裂后气井的生产历史拟合和预测,进而开展了参数敏感性分析。研究结果表明:(1)流固耦合模型可以考虑孔隙压实和裂缝变形的影响,功能扩展后的数值模拟器可以更准确地模拟致密介质中的页岩气渗流特征;(2)嵌入式离散裂缝网格剖分方法能够有效提高建模效率和数值模拟计算速度,支撑了页岩气井生产数据的高效模拟;(3)随着基质渗透率、裂缝渗透率、裂缝长度逐渐增大,页岩气井累计产气量逐渐升高,但增幅略有变小;(4)随着应力敏感系数的逐渐增大,单井累计产气量逐渐降低,但降幅逐渐变小。结论认为,该数值模拟技术可以应用于页岩气井的生产动态分析,可以为同类气藏的开发提供借鉴。

The flow mechanisms in shale gas reservoirs are complicated,so the traditional numerical reservoir simulator is not applicable to them.In order to effectively simulate shale gas reservoirs,this paper introduced the equivalent mathematical models(namely gas state equation,permeability model and gas adsorption model),established the embedded discrete fracture meshing method and then developed the fluid-solid coupling model.On this basis,production history fitting and prediction of gas well after the fracturing was carried out by using this newly developed fluid-solid coupling model,based on the Petrel geological modeling achievements of two horizontal wells in Zhaotong National Shale Gas Demonstration Area.Moreover,sensitivity analysis was performed on parameters.And the following research results were obtained.First,the fluid-solid coupling model can take into consideration the influence of pore compaction and fracture deformation and the numerical simulator with extended functions can simulate the flow of shale gas in tight medium more accurately.Second,the embedded discrete fracture meshing method can effectively increase the modeling efficiency and the computation speed of numerical simulation and support the efficient simulation of the production data of shale gas wells.Third,as matrix permeability,fracture permeability and fracture length increase gradually,the cumulative gas production of shale gas well increases gradually,but the increase amplitude gets smaller slightly.Fourth,with the gradual increase of the stress sensitivity factor,single-well cumulative gas production decreases gradually,but the decrease amplitude gets smaller gradually.In conclusion,this numerical simulation technology can be used to analyze the production performance of shale gas wells and provide the reference for the development of similar gas reservoirs.