基于改进三线性流模型的多级压裂页岩气井产能影响因素分析

Analysis of sensitive factors about multistage fractured well productivity in shale gas reservoirs based on modified trilinear flow model

页岩气多级压裂形成的复杂裂缝网络会改变其原有的气体渗流模式,形成多个独有的流动阶段。因此,常规的产能模型不能有效模拟其压力、流量变化规律。为了增加页岩气产能模拟精度和对压裂施工优化做出指导,在耦合三线性渗流和球形双重介质渗流模型的基础上,考虑解吸和滑脱等机理,建立了改进的三线性流产能预测模型,并进行了解析求解和数值反演。计算结果表明,页岩气的解吸对提高单井产能,延长稳产期具有重要意义;储层中的微裂缝能够通过控制气体在基质与人工裂缝之间的窜流最终影响页岩气井产能;人工裂缝导流能力对页岩气井产能的影响覆盖了整个生产周期的中前段,然而随着人工裂缝导流能力的增加,产能的增长幅度变缓,证明了页岩气藏不需追求高导流能力裂缝的理论,缝间距主要影响线性流时间的长短;汇聚效应在投产初期对产能具有不可忽视的影响。研究结果对于深化页岩气井生产动态认识和提高页岩气藏开发效率具有重要意义。

The complex fracture networks of multistage fractured shale gas reservoir would change the original gas flow regime,leading to some unique mobile phases.Therefore,the conventional flow models cannot effectively simulate the pressure and flux discipline.In order to improve the accuracy of production simulation and make guidance for the fracturing treatment,coupling the trilinear flow model and spherical dualmedium seepage model,the modified trilinear flow model considering the mechanism of desorption and slippage has been developed.According to the analytical solutions and numerical inversion of the model,the shale gas desorption could enhance the gas production and extend the production plateau.The microfracture in the reservoir could make great impact on the gas production by controlling the crossflow between hydraulic fractures and matrix.The hydraulic fracture conductivity could influence the productivity in the whole front-end production cycle.However,the production growth becomes slower with the increase of fracture conductivity.That is to say,the theory that to acquire high conductivity fractures in shale gas reservoirs is unessential.Furthermore,fracture spacing has great impact on increasing the length of time in linear flow regime.Convergence effect has a considerable impact at the beginning of the production cycle.The results in this paper could have further influence on the production performance and improve the efficiency in shale gas exploitation.