页岩气藏加密井压裂时机优化——以四川盆地涪陵页岩气田X1井组为例

加密井的压裂时机直接影响着页岩气藏最终的开发效果。为了有效地指导页岩气藏加密井部署与压裂施工,基于离散裂缝网络模型、有限差分模型及有限元模型,提出了一套页岩气藏加密井压裂时机优化方法：根据页岩气田开发现状及井网加密需求,系统考虑储层非均质性和天然裂缝发育特征,建立渗流—地质力学耦合条件下四维地应力演化及复杂裂缝扩展的多物理场模型,进而模拟加密井水力裂缝扩展形态、加密井及井组开发效果,最终优选出加密井最佳的压裂时机。以四川盆地涪陵页岩气田X1井组为例,利用该优化方法研究了加密井压裂时机和施工参数对其复杂裂缝扩展形态、单井及井组产能的影响规律。结论认为：①该优化方法能够有效模拟老井生产过程中储层物性及力学状态变化,预测压后产量变化,优选加密井压裂参数及压裂时机;②当加密井射孔簇间距减小、每簇施工液量增大时,水力压裂改造体积、裂缝密度增大,压裂后产量提高,但射孔簇间距过小、每簇施工液量过大时,则有可能会导致分支裂缝串通和重叠,降低压裂液效率、影响压裂后产能;③压裂时机越晚,加密井井筒附近分支裂缝越密集,但改造体积越小、初期产量越低;④当目标井组生产36个月进行加密井压裂时,井组累计页岩气产量最高、开发效果最优。

Optimization of fracturing timing of infill wells in shale gas reservoirs: A case study on Well Group X1 of Fuling Shale Gas Field in the Sichuan Basin

Fracturing timing of infill wells directly influences the ultimate development effect of shale gas reservoirs. In order to provide effective guidance for the deployment and fracturing treatment of infill wells in shale gas reservoirs, this paper proposed a set of method for optimizing the fracturing timing of infill wells in shale gas reservoirs based on discrete fracture network (DFN), finite difference model (FDM) and finite element model (FEM). According to this method, a multi-physics field model of 4D geostress evolution and complex fracture propagation coupled flow and geomechanics is established based on the development status and well pattern infilling demand of the shale gas field, combined with reservoir heterogeneity and development characteristics of natural fractures. Then, the propagation morphology of hydraulic fractures in the infill well and the development effect of the infill well (group) are simulated. Finally, the optimal fracturing timing of infill wells is determined. By taking Well Group X1 of Fuling Shale Gas Field in the Sichuan Basin as an example, this optimization method was applied to study the effects of fracturing timing and treatment parameters of infill wells on the propagation morphology of complex fracture and the productivity of single well and well group. And the following conclusions were reached. First, this optimization method can effectively simulate the change of reservoir physical properties and geomechanical state during the production of parent wells, predict the production after fracturing and optimize fracturing parameters and timing of infill wells. Second, as the perforation cluster spacing of infill wells is decreased and the fracturing fluid volume of each cluster is increased, the stimulated volume of hydraulic fracturing and the fracture density are increased and the production rate after fracturing is improved. If the perforation cluster spacing of infill wells is too short and the fracturing fluid volume of each cluster is too large, however, the branch fractures may be connected and overlapped, which will decrease the efficiency of fracturing fluid and impact the productivity after fracturing. Third, the later the fracturing timing is, the denser the branch fractures near the wellbore of the infill well is, but the smaller the stimulated volume is and the lower the initial production rate is. Fourth, when infill well fracturing is performed after the target well group production for 36 months, its cumulative shale gas production is the highest and the development effect is the best.