多井干扰下页岩储层应力场动态演化机理

The engineering problems of severe interwell interference and fast decreasing rate of single-well production become more and more serious after the shale reservoirs are developed by large-scale fractured wells. Thus, infill-wells are the future necessaries for stable shale-gas production in the later development period. The key question for improving the stimulation efficiency of infill-wells is reasonably designing the fracturing treatment in the multi-well interference induced stress field, and the question should be essentially solved by understanding the dynamic evolution mechanism of induced stress changes so that the relationship among the direction of fracture propagation, the direction of principal-stress and the direction of flux can be clarified. Aiming at the engineering difficulties in terms of low stimulation efficiency of infill-wells, this project focuses on well interference characteristics in the case of complex geological and multi-field coupling conditions. The multi-scale deformation mechanics of flow paths in shale will be studied to construct the multi-scale and multi-flow-regime gas/solid coupling model. The numerical simulation method for stress and pressure fields in 3D complex fracture networks with well and fracture interferences will be proposed to reveal the dynamic evolution mechanism of induced stress changes and figure out the fracture network structure with optimal productivity in the induced stress field, and finally provide theoretical foundation for developing geo-engineering integrated fracturing design method for infill-wells in shale reservoirs.

页岩储层经过大规模井网开发后，井间干扰严重，单井产量递减快，加密建井开发成为我国页岩气田后期稳产保供的必然选择，如何在多井干扰诱导应力场中进行加密井压裂设计是提高加密井压裂改造效率的核心问题，本质上需要解决多井干扰下页岩储层应力场动态演化机理，明确加密井裂缝优势发展方向与诱导应力场主方向、渗流主方向相关关系。针对页岩储层加密井开发压裂改造缝网效率差的难题，聚焦复杂地质与多场耦合下井间干扰特征，深入分析页岩储层多尺度流动通道变形力学机理，建立页岩多尺度多流态气固耦合力学模型，提出三维储层井间干扰、缝间干扰下应力场、渗流场数值模拟方法，揭示多井干扰下应力场动态演化机理，明确诱导应力场中气体最优产出条件下加密井压裂缝网结构，为研发页岩储层加密井地质-工程一体化压裂设计方法提供理论支撑。

页岩储层经过大规模井网开发后，井间干扰严重，单井产量递减快，需要重点研究多井干扰下页岩储层应力场动态演化机理。本项目针对页岩储层多尺度流动通道建立了有机质-无机质-天然裂缝三重连续介质模型，并将大尺度裂缝嵌入天然裂缝连续介质，构建了多重连续/离散裂缝模型(MC/DFM)。基于弹性多孔介质力学，建立了自由气渗流、吸附气表面扩散、吸附气非平衡解吸附、岩石变形的全耦合页岩气渗流数学模型，推导了纯孔院介质与包含裂原介质的主要物性参数的应力敏感模型，形成了一套描述页岩气在线弹性微纳多孔介质中流动的力学模型。基于流体压力/浓度场特征分析和浙进解析解构建了三类加强形函数捕捉离散裂缝的局部流场特征，解决了压后页岩海量裂缝及多尺度流动通道的流动模拟难题，形成了适用于页岩气渗流问题的高效值模拟技术，实现了致密油气藏多尺度裂缝的流动模拟，自主开发了基于扩展有限元的流固耦合数值求解器。本项目的研究成果对认识页岩气储层流动规律，并在此基础上制定气藏开发方案提供了理论基础。