致密油体积压裂缝网形成及多重介质流固全耦合流动模拟

Stimulated reservoir volume (SRV) fracturing has become the most efficient technology in tight reservoir formation treatment. In order to enhance well production as much as possible, it is necessary to create complex fracture networks by connecting hydraulic fractures with natural fractures away from well bore, and then increase contact area with formations and reservoir stimulated volume. Currently, the theoretical system of multiphysics coupling flow simulation for multi-porosity medium flow simulation has not been proposed based on the propagation and characterization of the complex fracture network induced by SRV fracturing. In terms of the features of the development of natural fractures in tight oil reservoirs, the interference of multi fractures during hydraulic fracturing and the existence of stress sensitivity in the process of exploitation, in this project, the rock mechanics, percolation theory and numerical simulation are used to do some relevant studies. Firstly, the modified displacement discontinuity method are applied to model and simulate fracture network propagation, and also characterize the structure of multi-porosity medium induced by complex facture network. And on this basis, to reveal the unsteady pressure and productivity features of SRV-fractured wells in tight oil reservoir, a mathematic unsteady well flow model is established in consideration of the flowing characteristics of multi-porosity medium. Finally, considering the mutual interaction between flow field and stress field for multiple mediums, the fluid-solid fully coupling mathematical models for two-phase flow are developed. Moreover, stimulation mechanisms are studied based on the coupling flow simulation model. We eventually develop an efficient fracture network propagation and flow simulation theory of SRV-fractured wells in tight oil reservoirs, which could provides certain theoretical and technical guidance for the optimization design of horizontal wells with SRV fracturing and the effective development of tight oil reservoirs.

体积压裂技术作为致密油增产改造的有效途径，是通过形成天然裂缝与人工裂缝相互交错的三维多重介质裂缝网络、增加储层改造体积以达到增产目的。目前，基于致密油体积压裂缝网扩展及表征的多重介质多场耦合流动理论体系尚未建立。本课题针对致密油储层发育天然裂缝、压裂存在多裂缝干扰、开发存在应力敏感等特征，依据岩石力学、渗流力学及数值模拟等理论开展相关研究。首先，利用改进的位移不连续法建立致密油体积压裂缝网扩展理论模型，模拟裂缝网络的形成过程，并进行复杂缝网多重孔隙介质结构表征；在此基础上，建立多重孔隙介质系统不稳定渗流数学模型，分析致密油体积压裂井不稳定渗流规律及产能特征；最后，考虑应力场与多重介质渗流的相互影响，建立两相流固全耦合数值模拟模型，探索不同开发方式增产机理。最终形成一套致密油体积压裂缝网扩展和多重介质两相流固全耦合流动模拟的系统理论方法，为致密油体积压裂优化设计及有效开发提供一定的理论指导。

体积压裂技术作为致密油增产改造的有效途径，是通过形成天然裂缝与人工裂缝相互交错的三维多重介质裂缝网络、增加储层改造体积以达到增产目的。目前，基于致密油体积压裂缝网扩展及表征的多重介质多场耦合流动理论体系尚未建立。本课题针对致密油储层发育天然裂缝、压裂存在多裂缝干扰、开发存在应力敏感等特征，依据岩石力学、渗流力学及数值模拟等理论开展相关研究。首先，利用改进的位移不连续法，建立了致密储层体积压裂裂缝扩展及结构表征一体化综合模型，模拟了复杂裂缝网络的形成过程，揭示了致密储层体积压裂裂缝扩展的规律及力学机理，并应用于鄂尔多斯盆地致密油矿场压裂优化设计，从方法与理论上合理解释并支撑了“每百米压一段”的矿场经验；在此基础上，考虑具有基质-天然裂缝双重孔隙和基于离散裂缝模型的缝网改造系统的流动特征，建立了致密油体积压裂多重孔隙介质单相不稳定渗流数学模型，并利用有限元方法对模型进行了数值求解，分析了两种典型试井模型理论曲线在各渗流阶段的流动形态特征，从定性和定量角度揭示了致密油多重孔隙介质多尺度流动规律；最后，在分析多重介质流固耦合作用机制及数学表征的基础上，建立并求解了致密油体积压裂水平井应力场与两相渗流场的流固全耦合数学模型，探索了鄂尔多斯盆地致密油开发的有效增产方式，认为在致密油开发过程中，对于未受效的水平井老井而言，越早进行蓄能补压措施，越有利于采出更多的原油。最终形成了一套致密油体积压裂缝网扩展及多重介质流固全耦合流动模拟的系统理论方法，相关研究方法及成果可为致密油体积压裂优化设计及进一步提高采收率提供一定的理论指导。