致密油气藏体积酸压复杂缝网扩展延伸仿真模型研究

In acid fracturing simulated reservoir volume (SRV), the dynamic propagation behavior of fracture network is affected by horizontal stress difference, approaching angle, natural fracture properties and acid-rock reaction. Currently, both propagation experiments and theoretical studies conducted are lack of integrated consideration of the influence posed by acid rock reaction and natural fracture properties, thus there is great blindness in the design of acid fracturing due to the blurred cognition of the essence and mechanisms in fracture network propagation and extension. In this project, tri-axial rock mechanics and large-scale true physical model tri-axial test systems will be applied to carry out multi-axis mechanical tests on rock samples with different dimension, the rock samples used contains fractures. Advanced test measurements such as acoustic emission detector, tracer agent and CT scan will be utilized to investigate the evolution characteristics of rock failure under the action of acid-stress and its influence factors, revealing the regularity and mechanisms of fracture dynamic propagation under acid damage. Based on the theories of fluid-solid coupling, damage mechanics, acid-rock reaction and random modeling, numerical propagation models of complex fracture network with a full coupling of fissured porous media rock deformation- multiphase seepage- water pressure-acid rock reaction will be established within the framework of extended finite element, to simulate the whole physical chemistry process of fracture network propagation and extension and to reveal the extended mode and essence of acid etching fractures, and thereby, to optimize the scheme of acid fracturing SRV. The research findings will promote the fundamental theory development of acid fracturing SRV for tight reservoirs, facilitate the R&D of relevant technologies and materials and enhance the design of acid fracturing SRV.

体积酸压过程中水平应力差、逼近角、天然裂缝性质和酸损伤都会影响到缝网动态扩展延伸行为。而目前开展的裂缝延伸实验及理论研究均未综合考虑酸损伤与天然裂缝性质的影响，造成缝网扩展延伸本质和机理认识不清，酸压设计存在极大的盲目性。本项目拟采用三轴岩石力学仪及大型物模真三轴测试系统开展含裂缝不同尺度岩样多轴力学试验，结合声发射仪、示踪剂和CT扫描仪等先进测试技术研究酸液-应力作用下岩石破裂演化特征及影响因素，揭示酸损伤作用下裂缝动态扩展延伸规律和机理。基于流固耦合，损伤力学、酸岩反应和随机建模等理论，构建扩展有限元框架下(XFEM)的裂缝性多孔介质岩石变形-多相流体渗流-水压力-酸损伤全耦合缝网扩展延伸数值模型，仿真模拟缝网扩展延伸物理化学全过程，揭示酸蚀缝网扩展延伸模式和本质，从而优化体积酸压方案。成果将推动致密油气藏体积酸压基础理论发展，加快体积酸压工艺和材料研发速度，提升体积酸压设计优化水平。

体积酸压过程中水平应力差、逼近角、天然裂缝性质和酸损伤都会影响到缝网动态扩展延伸行为。而目前开展的裂缝延伸实验及理论研究均未综合考虑酸损伤与天然裂缝性质的影响，造成缝网扩展延伸本质和机理认识不清，酸压设计存在极大的盲目性。因此，本项目基于流固耦合、损伤力学、酸岩反应和随机建模等理论，结合物理实验，开展了酸损伤作用下裂缝动态扩展延伸规律和机理研究。.完成的主要研究内容有：采用三轴岩石力学仪及大型物模真三轴测试系统开展含裂缝不同尺度岩样多轴力学试验，研究酸液-应力作用下岩石破裂演化特征及影响因素，揭示酸损伤作用下裂缝动态扩展延伸规律和机理；构建裂缝性多孔介质岩石变形-多相流体渗流-水压力-酸损伤全耦合缝网扩展延伸数值模型。.取得的主要研究进展有：建立了一套裂缝性多孔介质单相和多相流体渗流弱不连续问题的XFEM模型，以及岩石变形与多相流体渗流耦合的XFEM模型；构建复杂网络裂缝内酸液流动反应数学模型，形成了一套体积改造过程中复杂水力裂缝网络扩展延伸的系统理论和方法；开展了化学溶液(压裂液、酸液)作用下三轴压缩力学实验，揭示了酸损伤对岩石强度、变形参数和破坏模式影响；进行化学溶液(压裂液、酸液)-水压力作用下含裂缝大岩样多轴应力实验，对比分析不同条件下水力裂缝与天然裂缝相互作用及复杂缝网扩展延伸情况，探索裂缝相交作用模式及主要影响机制，揭示破坏全过程水力裂缝动态扩展延伸规律及机理。.项目研究成果揭示了水力裂缝与预制或随机天然裂缝相交作用延伸机理以及酸损伤情况下缝网延伸机理，实现对复杂网络裂缝动态延伸行为仿真模拟，深入讨论不同地质、工艺条件对裂缝延伸规律影响，优化体积酸压方案，揭示酸蚀缝网扩展延伸模式和本质，促进致密油气藏体积酸压基础理论发展，在一定程度上提升体积酸压设计优化水平，无疑具有重大的科学意义和价值。