裂缝型碳酸盐岩温度-裂缝渗流-酸岩反应-应力损伤耦合酸化机理研究

Gelled acidizing has been well recognized as a safe, high-efficient, and economical stimulation technique for deep naturally fractured carbonate reservoir development. The major challenge of this technology is whether the hydrocarbon flow channel, namely, the acid induced wormholes, can be successfully created. Theoretically, the formulation of wormhole is a coupled multi-process which involves temperature influence, fracture flow effects, acid-rock reaction, and stress damage. Current published acidizing methods seldom include the fully coupled process of the four mechanisms, showing obvious inability in simulating advanced acidizing treatment in these formations. This project will comprehensively apply multi-disciplinary theories involving petroleum engineering, fluids flow in porous media, heat transfer, reaction dynamic and rock mechanics to develop acidizing model coupling with multi-fields in fractured carbonate reservoir. Firstly, we digitally characterize surface morphology of natural fracture and develop a surface deformation model to obtain the initial natural-fracture width distribution under confining stress before acidizing. Based on this work, a reaction-heat-variation induced temperature field prediction model will be built as a function of time. The coupling of temperature-field prediction model and natural fracture acid-rock mass transport model is coupled through the influence of temperature change on acid-rock reaction rate. According to acid concentration distribution, fracture width evolution model will be established, and hence, post-acidizing natural-fracture width will be obtained. Finally, by coupling constitutive equation for acid damage with fracture deformation model and considering post-acidizing mechanical equilibrium of fracture surface, the updated post-acidizing flow channel will be found, achieving quadri-mechanism coupling. The solutions of above models will be derived through modern mathematical theories. Systematical analysis will be conducted to evaluate key factors that dominate post-acidizing results, provide valuable guidance for carbonate reservoir acidizing design, and improve and perfect acidizing theory in these formations.

胶凝酸酸化是深层裂缝型碳酸盐岩储层安全高效经济的重要增产改造技术。酸化后能否形成油气流动通道——酸蚀蚓孔，是制约此类储层酸化效果的瓶颈。酸蚀蚓孔的形成是温度-裂缝渗流-酸岩反应-应力损伤四场耦合结果，目前酸化理论鲜有考虑四场耦合影响，难以满足此类储层高效改造需求。本项目综合应用石油工程、渗流力学、传热学、反应动力学、岩石力学等学科理论，首先数字化表征天然裂缝面形貌，建立裂缝面受力变形模型，获取受力后酸化前初始缝宽分布；其次建立考虑反应热变化的温度场模型，通过温度对酸岩反应速率影响，耦合天然裂缝中酸液反应传质模型；再次基于酸液浓度分布，建立缝宽演绎方程，求取酸化后缝宽分布；最后耦合酸损伤本构方程，基于裂缝面受力变形模型寻求酸化后裂缝面力学平衡，更新酸化后流动通道分布，实现四场耦合酸化模拟。应用现代数学方法对模型求解，分析影响酸化效果的因素，指导裂缝型碳酸盐岩储层酸化设计，促进酸化理论进步。

本项目围绕裂缝型碳酸盐岩高效酸化增产机理的科学问题，结合我国深层裂缝型碳酸盐岩储层地质特征开展研究。完成了裂缝型碳酸盐岩不同尺度裂缝酸化模拟实验，揭示了酸蚀裂缝形态、流动能力形成过程，为数值模拟奠定了基础；开展了白云岩储层酸损伤实验，认识了酸液损伤对白云岩岩石力学强度影响；建立了考虑酸损伤影响的天然裂缝变形模型，认识了酸损伤前后天然裂缝受压变形规律；建立了“裂缝渗流-酸岩反应-应力损伤”三场耦合酸化模型和“温度-裂缝渗流-酸岩反应-应力损伤”四场耦合酸化模型，揭示了闭合应力、温度、注酸排量等对白云岩储层酸化效果影响，为深层白云岩储层高效酸化提供理论基础。理论研究成果成为立体酸压技术重要支撑之一，先后在四川盆地龙王庙、灯影组、栖霞组气藏试验30余井次，增产效果显著。研究成果获省部级奖励3项，授权中国发明专利8件、实用新型专利1件，申请中国发明专利1件；授权美国发明专利1件，申请美国发明专利2件，发表论文8篇，SCI、EI收录7篇，国际学术会议论文交流1次；项目负责人博士后出站，取得硕士研究生指导资格，培养研究生4人，已毕业2人，项目组成员1人晋升教授、1人晋升副教授。