基于相场法的水力裂缝扩展模拟技术现状及展望

Status and prospect of hydraulic fracture propagation simulation based on phase field method

水力压裂技术已经成为开发非常规油气不可或缺的重要技术,水力裂缝扩展数值模拟方法是认识水力裂缝扩展机理与扩展规律、优化水力压裂工艺参数的重要手段,其中相场法逐渐成为一种广泛研究和应用的水力压裂连续裂缝扩展模拟方法。为了进一步推进相场法水力裂缝技术不断发展与进步,在回顾相场法基础理论发展的基础上,总结和展望了基于相场法的水力裂缝扩展算法研究和应用现状,并对发展趋势进行了展望。研究结果表明:(1)相场法作为一种连续裂缝模拟方法,建立的位移场始终保持连续,不需要引入额外的准则,通过相场参数的演化自动追踪裂缝扩展路径,相较于离散裂缝模拟方法更容易处理不连续相、实现二维或三维空间内复杂的断裂过程,包括裂缝起裂、扩展、转向和分叉;(2)基于变分原理的热力学连续相场模型通过总能量最小化原理求解裂缝扩展路径,具有处理水力压裂等多物理场耦合问题的天然优势;(3)相场法采用具有宽度的损伤带描述裂缝面,存在计算成本高、精确定位裂缝尖端较为困难等技术难题;(4)相场法因其方法优势,有望在精准刻画不连续相、开发不同物理过程适配的数值模型基础上,进一步揭示多场耦合作用下的复杂水力裂缝扩展机理。结论认为,对相场法的研究有利于非常规油气储层改造技术的发展,有助于我国非常规油气开发事业的高质量发展。

Hydraulic fracturing technology has become an indispensable important technology for the development of unconventional oil and gas.Numerical simulation of hydraulic fracture propagation is an important method to understand the propagation mechanisms and laws of hydraulic fractures and optimize the engineering parameters of hydraulic fracturing.In recent years,phase field method has gradually become a widely researched and applied continuous fracture propagation simulation method for hydraulic fracturing.In order to further promote the continuous development and progress of the hydraulic fracturing technology based on phase field method,this paper summarizes the research and application status of the hydraulic fracture propagation algorithm based on phase field method and forecasts its development trend,after reviewing the development of the basic theory of phase field method.And the following research results are obtained.First,as a continuous fracture simulation method,the displacement field established by phase field method is always continuous,no additional criteria is needed,and the fracture propagation path can be automatically tracked through the evolution of phase field parameters.Compared with the discrete fracture simulation method,it is easier to deal with discontinuous phase and realize complex fracturing process in two-dimensional or three-dimensional space,including fracture initiation,propagation,turning and bifurcation.Second,the thermodynamic-consistent phase field model based on variation principle solves the fracture propagation path by the principle of total energy minimization,which has a natural advantage in dealing with multi-physical field coupling problems such as hydraulic fracturing.Third,phase field method adopts the damage zone with width to describe fracture surface,so it facies some technical difficulties in controlling calculation cost and accurately locating fracture tips.Fourth,thanks to its advantages,phase field method is expected to further reveal complex hydraulic fracture propagation mechanism under multi-physical field coupling on the basis that discontinuous phases are characterized accurately and numerical models suitable for different physical processes are developed.In conclusion,the researches on phase field method are beneficial to the development of unconventional oil and gas reservoir stimulation technology and to the high-quality development of unconventional oil and gas development business in China.