基于相场方法的径向井液态药高能气体与水力压裂复合压裂机理研究

As a pretreatment method of hydraulic fracturing, High Energy Gas Fracturing has been recognized by many scholars. At present, all the research objects are the perforated well. Because perforation is short and can't deeply connect target area, stimulation effect is not obvious. In this subject, a new process principle is proposed through injecting liquid propellant into radial well, utilizing the fractures of high energy gas and hydraulic fracturing to reach the target area and realizing the fracture network propagation. A three dimensional numerical model for radial well high energy gas fracturing is established coupling displacement field, phase field and high energy gas pressure field to simulate HEGF fracture dynamic propagation. The effect of in-situ stress, completion parameters, rock mechanics parameters, explosion mechanical parameters on initiation pressure, initiation position, fracture number and fracture shape of HEGF fracture is studied. On this basis, a physical model and governing equation for characterizing multiple fractures propagation and a three dimensional numerical model of stress -fluid flow- damage coupling for radial well hydraulic fracturing is established. Based on the theoretical analysis and numerical simulation, the influence of HEGF fracture shape, radial well completion parameters, fracturing fluid displacement and viscosity on hydraulic fracture morphology could be obtained and the fracture networking propagation mechanism could be revealed. It lays a solid theoretical foundation for the radial well hydraulic fracturing stimulation technology and its application and forms the key technical support for the radial well liquid propellant high energy gas fracturing and hydraulic fracturing.

高能气体压裂作为水力压裂的预处理手段已被广大学者认可。目前研究对象皆为射孔井，射孔孔眼较短，不能深入沟通目标区域，增产效果有限。本课题提出将液态火药注入径向井中，通过高能气体压裂联合水力压裂作用，达到沟通目标区域、实现裂缝网络化扩展的新技术路线。运用相场理论，建立径向井高能气体位移场、相场和高能气体压力场三场耦合的压裂模型，模拟HEGF裂缝动态扩展的典型特征。研究地应力、完井参数、岩石力学参数、火药燃爆力学参数对HEGF裂缝起裂压力、起裂位置、裂缝条数、扩展形态的影响规律。在此基础上，建立表征多条裂缝扩展的物理模型、控制方程和径向井水力压裂渗流-应力-损伤耦合三维裂缝扩展模型。通过理论分析和数值模拟，获得HEGF裂缝形态、径向井完井参数、压裂液排量、粘度对水力裂缝形态的影响规律，揭示裂缝网络化扩展机理。为径向井水力压裂增产技术及其现场应用奠定坚实的理论基础，并形成关键技术支撑。

高能气体压裂作为水力压裂的预处理手段已被广大学者认可。目前研究对象皆为射孔井，射孔孔眼较短，不能深入沟通目标区域，增产效果有限。本课题提出将火药注入径向井中，通过高能气体压裂联合水力压裂作用，达到沟通目标区域、实现裂缝网络化扩展的新技术路线。本项目采用实验测试（获取储层物性参数）、理论分析与模型构建相结合的方法，从建立高能气体燃爆压力力学模型、径向井高能气体压裂数值建模、径向井高能气体压裂裂缝起裂扩展机理和高能气体与水力压裂复合压裂机理4个方面进行了系统研究。结果表明：（1）对于未存在天然裂缝的径向井，高能气体燃爆后，优先在径向井趾段发生起裂；（2）最大水平主应力和最小水平主应力的改变分别对高能气体压裂裂缝的长度和宽度影响较明显；（3）径向井直径增加裂缝的长、宽皆减小，可见较小井径更有利于裂缝扩展；（4）压裂火药用量影响裂缝长度更明显，而多个起爆点只对裂缝宽度影响较明显；（5）若储层存在天然裂缝，压裂过程会优先从天然裂缝开始，且天然裂缝超过2.5m间距不易形成沟通缝；（6）天然裂缝并非越多越好，趾端存在裂缝情况下，趾端裂缝更易扩展；（7）储层中的微观裂缝对裂缝扩展的轨迹和形态有着较大影响，当微观裂缝从4个增加为12个时，裂缝的偏转角从31度增加为43度，增加幅度为38.7%；（8）高能气体压裂裂缝并不是越多越好，过多裂缝会干扰和抑制水力裂缝的有效扩展；（9）高能气体压裂的尖端应力区域越大，更有利于后期水力裂缝的产生较大的转向半径，水力压裂效果更好。（10）高能气体裂缝缝间距有一定合理取值范围，较大或较小都不利于水力裂缝的体积改造效率。