Generation and propagation characteristics of fluctuation pressure in hydraulic fracturing with unstable fluid-injection

不稳定注入水力压裂波动压力的产生与传播特性研究

Different from the stable injection mode of conventional hydraulic fracturing,unstable fluid-injection can bring significant dynamic effect by using variable injection flow rate,which is beneficial to improve the fracturing effect.Obviously,the propagation process of fracturing fluid along the pipe string is crucial.In this paper,the fluid transient dynamics model in the pipe string was established,considering the boundary conditions of variable injection flow rate and reservoir seepage,and the unsteady friction was also taken into account.The above model was solved by characteristics and finite difference method respectively.Furthermore,the influences of geological parameters and fluid injection schemes on fluctuating pressure were also analyzed.The results show that unstable fluid-injection can cause noticeable fluctuation of fracturing fluid in the pipe string.Simultaneously,there is attenuation during the propagation of pressure fluctuation.The variation frequency of unstable fluid-injection and well depth have significant effects on pressure fluctuation amplitude at the bottom of the well.This research is conducive to understanding the mechanism of unstable fluid-injection hydraulic fracturing and providing guidance for the design of fluid-injection scheme.

区别于常规稳定注液方式,不稳定注入水力压裂在施工过程中通过改变注入流量、利用流量变化产生的动态效应来提高压裂改造效果。其中压裂液沿管柱的流动规律对于压裂施工过程至关重要。本文建立了管柱内流体瞬态流动的动力学模型,该模型考虑了储层渗流与非恒定摩阻的影响。分别采用特征线法与有限差分法对上述模型进行求解。进一步分析了地质参数与注入方案对井底波动压力的影响。结果表明,不稳定注入可以使管柱内流体压力产生明显波动。此外,波动压力在传播过程中会发生衰减,注入流量变化频率与井深参数对井底的压力波动幅值影响显著。本研究有助于理解不稳定注入水力压裂的施工原理,并为压裂施工中的注液方案设计提供指导。