To study the mechanism of hydraulic fracturing with pulse injection theoretically, in this paper, the transient flow model of fracturing fluid in the pipe string was established, and it was solved by method of characteristics and finite difference method, respectively. Furthermore, the elastodynamic model of reservoir was also established. Based on the finite element method, the dynamic stress distribution in the reservoir was simulated and calculated. In addition, the influence of parameters in the pulse injection scheme on dynamic stress was analyzed. The results indicate that the unsteady injection produces a pulse pressure wave at the wellhead. The pressure wave propagates along the pipe string to the bottom of the well, and its amplitude attenuates due to the resistance loss. When the pressure wave propagates to the bottom of the well, it will be reflected and there is a superposition area of the downward pressure wave and upward reflection wave near the bottom hole. The bottom hole pressure of pulse injection is the sum of stable injection pressure and the above pressure wave. Simultaneously, this fluid pressure with pulse variation will stimulate reservoir to produce dynamic stress in its interior. The pulse adjustment time and adjustment amplitude in the injection scheme have a significant impact on the dynamic stress. The results of this paper are helpful to understand the mechanism of hydraulic fracturing with pulse fluid injection and provide guidance for its parameter design.

中文翻译：

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脉冲注水压裂井底动压与储层动应力模拟模型。

为了从理论上研究脉冲注入水力压裂的机理，建立了管柱内压裂液的瞬态流动模型，并分别采用特征法和有限差分法求解。此外，还建立了储层的弹性动力学模型。基于有限元方法，对储层中的动应力分布进行了模拟和计算。此外，分析了脉冲注入方案中的参数对动应力的影响。结果表明，不稳定注入会在井口处产生脉冲压力波。压力波沿着管柱传播到井的底部，其振幅由于电阻损耗而衰减。当压力波传播到井底时，它将被反射，并且在井底附近有向下压力波和向上反射波的叠加区域。脉冲注入的井底压力是稳定注入压力与上述压力波之和。同时，这种具有脉冲变化的流体压力将刺激储层在其内部产生动态应力。注射方案中的脉冲调节时间和调节幅度对动应力有重大影响。本文的结果有助于了解脉冲流体注入水力压裂的机理，并为参数设计提供指导。脉冲注入的井底压力是稳定注入压力与上述压力波之和。同时，这种具有脉冲变化的流体压力将刺激储层在其内部产生动态应力。注射方案中的脉冲调节时间和调节幅度对动应力有重大影响。本文的结果有助于了解脉冲流体注入水力压裂的机理，并为参数设计提供指导。脉冲注入的井底压力是稳定注入压力与上述压力波之和。同时，这种具有脉冲变化的流体压力将刺激储层在其内部产生动态应力。注射方案中的脉冲调节时间和调节幅度对动应力有重大影响。本文的结果有助于了解脉冲流体注入水力压裂的机理，并为参数设计提供指导。