Research and application of hydraulic fracturing fluid entry depth detection method based on water-hammer signal

Horizontal well staged fracturing method is a pivotal technology in the exploitation of unconventional oil and gas reservoirs. During the pump shut-in process, the water-hammer wave generated, which propagates along the wellbore and reflects at the fluid entry point and bridge plug. Pressure oscillation signals are observable at the wellhead during pump shut-in phase, which encapsulate information about the reflection period of the water hammer wave. By analyzing the pressure oscillation signal at the wellhead, it is possible to ascertain the depth of fluid entry in the process of hydraulic fracturing. In this paper, the water-hammer wave propagation model of wellbore and hydraulic fractures system is established and validated by using the field data. The relationship between wave velocity and reflection time is studied, finding the water hammer signal is a periodic resonance in the frequency domain. By picking up resonance frequency, the wave reflection period can also be obtained. In this paper, a novel frequency difference method (FDM) is proposed to calculate the reflection time in the frequency domain. The depth of the fracturing fluid entry point is determined by combining the echo time and wave velocity calculations. In this paper, field data from two field fracturing wells is collected. 10 staged waterhammer of wellhead pressure data are analyzed. The fluid entry point calculation results are consistent with the field results, which correlation coefficient is 99.6%. The results indicate the effectiveness of the proposed method. This paper provides a strong technical reference for determine fracturing fluid entry depth and hydraulic fracturing monitoring technology.