Location estimation of subsurface fluid-filled fractures: cepstral predominant peak analysis and numerical study

In various subsurface resource development or fluid piping problems, subsurface fluid-filled fractures often appear. Fracture location determination has always been critical in related fields. Acoustic wave reflection at the junction and boundary in the pipeline can carry information about the property of the system. By using the accompanying acoustic wave combined with the water hammer effect, the location of subsurface fractures can be estimated. A numerical fluid flow model for instantaneous shut-in is presented based on water hammer effect. Fluid penetration effects, wellbore storage effect and fluid inertial effect are considered. The fracture location estimation method called cepstral predominant peak (CPP) analysis is first proposed. By cepstral, we means the inverse Fourier transform of the logarithm of the estimated signal spectrum. Also the relationship between instantaneous shut-in pressure and cepstrum response is investigated in detail. To improve the robustness, CPP analysis based on Kaiser windowed cepstrum was used to identify the impulse period of fracture. Compared with original cepstrum, Kaiser windowed cepstrum has the better performance for CPP analysis. The proposed flow model is impactful as it can provide pressure data with known fracture locations. The data can be used to optimize and examine the performance of CPP analysis. A field experiment is conducted to validate the analysis about the acoustic wave in a pipeline system with fractures. The actual instantaneous shut-in pressure for an oil well is obtained. The experiment result shows the CPP analysis can get the fracture location efficiently and accurately, which can provide insights for engineering.