The diagnostic fracture injection test (DFIT) is widely used to obtain fracture closure pressure, reservoir permeability, and reservoir pressure during hydraulic fracturing operations. Conventional methods for analyzing DFIT data assume a vertical well drilled in ultra-low permeability reservoirs and account for potential multiple fracture closures. However, these traditional techniques have limitations and make assumptions that can conflict with each other, leading to greatly varying approximations of closure pressure and duration, especially for horizontal wells. To address this issue, a new method for detecting fracture closure pressure using continuous wavelet transform (CWT) analysis has been proposed.
The CWT method aims to decompose the pressure fall-off signal from DFIT into multiple levels with different frequencies. A "short wavy" wavelet function is stretched or compressed and placed at many positions along the signal. The wavelet is then convolved with the signal, yielding wavelet coefficient values. During the fracture closure process (pressure fall-off), the signal energy is observed, and the fracture closure event is identified when the signal energy stabilizes to a minimum level. To validate this new methodology, a predefined commercial fracture simulation case with known fracture closure parameters and actual field cases were utilized.
Additionally, the new CWT technique was calibrated and compared with a direct fracture deformation measurement tool called SIMFIP (Step-Rate Injection Method for Fracture In-Situ Properties). SIMFIP uses wellbore deformation measurements and strain gauges to directly observe fracture opening and closing during multiple DFIT tests. The publicly accessible SIMFIP data was used to evaluate the accuracy of the CWT method for closure detection. The findings indicate that the CWT method aligns well with the direct rock deformation measurements from SIMFIP and can identify the impact of complex closure events and pre-existing natural fractures. Consequently, the CWT technique shows great potential as an alternative to traditional approaches for more accurately detecting fracture closure pressure during hydraulic fracturing operations.
For More Infromations Please read the following papers:-
A New Technique for Estimating Stress from Fracture Injection Tests Using Continuous Wavelet Transform
https://www.mdpi.com/1996-1073/16/2/764
Validation of Estimating Stress from Fracture Injection Tests Using Continuous Wavelet Transform with Experimental Data
https://www.mdpi.com/1996-1073/16/6/2807