Fracwave

Introduction

Fracture closure detection has long been one of the most debated topics in petroleum and geothermal engineering. Determining minimum horizontal stress (Shmin) is essential for fracture design, reservoir management, and geomechanical modeling. Conventional approaches, such as the Nolte G-function, tangent method, and compliance method, rely on simplifying assumptions that often break down in unconventional reservoirs where fracture networks are complex and heterogeneous.

To overcome these challenges, we developed a novel fracture closure detection method based on the Continuous Wavelet Transform (CWT). Unlike traditional techniques, the CWT approach does not rely on pre-set assumptions about fracture geometry, stiffness, or leak-off behavior. Instead, it analyzes the pressure falloff signal in the time–frequency domain to identify fracture closure more robustly. This article summarizes the theoretical basis of the technique, its calibration through laboratory experiments, validation using field data, and its overall integration into modern workflows.

Theoretical Development of the CWT Technique

The foundation of the CWT method was established to address limitations in G-function derivatives and compliance analysis. By decomposing the pressure falloff signal into multiple frequency scales using the Morlet wavelet, CWT provides a “mathematical microscope” for identifying closure. Closure is marked by a distinct peak in wavelet energy followed by stabilization at a lower level.

Key advantages of this theoretical framework include:

• Independence from assumptions about fracture stiffness evolution or Carter leak-off models.

• Sensitivity to dynamic fracture behavior, including sequential closures in naturally fractured formations.

• Ability to distinguish closure signals from noise, which is especially valuable in field applications.

Theoretical modeling using synthetic pressure data and flow regime simulations confirmed that the CWT method consistently detected closure pressure more accurately than tangent or compliance methods.

CWT Fracture Closure Detection Technique Workflow

CWT Fracture Closure Detection Technique Criteria

Laboratory Calibration

Controlled laboratory experiments under true-triaxial conditions provided the first systematic calibration of the CWT technique. Samples of granite and sandstone were fractured under known minimum stress conditions, followed by pressure falloff cycles.

The results demonstrated that:

• CWT estimates of closure pressure consistently matched applied stress within about 5 percent.

• The method remained robust across rock types with different permeability and surface roughness.

• CWT resolved sequential closure events associated with natural fracture interactions, while tangent and compliance methods systematically underestimated stress.

These laboratory calibrations confirmed the technique’s accuracy and adaptability to different geomechanical settings.

Field Calibration with SIMFIP Measurements

The next stage of validation used field-scale data from the EGS Collab project, where fracture closure was directly measured with the SIMFIP tool. This probe records micron-level borehole deformation during fracture opening and closure, providing an independent benchmark.

CWT-based closure detection aligned closely with SIMFIP-derived stress values. The method also recognized complex closure behavior, including the influence of natural fractures and rough fracture faces. By comparison, conventional methods often produced inconsistent or underestimated values. The successful field calibration demonstrated that CWT can serve as a reliable tool in both geothermal and petroleum reservoirs, where stress estimation accuracy is critical.

Field calibration setup for CWT fracture closure detection technique.

Comparison between fracture closure using the new technique and measured fracture closure using SIMFIP tool

Integration and Comprehensive Review

A broader review of closure detection methods highlighted the limitations of conventional techniques. The tangent method tends to identify closure too early under nonlinear leak-off, while the compliance method often fails to provide consistent signatures in naturally fractured reservoirs.

By contrast, CWT functions as an assumption-free technique that can arbitrate between tangent and compliance interpretations. This enables a more reliable workflow for closure detection, improving confidence in stress estimation across diverse reservoir types.

Implications for Industry

The introduction and calibration of CWT fracture closure detection carry major implications for subsurface engineering:

• Improved fracture design from more accurate stress profiles.

• Reduced uncertainty in geomechanical models.

• Applicability across oil, gas, geothermal, and carbon storage projects.

• Integration into DFIT workflows as a benchmark method that reconciles discrepancies between existing techniques.

The CWT technique provides a universal and validated approach to fracture closure detection, enhancing both academic research and field operations.

For more details

• Gabry, M.A., Eltaleb, I., Ramadan, A., Rezaei, A., Soliman, M.Y. Hydraulic Fracture Closure Detection Techniques: A Comprehensive Review. Energies, 2024. DOI: 10.3390/en17174470
• Gabry, M.A., Eltaleb, I., Soliman, M.Y., Farouq-Ali, S.M. A New Technique for Estimating Stress From Fracture Injection Tests Using Continuous Wavelet Transform. 2022. https://doi.org/10.3390/en16020764
• Gabry, M.A., Eltaleb, I., Soliman, M.Y., Farouq-Ali, S.M., Cook, P.J., Soom, F.A., Guglielmi, Y. Validation of Estimating Stress from Fracture Injection Tests Using Continuous Wavelet Transform With Experimental Data. 2022. https://doi.org/10.3390/en16062807
• Gabry, M.A., Ye, Z., Ramadan, A., Ghassemi, A., Soliman, M.Y. Calibration of Continuous Wavelet Transform (CWT) Fracture Closure Detection Using Laboratory Hydraulic Fracturing Experiments. URTeC 4221618