Evaluating shale reservoir fracability using triaxial hydraulic fracturing tests

Due to the well-developed bedding planes in the Gulong shale oil reservoir in China, the prediction accuracy of traditional fracability evaluation models is limited, and the effectiveness of hydraulic fracturing stimulation is severely constrained. To address this issue and improve the accuracy of fracability prediction, this study conducted physical simulation tests of hydraulic fracturing in shale with multiple bedding planes and quantitatively characterized the parameters influencing fracture propagation. The key factors controlling both vertical and horizontal fracture extension were identified, and their weight coefficients were determined using the analytic hierarchy process. A comprehensive fracability evaluation model was developed, integrating both the formation environment and rock mechanical properties. The model was validated using actual well logging and production data from the Gulong shale oil reservoir. Results indicate that bedding plane characteristics significantly influence the final fracture morphology, the stress state governs fracture propagation direction, and injection parameters primarily enhance vertical fracture extension and bedding plane opening. The ranking of factor importance is as follows: bedding plane characteristics, stress difference, brittleness index, and rock strength. The model achieved a 62.5 % match between predicted fracability and actual production well contribution rates, representing a substantial improvement over traditional models. This study provides a scientific foundation for optimizing formation deployment and fracturing stage design in Gulong shale oil horizontal wells within the Daqing Songliao Basin, and offers technical support for the efficient development of unconventional reservoirs.