Crack Opening and Slippage Signatures During Stimulation of Bedded Montney Rock Under Laboratory True-Triaxial Hydraulic Fracturing Experiments

• Published in: Rock mechanics and rock engineering 2024-11, Vol.57 (11), p.9827-9845
• Main Authors: Abdelaziz, Aly, Grasselli, Giovanni
• Format: Article
• Language: English
• Subjects: Anisotropy; Axial stress; Civil Engineering; Crack initiation; Crack propagation; Earth and Environmental Science; Earth Sciences; Fluid pressure; Fracture mechanics; Geophysics/Geodesy; Hydraulic fracturing; Isotropic material; Isotropic materials; Laboratories; Mechanical properties; Mechanical stimuli; Oil and gas operations; Original Paper; Pressure; Pressure curve; Pressure drop; Pressure recovery; Rocks; Sedimentary rocks; Shale; Slippage; Stimulation; Stress propagation; Triaxial tests; Viscosity
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-024-04048-5

Hydraulic fracturing is a widely utilized technique for rock stimulation in geothermal and oil and gas operations. To fracture the rock, the pumped fluid pressure required should exceed the sum of the stresses at the injection point and the rock’s mechanical strength. In scenarios where the rock is isotropic, hydraulic fractures typically propagate in directions perpendicular to the minimum principal stress. Contrary to this conventional understanding, our research, involving a series of true-triaxial hydraulic fracturing tests on the finely laminated Montney shale formation, demonstrates that this principle does not hold for transversally isotropic materials. Our experimental findings indicate that fractures in such materials occur along the bedding planes, aligning against the intermediate principal stress rather than the minimum principal stress. Based on these observations, we propose a conceptual model that integrates the in situ stresses with the tensile anisotropy of the rock. Additionally, in our experimental work, we saw that change in viscosity of the injected fluid greatly influences the fracture geometry, which can be used to engineer the fracture initiation and propagation as it seems to inhibit the parting of the beddings and to reorient the fracture along with the principal stresses. Highlights Laboratory true-triaxial tests for transversally isotropic rocks exhibit hydraulic fractures against intermediate principal stress. Characteristics of the pressure curve during hydraulic fracturing can be used to differentiate tensile and shear/slip fractures. Tensile fracture during hydraulic fracturing indicates sharp pressure drop with faster pressure recovery. Rock fabric and fluid viscosity have great impacts on the fracture initiation, propagation and interactions during hydraulic fracturing.