Mechanical responses and fracture behaviors of pre-heat-treated carbonate rocks during hydraulic fracturing under different confining-axial pressures (Article in press)

Abstract

In this work, the mechanical responses and fracture behaviors of pre-heat-treated carbonate rocks during hydraulic fracturing under different confining-axial pressure conditions were systematically investigated. Using carbonate rock samples from the Gaoyuzhuang Formation in Xiongan New Area, China, hydraulic fracturing tests were conducted under equal confining-axial pressures (10, 20, 30, and 40 MPa) after different temperature pre-treatments (20°C, 70°C, 120°C, 170°C, and 220°C). By integrating fluid pressure monitoring, acoustic emission signal acquisition, and three-dimensional fracture morphology scanning, the coupled effects of the pre-treatment temperature and stress on fracture pressure, fracture propagation paths, and failure modes were systematically analyzed. The results demonstrate that pre-treatment temperature exerts a significant non-monotonic regulatory effect on rock mechanical behavior: moderate-low temperatures (70°C–120°C) enhance rock structural integrity, increasing both fracture pressure and fluid pressure growth rate, whereas high temperatures (≥170°C) induce micro-fracture networks through thermal stress, leading to material weakening. Increasing confining-axial pressure not only significantly raises fracture pressure but also suppresses thermal crack propagation, promoting a transition in failure mode from tension-dominated to shear-dominated. Three-dimensional fracture morphology analysis further reveals that both temperature and confining-axial pressure jointly regulate the fluctuation height and spatial complexity of fracture surfaces, with the 170°C pre-treated specimens exhibiting peak fracture surface roughness. The research results provide critical experimental evidence for optimizing parameters under coupled temperature-stress conditions in the hydraulic fracturing design of deep carbonate geothermal reservoirs.