The creep behavior of brittle rocks after high-temperature heat treatment holds significant implications for the advancement of deep subsurface resource utilization. The long-term creep mechanical responses of rocks post-heat treatment may manifest diverse tendencies amid varying confining pressures accompanying temperature escalation; However, the underlying causalities remain obscured and the research focusing on the macro-meso mechanical mechanism is scant. Based on a microcrack crack propagation model, five temperature-dependent microcrack model parameters deduced via independent experiments, including initial crack damage (D₀), fracture toughness (K_IC), crack extension stress corrosion index (n), characteristic crack propagation rate (v), and initial crack friction coefficient (μ), are introduced. A macro-meso fracture mechanics model for creep behavior of brittle rock after high-temperature heat treatment has been established. The stress-strain constitutive relationship of rock under the influence of heat treatment temperature is also obtained, which provides an important basis for the selection of stress states of creep deformation mechanism. The influences of temperatures and confining pressures on parameters such as rock initiation stress, peak strength, long-term strength, and creep failure time are studied. Empirical validation substantiates the rationale of the model. Particular emphasis is vested in delineating the impact of confining pressure on the creep fracture attributes of rocks, as temperature undergoes variations. This emphasis arises from the divergent trends characterizing the evolution of the initial crack friction coefficient with temperature fluctuation. The research findings analyze the short-term and long-term mechanical characteristics of heat-treated brittle rocks from a meso-mechanical perspective. This offers a clearer and more profound understanding of the mechanical mechanisms underlying the behavior of heat-treated brittle rocks.

Aiming at the engineering problems of rock damage and failure caused by long-term dry-wet cycle conditions such as the hydro-fluctuation belt in the Three Gorges reservoir area, this paper investigates the challenging issues of the micro-macro mechanical properties of brittle rocks under the combined effects of dry-wet cycles and direct tensile loading. However, due to the challenges in conducting direct tensile tests under dry-wet cycles, there is a scarcity of macro-micro mechanical models that account for both dry-wet cycles and direct tensile loading. Based on the coupled method of the theory of fracture mechanics and the experiment of dry-wet cycle, a macro-micro mechanical model of direct tensile fracture of brittle rock under the influence of dry-wet cycle conditions is proposed. The model is developed by considering the combined effects of the number of dry-wet cycles (n) and water content (ω) on fracture toughness (K_IC) and initial damage (D₀). It is then integrated with a direct tensile microcrack propagation mechanical model that considers initial microcrack damage and crack fracture toughness in rocks. The theoretical results for tensile strength, wing crack limit length l_lim, elastic modulus, and rock deterioration damage are compared with experimental data to validate the reasonableness of the model. The influence of initial crack angle φ, material parameter β, and other parameters on the variation of crack initiation stress and peak stress with the number of dry-wet cycles n is discussed. Furthermore, a comparative analysis is conducted to explore the effects of dry-wet cycles and single water content conditions on the deterioration degree of rocks.

This study investigates the causes of permeability decline in porous reservoirs under decreasing reservoir pressure by comparing laboratory experiments with well test data. Well tests indicate a greater sensitivity of permeability to pressure changes in reservoir formations compared to laboratory conditions and for this remain unclear. Field studies of permeability changes in northern Perm oil fields were conducted alongside laboratory experiments on core permeability under pressure. Results showed that highly permeable samples exhibited the greatest decline in permeability during elastic deformations, with reductions of 6% for limestones and 20% for sandstones. The relationship between permeability and purely elastic deformations for both rock types was accurately described by a power law. By comparing coefficients from field and lab studies, the mechanism of permeability decline in field conditions was established. A model incorporating elastic and plastic deformations of porous reservoirs was developed. The model considers the localization of plastic deformations in horizontal and vertical low-permeability deformation bands. Findings indicate that highly permeable formations are more susceptible to deformation band formation, particularly in thicker layers. The decrease in permeability was found to correlate strongly with the formation thickness, likely due to the formation of transverse deformation bands in pore layers.