Experimental investigation and numerical simulation on Multiphysics coupling of shale under laser irradiation

Abstract

As an efficient, clean and controllable rock-breaking technique, laser technology has shown significant potential for application in assisted fracturing of deep shale reservoirs. In this investigation, shale was selected as the research subject, and laboratory experiments on laser-induced rock fracturing were conducted to systematically investigate the fracture behavior of shale with different bedding angles under laser irradiation. An electromagnetic-thermal-mechanical (E-T-M) coupling model considering thermal damage accumulation was developed by combining the finite element method with the discrete element method. This model was employed to comprehensively analyze the physical response and fracture mechanism of shale under laser irradiation. The results indicate that: (1) Under laser irradiation, crack propagation of shale is bedding-dominated, with final fracture surfaces largely coinciding with bedding planes; (2) Shale with bedding angles of 45° and 90° exhibits lower specific energy (SE) and higher rate of penetration (ROP) under laser irradiation. (3) Laser pretreatment significantly increases the number of local cracks generated during subsequent mechanical loading and enhances the spatial distribution of these cracks. (4) The fracture process of laser-treated shale under loading can be divided into three distinct stages: initiation, propagation, and coalescence. Based on laser diameters, two distinct fracture modes are identified: laser-strong response mode and laser-weak response mode. Depending on bedding angles, fracture patterns are categorized as cross-bedding penetration mode and along-bedding penetration mode. These findings provide a pioneering theoretical foundation for the development and application of laser rock-breaking technology in assisting deep-layer shale gas extraction.