Research on temperature field distribution of nitrogen heating in oil shale based on fluent secondary development

Oil shale represents a non-conventional energy source characterized by substantial underground reserves. The application of nitrogen heating technology in oil shale mining constitutes a novel in-situ extraction method. This technology enhances pyrolysis efficiency in oil shale, increases the fluidity of crude oil, and strengthens fracture connectivity. However, the technology of nitrogen-heated oil shale extraction remains immature. Theoretical literature pertaining to energy-related issues fails to provide a definitive answer, and a comprehensive, systematic theoretical framework for reference is lacking. Furthermore, the industry lacks sufficient numerical simulation studies, suggesting a limited research depth and scope. Accordingly, based on fundamental theories such as Darcy's law and energy equation, this paper introduces reservoir parameters such as porosity and deduces a new theoretical equation: the energy equation in the process of oil shale mining. Guided by the theoretical framework, this study delves into the temperature field distribution during nitrogen heating of oil shale, elucidating the temperature variation patterns during the pyrolysis process. The study indicates that during the initial 50 days of heating, the temperature field undergoes rapid changes, exhibiting a limited range and uneven distribution. After 400 days, the temperature field alterations become gradual, and the pyrolysis zone in the oil shale reservoir stabilizes. The optimal production window for oil and gas extraction spans from 50 to 400 days. An appropriate increase in the gas injection rate can accelerate temperature field diffusion, though the effect diminishes beyond 4 m/s. By employing optimal injection-production ratios, fracturing layer numbers and spacings, as well as well pattern designs, the coverage of high-temperature areas can be substantially expanded, thereby enhancing mining efficiency. These research findings have the potential to advance oil shale exploitation technology and offer theoretical insights crucial for guiding engineering designs.