Evaluation of Sweet Spots and Feasibility Study of In-Situ Combustion in a Tight Glutenite Reservoir of Xinjiang

Sweet spot evaluation and in-situ combustion (ISC) (also known as high-temperature thermal oxidation) technology are research hotspots in the development of tight glutenite reservoirs with ultra-low permeability. However, significant challenges exist, including low accuracy of sweet spot identification and the feasibility of ISC in light reservoirs, as well as its safety risks. Therefore, this study focused on the tight glutenite reservoir with ultra-low permeability of the C oil formation in Block A of the Junggar Basin, Xinjiang and systematically investigated the main controlling factors of productivity, sweet spot evaluation, and the feasibility of ISC for enhanced oil recovery (EOR). First, by considering the geological and engineering factors, the Spearman rank correlation analysis method was employed to identify the controlling factors of productivity. Second, for the first time, crude oil viscosity was incorporated into the comprehensive sweetness index S, and sweet spots in the C oil formation of Block A were delineated based on an inverse relationship between crude oil viscosity and S, and a direct proportionality between the product of oil saturation and porosity with S. Finally, the feasibility study of ISC for light oil in tight reservoirs was conducted through one-dimensional combustion tube experiments, and the influence of reservoir physical parameters on the performance of ISC was investigated. The results indicate that crude oil viscosity is one of the key controlling factors for productivity under water flooding and fracturing development conditions. The three types of zones classified based on variations in the comprehensive sweetness index S effectively reflect the change in continuity of sediment supply. Higher crude oil viscosity and oil saturation are more conducive to coke deposition and heat accumulation, thereby facilitating the stable maintenance of a high-temperature oxidation front and improving displacement efficiency and ultimate recovery (with the highest recovery reaching 59.22% in the experimental results). The research results demonstrate that ISC technology is feasible for the development of tight light oil reservoirs, providing a theoretical basis for enhancing oil recovery in similar reservoirs.