Energy Reports (Nov 2022)
Numerical and experimental investigation of production performance of in-situ conversion of shale oil by air injection
Abstract
In-situ conversion of oil shale process has been appealing from economic and energy security perspectives. Conventional in-situ upgrading techniques use electric heaters to heat oil shale, not shale oil. However, the efficiency of electrical heating method is very slow which requires preheating more than a year. Most conventional heating technologies focused on using different heat injection methods converting the shale oil reservoirs. As shale is a poor heat conductor, many of attempts are still in the laboratory stage. The shale oil matrix is very tight and the pore scale ranges from micro to nano-meter. In this paper, we propose to inject air into hydraulically fractured horizontal wells to create in-situ combustion of shale oil in ultra-low permeability formations. Heat is introduced into the formation through multistage fractured horizontal wells, which enhances the contact area of exposed kerogen. This process uses combustion reactants as fuel feed stock to generate perpetual heating. Firstly, we used the laboratory tube combustion of shale oil results to validate the simulation model. Then, we upscale the simulation model to investigate the well productivity performance by in-situ upgrading of shale oil by air injection.The main objective of this work is to determine the technical feasibility of recovering shale oil resources by air injection. It involves the application of hydraulic fracturing technology to enhance the kerogen exposure to oxygen. Heat flows from the fracture into shale oil formation, gradually converting the solid kerogen into mobile oil and gas which can be produced via fractures to the production wells. Our simulation results in this paper have shown the potential of in-situ combustion process to improved oil recovery in shale oil reservoirs. Simulation result indicates that the key parameters controlling the well productivity include air injection rate, injected gas composition and fracture spacing. The available literature provides limited studies on the applicability of in-situ combustion of shale oil in very low permeability formations. The paper provides a comprehensive model that allows kerogen to undergo thermal cracking and oxidation process. The results of this study indicate that the developed kinetic model is feasible to model the kerogen in-situ conversion process induced by air injection.
