Numerical simulation of mechanism of high-pressure air injection (HPAI) in light oil reservoirs

Abstract

Based on the research progress of the crude oil oxidation-combustion model proposed by predecessors, this paper established a new multi-reaction model for high-pressure air injection (HPAI) process to compare the HPAI performance in reservoirs without water injection and high water cut reservoirs by numerical simulation. Results show that gas override is universal in air injection in light oil reservoirs before and after waterflooding, and is more apparent in strongly heterogeneous reservoirs. However, the produced oxygen concentration is very low all the time. For reservoirs that haven't gone through water injection, at high air injection rate oil is very likely to auto-ignite and keep high peak temperature and long time stable combustion front. However, there exists a critical value for the influence of air injection rate on the combustion front moving speed, above the critical value, oil recover factor increment is not obvious with the increase of air injection rate. At the same air injection rate, high water cut reservoirs are 6.3% lower in recovery factor than reservoirs without water injection, With high increase in GOR and high water recovery degree during HPAI process. It is suggested that polymer gel/ and or foam assisted air injection be taken to reduce GOR/ and or water cut in production wells. Key words: air injection, light oil reservoirs, reservoirs without water injection, high water cut reservoir, gas override, numerical simulation, mechanism study