The role of N2 as booter gas during Enhanced Gas Recovery by CO2 flooding in a porous medium

Mohammed, NUHU; Abbas, AJ; Enyi, GC

Abstract

Most research on CO2 flooding is focusing on CO2 storage than CH4 recovery and mostly simulation-based. To our knowledge, there have been limited reported experimental on CO2 injections capable of unlocking a high amount of the residual methane due to their miscibility effect. The empirical study has highlighted the impact of N2 as a buster gas during the Enhanced Gas Recovery (EGR) process by CO2 flooding. The N2 acts as a buster by re-pressurising the reservoir pressure before the CO2 breakthrough, enabling more CH4 recovery. It also acts as a retardant by creating a thin barrier at the CO2–CH4 interface, making it difficult for the CO2 to disperse into the CH4. This result in an extendable breakthrough, influencing the injected CO2 to migrate downward due to gravity for storage within the pore spaces. This study, a core flooding experiment at 1500 psig and 40 °C of pressure and temperature, respectively, was carried out to study the effect of N2 as buster gas during natural displacement in a porous medium (sandstone rock). The recoveries with N2 buster were better off than those without N2 buster (conventional CO2 flooding). Overall, an improved CH4 recovery and dispersion coefficient with substantial storage was noticed, with the optimum at 0.13 fraction of pore volume buster gas. Compared to the 0.4 ml/min optimum conventional CO2 injection, the results show a 10.64 and 24.84% increase in CH4 recovery and CO2 storage, respectively. 0.71 × 10-8 m2/s reduction in dispersion coefficient was recorded than the convention method. The additional CH4 recovery can provide extra revenue to offsets other operational expenses. This research signifies the potential of N2 as a buster medium on CH4 recovery, which can be applicable for pilot application within the oil and gas industry.

• Journal Article Type: Article
• Acceptance Date: May 7, 2021
• Online Publication Date: Jun 4, 2021
• Publication Date: Sep 1, 2021
• Deposit Date: Jun 7, 2021
• Publicly Available Date: Jun 4, 2022
• Journal: Journal of Natural Gas Science and Engineering
• Print ISSN: 1875-5100
• Publisher: Elsevier
• Volume: 93
• Pages: 104051
• DOI: https://doi.org/10.1016/j.jngse.2021.104051
• Publisher URL: https://doi.org/10.1016/j.jngse.2021.104051
• Related Public URLs: https://doi.org/10.1016/j.jngse.2021.104051