Effect of Oil Gravity and Pore Volume Injected (PVI) of Steam to PVI of Foam During Enhanced Oil Recovery by Steam-CO2-Foam Flooding

Abstract

Abstract In spite of CO2mobility reduction during CO2and surfactant solution co-injection, CO2-foam flooding in heavy oil reservoirs has relatively poor sweep efficiency due to the high viscosity the oil. Therefore, reducing the oil viscosity is necessary to improve CO2-foam sweep efficiency. For this reason, steam is injected initially during steam-CO2-foam flooding to reduce oil viscosity. Displacement process is followed using CO2and surfactant solution co-injection. In our previous experimental study, in order to highlight the potential of steam-CO2-foam flooding, three different oil recovery experiments were conducted using medium heavy crude oil (19 °API), including CO2-foam flooding after water flooding, CO2-foam flooding and steam-CO2-foam flooding. The results showed that steam-CO2-foam flooding increases oil recovery dramatically by simultaneous mechanisms such as oil viscosity reduction by steam, CO2dissolution in oil and emulsification by steam and surfactant. Furthermore, the effect of high surfactant concentration slug injection on steam-CO2-foam flooding performance was investigated. The results showed that slug causes the formation of viscous micro emulsions in front of CO2-foam flood and improves CO2-foam sweep efficiency. In this paper, the effects of oil gravity and pore volume injected (PVI) of steam to PVI of foam on the oil recovery during steam-CO2-foam flooding have been studied. The experiments are conducted using heavy oil (12 °API) and sand pack models under reservoir conditions of 1550 psi and 131°F. In order to investigate the effect of PVI of steam/PVI of foam ratio on the oil recovery, three different oil recovery scenarios have been conducted using heavy crude oil, including CO2-foam flooding only, steam-CO2-foam flooding including 0.14 PVI of steam/PVI of foam ratio and steam-CO2-foam flooding including 0.34 PVI of steam/PVI of foam ratio. The results show that in spite of decreasing oil recovery by decreasing API gravity of the oil during steam-CO2-foam flooding, increasing PVI of steam improves oil recovery. The steam-CO2-foam flooding process has the following benefits. (1) Combination of steam injection and CO2-foam flooding as a novel enhanced oil recovery (EOR) method to achieve favorable oil recovery. (2) The applicability of this EOR method in heavy and medium heavy oil reservoirs.