Direct Investigation of Oil Recovery Mechanism by Polymer-Alternating-Gas CO<sub>2</sub> through Micromodel Experiments
Rapheephan Laochamroonvorapongse, Virginie Beunat, Nicolas Pannacci, F. Douarche, Jirawat Chewaroungroaj, Falan Srisuriyachai
Abstract
High Resolution Image Download MS PowerPoint Slide CO 2 gas is one of the most effective injectants for enhanced oil recovery (EOR). New injection technique like polymer-alternating-gas (PAG) is aimed at further improving oil recovery efficiency from conventional gas injection; however, the oil recovery mechanism and fluid interactions underlying PAG have not yet been studied at a microscopic level. This study conducts the first micromodel study to better understand the relevant mechanisms and interactions of PAG at high pressure and temperature. Traditional methods, including water, polymer, CO 2, and water-alternating-gas (WAG), are also investigated and compared with PAG. The experiments use a rock-shaped micromodel glass and decane to represent reservoir oil. An oil miscibility test is performed by injecting CO 2 into a micromodel prefilled with decane at a temperature of 40 °C and pressure varying within 70–90 bar. Oil miscibility, as determined by the disappearance of an oil-CO 2 interface, is achieved at a pressure of 90 bar. When comparing the WAG and PAG methods, the PAG method is more effective in producing additional oil recovery of up to 6%. This is due to the polymer’s better displacement efficiency, stronger gas flow diversion effects, and slightly higher miscibility level. The observed oil recovery mechanisms are oil displacement, miscibility, flow diversion, oil swelling, and CO 2 dissolution and diffusion. This study proposes a simple miscibility test, proves the effectiveness of the PAG method, and demonstrates various phenomena related to oil recovery processes. Integrating those effects and new injection strategies in the simulation study will benefit the CO 2 -EOR field design.