Experimental investigation of EOR mechanisms for cyclic steam injection assisted by flue gas

In Colombia, Cyclic Steam Stimulation (CSS) is deployed as an EOR method to recover heavy oil. However, flue gas from steam generators is a stable long-term CO2 emission source in oil fields. And the adverse effects of this greenhouse gas cannot be ignored, becoming a concern in all countries worldwide. In this study, the cyclic steamflue gas co-injection process (CSS-FG) is proposed as an alternative to improve the performance of CSS, extend the lifetime of this technology, and collect and use the flue gas from steam generators to reduce greenhouse-gas emissions. In this investigation, CSS and CSS-FG were experimentally represented and compared to understand the effect of flue gas addition on the recovery mechanisms at the different stages of CSS, using a one-dimensional core physical simulation. For CSS representation, five steam injection cycles were carried out, and flue gas was added in a sixth cycle to analyze the effect of flue gas on the recovery factor after several stages. Likewise, in the CSS-FG displacement, five cycles were developed, where flue gas-steam was injected since the second to the fifth cycle. The results show that the final oil recovery factors of CSS-FG using 15% of flue gas molar ratio was 41.1%, compared to 15.2% of CSS. In addition, after five-cycle steam stimulation, the recovery factor increased up to 9.2% by adding flue gas in the sixth cycle. The differences in the recovery factors confirmed the synergy between the flue gas and steam even in mature stages of steam stimulation, which facilitated the identification of the recovery mechanisms associated with adding this gas. Phase interaction between the flue gas and heavy oil is promoted during the injection stages. Thereafter, flue gas expands rapidly in the production period, offering a push mechanism that accelerates the fluids production rate. Additionally, the porous medium pressure increases, and the fast depletion rate near the production port when adding flue gas cause foamy oil formation, improving the mobility of heavy oil since the dissolved gas cannot release from the oil because of its high viscosity. These experimental results provide theoretical guidance for improving the effectiveness of the CSS and demonstrate that CSS-FG is an essential method for reducing greenhouse-gas emissions in oil fields.