Assessing the Feasibility of Improving the Performance of CO2 and CO2-WAG Injection Scenarios by CWI

In water-wet systems, the oil recovery performance of CO2 and CO2-WAG injection scenarios is negatively affected when the injection pressure is below the minimum miscibility pressure and the spreading coefficient is negative. Under these conditions, the bypassed oil in the porous medium will have the minimum surface contact area with the injected CO2. Thus, injection strategies that can improve this contact can enhance the CO2 performance. This study aims to quantify the impacts of injecting carbonated water (CW) prior to CO2 injection on oil recovery by CO2 and CO2-WAG injection scenarios. For this aim, a series of integrated high-pressure and high temperature coreflood, micromodel and IFT experiments were performed using live crude oil. Coreflooding tests indicate that the preflush of CW improved the sweep efficiency of CO2 injection by 6.6% of the original oil in place. According to micromodel experiments performed under the condition of coreflood tests, during CWI period, CO2 partitioning from CW into the remained oil led to oil swelling, which in turn led to an increase in the remained oil saturation. Oil swelling also led to rupturing of the water layers shielded isolated oil ganglions and thus reconnection of isolated oil ganglions. Due to these changes, more oil will be accessible to the CO2 stream which in turn can favor the CO2 recovery performance. More importantly, IFT experiments showed that the preflush of CW impacts the interfacial tensions between the fluids (oil-water-CO2) and the spreading coefficient. Preflush of CW shifted the spreading coefficient from a negative value to a positive value. In a water-wet system, this shift maximizes the oil spreading or surface contact area between the CO2 and oil, and consequently favors the oil recovery performance of CO2 injection.