Experimental study on EOR performance of CO2-based flooding methods on tight oil

Abstract

The recovery of tight formation is fairly low after depletion, and the poor physical properties make it difficult for water to be injected. And when the oil is with high wax content, it is more difficult to develop. Recently, with the development of horizontal wells and multi-stage hydraulic fracturing, the problem of injectivity is solved to some extent. With these techniques improving injectivity of displacing fluids, this paper conducted a series of coreflood experiments, including CO2 flooding, water alternating gas (WAG), carbonated water injection (CWI), active carbonated water injection (ACWI) and active carbonated water alternating gas (ACWAG), to investigate the EOR performance of CO2-based methods on tight oil. Furthermore, the influences of injected volume, surfactant concentration and water-gas-ratio on recovery were investigated. It is the first time to explore the feasibility of CWI/ACWI/ACWAG on increasing the recovery of tight oil with high wax content.Experimental results revealed that ACWAG achieved the highest oil recovery (63.04%) among all methods. In addition, CWI yielded an oil recovery of 60.67% and it is the highest among WAG, CO2 flooding and CWI with the same amount of CO2 injected. ACWI reached 54.17% original oil in place (OOIP) with 0.5 pore volumes (PV) of active carbonated water injected. In this study, water-gas-ratio has not demonstrable influence on EOR performance. This paper uncovers the potential and application of CWI/ACWI/ACWAG in enhancing recovery of tight oil with high wax content.