EXPERIMENTAL ANALYSIS OF OIL DISPLACEMENT BY HYBRID ENGINEERED WATER / CHEMICAL EOR APPROACH IN CARBONATES

Abstract

Fast depletion in oil reserves has steered the petroleum industry towards developing novel enhanced oil recovery (EOR) techniques to get the most out of reservoirs. The standalone EOR methods such as engineered water flooding (EWF) and chemical EOR (CEOR) have associated merits and demerits. In this study, hybrid approaches utilizing engineered water (EW) and CEOR methods are investigated and the underlying mechanisms e.g., wettability alteration, interfacial tension (IFT) reduction, and mobility control are evaluated. Finally, the critical parameters influencing the performance of hybrid methods and criteria for selection of a hybrid method are presented. The hydrolyzed polyacrylamide polymer viscous and viscoelastic properties were analyzed as a function of pH. The effect of crude oil aging and temperature on wettability modification by EW was assessed by measuring contact angles. Various combinations of EW and CEOR were designed, and oil displacement tests were carried out to select the best formulation. Three coreflood tests were conducted to evaluate the effect of initial wettability on EW performance. Next, the hybrid EW/surfactant/polymer flooding (EWSPF) was performed and finally EW / alkali / surfactant/polymer flooding (EWSPF) was evaluated in slug-wise and continuous injection modes. All the coreflood experiments were conducted at 80 oC. The optimum pH range for the best polymer performance in terms of viscous and viscoelastic behavior was found to be 7-10. The contact angle measurements confirmed that EW was not suitable for water-wet reservoirs. A larger wettability shift towards water-wet condition by EW was observed at high temperature. The overall incremental oil recovery by hybrid EWPF in oil-wet medium was 16-20% higher compared to water-wet medium. Hybrid EWSPF provided additional oil recovery of 29% of original-oil-in-place (OOIP), comparable to hybrid EWPF. The best combination in terms of oil recovery and chemical consumption, was the hybrid EWASP flooding in slug-wise injection mode. This scheme resulted in 36% OOIP incremental recovery, 7% higher than EWPF and EWSPF scenarios and 3% higher than EWASP flooding in continuous injection mode. The overall performance of all hybrid combinations was better compared to their individual counterparts, as investigated by capillary desaturation tendency. These results are helpful in selection of a hybrid EOR method for a particular carbonate reservoir. The criteria for the implementation of EW based hybrid methods must include the assessment initial wettability of the rock, acid number of the crude oil, reservoir temperature, and compatibility between designed EW and chemicals.