Experimental Investigation of Various Methods of Tertiary Gas Injection

Abstract

Abstract Water alternating gas (WAG) injection is widely practiced for improved light oil recoveries. In this experimental study, we compare the WAG process against the continuous gas injection (CGI) process by conducting tertiary mode miscible and immiscible corefloods. Inferences resulting from performance evaluations using ‘conventional’ tertiary recovery plots were found inappropriate. Therefore, a new parameter ‘Tertiary Recovery Factor’ (the oil recovery per unit volume of gas injected) was defined, and used in conjunction with the CO2 utilization factor, for the evaluation of tertiary coreflood recoveries. The definition of TRF not only helped to demonstrate experimentally that miscibility development has a positive effect on oil recovery, but also showed that the WAG mode of injection is better than Continuous Gas Injection (CGI) when overall performances are considered. The WAG floods demonstrated continual increase in the TRF throughout the life of the flood, however, for CGI miscible flood, TRF crested at about 0.6 PV injection and later declined with increasing gas injection. These plots demonstrate that the WAG process has better CO2 utilization efficiency compared to CGI. These results indicate that optimum performance could be obtained by a combination of CGI and WAG modes of gas injection. This paper provides conceptual analysis and experimental demonstration of WAG, CGI and their combination at reservoir conditions.