Experimental investigation of miscible and immiscible Water-Alternating-Gas (WAG) process performance

When oil recovery per unit volume of gas injection was used as a parameter to evaluate the floods, the WAG mode of injection out-performed the CGI. As expected the miscible floods were found to out-perform the immiscible floods. At increased volumes of gas injection, the performance of miscible CGI flood, in spite of the high injection pressure, approached that of the low-pressure immiscible floods. A change in brine composition from 5% NaCl to 0.926% multivalent brine from Yates reservoir showed a slight adverse effect on tertiary gas flood recovery due to increased solubility of CO2 in the latter. The results of this study suggest that the optimum mode of gas injection is a combination process between CGI and WAG modes of gas injection.