OPTIMIZING CO₂ AND N₂ MISCIBLE GAS INJECTION FOR ENHANCED OIL RECOVERY IN THE LOWER INDUS BASIN, A SIMULATION STUDY

The depletion of oil reservoirs worldwide has led to the increased importance of enhanced oil recovery (EOR) techniques to maximize production from mature fields. This study focuses on optimizing CO₂ (Carbon di oxide) and N₂ (Nitrogen) miscible gas injection strategies for enhanced oil recovery in the Lower Indus Basin of Pakistan. Using advanced reservoir simulation techniques, the study aims to determine the optimal injection rates for maximizing oil recovery. This study evaluates the potential of both CO₂ and N₂ injection at variable injection rates as methods of recovering oil from the same depleted reservoirs Both injection gases were injected at similar injections rate using the same injection patterns so that a fair comparison can be conducted. The results indicate that there is a considerable difference in the efficiencies of recovery between the injection of CO₂ and N₂. For low injection rates (LIRs) of CO₂, there is a consistent increase in the recovery factors, in which the miscibility of CO₂ with oil is better than others. The recovery factors for CO₂ at those rates trended increasingly better, thus establishing CO₂ as an efficient technology for EOR in depleted reservoirs. On the other hand, the injection of N2 resulted in slight increases in oil recovery and having the advantage of pressure support, but it was observed immiscible with oil, which formed a very severe restriction to its displacement. More differences are revealed while comparing HIRs for both gases. The increase in rates of CO₂ injection were accompanied by the correlative increase in rates of oil displacement and in the recovery factors in all scenarios, which proved CO₂ to be one of the very effective EOR methods. Injecting N2 at higher rates was also somewhat problematic concerning efficiency in oil recovery. Although higher N2 rates improved maintenance of reservoir pressure, the resulting oil displacement was less than that from CO2. High operational costs were another concern that high injection rates (HIRs) of N₂ brought forth, and the question that arose was whether it was economically feasible compared to the great benefits that CO₂ achieved. These results emphasize the fact that the right injection gas method should be chosen so as to recover maximum oil content, and in this regard, CO2 has been proven to be a better one at HIRs in this region.