Feasibility Analysis of Ethane and Flue Gas Injection for Enhanced Oil Recovery with a Niger Delta Case Study

Abstract

Enhanced oil recovery (EOR) using ethane gas or flue gas has proven to be successful in some regions of the world, but these methods have not been implemented in the Niger Delta. This work investigates the technical and economic prospects of using ethane gas and flue gas injection for EOR in the Niger Delta. The motivation for this work is to find ways to monetize stranded gas reserves. The data from the Niger Delta case study was collected to screen for a candidate reservoir suitable for the application of ethane and flue gas injection. Firstly, the fluid was characterized using commercial PVT software. Secondly, the minimum miscibility pressure which is an important parameter in every miscible gas EOR was obtained using published correlations and simulation of slimtube experiment. Peripheral drive simulation model was developed using the data from the Niger Delta to investigate the techno-economic feasibility of applying ethane and flue gas EOR in the candidate reservoir. To determine the technical feasibility of gas injection, three production scenarios were evaluated during the numerical simulation of the reservoir performance. The first scenario is a 20-year simulation of the continuous production from the reservoir under natural depletion to serve as the reference case. The second scenario involves the injection of pure ethane gas, and the third scenario is ethane water- alternating-gas (WAG) injection whereby a slug of ethane gas is injected into the reservoir followed by water injection. The ethane gas-water injection cycle was repeated for a total period of 20 years. The three production scenarios (natural depletion, gas injection, and WAG process) were repeated using flue gas instead of ethane gas as the injectant in the second set of simulations of the case study. The injection rate of pure ethane and flue gas was 4MMscf/day. This same gas injection rate was used for the ethane WAG and Flue gas WAG followed by 3000 stb/day rate of water injection per WAG cycle. The results showed significant improvement in cumulative oil recovery from the EOR application compared to the natural depletion. A cumulative recovery of 46.7% of the stock tank oil initiallyin place (STOIIP) was obtained from ethane injection. The flue gas injection, ethane WAG and flue gas WAG yielded a cumulative recovery of about 48% of the STOOIIP compared to the reference case of natural depletion with a cumulative oil recovery of 34.3% of the STOIIP. The annual oil production was used as input in an economic analysis of the Niger Delta case study to evaluate the economic feasibility of ethane and flue gas injection in the region. The results showed that both ethane gas and flue gas EOR are technically feasible because they yielded a higher cumulative oil recovery compared to the natural depletion. It was also observed that both ethane and flue gas EOR processes are economically feasible; but flue gas EOR is more economically viable than ethane injection EOR. The economic advantage of the flue gas over the ethane gas EOR can be attributed to the high cost of the gas plant required to process the ethane gas needed for the injection. The methods and results of this study form the basis and can be considered a starting point for detailed investigation to the application of ethane and flue gas EOR as an option for utilization of gas injection in the Niger Delta.