Prediction of nitrogen diluted CO2 minimum miscibility pressure for EOR and storage in depleted oil reservoirs

Abstract

Injection of CO2 into depleted oil reservoirs can result in incremental oil recovery to help offset the cost of CO2 storage. This paper presents a thorough study of the effects of nitrogen on CO2 minimum miscibility pressure (MMP) for CO2 storage in depleted oil reservoirs. Nitrogen diluted CO2 MMPs for 55 model oil samples were calculated using the Peng–Robinson Equation of State (PR EOS) in the temperature range of 305–360K. Based on the modeling results, an analytical equation has been developed for predicting the ratio of impure CO2 MMP to pure CO2 MMP, Fimp. In this equation, Fimp is expressed as a function of the pseudo-critical temperature of the impure CO2, the critical pressures of CO2 and N2, and the reservoir temperature. For oil samples with molecular weights lower than a certain minimum value (Mmin) at various temperatures, a chart has been created for supplying a coefficient in the equation. Compared to commonly used Fimp correlations in the literature, this new correlation yields a more accurate match to the Fimp data found in the literature.