Miscible oil recovery utilizing N2 and/or HC gases in CO2 injection

Carbon dioxide miscible injection is one of the non-thermal effective enhanced oil recovery (EOR) methods. In the Middle East, particularly Abu Dhabi, pilot testing is already implemented in the Rumaitha Field for CO2 miscible injection. This paper investigates the means of improving CO2 miscible injection by enriching it with N2 and HC gases. The emphasis is on identifying CO2 solvent mixtures with reduced MMP to achieve miscibility at reasonable injection pressures in Abu Dhabi fields. The minimum miscibility pressure (MMP) of targeted oils from Abu Dhabi carbonate reservoirs with mixtures of N2, CH4, C2H6, and HC rich gases of varying composition with CO2 injection gas are evaluated through simulation. The first contact miscibility (FCM) and the multiple contact miscibility (MCM) of injected gases/oil mixture under reservoir temperature have been determined using WINPROP module of the Computer Modeling Group (CMG) simulator. In addition, the corresponding oil recovery factors for various N2/CO2 content displacements were calculated by 1-D compositional simulation of slim tube using BUILDER and GEM module of CMG Simulator. Results show that miscibility is predicted to occur with multiple contact miscibility (MCM): vaporization and/or condensation mechanisms. The increase of C2H6 concentration in the CO2 injected gas reduced MMPs for targeted Oil 1 by 100psi/10mol%. However, N2, CH4 and HC rich gas increments in CO2 injected gas increased the MMPs for targeted Oil 1. MMP was observed to be 2300psi for pure ethane with Oil 1. In addition, MMPs for targeted oils with N2/C2H6 and N2/CH4 injected gas mixtures are assessed. This study can open possibilities for future enriching of CO2 and N2 miscible injection to improve miscibility and recovery of oil. •MMP's of CO2 flooding enriched with N2/HC gases were predicted using CMG simulator.•Two target crude oils from Abu Dhabi carbonate reservoirs were utilized.•MMP's increase unfavorably as N2/CH4 concentration increased in the CO2 stream.•MMP's decrease favorably as C2H6 concentration increased in the CO2 stream.•The oil recovery factors for various N2/CO2 content displacements were calculated.