CO2 enhanced gas recovery (CO2-EGR) technology can exploit more natural gas fuels from the depleted gas reservoir and simultaneously sequestrate CO2 into the underground formation. The perforation position of CO2 injection well and injection parameters play key roles to the natural gas recovery of CO2-EGR applications. In this work, CO2-EGR simulations in a quarter of square ‘five-spot’ well arrangement of a depleted natural gas reservoir were carried out with perforation positions of CO2 injection well at the bottom, middle and top layers of the reservoir model. The optimal perforation position is determined as the top layer of the reservoir, and the reason should be attributed to the accelerated vertical displacement due to the gravity effect. Moreover, an optimization method was built by integrating genetic algorithm (GA) and TOUGH2 for the determination of the optimal injection rate. The optimal injection rate of CO2 is obtained as 0.0824 kg/s while the perforation is set at the top layer of the reservoir, and the final natural gas recovery achieves up to 65.37%. This work provides some insight for the CO2-EGR employment in the depleted natural gas reservoirs.
Keywords CO2 enhanced gas recovery, perforation position, genetic algorithm, optimization