Non-equilibrium Based Compositional Simulation of Carbonated Water Injection EOR Technique

Abstract

Carbonated water injection (CWI) is an augmented water injection strategy, which has great potentials for EOR and CO2 storage purposes. When carbonated water, CO2 enriched water, is injected into oil reservoirs, due to higher CO2 solubility in oil compared to that in water, CO2 migrates from carbonated water into oil. This improves oil mobility, due to swelling and viscosity reduction, which consequently increases oil production. Our core flood experiments show that during CWI, CO2 is transferred and distributed between water and oil gradually and thermodynamic equilibrium is not reached. Available compositional reservoir simulators, which are based on the instantaneous equilibrium assumption, do not capture the actual physics of CWI. In this work, a non-equilibrium based compositional simulator was developed to simulate the performed core flood CWI experiments more realistically. The developed two-phase flow simulator is currently suitable for one dimensional core experiments. It includes a mass transfer term to capture the kinetics of CO2 transfer between phases. Governing equations were derived based on the water, oil and CO2 components balance, and solved using the fully implicit finite difference technique. Black-oil (without mass transfer) and compositional (with mass transfer) modes of the simulator can be used for simulation of conventional water injection (WI) and CWI, respectively. A genetic algorithm based optimization software was also developed that can be linked to the simulator to history match the available production data and obtain the unknown parameters of the model. The simulator was used to model WI and CWI coreflood experiments conducted on a water-wet sandstone core fully saturated by Decane (with well-defined fluid properties). First, the WI experiment was simulated when an oil-water relative permeability (kro-w) was obtained by history matching of WI production data. The WI test was re-simulated by ECLIPSE100 (E100) commercial simulator using optimized kro-w. E100’s predictions of production data reasonably matched model’s results, which verify its integrity. Next, the obtained kro-w was used for simulation of CWI. Mass transfer coefficient, as the only remaining unknown parameter, was tuned to match the available CWI production data leading to an acceptable match. The simulator shows promising potentials for simulation and better understanding of CWI for practical field applications. Moreover, the structure of this simulator offers a solid foundation for other EOR methods where kinetics of mass transfer is important.