Understanding the physics behind which CO2 and water displaces oil in porous medium is of upmost importance for the success of any miscible CO2 WAG injection project. Coreflood experiments have to be designed efficiently to provide relevant information about complex three-phase flow mechanisms and ensure precise measurements of key reservoir parameters such as trapped gas saturation, CO2 relative permeability curves and hysteresis effects.
This paper presents an experimental study to investigate the effect of miscible cyclic CO2 injection on three phase relative permeability by performing a series of coreflood experiments in horizontal carbonate cores with light oil from a Middle East field. These experiments are designed using innovative data acquisition techniques to ensure data quality and allow accurate determination of reservoir microscopic properties. Produced volumes are monitored to provide material balance of each phase at both reservoir and laboratory conditions with a clear separation of flashed oil, condensate and gas. A full compositional analysis is then performed, using gas chromatography and liquid analysis of flashed oil and condensate, providing essential information for recovery calculation. Differential pressure across the core is also monitored for relative permeability estimation. Finally, in-situ saturation profiles are acquired in real time during experiments, using an X-Ray scanner capable of generating the two spikes of energy necessary for three-phase calculations. Redundancy in measurements, along with rigorous accounting of measurement uncertainties, allows a successful cross-check of all acquired data.
Methods of saturation estimation are discussed. Results show that for miscible corefloods, recovery strongly depends on how swelling and stripping mechanisms are accounted for.