Minimum miscibility pressure of CO₂ and oil evaluated using MRI and NMR measurements

The minimum miscibility pressure (MMP) between CO₂ and crude oil is a critical parameter for CO₂ enhanced oil recovery (EOR). Whilst different methodologies have been employed to determine MMP, these methods are either time-consuming or unable to be executed in the actual rock core samples from the relevant reservoir and as such, do not directly consider any accompanying kinetic effects. Here we consider a range of nuclear magnetic resonance (NMR) measurement techniques performed on a benchtop NMR apparatus in terms of their ability to estimate MMP; specifically 1D imaging, self-diffusion measurements and T₁/T₂ relaxation measurements. Such MMP measurements were performed on two model oils (decane and hexadecane), allowing for validation against comparable MMP literature data, and a local crude oil sample – in this case the results were compared against a PVT measurement performed using a high-pressure variable volume cell (VVC). Reasonably good agreement with these alternative sources of MMP data were realized via NMR measurements of self-diffusion; these provided consistent estimates of MMP for a wider range of oils when compared to 1D imaging and NMR relaxation measurements. NMR T₂ measurements however performed equivalently to self-diffusion measurements for higher viscosity fluids based on the limited number of samples studied; such measurements require much simpler NMR hardware and are more readily accessible in both the laboratory and in the field.