Magnetic resonance imaging of enhanced oil recovery processes in porous rocks
University of New Brunswick
Magnetic resonance imaging methods were employed to investigate fluid/pore surface interactions in enhanced oil recovery processes. The spin echo – single point imaging method was utilized to image fluid content and transverse relaxation time constant distribution along core plugs in water-shock and CO2 flooding experiments. Physical parameters dependent on the wetted pore surface area were reported in each experiment. In the water-shock experiments, the permeability spatial profile was calculated for fines migration in Berea core plugs. CO2 flooding of decane-saturated core plugs was performed under miscible and immiscible conditions. Under miscible conditions, the density of decane in the bound fluid layer was reduced with drainage by CO2. However, in the immiscible drainage of decane by CO2, the surface area wetted by decane did not decrease until the residual decane saturation was reached. It is hypothesized that decane forms non-continuous wetting films on the pore surface below the residual oil saturation during the drainage process. Partial derivatives of decane saturation were acquired with a smoothing spline interpolation and processed to compute saturation wave velocity, dispersion coefficient, and the advection-dispersion kernel. It was possible to observe leading and trailing shocks in the CO2 displacement of decane in a Berea core plug. Finally, building on the analysis of transverse relaxation time constant T2 distributions in rocks, it was recognized that non-ground eigenstates contribute to the relaxation of homogeneous magnetization of rocks in magnetic resonance relaxation experiments. This significant finding makes possible to calculate the confinement size of porous materials using magnetic resonance relaxation methods without any calibration. Several examples demonstrate the validity of this finding.