Correlation for miscible flood displacement efficiency in the San Andres with NMR relaxation

A set of San Andres crystalline dolomite cores was examined for the relationship between pore attributes discernible from NMR relaxation and miscible flooding displacement efficiency. A strong correlation was observed between the inferred abundance of long relaxation time components and laboratory measured residual oil to a multicontact miscible displacement process. NMR relaxation time distribution proved to be a simple, noninvasive, nondestructive indicator of flow performance in the 12 San Andres dolomite samples examined. Spin-lattice relaxation measurements were conducted on clean, brine saturated core end pieces from plugs taken adjacent to those used for flow displacement studies. Sample data were deconvoluted into a distribution of relaxation times, which is intimately related to surface-to-volume ratio distribution. The median relaxation times was determined to be the most sensitive statistic to convey flow performance. Residual oil saturation was adequately represented by a power law function of the median relaxation time. Relaxation time is recognized to be a function of pore size, shape, surface roughness, and mineral composition. It was determined through direct observation by scanning electron microscopy that variation between samples was principally due to pore size distribution. Samples with larger mean pore size were observed to be less efficiently swept. Larger pores within a distribution are envisioned to bias individual fluid flow pathways, causing significant stranding of oil.