Relative permeability is a critical parameter in reservoir engineering calculations and performance predictions using numerical simulation. Little has been published on the effect of core-scale heterogeneities on relative permeability. Small-scale rock heterogeneity can lead to directional-, length-scale dependent relative permeabilities, and distinct hysteresis characteristics.
This report presents relative permeability and capillary pressure data on a core that is characterized by millimeter-scale parallel laminated bedding. The core was characterized using petrographic analysis CT scanning, and minipermeametry. Anisotropy of relative permeability is demonstrated by comparing relative permeability measurements on a plug drilled parallel to the laminations with those of a plug drilled normal to the laminations. Steady-state and unsteady-state oil-water relative permeability data were collected using X-ray Scanning for insitu fluid saturation measurement. Measured secondary drainage curves show distinctive characteristics when the principal flow is parallel to laminations as compared to flow normal to the laminations. Porous plate and centrifuge capillary pressure measurements illustrate differential drainage and imbibition among laminations.
These results demonstrate relative permeability anisotropy attributed to capillary pressure contrast among small-scale laminations. The directional variability is not apparent from single-phase directional permeability measurements. Core plugs with more isoptropic permeability distribution show reduced impact of small-scale heterogeneity.
Using numerical simulation, a number of recent papers have shown that geologic heterogeneity at the core scale can impact reservoir-scale flow behavior. The ultimate goal of the work presented here is to improve the accuracy of simulated predictions of hydrocarbon recovery with relative permeability data that more accurately reflect the effective flow characteristics. The results provide valuable physical insight for relative permeability scale-up from which we make important conclusions relevant to choice and use of special core analysis.
This paper presents oil-water relative permeability data for primary drainage, imbibition, and secondary drainage for core plugs for which detailed characterization data were collected.