3D Pore Scale Characterisation of Carbonate Core: Relating pore types and interconnectivity to petrophysical and multiphase flow properties

Carbonate rocks are diverse and their pore space complex. Large scatter in petrophysical and multiphase properties of carbonates is caused by the variation in pore type, pore interconnectivity and the microporosity. To date the classification of the interconnectivity of the different pore types and pore shapes and their relative contribution to flow, electrical and displacement properties has been made on the basis of visual inspection and 2D thin section analysis. In this paper we present a 3D image and analysis study of a range of carbonate core material at a 3 micron scale. The 3D interconnectivity of the vugs, macropores, and meso/micropores is directly characterized. We undertake simulations of resistivity (m and n) and drainage capillary pressure directly on the image data under various wettability conditions. Prediction of drainage capillary pressure, m and n from image data are compared to laboratory measurements where available on the same core material and found to be in good agreement. The role of different pores and their interconnectivity are correlated to the behaviour of m and mercury injection capillary pressure for different cores. The distribution of fluids during drainage are directly probed within the 3D pore space via experimental and numerical methods. A strong complexity and variability in the RI curves for different carbonates is noted under different wettability conditions. The implications of structure and topology to relative permeability and ultimate recovery are also discussed.