Quantitative analysis of absolute permeability and porosity in carbonate rocks using digital rock physics

Reservoir rock properties, particularly porosity and absolute permeability, are cornerstone to any reservoir characterization project. Digital Rock Physics (DRP) is a newly emerged technique which has gained scientist's attraction to estimate petrophysical properties in sandstones reservoirs. Nevertheless, in carbonate reservoirs imaging pore structure remains challenging due to its heterogeneity at several length scales when compared to sandstone cores. This study aims to accurately characterize a carbonate core-plug from the Middle East using DRP. To achieve this, we apply multiscale imaging approach using a state-of-the-art micro-CT. After laboratory measurements, we scan whole sample with 39 µm resolution and extract a sub-plug for higher resolution scanning. We scan it at resolution of 5.25 µm, in which pore connectivity is not fully captured. Thus, we drilled a micro-plug from sub-plug and scan it at resolution of 0.39 µm. At this scale, pore connectivity is revealed from top to bottom in the 3D image. We estimate porosity of segmented micro-plug images and integrate to core-plug scale by including visible pores of sub-plug and core-plug. We use Lattice Boltzmann Method (LBM) to simulate fluid flow. We implement two approaches to examine the variability of derived permeability. First, we compute the permeability of the whole 3D micro-plug image. Second, we systematically divide the whole 3D image into small blocks and estimate the effective permeability of blocks by simulating Darcy flow through them. The porosity from images is comparable with laboratory measurements. The difference between them is 1 pu. The permeability value from first approach are in good agreement with experimental result. However, the second approach overestimates laboratory measurement by 40 percent. Yet, the results from both approaches are comparable to laboratory permeability.