PORE-SCALE SIMULATION OF TRANSPORT PROPERTIES OF CARBONATE ROCKS USING NANOSCALE FIB-SEM 3D IMAGES

The pore structure of a carbonate rock sample collected from Thamama B gas reservoir located in Abu Dhabi was imaged using focused ion bean - scanning electron microscopy (FIB-SEM). The 3D image (27.72 × 26.64 × 33.75 µm) at 9 nm pixel resolution was used as an input to the Naiver-Stokes equation solver of Comsol Multiphysics software to calculate the absolute permeability and effective diffusivity of gases (H₂S, CO₂, CH₄). Calculated effective diffusivities were used to derive tortuosity values for the three spatial directions of the pore structure. The widely employed correlation: τ = D⁰ ϕ/ D^eff used to calculate tortuosity (τ) as function of simulated effective diffusivities (D^eff) leaded to inaccurate tortuosity values. On the other hand, absolute permeability values derived from pore-scale simulations using Darcy's equation has been confirmed to reproduce measured permeability values. Pore-scale simulations are emerging as an important alternative to directly estimate the transport properties of porous media. However, given the limitations on the rock sample size that can be analyzed using current FIB-SEM methods and high computational demand to perform simulations at the nanoscale level, this presentation aims to highlight the constraints and challenges in estimating transport properties of carbonate rocks using direct numerical simulations at the nanoscale level.