3D MODELLING AND FLUID FLOW SIMULATION WITHIN DEFORMATION BANDS IN CARBONATE GRAINSTONES

In this study, we investigate the pore-network properties and the permeability of deformed porous carbonate grainstones located in Sicily and Abruzzo regions (Italy). Even though the studied rocks present similar values of porosity, their permeability varies between three to four orders of magnitude. In order to explain this difference in permeability, a three-dimensional (3D) quantitative analysis of the morphological and textural properties (i.e. porosity, specific surface area, pore connectivity) of the porous phase. The 3D images used for this analysis were acquired by means of synchrotron-based X-ray computed microtomography (micro-CT) technique. In addition, the segmented X-ray micro-CT images were used as input data for a simple-phase fluid flow pressure-driven fluid flow simulations implementing the Lattice-Boltzmann Method (LBM). The Bhatnagar-Gross-Krook (BGK) collision operator, with a single relaxation parameter, Ω, was implemented, in combination with the Bounce-Back rule. Once the simulation reached a steady state condition, the permeability values of DBs and surrounding host rock were estimated applying the Darcy’s law. Permeability results were validated by comparing with in situ air mini-permeameter measurements previously reported in literature.

Results indicate that within the porous host rocks, the effective porosity and the specific surfaces area have the main control on permeability. Moreover, the specific surface area variation between the studied grainstones explains the permeability differences in despite of their similar porosity values. Within the DBs, the effective porosity generally decreases due to the combination of compaction and cementation processes causing a reduction of permeability in comparison with the surrounding host rock. However, pore dissolution and fracturing cause a local enhancement of permeability if they are present within DBs. Consequently, permeability is highly anisotropic offering a preferential permeability enhancement in a direction parallel to the DB strike.