The Use of Synchrotron-Based X-ray Microtomography for the Pore Network Quantitative and Computational Fluid Dynamics Experiments on Porous Carbonate Rocks

In carbonates rocks, the textural properties of the pore network (e.g., pores size distribution, pores shape, pores connectivity and tortuosity), and therefore the porosity and permeability, are highly variable due to primary depositional conditions, diagenesis processes and deformation. For this reason, the quantitative characterisation of carbonate reservoirs, in terms of porosity and permeability, is challenging. This study presents a methodology for investigating the pore network in carbonate rocks using high-resolution synchrotron X-ray computed microtomography (SR micro-CT). This could be combined with computational fluid dynamics (CFD) simulations for obtaining information about fluid transport and calculated the permeability of the samples. Using key samples from rocks corresponding to porous and tight carbonates exposed in south and central Italy, the methodology has been applied to three different study cases: rapid characterisation of porous carbonate reservoirs (Abruzzo, central Italy), quantitative analysis of deformed porous carbonates (Sicily, south Italy), and pore-scale assessment of fractures hosted in tight carbonates (Murge, south Italy). Some samples may contain deformation structures (i.e. deformation bands, fractures) or may be altered by diagenesis (e.g., cementation, dissolution). The pore space can be filled by a single fluid phase (i.e. air) or multiple (i.e. bitumen and trapped gas). The selected rock samples were scanned by means of phase-contrast synchrotron SR micro-CT at the SYRMEP beamline of the Elettra synchrotron in Trieste (Italy). The tomographic images were acquired using a multi-resolution approach with a pixel size variable in the range of 1.0–2.4 μm depending on the grain size distribution of the rock sample. After reconstruction, images were filtered and segmented for characterising the pore phase. The resulting images were used for both performing a quantitative pore network analysis of the studied rock samples and CFD experiments (multiple relaxation times lattice-Boltzmann method, MRT-LBM) using the open source software PALABOS.