3D Characterisation of Microporosity in Carbonate Cores

Carbonates, accounting for majority of oil and gas reservoirs, are well known for their broad, but complex, pore size distribution and pore geometries. Generally the heterogeniety of carbonates is dominated by submicron porosity. This substantially affects log measurements of petrophysical properties resulting in erroneous reserve estimation, production and recovery rates. This feature of carbonates strongly encourages the topological and morphological pore scale characterisation at the submicron level. In this paper, we use micro Computed Tom ography(μCT) and Focussed Ion Beam (FIB) microscopy to describe 3D imaging of microporosity in carbonate core samples. Micro-CT is capable of acquiring 3D images of individual cores at the macropore level down to resolutions of a few microns. However, a great limitation is that it cannot directly access microporous regions. For those regions we use Focussed Ion Beam microscopy to mill and an electron beam to image the exposed surface at a resolution down to few nanometres. FIB is employed to study the general structure of the microporosity and in particular its connectivity. This generalised structural information is then related back to the sub-resolution micro-porosity in the μCT. By combining μCT and FIB one can undertake a study of permeability and resistivity of core material incorporating both the macroporosity and microporosity over many length scales.