Micro-CT facility for imaging reservoir rocks at pore scales

A micro-CT facility for imaging, visualizing and calculat- ing sedimentary rock properties in three dimensions (3D) is described. The facility is capable of acquiring 3D X- ray CT images made up of 20003 voxels on core plugs up to 5 cm diameter with resolutions down to 2 μm. This allows the 3D pore-space of a rock to be imaged across several orders of magnitude. In parallel with standard microscopic techniques, the spatial distributions of different mineralogies can be identified. We demonstrate the capabilities by imaging a reservoir carbonate core at different resolutions. First, an image of a 4 cm diameter plug is analysed at a resolution of 42 μm. This allows one to deduce the size, shape and spatial distribution of the disconnected vug porosity. Within the imaged volume over 30000 separate vugs are identified and a broad vug size distribution is measured. From higher resolution images (2.5-20 μm) on a 5 mm diameter subset of the core one can measure characteristic (intergranular) pore sizes. The apparent porosity of the core increases with enhanced image resolution. This behaviour implies a continuum of pore sizes exist within the core at these resolutions. Carbonate sediments have been conventionally described by a discrete bi- or tri-modal pore size distribution; in contrast our analysis exhibits no distinct pore sizes but a broad distribution of pore size spanning over more than two orders of magnitude.