The understanding of petrophysical and multiphase flow properties is essential for the assessment and exploitation of hydrocarbon reserves; these properties in turn are dependent on the 3D geometric and connectivity properties of the pore space. The determination of the pore size distribution in carbonate rocks remains challenging; extreme variability in carbonate depositional environments and susceptibility to a range of post-depositional processes results in complex pore structures comprising length scales from tens of nanometers to several centimeters. To increase understanding of the role of pore structure on connectivity, conductivity, permeability and recoveries requires one to probe the pore scale structure in carbonates in a continuous range across over seven decades of length scales (from 10 nm to 10 cm) and to integrate information at these different scales. In this paper experimental techniques including micro-computed tomography, backscattered scanning electron microscopy (BSEM), and Focussed ion beam SEM (FIBSEM) are used to probe the pore scale structure in carbonates across many decades of scale. Registration techniques are then used to couple information at different length scales. First an image of a 3D plug (4 cm, 20 micron voxel size) is correlated to a sample at macroporous resolutions (8 mm diameter, 4 micron voxel size). We then focus on coupling SEM and FIBSEM data at submicron resolutions to micro-CT data at ≈ 3–5 micron resolution. For pixel perfect registration of SEM images, an accurate template has been developed to remove warp artefacts introduced by the SEM scanning procedure and we have successfully mapped the sub-resolution porosity and pore sizes visible in the SEM image to gray scale levels in the 3D image. FIBSEM also allows one to investigate the 3D structure in samples down to tens of nanometers. We briefly discuss how this multiscale information can be used as a method for enhanced analysis of petrophysical properties of carbonates.
The structure and dynamics of carbonate reservoirs are of crucial importance to the oil and gas industry as carbonate reservoirs are believed to contain more than half the world's oil. Predicting petrophysical and multiphase flow properties in carbonates is challenging due to the nature of the deposition and diagenesis which results in pore scale features and heterogeneity at multiple length scales. To better understand the properties of carbonates information on the range of pore scales must be obtained; in principle, at scales from tens of nanometers to metres (Biswal etal., 2007). In this paper we describe the ongoing development and integration of a range of experimental and computational tools which can assist one in probing the pore scale structure of carbonates across many decades of scale in an integrated fashion. We focus on integrating geological heterogeneity from the 4 centimetre (plug) scale to the 100nanometer scale.
This section describes the 3D tomographic, the 2D BSEM and the 3D FIBSEM experiments, as well as the computational procedures used to analyse the data.
Plug samples of carbonate core were received in the laboratory.