AAPG Annual Convention and Exhibition

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Multi-Length Scale Investigations of Carbonate Heterogeneity


In the modern geosciences, questions of length scale are becoming increasingly relevant. With the rapid growth in carbonate research, selecting the correct length scale is of critical importance due to the variety of features present in these samples and their various sizes and spatial distributions. Carbonates are also highly heterogeneous, which further complicates the problem: the features may be quite localized and achieving representative volume elements is very difficult using traditional techniques. A multi-length scale investigational approach is required in order to properly characterize these specimens, capable of capturing a representative elementary volume (REV) at each length scale. This is currently achieved through a combination of industrial CT with micro-CT, nano-CT, and electron microscopy. Here, we present an extension of the X-ray computed tomography approach to the novel platform of X-ray microscopy (XRM). The XRM technique uses a system of light- and/or X-ray optics to produce a precise image of geological microstructures, with tunable fields of view up to 10s of mm and tunable resolutions down to the 10s of nm. We then demonstrate how this technique may be extended to the highest-resolution approaches of focused ion beam coupled scanning electron microscopy (FIB-SEM). Modern XRMs and FIB-SEMs are also enabling material identification, captured both structure and composition within one specimen. The intrinsic non-destructive nature of X-ray imaging is particularly attractive due to its natural preservation of the sample during imaging for multi-length scale and in situ experimentation. This allows for multiple regions of interest to be virtually extracted from larger plug specimens via the technique of interior tomography, allowing the fine details of pore networks to be examined without the disruptions of sectioning techniques. Coupling the multi-length scale approach with the technique of interior tomography (“Scout and Zoom”) allows targeted high resolution scans, delivering a more efficient utilization of imaging times and potentially reduced time to results. The non-destructive nature is also giving rise to novel flow studies and geomechanics investigations in situ, enabling simultaneous model generation and validation on the same sample as a function of time, in a so-called “4D” approach. Some preliminary examples of interior and 4D flow-cell studies will also be presented.