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Abstract:Modern scanning electron microscopes often include software that allows for the possibility of obtaining large format high-resolution image montages over areas of several square centimeters. Such montages are typically automatically acquired and stitched, comprising many thousand individual tiled images. Images, collected over a regular grid pattern, are a rich source of information on factors such as variability in porosity and distribution of mineral phases, but can be hard to visually interpret. Additional quantitative data can be accessed through the application of image analysis. We use backscattered electron (BSE) images, collected from polished thin sections of two limestone samples from the Cretaceous of Brazil, a Carboniferous limestone from Scotland, and a carbonate cemented sandstone from Northern Ireland, with up to 25,000 tiles per image, collecting numerical quantitative data on the distribution of porosity. Images were automatically collected using the FEI software Maps, batch processed by image analysis (through ImageJ), with results plotted on 2D contour plots with MATLAB. These plots numerically and visually clearly express the collected porosity data in an easily accessible form, and have application for the display of other data such as pore size, shape, grain size/shape, orientation and mineral distribution, as well as being of relevance to sandstone, mudrock and other porous media.

High-speed neutron tomographies (1-min acquisition) have been acquired during water invasion into air-filled samples of both intact and deformed (ex situ) Vosges sandstone. Three-dimensional volume images have been processed to detect and track the evolution of the waterfront and to calculate full-field measurement of its speed of advance. The flow process correlates well with known rock properties and is especially sensitive to the distribution of the altered properties associated with observed localized deformation, which is independently characterized by Digital Volume Correlation of X-ray tomographies acquired before and after the mechanical test. The successful results presented herein open the possibility of in situ analysis of the local evolution of hydraulic properties of rocks due to mechanical deformation.

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The Anschutz Ranch East Field is a large asymmetric anticlinal trap in the Wyoming-Idaho-Utah thrustbelt of the western USA. The aeolian Jurassic Nugget Sandstone reservoir unit is a layered sequence of dunes and stratigraphically flat interdunes. This interpretation is supported by patterns of reservoir performance in the gently-dipping, nearly planar backlimb of the fold where there is little structural deformation. Structural features which developed during emplacement of the Anschutz Ranch East truncation anticline are partially dependent on the distribution of lithofacies, and the changes in rock properties which result from the deformation are overprinted onto the pre-existing rock properties. An extensive coring programme demonstrates that most of the strain in the Nugget Sandstone is in the crest and forelimb of the fold. Throughout the structure, the deformation is primarily of the compactive (sealing) type, leading to lowered porosities and permeabilities, and thus both to degraded reservoir quality and to flow barriers. Structurally-created low-permeability zones are identified or interpreted at a range of scales, and production histories provide sufficient evidence to establish the role of the larger features as flow partitions.