On-site geological core analysis using a portable X-ray computed tomographic system
Barry M. Freifeld, Timothy J. Kneafsey, Frank R. Rack, 2006. "On-site geological core analysis using a portable X-ray computed tomographic system", New Techniques in Sediment Core Analysis, R. G. Rothwell
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X-ray computed tomography (CT) is an established technique for non-destructively characterizing geological cores. CT provides information on sediment structure, diagenetic alteration, fractures, flow channels and barriers, porosity and fluid-phase saturation. A portable CT imaging system has been developed specifically for imaging whole-round cores at the drilling site. The new system relies upon carefully designed radiological shielding to minimize the size and weight of the resulting instrument. Specialized X-ray beam collimators and filters maximize system sensitivity and performance. The system has been successfully deployed on the research vessel JOIDES Resolution for Ocean Drilling Program’s legs 204 and 210, at the Ocean Drilling Program’s refrigerated Gulf Coast Core Repository, as well as on the Hot Ice #1 drilling platform located near the Kuparuk Field, Alaska. A methodology for performing simple densiometry measurements, as well as scanning for gross structural features, is presented using radiographs from ODP Leg 204. Reconstructed CT images from Hot Ice #1 demonstrate the use of CT for discerning core textural features. To demonstrate the use of CT to quantitatively interpret dynamic processes, we calculate 95% confidence intervals for density changes occurring during a laboratory methane hydrate dissociation experiment. The field deployment of a CT represents a paradigm shift in core characterization, opening up the possibility for rapid systematic characterization of three-dimensional structural features, and leading to improved subsampling and core-processing procedures.
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Marine sediment cores are the fundamental data source for information on seabed character, depositional history and environmental change. They provide raw data for a wide range of research including studies of climate change, palaeoceanography, slope stability, oil exploration, pollution assessment and control, seafloor survey for laying cables, pipelines and construction of seafloor structures. During the last three decades, a varied suite of new technologies have been developed to analyse cores, often non-destructively, to produce high-quality, closely spaced, co-located downcore measurements. These techniques can characterize sediment physical properties, geochemistry and composition in unprecedented detail. Palaeoenvironmentally significant proxies can now be logged at decadal, and in some cases, annual or sub-annual scales, allowing highly detailed insights into climatic history and associated environmental change. These advances have had a profound effect on many aspects of the Earth Sciences and our understanding of the Earth's history.
In this volume, recent advances in analytical and logging technology and their application to the analysis of sediment cores are presented. Developments in providing access to core data and associated datasets, and advances in data mining technology in order to integrate and interpret new and legacy datasets within the wider context of seafloor studies are also discussed.