Logging-while-coring – new technology for the simultaneous recovery of downhole cores and geophysical measurements
D. Goldberg, G. Myers, G. Iturrino, K. Grigar, T. Pettigrew, S. Mrozewski, 2006. "Logging-while-coring – new technology for the simultaneous recovery of downhole cores and geophysical measurements", New Techniques in Sediment Core Analysis, R. G. Rothwell
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A newly developed logging-while-coring system was deployed during Ocean Drilling Program legs 204 and 209 off the coast of Oregon and near the Mid-Atlantic Ridge. The system consists of two existing devices modified to be used together — a Schlumberger Resistivity-at-the-Bit* tool, and a Texas A&M University wireline-retrieved core barrel and latching tool. The combination allows for precise core-log depth calibration and core orientation within a single borehole, and without a pipe trip. These tests, conducted in clay-bearing sediments (Leg 204) and in crustal peridotite and gabbroic rocks (Leg 209), mark the first simultaneous use of coring and logging-while-drilling technologies. Sediment cores were recovered with 33% recovery, on average, and as high as 68% to 75 m depth below the sea floor. Core recovery in crustal rocks was only 1–2%, however, penetrating to 21 m depth below sea floor, which is attributed to a problem with the core catcher. High-resolution logs were recorded in the downhole tool memory over the entire drilled intervals at both test sites. It is anticipated that logging-while-coring systems will be utilized more routinely where rig time constraints may otherwise preclude coring in difficult drilling environments.
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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.