HR: 0800h
AN: PP11A-0205    [Abstracts]
TI: Improving the Accuracy of Core Location and Recovery Estimates Through the Integration of Core Data, Wireline Logs and Drilling Parameters: an Example From IODP Expedition 310, Tahiti Sea Level
AU: * Inwood, J
EM: ji18@le.ac.uk
AF: University of Leicester, Department of Geology, University Road, Leicester, LE1 7RH, United Kingdom
AU: Brewer, T
AF: University of Leicester, Department of Geology, University Road, Leicester, LE1 7RH, United Kingdom
AU: Braaksma, H
AF: Universite Montpellier 2, Laboratoire de Tectonophysique CC49, Montpellier, 34095, France
AU: Braaksma, H
AF: Exxon Mobil, Upstream Research Company, Houston, TX N108, United States
AU: Pezard, P
AF: Universite Montpellier 2, Laboratoire de Tectonophysique CC49, Montpellier, 34095, France
AB: In palaeoclimate and sea-level studies accurate depth positioning of core pieces is critical in assessing the usefulness of a specific drill site. The location and amounts of core recovered during a drilling program can often place severe constraints on the subsequent applications of core measurements. The principle objectives of Expedition 310 are to establish the course of postglacial sea level rise at Tahiti in the South Pacific, to define sea surface temperature (SST) variations for the region over the period 20 to10 ka, and to analyse the impact of sea level changes on reef growth and geometry. Average conventionally-calculated core recovery for the 37 boreholes drilled during this expedition is 57.47 percent, although for an individual borehole core recovery is highly variable. Depth inaccuracies increase as recovery falls below 100 percent as, by convention, core is placed at the top of the core barrel run from which it was recovered. Careful integration of datasets can improve the positioning of core. The Expedition 310 logging programme included the collection of high resolution optical and acoustic images. Visual correlation of the recovered core with these image logs provides an extremely effective method of integrating these datasets. Comparison of drilling parameters (rate of drilling, pullback pressure and torque on bit) with the downhole logs indicates a clear correlation between these datasets and allows the logging data to be accurately matched to the drilling data. The final integrated depths comprise the underlying framework for all subsequent scientific analyses of recovered core employing interpretations based on depth. There are two principle outcomes of the integration process: (i) Accurate depth positioning can be achieved. In coral reefs where regions of high porosity and large void spaces are common, without careful integration of discrete core pieces with continuous records of the nature of the borehole, large depth errors can result and propagate through analyses. (ii) Core recoveries can be accurately estimated. Estimates based on core alone cannot take into consideration meso or macro scale porosities. Utilising continuous geophysical measurements allows areas of high porosity to be identified and incorporated into the calculation of recovery percentages.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0915 Downhole methods
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 4916 Corals (4220)
DE: 4994 Instruments and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting