14 - European Consortium for Ocean Research Drilling

ECORD Newsletter # 14 - May 2010 - www.ecord.org 19Fig. 2: Simon Barry, lead Logging Engineer from Montpellier, deploysone of the slimline logging tools during the New Jersey Shelf Expedition313 (photo Jenny Inwood © ECORD/IODP).A second data collection phase is conducted onshore at theUniversity of Bremen, prior to and during the Onshore ScienceParty (OSP). EPC is responsible for a range of core measurementsworking closely with Bremen personnel and the Science Partypetrophysicists. For the New Jersey Shallow Shelf Expedition 313,EPC was responsible for more than ten different measurementson around 1300 m of recovered core. Measurements on wholecores, prior to core splitting during the OSP, normally includenatural gamma radiation, using EPC Leicester’s Geotek MSCL-XYZ and discrete thermal conductivity measurements, using asystem provided by EPC Aachen. Once the cores are split, colourreflectance spectrophotometry, high resolution line scanning anddiscrete measurements, including p-wave velocity and moistureand density, are undertaken.In the Tahiti Sea-Level Expedition 310, high-resolution, mmscale,optical and acoustic images combined with continuousborehole geophysical measurements enabled correct core depthsto be established ensuring accurate sea-level reconstructions.The optical and acoustic image logs revealed the highly porouscharacter of the formations drilled and cored. The data determinedthat true recovery was greater than 90%, much higher than theconventionally calculated average recovery of 54.5%.Fig. 3: Amplitude acoustic image (left) of theborehole wall revealing key lithological boundariesfrom successions on the New Jersey Shelf, logged aspart of Expedition 313. The 3D images combinethis acoustic image with (middle) mean travel timesignal and (right) the magnetic susceptibility signal.Preliminaryanalysis of loggingdata from NewJersey ShallowShelf Expedition313 demonstratesthat downdepositionaldip changesin individualsequences arecharacterisedby changes inthe physicalproperties ofthe sediments,including naturalgamma radiation,magneticsusceptibility and resistivity. Continuous spectral gamma logsenable assessment of lithologies in lower core recovery intervals.Acoustic image logs provided early information on the visualcharacteristics of key surfaces before the core was split (Fig.3).Core Petrophysics on MSP ExpeditionsOffshore core logging operations are carried out by an ESOPetrophysicist, from EPC, who works alongside petrophysicists fromthe Science Party. EPC Leicester supplies a Geotek Multi SensorCore Logger (MSCL-S) system and MSCL-S measurements includegamma density, P-wave velocity, non-contact resistivity and magneticsusceptibility (Fig.4). The Petrophysics Staff Scientist completes anydata processing required, the final depth shifting and correlation ofrepeat runs within a borehole and works with the ESO Petrophysicistto integrate the downhole logging and MSCL data sets.Fig. 4: The Geotek MSCL-S, housed in the Petrophysics container, provides highresolutionwhole-core logging data including gamma density, P-wave velocity,non-contact resistivity and magnetic susceptibility (photo Frank Bosch).Why take petrophysical measurements on core?Core petrophysics data are used in tandem with the downholelogging and other geological data to help identify key boundariesand trends in individual boreholes, enable correlation betweenboreholes and formations. These data are used to developlithostratigraphic frameworks for carbonate, siliciclasticand igneous successions. During New Jersey Shallow ShelfExpedition 313, the gamma density was used in the preliminaryidentification of key seismic reflectors in the recovered core.Magnetic susceptibility and spectral gamma ray data, measuredduring downhole logging, were directly compared with trendsmeasured on the recovered core ensuring a precise and calibrateddataset.The FutureAt each EPC centre, researchers work within dedicated facilitiesusing a range of software packages to optimise the evaluationand interpretation of downhole logging data and facilitate corelogintegration. EPC applies IODP and archive ODP, downholelogging and core petrophysics data in a range of collaborativeresearch projects, including using log and physical propertiescharacterisation for the evaluation of facies, sediment compositionand ocean crust lithostratigraphy. EPC will continue its activeinvolvement with the IODP operations and research that haverevolutionised our view of Earth history and global processesthrough ocean basin exploration.Sarah Davies, EPC Co-ordinator