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doi:10.2204/iodp.sp.339.2011

Logging/Downhole measurement strategy

The downhole measurement plan aims to provide characterization of in situ formation properties and establish the link between features in the borehole and reflectors in the seismic sections. Identifying the nature and depths of the main seismic reflectors and unconformities will be key to understanding the depositional history of the sediment sequences drilled during the expedition.

Wireline logging is planned for the deepest hole at all but one of the sites of Expedition 339. Logging is not currently planned for proposed Site SHACK-04A, which is to be quadruple-cored to 150 mbsf, although logging the site would become feasible if the target depth was deeper. Standard IODP tool strings will be deployed at each logged site. The first run will be the triple combination (triple combo) tool string, which logs formation resistivity, density, porosity, natural gamma radiation (NGR), and borehole diameter. The diameter log provided by the caliper on the density tool will allow assessment of hole conditions (e.g., any washouts of sandy beds), log quality, and the potential for success of the following runs. The second run will be the Formation MicroScanner (FMS)-sonic tool string, which provides an oriented 360° resistivity image of the borehole wall and logs of formation acoustic velocity, NGR, and borehole diameter. The third run will be a check shot survey using the Versatile Seismic Imager (VSI) tool at ~25 m station spacing. The seismic source for the check shots will be a generator-injector air gun, and its deployment is subject to the IODP marine mammal policy; the check shot survey would have to be postponed or cancelled if policy conditions are not met. Details of the logging tools are available at iodp.ldeo.columbia.edu/TOOLS_LABS/tools.html.

Proposed Site GC-04B will be cored to 1139 mbsf. Sites this deep take longer to drill; therefore, there is increased risk that the logging hole will partially collapse and that only part of the hole can be logged. To reduce the risk of incomplete site characterization and provided there is sufficient time available, proposed Site GC-04B will be logged in two steps. The upper part will be logged in one of the APC/XCB holes and the lower part in the RCB hole.

Downhole logging data will provide the only stratigraphic data where core recovery is incomplete, especially in the lower part of the sites where they are single-cored with RCB. To provide the link between the borehole stratigraphy and the seismic section, check shot surveys will give depth to seismic traveltime conversions and sonic velocity and density data will be combined to generate synthetic seismograms for detailed well-seismic correlations.

Formation temperature measurements

Temperature measurements are planned for all sites to reconstruct the thermal gradient at each location. Typically, ~4–5 measurements are made at one hole per site using the APCT-3 and potentially supplemented by the SET if necessary where sediments are more consolidated.

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