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doi:10.2204/iodp.sp.341.2011

Downhole measurements strategy

Wireline logging

We plan to acquire wireline logs from all sites proposed in the primary operations plan. Three standard IODP tool string configurations will be deployed in the deepest hole at each site. These are the triple combination (triple combo), Formation MicroScanner (FMS)-sonic, and Versatile Seismic Imager (VSI) tool strings (Fig. F21).

At each site logged the first tool string deployed will be the triple combo, which will measure density, neutron porosity, resistivity, and natural and spectral gamma ray, along with caliper. The caliper log provided by the density tool will allow an assessment of hole conditions and the potential for success of subsequent logging runs. The second run will be the FMS-sonic and will record gamma ray, sonic velocity (for compressional and shear waves), and high-resolution electrical images. The compressional velocity logs will be combined with the density logs to generate synthetic seismograms for detailed seismic-log correlations. To calibrate the integration of well and seismic data, the third run in each hole will be a vertical seismic profile (VSP), recorded with the VSI, which will require use of a seismic sound source. The expected spacing between stations will be 50 m over the entire open interval of each hole logged. Spacing could be reduced for specific targets or adjusted for hole conditions. The seismic sound source used during the check shot/VSP survey will be subject to the IODP marine mammal policy and may have to be postponed or cancelled if certain policy conditions are not met. For more information on specific logging tools, please refer to iodp.ldeo.columbia.edu/TOOLS_LABS.

At three of the five primary sites we plan to deploy the high-resolution Lamont Doherty Earth Observatory (LDEO) magnetic properties tool string. This consists of the Magnetic Susceptibility Sonde (MSS) in combination with the Multisensor Magnetometer Module (MMM). These tools will acquire total field and three-axis magnetic field measurements and magnetic susceptibility. The MMM and MSS are currently under development at LDEO-Borehole Research Group (BRG), and it is anticipated that they will be available for deployment during Expedition 341.

At sites (GOAL-17B and GOAL-15C) where the magnetic properties tool string is not deployed, the triple combo will be modified to replace the Dual Induction Tool (DIT-E) resistivity tool with the MSS; this is called the “paleo-combo” (Fig. F22).

Formation temperature measurements

The downhole measurement plan includes a depth series of reconnaissance temperature measurements at Sites GOA16-1A and GOA18-2A within the Surveyor Fan, principally using the APCT-3 tool, supplemented by the SET if necessary where sediments are more consolidated. The scientific objective of the temperature measurement plan is to provide sufficient data to reconstruct the thermal gradient at each site. This information will help constrain the subduction inputs and the history of burial diagenesis.

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