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doi:10.2204/iodp.sp.317.2009 Logging/downhole measurements strategyOne of the primary objectives of the logging program will be to provide precise seismic/well correlations to constrain the seismic stratigraphy of the Canterbury Basin. Identifying the natures and depths of the main seismic reflectors and unconformities will be key to understanding the respective influences of local tectonics and eustasy on the depositional history. Logging operations will consist of three runs in the deepest hole of each site. In addition, because of the unstable nature of the formation expected in these sediments and of the need for accurate logs in the shallower sequences, the upper sections of the sites with the deepest penetration (>1000 mbsf) will also be logged after completion of APC/XCB operations (Site CB-03B) or with a dedicated logging hole (Site CB-04B). In each hole logged, the first run will be the triple combination (triple combo) tool string, which will record resistivity, neutron porosity, bulk density, and spectral natural gamma ray. The caliper log provided by the density tool will allow assessment of hole condition, log quality, and the potential for success of the following runs. The second run, with the Formation MicroScanner (FMS)-sonic tool string, 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 final run in each hole will be a VSP, recorded with the Versatile Seismic Imager (VSI). The seismic source for the VSP will be a 105 in3 GI air gun, positioned ~2 m below sea level, and offset by ~50 m from the side of the ship. The expected vertical spacing between stations will be 20 m over the entire open interval of each hole logged. Spacing could be reduced for specific targets such as prominent unconformities. For more information on specific logging tools, please refer to iodp.ldeo.columbia.edu/TOOLS_LABS. |
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