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doi:10.2204/iodp.sp.314.2007

Measurement and logging-while-drilling tool capabilities

Density and porosity

The adnVISION tool includes neutron porosity measurement and induced gamma density. It is an azimuthal measurement and provides 16 sector borehole density images. The sector data are subsequently grouped into four quadrants (up, down, left, and right), oriented with internal magnetometers. For proper environmental corrections, the adnVISION will also measure standoff from the tool to the borehole wall in quadrants using an ultrasonic caliper.

Resitivity and resistivity imagery

The geoVISION resistivity tool is based on RAB technology, which was designed to provide real-time at-bit resistivity data, and provides azimuthally focused laterolog measurements for detailed geological mapping. The sensors include ring and bit resistivity and three azimuthally oriented focused button electrodes for imaging capabilities. The three button electrodes are ~1 inch in diameter and are longitudinally spaced along the axis of the tool. The spacing provides multiple depths of investigation for quantifying invasion profiles and fracture identification (drilling induced versus natural). These azimuthally acquired button measurements are displayed as full-bore images to graphically describe formation resistivity. For environmental correction of the resistivity measurements, drilling fluid resistivity and temperature are also measured.

Natural gamma radiation

The spectral gamma radiation detector included in the geoVISION tool measures and classifies natural radioactivity in the formation and provides a common reference for correlation and depth shifting between multiple logging (LWD and wireline logging) runs and core data.

Sonic velocity

The sonicVISION sonic-while-drilling tool delivers real-time interval transit time data for compressional waves. Measurement range is given between 40 and 230 s/ft (1.3 and 7.6 km/s) depending on mud type, but intensive processing is required to obtain reliable sonic velocity measurements in the relatively slow formations expected during Expedition 314. In LWD operations the sonic processing parameters are conventionally set at the surface, before the tool is run in the hole. This results in possible mislabeling of arrivals (especially for slow formations) and limited confidence levels, as only the end result of downhole processing is seen uphole in the real-time log. Full waveform data are recorded in memory, however. Advanced onboard postprocessing should allow fine tuning of sonic acquisition parameters and so extend the range of measurement out to the mud velocity, a key feature for achieving the scientific objectives of this cruise, including log-seismic ties. Additional quality control (QC) is performed using automatic station measurements made during a pipe connection. In this noise-free environment, the tool is able to take a "station" measurement that is then sent uphole, when pumping resumes, for further QC of the real-time log.

Zero-offset vertical seismic profile

The seismicVISION LWD system delivers time depth/velocity information to provide interval velocity. The seismicVISION tool, which contains a processor and memory, receives seismic energy from a conventional air gun suspended from a crane on the drillship. After acquisition, the seismic signals are stored and processed downhole, and check shot data and quality indicators are transmitted uphole in real time via connection with the MWD pulse system. Waveforms are recorded in the tool memory for further processing after a bit trip.

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