The very good to excellent core recovery at Leg 150 slope sites (88% mean) was due largely to the abundance of fine-grained sediments; however, problems arose whenever sands were encountered. Sand is likely to be much more prevalent at shelf Sites MAT-8B and -9B, and logging will consequently take on a particularly important role in meeting the objectives of facies characterization. Even in mudstones, Leg 150 operations relied exclusively on the Side-Entry Sub (SES) technique of wireline logging, which left the pumps online during the logging operation so that fluid circulation was available to clear downhole obstructions. Unfortunately, SES cannot be used at sub-bottom depths greater than the water depth, and hence will not be available at either Sites MAT-8B or -9B. LWD is a cutting-edge technology still being developed in the oil industry, but it has been used successfully on both the accretionary wedges in Barbados (Legs 156 and 171B) and Costa Rica (Leg 170). Although LWD has drawbacks‹lack of sonic, Formation MicroScanner (FMS), and geochemical log data‹it is rich in positives. Two examples are (1) in borehole conditions typical of ODP operations, LWD is likely to provide the best gamma-ray, density, porosity, and caliper logs possible by measuring these data within minutes of being drilled (because the sensors are a few meters above the bit); and (2) LWD is nearly certain to save time over standard wireline logging (although this will also be attempted at a minimum of one site, probably Site MAT-8B), which requires drilling to TD, then logging a potentially unstable hole from there back up to ~100 meters below seafloor (mbsf); and (3) LWD provides log data from the mudline downward, which will be critical for the sea-level objectives proposed for Leg 174A. In particular, LWD will provide logging details of 0-100 mbsf that will be crucial for tying the Pleistocene (Sites MAT-13A to D) on the continental slope/Hudson Apron to coeval sections to be sampled at Sites MAT-8B and -9B.

LWD tools consist of special drill collars placed in the bottom-hole assembly (BHA) that contain measurement sensors providing physical property data while the formation is being drilled. Data are recorded in nonvolatile memory and downloaded once the BHA is retrieved to the rig floor. The LWD data recorded as a function of time are then merged with the pipe depth as a function of time measured at the surface to obtain a depth-based log. Two LWD tools are currently available with the following specifications.

Compensated Density-Neutron (CDN) Tool
The CDN contains two radioactive sources that generate neutrons (AmBe) and gamma-rays (137Cs). Neutron absorption depends on the hydrogen content, and because hydrogen atoms are present in pore waters, this provides a proxy indicator of porosity. Gamma-ray scattering is a function of electron density, which in turn is a function of bulk-density. Absorption of gamma rays, through the photo-electric effect, is a function of the average atomic number, providing an indicator of mineralogy. The CDN tool also provides two options to estimate the borehole diameter necessary to determine corrections to the data:

Compensated Dual Resistivity Tool (CDR)
The CDR uses an electromagnetic (2 Mhz) wave generated at a source antenna and measures both the phase and attenuation at a receiver antenna. A scintillation detector measures natural radioactivity, including separation into its main spectral components:

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