Abstract:
A newly developed logging-while-coring system was deployed and tested during Ocean Drilling Program Legs 204 and 209 on Hydrate Ridge off the coast of Oregon and on the Mid-Atlantic Ridge. The system consists of two existing devices modified to be used together--a Schlumberger Resistivity-at-the-Bit (super TM) tool and a Texas A&M University wireline-retrieved core barrel and latching tool. The combination allows for precise core-log depth calibration and core orientation within a single borehole, and without a pipe trip. These tests during Leg 204 and Leg 209 mark the first simultaneous use of coring and logging-while-drilling technologies. The first test was conducted in 788.5 m (2586 ft) water depth at the crest of southern Hydrate Ridge (Site 1249) in clay-bearing sediments. Eight cores were recovered from Hole 1249B with 32.9% recovery, on average, through an interval from 30-75 m (98-246 ft) below the seafloor and as high as 67.8% recovery in one core (Bohrmann et al., 2003). All eight cores were processed and archived on board the D/V JOIDES Resolution following normal ODP core handling protocols (Ocean Drilling Program, 1999). High resolution logs and image data were recorded in the downhole tool memory over the entire 74.9 m (245 ft) drilled interval. The log data were processed post-cruise and correlated to recordings of conventional logs in nearby Hole 1249A. The logging-while-coring system was also deployed in lower crustal (Kelemen et al., 2004, in press) in a 20-meter (65 ft) deer hole during ODP Leg 209. It is expected that the logging-while-coring systems will be utilized more routinely at other drilling locations, where rig time constraints may otherwise preclude coring in difficult drilling environments.