Western and Central Pacific
During Leg 132, tests were conducted at two sites (Sites 809 and 810) to refine the hard rock guide
base (HRB), drill-in bottom hole assembly (DI-BHA), and diamond coring system (DCS),
hardware required to meet future endeavors at difficult-to-drill sites and the long-standing objective
of core recovery from axial regions of active spreading ridges. The HRB is a quickly deployable
seafloor structure that stabilizes a drill bit/bottom hole assembly while initiating a hole in hard bare
rock. It can accept a seafloor slope of up to 25 deg, allow for the support of one or more casing
strings, and accommodate moving or recovery options. The DI-BHA is intended to isolate unstable
formations, allow separation from the drilling assembly without retrieving the bit, provide adequate
bit life, allow nested deployment capability in multiple unstable zones, provide drill
collars/connections capable of surviving rotation above the seafloor without lateral support, and
provide a through-bore for the deployment of wireline coring systems through the isolation strings.
The DCS is a wireline coring system capable of drilling and coring through highly-fractured,
poorly cemented, crystalline rock.
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