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Hard Rock Base


Description

The Hard Rock Base (HRB) is designed to focus the direction of the drill bit into hard irregular seafloor surfaces otherwise undrillable.

Specifications

  • Dry weight (unballasted) = 41,400 lbs
  • Submerged weight (unballasted) = 36,000 lbs
  • Approximate submerged weight (ballasted) = 125,000 lbs
  • Reentry cone diameter = 8 ft
  • Reentry cone uprighting moment factor of safety = 2.5
  • Factor of safety against leg bolt shear = 19
  • Maximum design tilt (into side) = 25°
  • Maximum design tilt (into corner) = 30°
  • Maximum recommended operational limit = 20°
  • Leg extension beneath base = 3 ft
HRB diagram

Problems Associated with Landing an HRB

  • Seafloor slope
  • Seafloor stability
  • Sediment thickness
  • Sufficient area suitable to land base
  • Weather/sea state/water depth conditions
  • BP471 not suitable or efficient as a survey vessel
  • Very rugged canyonous topography

Design/Deployment Capabilities

  • Can be set on hard bare rock outcrops with flat or irregular topography on slopes less than or equal to 20°
  • Requires sediment cover to be less than 3 ft
  • Recoverable/Redeployable
  • Can be relocated on the seafloor

Considerations of Using an HRB

  • Permanent/long term reentry site
  • 1, 2, or 3 casing strings required
  • Time required to under ream or hole open
  • Time to locate/position/run HRB
  • Adequate survey of seafloor deployment area
  • Space availability on BP471 for support hardware of HRB/casing (when considering multiple HRB deployments)

Input Data for Landing an HRB

  • Mechanical tilt indicator (Bullseye)
  • maximum range = 23.5°
  • Electronic tilt beacon (Note 1) = 40°
  • Mesotech (Note 2) = Limited
  • Visual form V.I.T. (Note 2) = Limited

Notes

Electronic Tilt Beacons have experienced some freezing and/or erratic behavior due to rugged reentry cone shielding or topography.

Need experience to interpret results/data.



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