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

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.