Subsea Glory Holes© Chevron 2007

Subsea Glory Holes

A brief Overview of Construction methods used on the Grand Banks

Kevin HewittFrontier Development Group

Chevron Canada Ltd.

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AGENDA

The origin of subsea ‘Glory Holes’

• Used in the Beaufort Sea since 1975

Terra Nova 1998/99 (95m Water Depth)

• Large diameter drill bit from the ‘Sea Sorceress’

• Trailing suction hopper dredge ‘Queen of the

Netherlands’

White Rose 2002/3/7 (120m Water Depth)

• Clam shell from ‘Seahorse’ fall-pipe vessel

• Trailing suction hopper dredge ‘Vasco da

Gama’

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Things not covered in detail….

Geotechnical conditions

Productivity rates

Survey systems

Mechanical systems

Technical issues

Contractual issues

Costs

But I do have lots of photos of ships…

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Beaufort Sea Experiences

The first subsea ‘glory hole’ (Gold mining term) was excavated in the Beaufort Sea in 1975.

The purpose of these ‘glory holes’ was to

protect a single subsea

wellhead from keels of

pressure ridges during

the winter.

Potential for scours in

up to 50m water depth.

Primarily used large

diameter drill bits.

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20 Foot (6.0m) Diameter Drill Bit (or Drill Head)

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20 Foot (6.0m) Diameter Drill Bit

Basically a ‘rotary plough’ – skewed steel disk

cutters on a hydraulically driven bit face.

Cuttings dragged to central spoil suction pipe and

airlifted to the surface.

Hydraulic power supplied by portable units on the

vessel deck.

Operates from a MODU and the marine riser is

lowered on a special kelly.

Rotary plough glory hole bits have been used

successfully since 1977, as follows:

Rotary Plough Glory Hole Bit History

12ft diameter ‘skewed dished cutter’ prototype

developed in 1977.

17ft diameter version successfully drilled glory holes

every year from 1979 to 1985 – no equipment failures.

20ft diameter enhanced design in 1986. Seven holes

drilled to date – no equipment failures:

Dome Petroleum (Can. Beaufort Sea) – one hole 1986.

Shell Western E&P (Chukchi Sea) – four holes 1989-1991.

Chevron USA (Chukchi Sea) – one hole 1991.

Amoco USA (US Beaufort Sea) – one hole 1991.

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Typical deployment vessel (Explorer II)

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20 Foot (6.0m) Diameter Drill Bit

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East Coast Oil & Gas Fields

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Large Icebergs are the issue

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Terra Nova production scenario

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First attempt at Terra Nova (WD 95 m) -‘Sea Sorceress’ (now Intrepid), 1998

Originally the Arctic Kiggiak. A1 Barge; 116 x 32m; Used to clam-shell a glory hole in the US Beaufort in 1985. Four point mooring.

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Terra Nova, ‘Sea Sorceress’, 1998

The intent was to use a ‘DeBeers diamond mining’ type

drill system to excavate four large volume holes (in

order of 20-40,000 m3 per hole) by ‘cookie cutting’

multiple overlapping single shafts.

System uses ‘non-skewed’ cutters that cut by

compression.

Rather than an hydraulically driven cutting face, torque

was applied at the surface.

Result was “a pizza pan on the end of a length of

spaghetti”.

This design, in combination with encountering boulders

and ‘hard pan’ plus North Atlantic sea states, resulted

in a failed operation.

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Terra Nova, 1999 (WD 95 metres)

The ‘jumbo’ Trailing Suction Hopper Dredge (TSHD)

‘Queen of the Netherlands’ was commissioned.

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Queen of the Netherlands (with Terra Nova extension)

Equivalent in size tothe proposed 1980’s‘Arctic Super Dredge’– but with greaterdepth capability.

‘Queen of the Netherlands’

A 173 m long, 23,350 m3 hopper with DP & DT.

The 1200 mm suction pipe was extended to 140 m and

included an underwater pump.

Pipe composed of 4 sections, each about 35 m long.

Dynamic analyses undertaken to determine operational

limits and potential fatigue.

System included extensive monitoring:

• Directional wave buoy.

• Axial pipe force.

• Pipe angles and draghead position.

• Lifting wire tensions.

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Queen of the Netherlands (with Terra Nova extension)

Worked in DT mode in aforward and then reversecycle. Average cycle timeof 12 minutes – 1.5 to 2minutes being dredging.

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Sailing into St. John’s, early May 1999

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Docking in St. John’s, early May 1999

‘Queen of the Netherlands’ – Extended portion of drag arm

‘Queen of the Netherlands’ –Underwater pump

‘Queen of the Netherlands’ – working in semi-submersible mode

‘Queen of the Netherlands’ - View from the bridge while at Terra Nova

Draghead details including boulders

Some boulders were quite large!

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Completed 4 glory holes in 4 months!

White Rose – 2002/3 (WD 120 metres)

The extended water depth (25 m greater than at Terra

Nova) initially excluded a TSHD.

A system was constructed in 2002 involving a large (16

m3) heave compensated grab deployed from the DP

Class 2 fallpipe vessel ‘Seahorse’ (162m x 38m).

Four thrusters provide precise positioning.

Two lifting points – one forward and one aft – enabled

material to be moved while the vessel remains

stationary.

Three Glory Holes were required – Southern, Central

and Northern.

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‘M. V. Seahorse’ in 2001 – Contracted for Rock dumping at Terra Nova

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The assembled 16 m3 Grab system in Huisman yard, Schiedam. June 2002.

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Installing the skid in Huisman yard, June 2002.

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July 2002 with the new grab system

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Trials in Europoort, July 2002

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View of forward lifting point, Europoort

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St. John’s, August 2002 after trials in Stavanger and English Channel

Deployment sequence (outside St. John’s), August 2002

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‘Nerve Centre’ on the Seahorse

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Southern excavation, Sept. 2002

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An atypical day at White Rose, 2002

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Heading back to site, April 2003

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Numerous technical problems were encountered, including fatigue cracking

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The consequence of boulders! 2003

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Another set of repairs in St. John’s!

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Incremental survey of Southern Glory Hole, May 24th, 2003

White Rose – 2002/3 (WD 120 metres)‘Vasco da Gama’ TSHD

Due to the requirement to complete all three glory holes

in the 2003 season, the TSHD ‘Vasco da Gama’ was

mobilized from Singapore to dredge the central hole.

A 200 m long, 33,000 m3 TSHD, also with DP & DT.

The 1400 mm suction pipe had been extended in

Singapore to 150 m as a back-up for White Rose, and

included an underwater pump.

Vessel transited via Suez Canal and Spain (which meant

several people from Newfoundland had the benefit of an

Atlantic crossing!)

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‘Vasco da Gama’ (200m, 33,000 m3)

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Queen of the Netherlands (with Terra Nova extension)

Worked in DT mode in aforward and then reversecycle. Average cycle timeof 12 minutes – 1.5 to 2minutes being dredging.

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‘Vasco da Gama’

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Discharging Operation

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Installation of Underwater Pump in Singapore, 2003.

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Installation of 1400 mm Drag-arm

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Deploying the drag-arm at White Rose

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Deployed drag-arm at White Rose

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Vasco da Gama draghead

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Retrieving the draghead

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Collecting Boulders! (Worse in 2007!)

A ‘larger’ boulder

A sample of ‘hardpan’

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Fatigue!

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Transferring the problem (and again in 2007!)

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Returning to St. John’s for repairs

Repairs at dockside

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Incremental Survey

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Completion in September, 2003

Grand Banks Summary

First Terra Nova attempt in 1998 was a failure.

The ‘Queen of the Netherlands’ completed five glory holes in one full season in 1999 at Terra Nova with no significant technical problems.

Despite many teething problems, as a result of using a new and sophisticated system, the ‘Seahorse’ completed two holes at White Rose in 2002/3.

The ‘Vasco da Gama’ completed one glory hole at White Rose, with some technical problems, in six weeks in 2003. Similarly it completed another glory hole in a two month period in 2007.

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Heading home! Time for Questions?