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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.
2
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’
3
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…
4
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.
5
20 Foot (6.0m) Diameter Drill Bit (or Drill Head)
6
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.
8
Typical deployment vessel (Explorer II)
9
20 Foot (6.0m) Diameter Drill Bit
10
East Coast Oil & Gas Fields
11
Large Icebergs are the issue
12
Terra Nova production scenario
13
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.
14
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.
15
Terra Nova, 1999 (WD 95 metres)
The ‘jumbo’ Trailing Suction Hopper Dredge (TSHD)
‘Queen of the Netherlands’ was commissioned.
16
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.
18
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.
19
Sailing into St. John’s, early May 1999
20
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!
27
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.
29
‘M. V. Seahorse’ in 2001 – Contracted for Rock dumping at Terra Nova
30
The assembled 16 m3 Grab system in Huisman yard, Schiedam. June 2002.
31
Installing the skid in Huisman yard, June 2002.
32
July 2002 with the new grab system
33
Trials in Europoort, July 2002
34
View of forward lifting point, Europoort
35
St. John’s, August 2002 after trials in Stavanger and English Channel
Deployment sequence (outside St. John’s), August 2002
37
‘Nerve Centre’ on the Seahorse
38
Southern excavation, Sept. 2002
39
An atypical day at White Rose, 2002
40
Heading back to site, April 2003
41
Numerous technical problems were encountered, including fatigue cracking
42
The consequence of boulders! 2003
43
Another set of repairs in St. John’s!
44
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!)
46
‘Vasco da Gama’ (200m, 33,000 m3)
47
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.
48
‘Vasco da Gama’
49
Discharging Operation
50
Installation of Underwater Pump in Singapore, 2003.
51
Installation of 1400 mm Drag-arm
52
Deploying the drag-arm at White Rose
53
Deployed drag-arm at White Rose
54
Vasco da Gama draghead
55
Retrieving the draghead
56
Collecting Boulders! (Worse in 2007!)
A ‘larger’ boulder
A sample of ‘hardpan’
59
Fatigue!
60
Transferring the problem (and again in 2007!)
61
Returning to St. John’s for repairs
Repairs at dockside
63
Incremental Survey
64
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.
66
Heading home! Time for Questions?