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TAMU - Pemex
Offshore Drilling
Lesson 12
- Special Problems- Rigs
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Lesson 12 - Special Problems
Special Problems
Navigation
Workboats
Tides
MiscellaneousAPI RP 2P- Spread Mooring
Rigs, Arctic Drilling, etc.
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Figure 9.1. Navigation using circular grid
Navigation
Measured
distanceKnown
distance
Measured
distance
M
A B
Need two or more fixed radio stations - electromagnetic signals. Circular Navigation System. Short range.
Quite accurate. Stations A & B can be on shore or on platforms. A third station may be needed...
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Fig. 9-2. A
hyperbolic grid
formed bytaking the
difference in
distance to thefixed stations A
and B.
Stations A & B are contacted simultaneously. Difference in arrival times locates you on a hyperbola.
A third station is needed to specify where on the hyperbola. Not very accurate. A & B are slave stations.
0
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Figure 9.4 - Relative geometry of shipboard
user and satellite
Time T3
Computer
Receiver
Time T2Satellite Orbit
Time T1
On the first pass, position to ~ 1/10 mile. After several passes ~ 100 ft. 9 EA 2-minute messages
are available on each pass. Utilizes Doppler frequency shift.
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Comparison of Vessel Characteristics
Property Workboat Drilling Vessel
Primary In Transit Moored
location
Location Maneuver or Moored
during or go to
Storm harbor
Vessel Generally bad, Must
motion but of minor be low
concern
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Comparison of Vessel Characteristics
Property Workboat Drilling Vessel
Load Load and unload For drilling
arrangement part of cargo, then operation
ballast to safe trim efficiency
Loading and Easy to load and Relatively little
unloading discharge full cargo cargo change
Maneuver- Very important Relatively
ability unimportant
Propulsion/ 2 to 4 hp/ton Less than
displacement 1 hp/ton
load line limit
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Table 9-3: Characteristics of Offshore Supply Vessels
Ship No. 1 Ship No. 2
Len th Overall LOA 185 200
Length beam (LB) 166 185
Depth, molded (D) 169 186
Lightshipdisplacement, LT
816 844
Fuel, gal 185,000 183,000
Potable water, gal 32,969 31,250
Drill water, bbl 3,880 6,400
Length after-deck 92.6 105
No. dry mud tanks(P-tanks)
4 @ 1,060 ft3
4 @ 1.1125 ft3
Gross tonnage 699
Note: Volumes in bbl, gal, cu.ft - all in one table
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Table 9-3: Characteristics of Offshore Vessels:
Maximum Deck Cargo
Ship No. 1 Ship No. 2
Deck cargo, LT 394 500
Displacement, LT 1,613.1 1,932.4
Fuel Oil, LT 127 395.4
Potable water, LT 62.4 56.4
Drill water, LT 207 65.55
Draft (H) 141 15
Freeboard, ft 2.67 3.50
Trial speed, kts 13.7 15
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Drill Water Fuel Tanks
Pneumatic Tanks
EngineRoom
Fresh Water
The workboat brings supplies for drilling a well. Places anchors. Most tanks are below deck.
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Maximum Storm Condition: North Sea
With 496 ft leg
Water depth 310 ft
Max wave height 85 ft
Corresponding wave
period
14 sec
Max wind velocity 89 kts
Air gap 65 ft
Current 1.6 kts
Penetration 10 ft
*Cantilever extended 55 ft alt; Full dynamicanalysis
Jack-up
Rig
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Dimensions and Capacities
Jacking SystemNumber 3 X 12 pinions
Size 1,000 kips (446 T) per pinion continuous jacking
Size 1,600 kips (726) per pinion maximum holdingJacking speed 1.55 ft/min.
Rack Chock System
6 racks per leg for 3 legsDesign Friede & Goldman
39,000 kips capacity--- hydraulic
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Figure 9.8 - Idealized oscillations of tides
Neap Tide
Once or twice per day
MeanWater
Level
Spring tide
14-19 Days
Tide = sea level oscillations of approximately daily or twice per day. Affect KB height above ML.Measurements should be normalized to Mean Water Level. Tides vary from
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Figure 9.9 -Typical
tide curves
for UnitedStates
ports.
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Figure 9.9 - Typical tide curves for
United States ports
Boston
New York
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Figure 9.9 - Typical tide curves for
United States ports.Hampton Roads
Savannah River Entr.
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Figure 9.9 - Typical tide curves for
United States ports.Key West
Pensacola
Galveston
NOTE: Pensacola - almost disappears! Galveston - from 1 to 2 cycles per day!
210
Ft
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API RP 2P
January 1
1984
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Figure 9 - Basic Catenary Relationships
)P/WX(sinh)W/P(s)1)P/WX((cosh)W/P(Y
)W/P(s)W/PY(
hh
hh
2
h
22
h
?
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Figure 10.
Force
Geometry
and Vecto r
Diagram
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Fig. 11 - Example Analysis Wind Areas
NOTE: API RP 2P
has different
force equations
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Acoustic Position Reference System.
Source: Honeywell
Beacon-
signal
transmission
Wellhead
assembly
Sea bottom
Hydrophones
Hydrophone signal
Ship position
Wellhead
position
Position Indicating
Display
Vessel
Short base Line phase comparison system
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Tilt Indicator for Guide Structures
May be mounted on temporary guide base. View with camera. Start hole within 1/2 deg. of vertical.
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Offshore Drilling Structures
Offshore Drilling Structures
Fixed
Floating
Tension Log
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Ice Floes in the Beaufort Sea
Can be up to 10 miles * 20 miles * 200 ft
It is a good idea to get out of the way when one of these babies comes along! Glory Hole may be needed
52,800 * 105,600 * 200 * 62.4 * 0.9 = 6.26 E13 lbs 31 billion tons!
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28Typical Jack-up & Platform layout
Spud Cans
Platform Piles
WL
ML
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Fixed Jacking System with Leg Locking Device
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NobleDrillings
Cecil
Forbes
A Jack-Up
Rig
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Shells
Cognac
Conventional
20-wellPlatform
Wells are
directionally
drilled
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Shells
Bullwinkle
Worlds tallest
offshore
structure
1,353 water
depth
Production
began in 198945,000 b/d
80MM scf/d
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Small
concrete
monotowerconcept
Concrete
MonotowerConcept
GravityStructure
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Several
guy wiresand clump
weights
support a
compliantplatform.
Guy wires
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A semisubmersible with floats that are located
below the waterline when drilling
Main Deck
Column
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Sonats A Semi-
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Sonat sGeorge
Washington
A Semi-
Submersible
Rig
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Zapatas
Trader
A Drillship
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Production
Platform
Steel Tubes
Several
tensioned
tubes hold a
tension-leg
platform on
station.
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