12. Special Problems

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TAMU - PemexOffshore Drilling

Lesson 12

- Special Problems

- Rigs


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Lesson 12 - Special Problems

Special Problems

Navigation

Workboats

Tides

Miscellaneous API 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. CircularNavigation 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 gridformed by

taking 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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Drillship

R.F. Bauer

Global MarineWD = 2000'


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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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9 3:

N N

85

( ) 66 85

( ) 69 86

8 6 844

85 83

3 969 3 5

3 88 6 4

9 6 5

N( )

4 @ 63

4 @ 53

699

N :


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Table 9-3: Characteristics of Offshore Vessels:Load Line Data

Ship No. 1 Ship No. 2

Draft H 1410 156

Length water lineLWL

166 185

Displacement, LT 1,767 2,050

The workboat is the workhorse of the offshore industry. One per ship? Less? Up to 3!


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1

1 1 1 1

1 7

7

1 1 1

7

1 7 1


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Drill Water Fuel Tanks

Pneumatic Tanks

Engine

Room

Fresh Water

The workboat brings supplies for drilling a well. Places anchors. Most tanks are below deck.


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Maximum Storm Condition orth Sea

With 496 ft leg

Water depth 31 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 1 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

Mean

Water

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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United States ports.

Hampton Roads

Savannah River Entr.


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United States ports.

Key West

Pensacola

Galveston

NOTE: Pensacola - almost disappears! Galveston - from 1 to 2 cycles per day!

21

0

Ft


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API RP 2P

January 1

1984


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Figure 9 - Basic Catenary Relationships

X1X

222

!!

! ?


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Figure 10.

Force

Geometry

and Vector

Diagram


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Fig. 11 - Example Analysis Wind Areas

NOTE: API RP 2P

has differentforce equations


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Acoustic Position Reference System.

Source: Honeywell

Beacon-

signaltransmission

Wellhead

assembly

Sea bottom

HydrophonesHydrophone 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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Typical 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-well

Platform

Wells are

directionally

drilled


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Shells

BullwinkleWorlds tallest

offshore

structure

1,353 water

depth

Production

began in 198945,000 b/d

80MM scf/d


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Small

concrete

monotower

concept

Concrete

Monotower

Concept

GravityStructure


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Several

guy wiresand clump

weights

support acompliant

platform.

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

George

Washington

A Semi-

Submersible

Rig


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Zapatas

Trader

A Drillship


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Joides

Resolution

Ocean DrillingProgram


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Production

Platform

Steel Tubes

Several

tensioned

tubes hold atension-leg

platform on

station.


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12. Special Problems

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