1. offshore drilling introduction
DESCRIPTION
Offshore drilling_ IntroductionTRANSCRIPT
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Drilling Rigs
Drilling Systems
Drilling Rigs
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Drilling Team Drilling Rigs Rig Power System Hoisting System Circulating System . . .
Rotary Drilling
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The Rotary System The Well Control System Well-Monitoring System Special Marine Equipment Drilling Cost Analysis Examples
Rotary Drilling - cont’d
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Noble Drilling’s
Cecil Forbes
A Jack-Up Rig
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Sonat’s George
Washington
A Semi-Submersible
Rig
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Zapata’s Trader
A Drillship
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8TENSION LEG PLATFORM
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Shell’s Bullwinkle
World’s tallest offshore structure
1,353’ water depth
Production began in 1989
45,000 b/d80MM scf/d
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Fig. 1.5
Classification of rotary drilling rigs
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Drilling OperationsField Engineers, Drilling Foremen
A. Well planning prior to SPUDB. Monitor drilling operationsC. After drilling, review drilling results and
recommend future improvements- prepare report.
D. General duties.
What are the well requirements? Objectives, safety, cost
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Criteria for determining depth limitation
Derrick Drawworks Mud Pumps Drillstring Mud System Blowout Preventer Power Plant
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A Rotary Rig Hoisting System
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Projection of Drilling Lines on Rig Floor
TOTAL
E = efficiency = Ph/Pi = W/(n Ff ) or Ff = W/(nE)… (1.7)
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Load on Derrick(considering friction in sheaves)
Derrick Load = Hook Load + Fast Line Load + Dead Line Load
Fd = W + Ff + Fs
F WWEn
Wn
E EnEn
Wd
=
1
E = overall efficiency: E = en
e.g., if individual sheave efficiency = 0.98 and n = 8, then E = 0.851
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Example 1.2A rig must hoist a load of 300,000 lbf. The drawworks can provide an input power to the block and tackle system as high as 500 hp. Eight lines are strung between the crown block and traveling block. Calculate1. The static tension in the fast line when upward motion is impending,2. the maximum hook horsepower available,
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Example 1.2, cont.
3. the maximum hoisting speed,4. the actual derrick load,5. the maximum equivalent derrick load, and,6. the derrick efficiency factor.
Assume that the rig floor is arranged as shown in Fig. 1.17.
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Solution1. The power efficiency for n = 8 is given as 0.841 in Table 1.2. The tension in the fast line is given by Eq. 1.7.
lbnE
WF 590,448*841.0
000,300
( alternatively, E = 0.988 = 0.851 )
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Solution
2. The maximum hook horsepower available is
Ph = Epi = 0.841(500) = 420.5 hp.
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Solution3. The maximum hoisting speed is given by
v
PWbh
hp
ft - lbf / minhp
300,000 lbf = 46.3 ft / min
420 533 000
.,
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Solution to 3., cont.
To pull a 90-ft stand would require
t 90
1 9 ft
46.3 ft / min . min.
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Solution 4. The actual derrick load is given by
Eq.1.8b:
FE EnEn
Wd
1
=1+0.841 +0.841(8)
0.841(8)(300,000)
= 382,090 lbf.
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Solution 5. The maximum equivalent load is given
by Eq.1.9:
lbfF
WnnF
de
de
000,450
000,300*8
484
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Solution
6. The derrick efficiency factor is:
000,450090,382
FFE
de
dd
84.9% or 849.0E d
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Drillship - moored
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HeaveSurgeSway
RollPitchYaw
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Motions restricted to the horizontal planeSURGE: Translation fore and aft (X-axis)SWAY: Translation port and starboard (Y-axis)YAW: Rotation about the Z-axis (rotation about
the moonpool)
Motions that operate in vertical planesHEAVE: Translation up and down (Z-axis)ROLL: Rotation about the X-axisPITCH: Rotation about the Y-axis
Vessel Motions
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Wave Direction
Beam Waves
Quartering Waves
Head Waves
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Significant Wave Height, ft
Roll vs. Significant Wave Height
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Significant wave height is the average height of the 1/3 highest waves in a sample.
EXAMPLE The significant wave height in the following sample is 24 ft.
7, 21, 19, 11, 18, 26, 13, 17, 25
[ Sign. WH = (21 + 26 + 25) / 3 = 24 ft ]
Avg. WH = (7, 21, 19, 11, 18, 26, 13, 17, 25) / 3 = 17.4 ft
What is Significant Wave Height?
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Significant Wave Height, ft
Heave vs. Significant Wave Height
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Heave vs. Wave Approach Angle
BOW BEAM
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Roll & Pitch vs. Wave Approach Angle
BOW BEAM
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Typical Vessel Motion Limits - Criteria
Operation Wave Height Heave ft ft
Drilling Ahead 30 10Running and Setting Casing 22 6Landing BOP and Riser 15 3Transferring Equipment 15 -
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SHIPSEMI
10% vs. 1.5 %
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What is “lt” ?
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Some Definitions
Freeboard
Draft
Width
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G = center of gravity. B = center of buoyancy
G is above B!
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NOTE: B has moved!
GZ = righting
arm
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Dynamic Stability - for certification
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Dynamic Stability
For adequate stability, the area under the righting moment curve to the second intercept or to the down-flooding angle, whichever is less, must be a given amount in excess of the area under the wind heeling moment curve to the same limiting angle. The excess of this area must be at least 40% for shiplike vessels and 30% for column-stabilized units (see Fig. above).
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Free Surface Effects
CG moves!
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Tall, narrow tank is more stable ...
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Effect of Fluid Level in Tank
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Mom
ent A
rm (o
nly)
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Effect of Partitions in Tank
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The Vessel - Classification
Three classification societies are particularly important to offshore drilling. These societies are: