1. Offshore Drilling Introduction

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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: