Design of an ultra deep-water drillship with crude oil storage capacity type II

(1)

Design of an ultra deep-water cdrillship

with crude oil storage capacity type II

t

It Delft report nr. OvS 98/10

(2)

I

Design of

an ultra deep-water drillshipi

with crude oil storage capacity

Till, Delft

Type 2

--

-a

GUSTO

(3)

TU Delft, Mar'itieme Techniek

Supervisor: Jr. H. Boonstra

Professor: Prof. Ir. A. Aalbers

Report nr. OvS .98/10

Schiedam, 1998

mks

TU Delft

Design of an ultra deep-water drillship

with crude oil storage capacity

TYPE II

ii

M. Spilker

E.F.J. van Leeuwen

IHC Gusto Engineering BY

Supervisor: Jr. J. Lusthof

-7

GUSTO

(4)

Preface

This report forms part of our graduation work at TU Delft, Maritieme Techniek. The

entire work is performed by order of IHC Gusto Engineering BV.

This report contains a design study of a modern drillship.

We acknowledge the many engineers at Gusto Engineering, particularly those of the

naval architectural design department for their enthusiastic support. We clearly

wouldn't have come so far without them. Much credit goes to Jr. Boonstra from Delft

University of technology for running the offshore department at the faculty where

offshore belongs: Maritieme Techniek!

Schiedam, June 25 1998

E.F.J. van Leeuwen

M. Spilker

(5)

Introduction

As a response to the huge demand for deep-water drillships, this report contains the

design of a DP drillship with storage capacity.

Special attention was paid to the logistics of pipes and riser joints. The vessel is

equipped with two box-type drilling masts. One is dedicated to make hole, the other

one can be used to assemble joints.

This ship has a working name Drilling mast.

In chapter one some design considerations are given, accompanied by a rough

description of lay out and performances. In the other chapters all relevant aspects of

the design, such as stability, DP-system and hull strength are discussed.

The design is based on specifications formulated by IHC Gusto Engineering By and

TU Delft. Those requirements can be found on the following pages.

(6)

GUSTO

ENGINEERING

Order

Fax no

Date

Page

:

6204

4-Jun-98

2 De afstudeerders zullen ieder afzonderlijk een dynamisch gepositioneerd diep water boorschip

met olie opslag capaciteit ontwerpen met inachtneming van de relevante gedeeltes van het

cursuswerk.

Het ontwerp zal de volgende scheepsbouwkundige aspecten omvatten:

Ontwerp aspecten:

Weerstand en voortstuwing

Electrisch vermogen

Downtime (vereenvoudigd)

Grootspant

Veiligheid

Bouwprijs berekening

Omgeving condities

Waterdiepte

Boordiepte

single line diagram

elektrische balans

scheepsbewegingen

indeling / lay-out

De te ontwerpen schepen moeten voldoen aan de volgende eisen:

Gemeenschappelfike ontwerpeisen:

Klassificatie

Operationeel gebied

DNV

DP notatie Dynpos AUTRO

Wereldwijd, nadruk op:

GOM

Brazilie

West-Afrika

Max. drilling

Hs

6.0 m

Tp

10-13 sec

V,nd

25.0 m/sec

Vcurrent 1.1 m/sec

Stand-By (Riser disconnected)

Hs

10.0 m

Tp

15-18 sec

Vwind

30.0 m/sec

Vcurrent 1.1 m/sec

Transit, wereldwijd

10.000 ft

30.000 ft onder rotary

Stabil iteit berekening

intact

lek

Langsscheepse sterkte

Dynamisch postioneren

thruster lay-out

omgevingskrachten:

wind

stroming

golven

(7)

GUSTO

ENGINEERING

Order

Fax no.

Date

Page

3 Afzonderlijke ontwerpeisen:

Schip 1

Derrick

conventioneel (54' x 54' x 190')

hookload 726 t

Vrij dek opperylak

500 m2

Bij het ontwerp van schip 1 zal speciale aandacht besteedt worden aan een minimale

hoofdafmetingen vergroting ten gevolge van de vrije dekoppervlak eis.

Schip 2

Derrick

nieuw ontwerp, by. Huisman

ltrec Dual Mast

hookload 726 t

Vrij dek oppervlak

geen eis

Bij het ontwerp van schip 2 zal speciale aandacht besteedt worden aan de logistiek m.b.t.

riser, en drillpipe handling en opslag.

Crude Oil

100.000 bbls

Brine

2 x 700 m3

Mud

1750 m3totaal

Silo's

12 x 60 m3

Base Oil

300 m3

Drilling Water2000 m3

Bulk (zakken)

400 t

Risers, tubulars, casing, drillpipes volgens

water- en boordiepte

Setback

-

650 t

Riser tensioning

8 x 2 tensioners, totaal 1162 t

.

Crude Oil Productie

-

20.000 bbls/dag

Crude overslag

stern offloading

Accommodatie

-

150 man

min_ 12.5 kn, proeftocht

Opslag capaciteit

Consumables voor 90 dagen operatie

Scheepssnelheid

(8)

1 Design considerations

3 1.1 Principal dimensions

3 1.2 Hul!form

3 1.3 General arrangement

4 1.3.1 Lay-out

4 1.3.2 DP system

4 1.3.3 Accommodation

5

1.3.4 Production facilities

5

1.3.5 Engine rooms

5

1.3.6 Deck cranes

5

1.3.7 volumes

5

1.4 Drilling equipment and logistics

6 2 Intact stability

7 2.1 Introduction

7 2.2 Stability requirements

7 2.3 Loading conditions

8 2.3.1 Summary of loading conditions

9 2.4 Wind heeling moment curves

9 2.4.1 General

9 2.4.2 Calculation of wind heeling moment curves

9 2.4.3 Results

10

2.5 Results of intact stability calculations

10 3 Damage stability

11 3.1 Requirements

11 3.2 Results

12 4 Resistance and propulsion

15 4.1 General

15 4.2 Resistance

15 4.3 Thrusters for main propulsion and DP

15 4.4 Results

15 5 DP Station keeping

15 5.1 DP-requirements

15 5.2 Thruster system

15 5.3 Environmental forces

16 5.3.1 Wave drift forces

16 5.3.2 Current forces

17 5.3.3 Wind forces

18

5.3.4 Riser force

19

TYPE H

1

(9)

5.4 Thruster forces and consumed power

19 5.4.1 General

19 5.4.2 Environmental conditions

19 5.4.3 Intact thruster system

70 5.4.4 DYNPOS AUTR failure

5.4.5 DYNPOS AUTRO failure

20 5.4.6 Total power balance

21 6 Power generation and distribution system

22 6.1 Power generation

22 6.2 Power distribution system

22 6.3 Load balance

23 7 Down time

24 7.1 Motions

24 7.2 Downtime

25 8 Hull strength

26 8.1 Loadings

26 8.2 Midship section

26 8.3 Results

27 8.3.1 Material

27 9 Hull weight

28 10 Building price

30 Appendix

31 TYPE II

2 DRILLING MAST

20

(10)

1 Design considerations

1.1 Principal dimensions

The principal dimensions are determined by using a concept exploration model. A full

description of this model can be found in report "Design aspects of an ultra

deep-water drillship with storage capacity". By selecting a large breadth, possible future

modifications of the vessel are accounted for in ways of stability.

This leads to the following main dimensions:

1.2 Hul !form

The following choices have been made regarding the hullform:

Large midship section to reduce fabrication costs.

Pram-form aftship, which will provide a good flow to the main propulsion

thrusters.

V-form foreship to obtain good motion characteristics.

Wide cylindrical bow to accommodate the fore thruster.

appendages:

Scheg to increase directional stability and to ease dry-docking of the vessel.

Bilge keels to restrict roll motion.

On the following pages a body plan and a lines plan can be found.

TYPE II

3 DRILLING MAST

Length overall

202,0 m

Length between perpendiculars

188,8 m

Breadth

35,6 m

Depth at side

17,6m

Design draft

9,0 m

Displacement

48.000 tnj

(11)

drilling mast

FL 0

5.0

(12)

-drilling mast

0. 0

5. In

10.0 is. 0

(13)

4

a

2

4

6

Ilan deck Ical MI et

Lnos

pa

14 15 1.6 17 18 19 2 C,

Principal dimensions

Length between perpendiculars

188.8 Length overall 202.0 no Breadth 35.6 m Depth 11.6 m Draught 'ranter 8 re Lb at transit draught 0.78 21.1m 7 8

9

10 11 12 13 3

(14)

1.3 General arrangement

1.3.1 Lay-out

For 'drawings of the general arrangement, reference is made to appendix 1 and

drawing nr. 6204.0001.501

6204.0001.503.

As drilling is the main activity of the vessel, positioning of all' drilling equipment has

been given first priority. Short lines and free access to the drilling area benefits

to

high drilling efficiency. All piping is stored above main deck, in front of the drillfloor.

'Consequently, the moonpool is situated relatively far aft. Below deck level, two crude.

al tanks occupy the space between the drilling area and the accommodation

area..

These tanks have a total capacity of over 100.000 bbls. For reasons of safety, the

accommodation is placed at the fore ship, the power generation set, production

module and ground flare are placed downwind of the drilling, area.

Drilling section

Accommodation

Production

platform

Pratioratimi

_{ir.uranionnoil}

rr

VA

Power generation

Crude oil storage

113.2 DP system

The vessel will he dynamically positioned by means of two azimuthing thrusters at

the stern and four azimuthing retractable thrusters below keelplane level.

_{All thrusters'}

,are installed in containerised units (appendix 1) with a retraction system to retract

'them above waterline level or even main deck level for major overhaul.

_{The deck}

above the thrusters has been kept free.

The DP system fulfils DNV DYNPOS AUTRO requirements.

_{A 'complete redundant}

system for power generation, power distribution', controls and thrust generation is

applied.

TYPE II

DRILLING MAST

(15)

1.3.3 Accommodation

The accommodation block is designed to quarter a total of 150 persons. The cabins

are divided over six decks. The most upper deck accommodates the navigational

bridge. Furthermore, two decks are in use for supporting services and equipment, such

as: mess room, offices, stores, galley, recreation room, laundry, etc.

The accommodation will be situated in the foreship just aft of the collision bulkhead.

The length of the accommodation block is 24m, the maximum breadth 26m.

1.3.4 Production facilities

The production facilities, intended to perform extended well tests and early

production, will be accommodated on a raised platform on top of the main deck, near

the stern. The dimensions of the platform are: 20m x 25m. It is designed for a

throughput of up to 20.000 bbls/day. At this flowrate, the vessel is able to produce

five days uninterrupted, before offloading.

The production platform is able to cover the following functions:

Separation of crude oil, produced water and gas.

Treatment of oily water to satisfy the applicable code requirements for dumping.

Export metering.

1.3.5 Engine rooms

The vessel has two completely separated engine rooms, to satisfy DYNPOS-AUTRO

requirements. Each engine room contains 4 generator sets of 5200 kW each

(alternator output at MCR).

1.3.6 Deck cranes

Three pedestal cranes will be installed on the vessel on main deck level to load,

unload and handle drillpipes, casing, risers or other weights. The capacity of all three

cranes is 20 ton at 35 m, or 75 ton at 25,5 m.

1.3. 7 volumes

TYPE II

5 DRILLING MAST

Volume (m')

Mud

2.000 Brine

1.400 Drilling water

2.300 Base oil

400 MDO

4.600 Crude

1.8068

S loptank

1.025 Potable water

1.095 water ballast

17.000

-'

(16)

1.4 Drilling equipment and logistics

The layout of the drilling section is optimised for ultra deep-water applications. For

this purpose, two mast-type drilling derricks' are installed just behind the drillfloor.

The main mast, which is located at centerline, is suitable to perform all operations of

a

conventional drilling derrick. The rotational action will be provided by a topdrive.

The auxiliary mast, which is located 6,5 m. starboard of the main mast, can be used to

remove operations out of the critical path, which reduces completion time

considerably. Examples of such operations are:

Building up casing assemblies

Preparing riser joints

Making up bottom hole assembly

Another feature that will speed up the drilling process, is the use of drillpipe cassettes.

One cassette can hold 40 stands of 5- drillpipe. All drillpipes can be stored in triples.

Furthermore, the entire cassette can he lifted into the setback area. Consequently 120

pieces of 5" drillpipe are handled in one action, rather than in 120 actions, not to

mention the uncalled-for screwing and unscrewing. An impression of such a cassette

is given in figure 1.1.

Figure 1.1

Drillpipe cassette

All pipe handling will be taken care of by means of overhead

_{cranes and dragways.}

The overhead cranes pick up the pipes, riser joints, casing and cassettes from their

horizontal racks and lay them down onto either the main mast dragway,

or the

auxiliary mast dragway. This system provides high operability with regard to ship

motions. Overview pictures of the pipe area can be found on the next

pages.

Design specifications as from Huisman ltrec's mast design.

TYPE II

6

(17)

Pipe rack capacity

Pipe deck layout

Drillpipe cassettes

8 *

drillpipe

3 * 5" landing string

4 * 3" workover

IV workover riser

0

7" completion riser

Casing 30"

200 in

Casing 20-

800 in

Casing 13"318

2000 m

Casing 9"5/8

3500 m

Drillpipe 5"

9000 m

Drillpipe 5" landing string

3000 m

Drillpipe 3" workover

9000 m

Drillcollars 7-

1000 m

Riser 10" workover

3000 m

Riser 7" completion

3000 m

Free space

2000 m (7"equiv.)

Free pipe rack

fl

Free pipe rack

Drillcollars

20" casing

9"5/8 casing

13"318 casing

30" casing

5"

I

(18)

It

rittent/

-

,

_#1

(19)

(20)

rg

(21)

2 Intact stability

2.1 Introduction

The intact stability of the vessel is investigated for seven relevant loading conditions.

Three fundamentally different operations can be recognised:

Transit operation

Drilling mode

Testing mode

Furthermore, a loading condition is defined to examine the stability characteristics

during survival conditions.

2.2 Stability requirements

The applicable stability criteria of the vessel have been summarised below. The

criteria are as per the DNV Rules for classification of Steel ships, DNV Rules for

Mobile Offshore Units and the IMO MODU CODE.

The applicable stability criteria are:

I. The maximum righting arm should occur at an angle of heel preferably exceeding

300 but not less than 25°.

2. The righting lever GZ should be at least 0,20 m at an angle of heel equal to or

greater than 30'.

3. The area under the righting lever curve (GZ) up to an angle of heel of 30° should

not be less than 0,055 mrad.

The area under the righting lever curve (GZ)up to an angle of heel of 40° should

not be less than 0,090 mrad. or the angle of flooding Of if this angle is less than

40°

The area under the righting lever curve (GZ) between the angles of heel of 30° and

40° or between 30° and Of if this angle is less than 40°, should not be less than

0,030 mrad.

The initial metacentric height GM° should not be less than 0,15 m.

The area under the righting lever curve (GZ) to the second intercept or

dovvnflooding angle, whichever is less, should be not less than 40% in excess of

the area under the wind heeling curve to the same limiting angle.

The range of the righting lever curve (GZ) should be at least 30°.

The angle of second intercept between wind heeling lever and righting lever

should be at least 30°.

TYPE II

DRILLING MAST

(22)

2.3 Loading conditions

Relevant loading cases are drawn from a typical well program. The following stages

can be recognised:

Move vessel on to location

Drill 36" hole to 1.000 ft below seabed

Run & cement 30" casing

Drill 26" hole to 2.000 ft below seabed

Run & cement 20" casing

Install 18-3/4 BOP and riser

Drill 16" hole to 9.000 ft below seabed

Run & cement 13"318 casing

Drill 12"1/4 hole to 15.000 ft below seabed

Run & cement 9"5/8 casing

Drill 8"1/2 hole to 20.000 ft below seabed

Run & cement 7- liner

Disconnect BOP and riser

Run X-mas tree & 7" completion riser

Well testing

Plug & suspend well

Sailing home

Emergency disconnect LMRP during drilling or test

The following loading cases are defined:

TYPE II

DRILLING MAST

Condition

Well program stage

1

Sailing 90% consumables

1

2 Sailing 10% consumables

Drilling, BOP connected, 90% consumables

7- 17

4 Drilling, BOP connected, 10% consumables

7 _ 17

5 Testing 90% consumables, 98% crude storage

13,14,15

6 Testing 50% consumables, 50% crude storage

13,14,15

7 Testing 10% consuMables, 98% crude storage

13,14,15

8 Survival condition, 10% consumables

18 3..

'9.

a

17..

(23)

2.3.1 Summary of loading conditions

In all loading conditions taking in ballast water has minimised the trim of the vessel.

2.4 Wind heeling moment curves

2.4.1 General

The wind heeling moment curves are based on the guidelines presented in the IMO

MODU Code and DNV Rules for Mobile Offshore Units (part3, ch.2, sec.6).

In the guidelines two wind conditions are defined for intact stability. For offshore

service conditions a minimum wind velocity of ve = 36 m/s should be applied, and a

minimum velocity of vc = 51,5 m/s is defined for severe storm conditions. For loading

condition 1 to 7 (sailing, drilling, testing) the wind velocity of 36 m/s is used and for

survival conditions (cond.8) the wind velocity of 51.5 m/s is used.

2.4.2 Calculation

of

wind heeling moment curves

The wind heeling moment curves as required by the rules have to be transformed in

such a manner so that they can be implemented in PIAS.

The wind heeling moments in PIAS are based on the wind contour of the vessel.

Because the only input required for the calculations is the windpressure, this value has

been adjusted for the shape and height coefficient to obtain the wind heeling moments

defined by the Rules for the various sections. In appendix 2 the windpressures at the

different levels for the different conditions used in the stability calculations are

presented.

For the various draughts formally the change of the height coefficient has to be taken

into account. PIAS takes the influence of the change of the area for the hull for the

different draught into account but neglects the change of the height coefficient. The

deviations due to this method are very small and neglected. At smaller draughts the

wind heeling moment will be calculated a bit too small and for larger draughts a bit

too high.

The calculation of the heeling moments can be found in appendix 2.

TYPE

DRILLING MAST

Loading condition

1

2

3

4

5

6

7

8 Displacement (t)

44725

35797

47794

40908

54034

51454

48641

36221

Draught (m)

8,23

6,78

8,72

7,61

9,74

9,31

8,87

6,85

Trim (m)

-0,43

-0,04

-0,70

-0,53

0,91

0,03

-0,04

-0,19

VCG (m)

12,98

13,91

11,85

12,51

12,58

11,52

13,31

13,75

LCG (m)

95,75

97,76

94,88

96,00

97,06

95,82

96,03

97,37

GMsolid (m)

5,10

6,10

5,78

6,28

4,26

5,61

4,17

6,151

GM' (m)

3,99

3,97

4,35

4,24

2,37

3,15

2,12

4,455

' "

(24)

2.4.3 Results

The wind heeling moments, as calculated according to MODU code and DNV Rules.

are translated into wind pressures for the contour as defined in PIAS.

Wind pressures for PIAS

2.5 Results of intact stability calculations

All loading conditions comply with the stability criteria as stated in § 2.2.

A summary of the stability calculations can be found in appendix 2.

TYPE II

10 DRILLING MAST

Moment (kNm)

Displacement (t)

Lever (m)

V = 36 m/s

82.937

43.243 0,195

V = 51,5 m/s

169.729

43.243 0,400

V = 25,8 m/s

42.597

43.243 0,100

Pressure (kg/in-')

Elevation (m)

V= 36 m/s

V = 51,5 m/s

V = 25,8 m/s

0-15

128

268

67 15 - 30

145

292

73 30 - 45

160

320

80 45 - 60

170

340

85 60 - 75

180

360

90 75 - 90

190

380

95 90 - 105

200

400

100 Attained value per loading condition

rit

Req.

1

2

3

4

5

6

7

8

1

25,0

33,7

29,7

34,5

33,3

32,9

33,5

32,1

30,9

2 0,20

2,52

2,01

2,75

2,49

1,73

2,16

1,65

2,29

3 0,055

0,621

0,579

0,672

0.643

0.402 0,510

0,375

0,648

4 0,090

1,060

0,899

1,159

1.073 0,691

0,883

0,641

1,026

5 0,030

0,439

0,320

0,488

0,429

0,290

0,373

0,266

0,378

6 0,15

3,99

3;97

4,35

4,24

2,37

3,15

2,12

4,46

7 1,4

7,8

4,7

8.1 6,8

6.4 7,9

5,2

2,6

8 30,0

61,4

53,3

65,4

60,0

55,0

59,4

52,1

56,5

9 30,0

60,8

52,3

64,9

59,3

54,3

58,8

51,4

54,5

,

(25)

--3 Damage stability

3.1 Requirements

Regarding the fact that the vessel is subdivided in many small compartments, no

difficulties are expected in meeting the damage stability criteria. Nevertheless, the

most critical damage cases will be examined.

IMO MODU Code regulations are to be satisfied for all loading conditions, MARPOL

regulations only apply to conditions with oil in cargo tanks (conditions 5,6 and 7)

IMO MODU Code

Requirements:

The metacentric height in the flooded position is positive.

The area under the righting moment curve shall be at least equal to the area under

the wind moment curve up to the second intercept of the curves.

The extent of damage to be applied is the flooding of any one compartment.

The wind moment curve should be based on a wind velocity of 25,8 m/s.

MARPOL

Requirements:

In flooded condition the angle of inclination < 300

In flooded condition the righting lever has at least a range of 20° beyond the

position of equilibrium in association with a maximum residual lever of at least

0,1 m within the 20° range.

The area under the curve within this range shall not be less than 0,0175 mrad.

Longitudinal extent of damage:

10,97 m

Transverse extent of damage:

7,12 m

Vertical extent from baseline upward without limit.

The wind moment curve should be based on a wind velocity of 25,8 m/s.

TYPE II

11

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3.2 Results

For the requirements as stated in § 3.1

,

the maximum allowable VCG' is calculated at

several drafts. The outcomes are represented in figure 3.1. The maximum allowable

VCG' for the individual damage cases can be found in appendix 3.

Maximum allowable VCG'

Figure 3.1

Maximum allowable VCG'

The characteristics of the loading conditions that were used for the intact stability

calculations are plotted in this graph. It becomes clear that all requirements are

satisfied. As a reminder, a summary of loading conditions is given underneath.

TYPE II

₁₂

DRILLING MAST

Condition

1

Sailing 90% consumables

2 Sailing 10% consumables

Drilling, BOP connected, 90% consumables

4 Drilling, BOP connected, 10% consumables

5 Testing 90% consumables, 98% crude storage

6 Testing 50% consumables, 50% crude storage

7 Testing 10% consumables, 98% crude storage

8 Survival condition, 10% consumables

24 22 20 18 E9

>

16 14 12 10

8e

4

1

IMO MOD U C ode

7

3.

5

6 MAR P DL

4 5 6 7 8 9 10 11 12

Intact draft lm I

3

(27)

4 Resistance and propu Ision

4.1 General

The propulsion consists of two azimuthing thrusters above keel level at the stem. For

the sailing condition a transit speed of 12,5 knots is considered. This transit speed is

regarded as a trial speed.

4.2 Resistance

The resistance is calculated according to Holtrop and Mennen

"A statistical Re-analysis of Resistance and Propulsion on

Data". Ordinary moonpool designs have a great impact on the

overall resistance. Model tests at MARIN showed that

alternative moonpool designs could reduce the added resistance

due to the moonpool by as much as 25%. For this vessel an

alternative moonpool is selected with a wedge on the upstream

side and a cut-out on the downstream side of it. According to

MARIN model tests on ships with similar thruster and

moonpool configurations, a resistance increase of 52% of the

bare hull resistance is estimated (12% due to the moonpool and

40% due to thruster headboxes).

Ordinary moonpool

Alternative moonpool

4.3 Thrusters for main propulsion and DP

For the two main propulsion/DP thrusters at the aft LIPS fixed pitch thrusters type

FS3500 are selected.

Technical data:

MCR 5000 kW at 600rpm

Prop. diam. 3500nun in nozzle

w = 0,15

Design speed 7 knots

Thrust at bollard pull 790IN

TYPE II

13

(28)

4.4 Results

For five drafts the resistance is calculated and the main propulsion azimuthing

thrusters are selected. In the following figure the relation between required and

delivered thrust is shown. In trial condition the draught will be approximately 9m

(loading condition: sailing, 90% consumables).The output of the resistance

calculation can be found in appendix 4.

9

10 ill

L2

13

14

15 V(1{4

t=6m

sit=7m

t=8m

--x t=9m

t=l0m

2 x 5MIN ithrusL

TYPE II

414,

DRILLING MAST

1400

1200

80001

800

600

400

200

(29)

5 DP Station keeping

5.1 DP-requirements

For the assignment of DYNPOS-AUTRO notation, the following general

requirements are to be complied with:

An automatic positioning system with redundancy in technical design and physical

arrangement. This is to compensate for incidents of fire and flooding in addition to

technical failures.

This leads to:

Installation of an independently operating automatic and manual control system

Redundancy of position reference systems and sensors

Redundancy of thrusters and power generating- and distribution systems

5.2 Thruster system

The vessel will be equipped with the following thruster layout:

This system will secure maintenance of position and allows the vessel to keep its

heading in a range of plus or minus 400 around the optimum heading, at the worst

scenario.

The power generation system consists of two separate engine rooms. Each engine

room delivers 17,7 MW at 85% MCR.

TYPE II

DRILLING MAST

Power

(kW)

Thrust

(kN)

2 azimuthing thrusters for DP and main propulsion (1 & 2)

5000

790 4 retractable azimuthing thrusters below keelplane (3, 4, 5, 6)

3300

590 T4

T6

,

T5

T1

T3

T,

(30)

5.3 Environmental forces

The environmental forces acting on the vessel during DP operations consist of:

Wave drift forces

Current forces

Wind forces

Riser forces

5.3.1 Wave drift forces

The wave drift forces are calculated using Gusto's computer program

FACET-DRIFT, a wave drift program based on a pressure integration technique. The panel

model of the vessel is presented in figure 5.1.

Figure 5.1

Panel model for calculation of drift & current forces

TYPE II

16

(31)

53.2 Current forces

The current forces acting on the vessel are calculated using Gusto's computer

program CURRENT. This program determines the flat plate friction resistance and

the pressure resistance of an arbitrary hull-shape. The program was validated against

model-test experiments with large tankers.

The same pallet model was used as for the calculation of drift forces (see figure 5.1).

Results for a current of l' mis

,C n tiosces,F LON), 1019 MO san 35,kNI 200,

OM*

Ulf

avow

260

11111111.11nrii iiTAwn,00

250 **r Al

vt41

10 0 00 240 a Current forces Fy (kN) f-loimor = 161 3 kN 20

AUS

210

Miss

60 140 220 70 100 30 10 50 ea 70 BO

TYPE II

17 DRILLING MAST

290 310 320 270 200 0

(32)

5.3.3 Wind forces

The computer program WINDOS is used to determine the wind forces on the vessel.

The computational model is based on a so-called building block approach. This means

that a structure is thought to be built up by standard components with known force

characteristics. The model is represented in figure 5.2.

Figure 5.2

Block model for WINDOS

Results for a wind speed of 1 m/s

310320

3.30 liliro..30

10134$3.W ind force s (kN1 40 50 300

_-4111111"4-

60 290

IIINO

"40

70

Ira& ,'

Alr

. 000

11111:1*--,v4gIntigfil

suagw---

--..-4Imalw

06._*411q ii

i 424

WWA

'May.

rMIL

0 IV

220 210

/111110%.

150 140 2

11.11111

10 1 0 0 180 280 270 280 250 240 230 13o 120 110

Fa

Fy

TYPE II

DRILLING MAST

80 90 100

(33)

5.3.4 Riser force

The riser forces are calculated according to the following formula:

I seawater

V2current

* Cd * L* D

The current profile is derived from Gulf of Mexico data.

For the capability calculations of the intact thruster system, a high current of 1,1 m/s

is applied, resulting in a riser force of 170 IN.

For a DYNPOS-AUTRO failure, a low current of 0,75 m/s is applied, resulting in a

riser force of 80 kN.

5.4 Thruster forces and consumed power

5.4. 1 General

For several environmental conditions DP power plots are prepared. Furthermore, the

thruster use of all thrusters at each heading is calculated for these conditions. For both

intact and damaged condition (DYNPOS AUTRO) a capability plot is prepared. This

data can be found in appendix 5.

5.4.2 Environmental conditions

DP calculations are performed for several environmental design conditions.

Condition I and 2

Max. drilling

Condition 3 and 4

Stand - by

Condition 5 and 6

DYNPOS AUTR

Condition 7 and 8

DYNPOS AUTRO

condition

Hs

(m)

Tp

(s)

. Wave dir.

(deg)

Vwind

(m/s)

Wind dir.

(deg)

Vcurrent

(m/s)

CUT. dir.

(deg)

1

6,0

11,5

180

25

180 1,1

180

2 6,0

11,5

180

25

90 1,1

180

3 10,0

16,5

180

30

180 1,1

180

4 10,0

16,5

180

30

90 1,1

180

5 6,0

11,5

180

25

180 1,1

180

6 6,0

11,5

180

25

90 1,1

180

7 5,8

10,3

180 20,6

180 0,75

180

8 5,8

10,3

180 20,6

90

0.75

180 TYPE II

19 DRILLING MAST

' I

(34)

5.4.3 Intact thruster system

For the intact system the following results are found:

5.4.4 DYNPOS AUTR failure

For DYNPOS AUTR operations, regulations are such that during any single failure,

the total system shall not lead to critical situations caused by loss of position or

heading. The most onerous situation is the lost of one of the stern thrusters. The

results are then:

5.4.5 DYNPOS AUTRO failure

In case of a DYNPOS AUTRO failure, one engine room or one main switchboard

room is out of order. The DP arrangement is such that in this case either thruster 1 and

5 or thruster 2 and 4 are out of order. The calculated power consumption is then:

TYPE II

DRILLING MAST

Environmental

condition

Required power (MW)

Available thruster

power (MW)

Heading 180° off stern

Heading 150° off stern

1

5,8

11.8 23,2

7 _10,2

7,4

23,2

3 7,2

14,6

23,2

4 14,4

11,6

23,2

Environmental

condition

Required power (MW)

Available thruster

power (MW)

Heading 180° off stern

Heading 150° off stern

5 5,7

11,6

18,2

6 10,1

7,3

18,2

Environmental

condition

Required power (MW)

Available power

(MW)

Heading 180° off stern

Heading 150° off stern

7 4,9

8,9

14,9

8 6,9

4,6

14,9

20

,

(35)

5.4.6 Total power balance

For drilling operations a power balance is made. Consumed power for drilling and

hotel is estimated at 7 MW. For the most onerous situations the power balance is

made up.

Intact (envir. 3&4)

The amount of available power (35,4 MW) is sufficient in intact condition.

DYNPOS AUTRO (one engine room down, envir. 7&8)

The amount of available power (17,7 MW) is sufficient to satisfy DYNPOS AUTRO

regulations.

TYPE II

21 DRILLING MAST

Power consumption (MW)

Heading 180° off stern

Heading 1500 off stern

DP

14,4

14,6

Drilling & hotel

7,0

Power consumption (MW)

Heading 1800 off stern

Heading 150° off stern

DP

6,9

8,9

Drilling & hotel

7,0

TOTAL

21,4

21,6

TOTAL

13,9

15,9

I

(36)

6 Power generation and distribution system

6.1 Power generation

The power generation will be diesel electric. Two separate engine rooms are situated

near the stern of the vessel. This secures that no exhaust gas will run over the drilling

area or heli-deck, thereby improving workability. Each engine room contains four

Wartsila 12V32 engines and alternators. The total power supply is 41,7 MW at MCR.

Technical data Wartsila 12V32

TYPE II

22 DRILLING MAST

Engine output

5400 kW (MCR)

Alternator output

5210 kW (MCR)

# revolutions

720 rpm

Fuel consumption

180 g/kWh

6.2 Power distribution system

The power distribution system is presented in the key one-line diagram on the next

page.

The power from the alternators is directed to two main switchboards. Each

switchboard is connected to three thrusters. Redundancy is built in by application of

tie lines, circuit breakers and change-over switches at two thrusters. Primary power

for main consumers will be generated and distributed at 6,6 kV, 3phase, 60 Hz.

Secondary power for auxiliary consumers and emergency power will be distributed at

440 V. 3phase, 60 Hz. Lighting and small power will be 230 V. single phase, 60 Hz.

Main drilling equipment will be fed by 600V DC.

(37)

main switchboard 6,6 kV - 60 Hz Thruster 1 Thruster 3

r--iuxil:airy swtchtinard 1 440V 230 V ighting Thruster 5 SCR switchboard 1 tie-line he-line

X

shore connection

main drilling equipment

600 V

230 V emergency lighting

SCR switchboard 2 emergency generator

1200 kW Thruster 2 emergency _switchbo:, 640 V 230 V I ghting

KEYPLAN

Thruster 4

r-clean supply switnboard

440 V

460 V for navigation equipment and radio station

switchboard 2 :.4 V Thruster 6 ; man switchboard .7 6 6 wV - 60 tie _ T T3

SYMBOLS

4

0

10

1,\I 1

MDiesel engine

Frequency converter AC Generator AC Motor Change-over switch circuit breaker

X

8 MAIN GENERATORS

6510 kVA

5210 kW

11" 01-..111 , !

720 rpm

60 Hz

engine room;

KEY 0\E-LINE DIAGRA V

1

-tie-line

0

14 16 15

(38)

6.3 Load balance

For five conditions the electrical loading by thrusters, 'drilling equipment, hotel

facilities and auxiliary equipment is presented in an electrical load balance.

The five conditions are:

Harbour

Sailing

Drilling moderate weather (thruster loading 15%)

Drilling rough weather (Hs = 6m, V, = 25 "Vs, Vc = 1,1

mis,

heading 200)

is

DNV DYNPOS AUTRO

(115

= 5,8m, V, = 20,59 "Vs,

Ve

= 0,75 "Vs, heading 30,

(one engine room and two thrusters out of order)

The results of the DP-calculation have been used for the loading from the thrusters.

The total load balance can be found in appendix 6, the results and the loading on the

generator sets are presented in table 6.1.

Table 6.1

Load balance and loading on generators

TYPE II

23 DRILLING MAST

harbour sailing i i drilling moderate weather drilling rough weather (condi) DYNPOS I AUTRO (cond7) thrusters 0 9474 I

..

9879 I 9401 Ship's auxiliaries 1265 1490 2819 3410 3410 SCR Drilling system Drilling auxiliaries 0 n v o I 76 ' 4967 1930 4967 2006 4967 2006 . [

otal required

1265 ' i i 11040 133801 20263 I 19785

I rated power power power power power

power at (MCR) (MCR) (MCR) I (MCR) (MCR)

power supply MCR

on/off

(kW) 1

1

on/off (kW)

on/off

(kW)

Ion/off

(kW)

on/off

(kW) Engine room 1

gen.sel ill 5210 I 5210 1 5210 F 5210 li 5210 out 0

gen.set 2 5210

0

0 0 10 1 I 52101 1 II 52(0 out

a

gen.set 3 gen.set 4 5210 5210 0 0 '0 0 o 0 o o

0,

o o o 1 o o o o out out 0 0 Engine room 2 1 gen.set 5 5210 0 0 I I' 5210 I 5210 1 1 5210 I 5210 gen.set 6 5210 0 o It 5210 0 0 1 5210 1 5210 gen.set 7 I 5210 0 o o o 0 o I 1 5210 ill 5210 gen.set 8

5210,

0 0 o 0 o

o

o ' o 1 5210

emergency! harbour generator I 500 0 0 0 0 0 0 0 0 0 0

(39)

7 Down time

7.1 Motions

For a typical drilling condition with a draught of 8,5m the motion behaviour is

determined. The program "Seaway" is used to calculate the motion characteristics.

The "Seaway" output and RAO's can be found in appendix 7a. For the downtime

calculation the motion behaviour in several specific seastates is needed. The Jonswap

wave spectrum for eleven zero crossing periods with peak enhancement factor 2 and a

significant wave height of lm. is used. Since Seaway output is in significant values,

all values are transformed into maximum amplitudes by multiplication of 1,86. The

motion behaviour in those eleven seastates is suitable for implementation in the

program "Downtime". In the following graphs the motion behaviour is presented. The

unit on the y-axis is m/m for heave and deg/in for roll and pitch.

1 40 1 20 1.00 0.80 060 0 40 0.20 0.00

Heading dialdeg

5 10 15 20 25 30 35 T, (a) heave oach 1.40 1.20 1.00 0.80 0.80 0.40 0.20 0.00 Heading 150 deg 5 10 15 20 25 30 35 T. heave roll [oh 1.40 1.20 1.00 080 0.60 0.40 0.20 0.00 Heading 165 deg 0 5 ID 15 20 25 30 35 T. Is) 4. heave

I. roll

TYPE II

24 DRILLING MAST

4 a

(40)

7.2 Downtime

The motion behaviour in those eleven seastates is suitable for implementation in the

program -Downtime". This program linearises the relation between wave height

and

motion behaviour by multiplying the wave height from the wave scatter diagram with

the Seaway output for Hs = 1m. If this value is larger than the criteria downtime

increases. Downtime is calculated for three headings (150°,165°and 180°)and for

three sets of criteria. The wave scatter diagram of the Golf of Mexico (area 15) is

used.

The following criteria are used (maximum amplitudes):

The results of "Downtime" are tabelised below. Downtime plots are in appendix 7h.

The yearly downtime is estimated by simulating a typical drilling program. This

method is described in report 6204.1000.301, page 102-103. The results are below.

criterium

# 3 hours int.

downtime

hours

Heave

Roll

Pitch

Running casing

1,5 m

1,5 °

Drilling

3,0 in

2,5 °

Tripping

3,75 m

3,5 °

Heading

Casing

Drilling

Tripping

180°

3,37%

0,26%

0.11%

165°

3,37%

0,26%

0,11%

150°

6,54 %

1,38 %

0,22 %

drill eval. pilot

2 16

7%

3.48 reenter and open

2 16

7%

3.48

run &

cement

1 8

28%

6.61

open pilot

2

24

11%

7.57

run&

cement

1

20

18%

11.00 run riser

1

20

18% 11.00

land BOP

1 8 28% 6.61

BOP test

2 8

4%

0.90 tripping

3

36

1%

0.85

drill 2

48

1% 1.39

log&open 2 62 7% 13.09

run

&

cement

1 16 15%

7.20 test stack

2 8

4%

0.90 tripping

3 150 1%

3.55

drill 2

200

1% 5.81 log 1

40 4%

4.80

run 1

24 22%

15.51

test BOP

2

8

4%

0.90 tripping

3 72 1%

1.70

drill 2 96 1%

2.79

log 1

40

18% 22.01

disconnect

2 3 1%

0.13 pull riser

1 13 36%

14.02 plug and abandon

2

24

11%

7.57 total

2880

5.31%

152.90 Annual downtime

20.44 days

TYPE II

25 DRILLING MAST

L

I

(41)

8 Hull strength

The longitudinal strength is calculated according to DNV regulations. A midship

section is designed following the rules with respect to local and global strength.

8.1 Loadings

The stillwater bending moments and shear forces are calculated for all typical loading

conditions, as defined in chapter 2. The maximum bending moments and shear forces

occur at condition "Sailing, 10%" and "Testing 98% crude, 90% consumables"

respectively for bending moment and shear force. The calculated values are compared

with the design stillwater bending moments and shear forces as stated in the rules. A

plot can be found on one of the following pages. The shaded area on the plot

represents the deck opening in the moonpool area, with longitudinal extension. For

the bending moment the design value is applied, for shear force the calculated value.

8.2 Midship section

The most awkward location is around the moonpool area. Figure 8.1 displays the

cross section in this area. The black members are considered effective; the red

members do not contribute to the longitudinal strength.

Figure 8.1

Cross section

The dimensions of stiffeners are dictated by local strength requirements. Plate

thickness is dictated by global strength requirements. For details of the calculation,

reference is made to appendix 8. A drawing of the cross section can be found

on one

of the following pages.

TYPE II

26

(42)

AbsoLute shear force curves

loading condition testing 98% crude, 90% consumables

DNV

31)81 h19

from loading conditions

Bending moment curves

loading condition sailing 10% consumables

1184964 kNm

from loadin onditions

45258 kN

Str ctura[ Loading co parson between

(43)

I 1 1 14 14 3500 4100 3950 6250

vidship section

HP 220e10 t HP 180x10 HP 240x12 HP 240x13 HP 180x10 I HP 220x10 HP 240e13 HP 1E1000 L 11 rn

CLASS

DET NORSKE VERITAS

Principal dimensions

Requirements

Midship section mudulus about the neutral axis

14,24 ml

Midship moment of inertia about the neutral axis

103.26 in'

Combined thickness lbhd & side plating far shear

19,27 mm

Attained values

Material

All transverse plating and slit fenersin

midship area NV-NS, yield stress 235 N/mm2 All longitudinal plating and stiffeners in rrodsImp area NV-32. yield stress 315 NM&

Rule length 188.8 in Breadth 35,6 m Depth 17,6 m

Draught for rules scantlings

11,0 in

Neutral axis from keelplane

8,11 in

Section modulus at main deck

14,37 ins

Section modulus at bottom

16.80 m3

Moment of inertia about the neutral axis

136 31 mi.

BaSIE

rs_o

s

pha

iiids

section

HP 201 HP 240x12 22 I

p

W

(44)

8.3 Results,

Due to the lack of effective material in the upper region of the cross section, the

section modulus at main deck is a critical requirement. In order to minimise the hull

steel weight, the neutral axis is raised as much as possible, to 8,11 m from keelplane.

JResults' from strength calculation:.

8.3.1 Material

All longitudinal plating and stiffeners in the midship area will' be high strength steel

NV 32, yield stress 315 N/mm2.

All transverse plating and stiffeners, as well as all material outSide the midship area,

will be mild steel, NV NS, yield stress 235 N/ nun2

In this context, the midship area runs from the fore engine room bulkhead to the aft

accommodation bulkhead. In the weight calculation, this area is referred to as section.

2

5.

4.1.=

TYPE II

27 DRILLING MAST

Required

Attained

Section modulus about neutral axis

Z

14,24 m3

Zdeck

14,37 m

Zbottom

16,80 m

Maximum stress

-

°deck

222 N/mm

°bottom

190 NA=

Moment of inertia about neutral axis

I

103,26 m

] 1

136,31 in

Combined thickness lbhd & side plating

for shear requirements

19,27

(45)

9 Hull weight

Based on the midship cross section as derived from the strength calculation the basic

hull weight is calculated. The ship is longitudinally subdivided in six sections with a

more or less similar cross section. The objective is to get a cross sectional area and

multiply this with the length of the section. The area of the midship section as

calculated in the strength calculation is directly used in this weight calculation with a

reduction for the fore and aft ship. For each section, steel in decks and longitudinal

stiffeners, which is not accounted for in the strength calculation, is added to the cross

sectional area of that section. Transverse stiffeners (bulkheads, webframes and floors)

are added to the longitudinal members and the total volume of steel can be calculated

with an additional 5% for brackets. In figure 9.1 the sectional subdivision is

presented, the outcome is presented in table 9.1.

The total hull steel weight is 8899 ton of which 46% is made of high strength steel.

The total hull steel weight of 8899 ton is close to the estimated value by the method of

Johnson, Hagen and Ovrebo (8881 ton).

Table 9.1

Hull weight calculation

TYPE II

28 DRILLING MAST

Longitudinal

P...0 7.85 kElern'

section 1 section 2 section 3 section 4 section 5 section 6

A A A A A A

(cm') (cm') (cm2) (cm') (cm) (cm')

strength 29857 strength 29857 strength 29857 strength 29857 strength 29857 strength 29857

dock 3200 deck 3200 moonpool 4186 deck 3200 deck 3200 deck 3200

bottom 2000 bottom 2000 cofferdam 5632 bottom 2000 bottom 2000 bottom 2000

tanktop 1750 tanktop 1750 tanktap 1750 tanktop 1750 tanktop 1750

center girder 371 center girder 371 center girder 371 center girder 371 center girder 371

deck 1 4576 deck/ 4576 deck 1 4576 deck 1 4576

deck2 4576 deck/ 4576 deck2 4576 deck2 4000

reduction -11583 deck 3 3500

reduction -9851

Iota tote , 11 tote Iota V. _tote _{t Iota}

volume

section A Length A x L Weight LCG moment

(cm') Intl (MI/ Id Irn)

1 34747.5 38.80 135 1058 13 13758 2 46330 34.40 159 1251 50 62054 3 39675 12.80 51 399 73 29182 4 46330 13.60 63 495 86 42735 5 37178 60.00 223 1751 123 215734 6 39403.2 41.80 165 1293 174 225100 transverse tt I-) Main bulkheads 88.53 7 620 95 58874 Small bulkheads 50.35 8 403 95 38263 Webtrames 4.97 75 373 95 35438 Floors 1/.11 75 833 95 7914-8

total 8475 94.42

Total hull steel weight iincl 5%)

8899

I

3414/.b 494031

(46)

anj

ii

'ran

Erfln

Is

a

raltaliZIPMEN.P.20161111.1

minn"

I

ir

EMI

tel.

I I wlknri WOW 11

Figure 9.1'

Sectional subdivision

TYPE II

29

(47)

10 Building price

For the estimation of the building price, the ship is subdivided in groups (same as

those used in the weight calculation), a sample of such a group is shown in table

10.1.,

Two large posts are steel and drilling equipment. The primary steel costs are

estimated to be 2,5 $/kg for mild- as well as for high strength steel (included

manufacturing), since the price difference for mild and high strength steel is very

small, hfl 0,79 for mild steel and hfl 0,90 for high strength steel. The price of

secondary steel is estimated to be 8 $/kg. The group steel weight is presented in table,

10.1. The other large post is drilling equipment. Total drilling related equipment is

estimated to cost 75 min $

For the other posts a price per kg is estimated or manufacturers are consulted

for exact

prices. In table 10.2 the weight and price of the weight groups is summarised. The

total building costs are estimated to be 183.6 mm n S.

Steel weight

Table 10.1.

Steel weight group

sn put

1 n r

W-

vcg Mg

Tcosts/t

(t)

(m) (m)

costs

primary

steel hull

8899

9.5

94.4 2.5 22,24g

sr econdary steel

400

10.6

94.4

/

8.0 310d

,_

I

reinforcements thrusters

4

80

5.0

120.01

8.0

6401

reinforcements main thrusters

2

50

5.0

0.01

8.0

400 crane pedestral

3 51

17.6 80.01 191.0

57j

engine foundation

208

6.3

17.61

8.0 1,666

shale shaker house

.

115

27.6

66.01' .8))0

920 ubstructure

&

drillfloor

funnels

500

50

24.9

23.6 73.4'

25.0

3.5

.1,750, 1 I

3.5

175 ,skeg

50

1.5 17.0; ,

3.5

175.

contingency 2,5%

260

10.7

94.4111

8:0

2,081)

output

weight.

10663

meg

10.4 lcg

90.6 costs

33,821

TYPE II

30 DRILLING MAST

(48)

Table 10.2

Building costs

TYPE II

31 DRILLING MAST'

Lightship

group

weight

portion

It)

VCG

L CG ,

Ord

Cm) 1,01;01.000

Casts

1

Drilling

Steel weight

10,663 52.84% significant

10.44 '90.63

33,821

equipment

2

Major rig equipment

11,145

5.67% significant

46.45

65.14

3

Mud system'

675 3.34% significant

20.17

56.83

4 Subsea equipment

1,250

6.19% significant

21.92

74.89 75c004

Marine riser system

5

.215

1.07% significant

20.67 127.40

6

Pipe handling

210 1.04% significant

19.70 111.32

7

Substructure piping

95, 0.47% not significant

23.00

73.20 Systems

8

Diesel engines

830 4.11% significant

'9.40

18.00 8,400

9 Mooring & SK systems

490 2.43% significant

10.65

80.15 18,2561

10 Electrical system

375 1.86% significant

12.40

87.27 15,0001

Auxiliary systems

11

1750 8.67% significant

10.64

95.00

2

Topsides

.300

1.49% significant

23.60

15.001

5,100

13

Crude handling

283 1.40% significant

18.84

36.081

4,500

rersonel

14 Accommodation

1,305

6.47% significant

,27.111 165.77

18,280

5

Material handling

350 1.73% significant

36.10

78.20 3,750

6

Lifesaving & rescue

245 1.21% significant

23.17 162.04

1,500

(49)

Appendices

Appendix 1 General arrangement

Thruster retrieving system

Appendix 2 Wind heeling moments calculation

Hydrostatic particulars

Tank arrangement

Intact stability calculations

Appendix 3 Damage stability

Appendix 4 Resistance calculation

Appendix 5 Capability / feasibility plots

Appendix 6 Load balance

Appendix 7a

Seaway output

FtA0

plots

Appendix 7b

Down time plots

Appendix 8

(50)

Appendix 1 General arrangement

(51)

Longitudinal section

centerline

narlans

product..., plateare

116 ..1*.".7.:!

twice, heard room man env.

essie ancear engme noon ad( store 114 e ece _nin scar se mod woman;

foundation [Sells" ases aunts led Lc moos

e canons

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