Optimum Compressor Selection To Maximize Brent Field Gas Production

Optimum Compressor Selection To Maximize Brent Field Gas Production

Rotating Equipment Engineering Meeting 2006 Western Region (REEM 2006) 13-15 November 2006, The Hague, Netherlands Thomas Schneider, CEng MIMechE Shell EPE, Brownfield Project Engineering

Riccardo Brogelli, Ing. GE Oil & Gas Nuovo Pignone, Compressor Design

Optimum Compressor Selection To Maximize Brent Field Gas Production

• Changing Operational Requirements • Compressor Design Challenges • Brownfield Construction Challenges

• Questions

Brent Field STOIIP = 3800 MMstb GIIP = 7500 Bscf

N

140 m

2.5 km

500 km

50% Shell 50% ExxonMobil

15 km

5 km

Brent Field Production Profile 1982 : Start of gas export

1997 : Start of depressurization

Compressor Optimisation Opportunity

gas oil

1975 1980 1985

1990

1995

2000

2005

2010

Brent Reservoir Pressure Brent Reservoir Pressures @ Datum (8700fttvdss) 6000

Value Proposition:

5000

Ultimate gas recovery

+ 1 Bscf / psi

Pressure [psi]

4000

reduction in ultimate reservoir pressure

3000

Ultimate Pressure: Base = 1650 psi LPO+EV = 1300 psi LPOP = 1150 psi

2000

1000

Brent B1 Brent B2 Brent B3 Brent B4 Target

Start depressurization

0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Brent Late Life Strategy Map Brent B

Platforms Brent C

SEGAL Brent D

Onshore Compression Reduce “Mini” suction “Mini” suction “Mini” suction FLAGS booster booster booster Pressure Do “Matched” “Matched” “Matched” Nothing Suct. booster Suct. booster Suct. booster Tie-back

Tie-back

Tie-back

Replace HP Replace HP Replace HP Compressor Compressor Compressor Do nothing Discharge Booster

Do nothing

Do nothing

Strategies : No Further Investment Lowest Cost LPOP OPEX Reduction 3rd Party Processing Maximum Recovery Enhanced Voidage Not Feasible

Concept (a) – BD/BB/BD LPOP upgrade Concept (b) – BC LPOP Hub / BB+BD Tie-back

“Mini” suction booster optimally sized for expected late life production.

“Matched” suction booster optimally matched to existing HP compressor.

Brent Late Life Concepts BC

BB

Concept (a): “High Head” LPOP Replacement Compressor on BB, BC & BD:

BA

BD

Penguins

FLAGS

LiftGas

Concept (b): “Matched” LPOP Suction Booster on BC, Wellstream Tie-back of BB & BD

BA

EV

BB

BC

EV Power + Comms

FLAGS

BD

Penguins

EV Power + Comms + LiftGas

Gas Export Compression Train HP1 Suction

HP1 Discharge

GEARBOX MAAG GB-50

HP2 Discharge

GAS TURBINE DRIVER RB-211

HP2 Suction

CENTRIFUGAL COMPRESSOR NUOVO PIGNONE 2BCL506-8/A

~ 2.2 m

~30t

FOUNDATION

~ 4.6 m

Brent LTFD Gas Process Scheme Lift Gas to wells

V-49400 (HP1)

V-49400 V-49400 (HP2)

TEG Contactor V-49600

Gas Export To FLAGS

E-49171

HP wells

E-49181

E-49191

HP Separator V-42100

K-49300 (LP1)

x2 EV wells

K-49300 (LP2)

x2

LP Separator V-42120 E-49140/45

Oil Storage/Export

LP flare k/o drum

E-49150/60

Process Verification “Minimize Change” • Changes to actual volumetric flow – Some recycle valve and LCV resizing

– No piping or vessel changes – manage increased velocity

• Changes to pressure – TEG contactor – reduced efficiency requires stripping gas

– LP compressor - decoupled using discharge throttling valve – Fuel gas supply assurance – trip logic changes – No change to relief pressures

• Increase in compressor discharge temperatures – Process cooler re-rating – heat transfer capacity essentially unchanged – Piping and valve rating – change to valve seat/seal materials – Pipe stress analysis - modified HP1 discharge spool geometry

– Instrumented protection (SIL) - added cooler high temp trip

Brent HP& Compressor OperatingEnvelopes Envelopes Brent Inflow Compressor

HP1 Suction Flow [10^6 scm/d]

14 12

HP2 Discharge 140 bar-a Mol Weight 21 kg/kmol

10

Approx Brent gas inflow capacity (with gaslift)

Year 1997

Year 2000

8 Year 2003

6

Gaslift

Year 2006

4

HP1

Export

HP2

2 HP Sep

Fuel Gas

0 5

10

15

20

25

30

35

HP1 Suction Pressure [bar-a]

40

45

Brent HP& Compressor OperatingEnvelopes Envelopes Brent Inflow Compressor

HP1 Suction Flow [10^6 scm/d]

14

HP2 Discharge 140 bar-a Mol Weight 21 kg/kmol

12

original

Year 1997

10 Year 2000

rewhee l

8

Year 2003

6

upgraded (subject of this presentation)

4 2

Gaslift

Year 2006

HP1

HP Sep

Export

HP2

Fuel Gas

0 5

10

15

20

25

30

35

HP1 Suction Pressure [bar-a]

40

45

Brent HP CompressorEnvelopes Operating Envelopes Brent Compressor 20

compression ratio

15 upgraded 10

rewheel 5 original mol weight: 21.1 kg/kmol suction temp: 30 degC

limited to max 27 MW power

0 5

10

15

20

1st stage suction flow [103 acm/d]

25

Brent Compressor Comparison Original (2BCL506/A) 35 / 140

Rewheel (2BCL506/A) 20 / 140

Upgraded (2BCL506-8/A) 8 / 140

Polytropic Head 1st / 2nd stage (m)

~8500 / 8100

~13000 / 11800

~21000 / 18500

No. of Impellers

3+3

3+3

4+4

Bearing Span (mm)

1953

1953

2166

Max. Continuous Speed (rpm)

8085

9083

9508

600

630

630

Psuct. / Pdisch. (bar-a)

Impeller Diameter (mm) Impeller Material

ASTM A182 Gr F22

ASTM A705 Gr 630

X5CrNi16.4 (Virgo 38)

Upgraded Compressor Rotor / Stator Bearing Span = 2166 mm Rotor Weight = 1310 kg

MCS = 9508 rpm

Optimum Compressor Selection To Maximize Brent Field Gas Production

• Changing Operational Requirements • Compressor Design Challenges • Brownfield Construction Challenges

• Questions

Upgraded Compressor Design Brief Objectives Maximize head Wide operating range

Materials suitable for sour duty

Constraints Same shaft centre-line & base plate as original compressor Crane constraint - Casing weight lower than 18T Nozzle loads up to 5x NEMA

Casing Design Optimisation

Reduced thickness at HP2 suction end

High thickness where necessary

Low thickness where not necessary

GE NP Patent: eccentric casing

Inlet Volute Optimisation

original

improved

Impeller Design Optimisation Full factorial DOE on axial symmetric FEA

VERIFICATION Phase: final 3D check

Design References – Kirk-Donald • K-D used to compare rotor-dynamic criticality of similar designs • All Brent compressors in “warning zone” • Upgrade compressor criticality reduced by increasing shaft stiffness • Risk compounded by not having a string test ➔ complete rotordynamic computational analysis required

max continuous speed first critical speed at infinite bearing stiffness

Pd = discharge pressure Ps = suction pressure

Undamped Critical Speed Map • 1st critical speed far below operating speed range → highly flexible rotor • 2nd critical speed in zone of MCS - but highly damped

1st Critical Speed – Field Results NDE Bearing

1x Amplitude [m]

A.F.=1.76 1st critical speed = 3500 rpm

Shaft speed [rpm]

Compressor Seal Detail HP2 Impeller eye labyrinths swirl breaks

Shunt holes Interstage Tapered Honeycomb

HP1 Impeller eye labyrinths swirl breaks

Honeycomb Taper Selection Brent Compressor Stability vs. Center Seal Divergence (Nominal Bearings) at maximum continuous speed and maximum pressure ratio

2nd stage discharge

1st stage discharge

Interstage Diaphragm Deformation Ambient temperature

Honeycomb seal

Flow Intermediate Balance drum

Differential movement of Inter-stage diaphragm From cold to hot

2nd stage discharge

1st stage discharge

Interstage Diaphragm Deformation Increasing temperature

Honeycomb seal

Flow Intermediate Balance drum

Differential movement of Inter-stage diaphragm From cold to hot

2nd stage discharge

1st stage discharge

Interstage Diaphragm Deformation Increasing temperature

Honeycomb seal

Flow Intermediate Balance drum

Differential movement of Inter-stage diaphragm From cold to hot

2nd stage discharge

1st stage discharge

Interstage Diaphragm Deformation

Differential movement of Inter-stage diaphragm From cold to hot

Maximum temperature

(hot) 0.10 mm

Honeycomb seal

0.44 mm (cold)

Intermediate Balance drum

Flow

90 mm

Honeycomb Clearance Check - Seal in “cold’ condition - Running at 1st critical speed - Vibration at alarm limit

vibration orbit “inlet clearance” (0.70 mm) 0

“cold outlet clearance” (0.60 mm) “hot outlet clearance” (0.26 mm)

Optimum Compressor Selection To Maximize Brent Field Gas Production

• Changing Operational Requirements • Compressor Design Challenges • Brownfield Construction Challenges

• Questions

Construction Challenges 1. Minimize duration of shutdown and production deferment

2. 18t weight limit on boat-to-platform lift due to crane capacity 3. Safely manoeuver 35t compressor through a congested module and lift onto existing elevated baseplate 4. Install 32 pre-fabricated spools without hotwork, ensuring stress-free alignment with existing tie-in points

5. Perform offshore performance / stability trial of new machine

Brent Platform Replacement Process Module (RPM) installed

by LTFD Project.

Access to gas comp on Level 2

Brent Charlie

West crane (boat-to-platfom Max lift 21 t)

Brent Compression Module HP Compressor

Compressor Assembly Trials Casing Lift

Bundle Lift

Compressor Assembly Frame

Mechanical Handling (1/4) Temporary gantry frame with pneumatic hoists/trolleys New HP gas compressor

LP gas compressor Old HP gas compressor Temporary rail system (for load distribution) Empty compressor cradle

Mechanical Handling (2/4) Before shutdown: Install rail system

During shutdown: Install gantry and hoists for compressor lift

Live process piping

After removal of piping

Mechanical Handling (3/4)

Mechanical Handling (4/4)

Piping Dimensional Control

Laser Scan Survey (Point cloud image)

Clash Checks CLASH CLASH CLASH CLASH

CLASH

Gantry and Hoist System Trials

Pipe spool removal

Compressor Installation (1/3)

Compressor Installation (2/3)

Compressor Installation (3/3)

Completed Installation

Conclusions • Business case to lower suction pressures and maximize Brent gas production in late life • Two-step upgrade minimized risk and lifecycle cost

• Technical innovation enabled GE-NP to conceive limit state compressor designs not possible earlier • State-of-the-art modeling and verification gave confidence to install upgrades without string test • Attention to planning, practice and procedures overcame brownfield installation challenges

How NOT to replace the Brent compressor …

(Safety Awareness Posters illustrate hazards of the various activities)

3

1

2 In shutdown: remove pipes & install gantry

pull compressors over rails

5

Pre-shutdown: assemble compressor & install rails in module

4 reinstate & commission

lift compressors using gantry

Optimum Compressor Selection To Maximize Brent Field Gas Production

• Changing Operational Requirements • Compressor Design Challenges • Brownfield Construction Challenges

• Questions

Optimum Compressor Selection To Maximize Brent Field Gas Production 9th European Fluid Machinery Congress 23-26 April 2006, The Hague, Netherlands

Thomas Schneider, CEng MIMechE Shell EPE, Brownfield Project Engineering Riccardo Brogelli, Ing. GE Oil & Gas Nuovo Pignone, Compressor Design

Brent Projects Team Members

Gantry and Hoist System Trials

Control console with load gauges for each hoist

Rail and Cradle System Trials

Rail and Cradle System Trials View from inside module (looking to entrance)

Pneumatic pulling hoist attached to pad eye

View from entrance (looking into module)

LPOP 2BCL508/A stator – HP2 Honeycomb Impeller eye labyrinths labyrinth seal with swirl breaks Shunt holes

Honeycomb Induced Instability Kxx Stiffness Kxx vs Frequency 1.00E+08

Pre-swirl 5.00E+07 0.5 0.4

0.00E+00 0

2000

4000

6000

8000

10000

12000

0.2 0

-5.00E+07

-0.2 -0.4 -0.5

-1.00E+08

-1.50E+08