running in a new platform

Running-in a new platform!
When the real world does not obey your design basis
Martin Olldag Bay
Leif Blidegn
DONG E&P
Geilo 28 March

Content
 The Siri Complex
 Design basis and expected challenges
 CO2 Corrosion
 Scaling
 Real-life and unexpected challenges
 Deviations in flowrates and temperature
 Compressor performance
 Wax precipitation
 Severe slugging
 Conclusion

The Siri Complex
A
56095607 5608
B
5606
D
55095508
C
0002
5507
5605
5505 5506
B
0003
A
5604
5504
E
039
570957080009 00100008 5707
0004
0011
5610
5603
5510
5503
031
5706
5710
0005
0012
038
0001
030
F
0007
Projection: Mercator (world) [not to scale]
Operator
DONG Energy
Hess
Mærsk
Fields
Gas
Gas Condensate
Gas & Oil
Oil
Oil & Gas
4° 6°
56°
Nini Øst
Nini Vest
Nini
Sofie
Stine Segment-2
Stine Segment-1Siri
Siri Nord
Connie
Francisca
Cecilie
Rau
Lulita
Harald
Amalie
Svane
Hejre
Svend
Q1
Syd Arne
Bertel
Kim
Gert
Ravn
Elly
Valdemar
Adda
Roar
Rolf
Dagmar
Gorm
Halfdan
Lola
Tyra
Tyra Sydøst
Halfdan/NE
Skjold
Dan Alma
Kraka
Regnar
4/956/95
16/9813/06
1/90
7/86
9/95
4/98
1/06
5/98
14/06 7/89
2/06
Norwegian
Shelf
Danish
Shelf
British
Shelf
Dutch
Shelf
German
Shelf
3/07
8°

The Siri Complex
Nini
Cecilie Siri
10" Water Injection
6/10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
CecilieCecilie SiriSiri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East

The Siri Complex
 Siri
 Wellhead and process platform
 First oil March 1999
 Tank capacity 40.000 m3
 Bed capacity 60 pers.
 Weight 11.000 Tonnes
 Reinjection > 95%
 Design capacity 50.000 barrels/day

The Siri Complex
 Stine Segment 1
 Subsea template
 First oil May 2004

The Siri Complex
 Nini A
 Unmanned wellhead platform
 First oil August 2003
 Monotower platform
 Weight 2900 Tonnes
 6 Producers
 4 Injectors
 Cecilie
 First oil August 2003
 3 Producers
 1 Injector

The Siri Complex
 Nini East
 First oil February 2010
 2 Producers
 1 Injector
 Drilling ongoing

Design Basis
 Expected Challenges
 CO2 Corrosion
 Scaling

CO2 Corrosion
 High CO2 content in Nini East reservoir – 0.76 mol%
 Will spread to all producing platforms via liftgas
 Existing platforms designed for low CO2 content
 A new corrosion strategy was needed

CO2 Corrosion
 Selection of an appropriate corrosion inhibitor was based on laboratory
testing, which clarified:
 Inhibitor performance - including persistency on pipe wall and pitting corrosion;
 Tendency to form precipitation of gunk or solid matter;
 Thermal aging and corrosion tendency of neat inhibitor;
 Compatibility with scale inhibitor under topside and down-hole conditions;
 Protection of welds with nickel content.

CO2 Corrosion
 Followed up by offshore test on Stine

CO2 Corrosion
 The corrosion monitoring program was expanded further to include:
 Online ER-probes (Electrical Resistance) on satellite platforms, logging actual corrosion
rate every 6th
hour. The addition of an ECN-probe (Electrical Chemical Noise) is being
considered;
 In-line corrosion coupons with welds;
 Ultrasonic and radiographic WTM (Wall Thickness Measurements);
 Collecting pigging debris for analysis;
 CMU (Corrosion Monitoring Unit) coupled to side-streams, where coupons are evaluated.
 Analysis of water composition and residual corrosion inhibitor.

Design Basis
Nini
Cecilie Siri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East
Material Selection
Inhibitor Injection via Lift Gas
Pigging Debris Analysis

Design Basis
Nini
Cecilie Siri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East
ER probes and coupons

Design Basis
Nini
Cecilie Siri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East
Sidestream Corrosion Rigs

Design Basis
Nini
Cecilie Siri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East
Routine sampling

Design Basis
Nini
Cecilie Siri
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini East
NiniNini
10" Water Injection
4" Gas lift
4" Gas lift
13 km
7 km
9 km
12" Multiphase
8" Multiphase
Stine S1
Umbilical
32 km
Nini EastNini East
Risk Based Inspection

Scaling
 The alternation in composition would result in scaling
0
2
4
6
8
10
0 50 100 150 200 250
SaturationRatio
Pressure (Bar)
Siri SCA 2
CaCO3
BaSO4
Reservoir
Bottom Hole
Wellhead
Separator
Degasser

Scaling
 An injection system of scale inhibitor via lift gas has been installed, in order
to mitigate scaling.
 Selection of appropriate scale inhibitor included following tests:
 Tendency to precipitate or gunk;
 Scale inhibition efficiency;
 Compatibility with other chemicals.

Real-life
 Real-life and unexpected challenges
 Deviations in flow rates and temperatures;
 Compressor performance;
 Wax precipitation;
 Severe slugging.

Actual Flowrates
 The actual flowrates was lower than expected
0
500
1000
1500
2000
2500
19.02 10.04 30.05 19.07 07.09 27.10
OilSm^3/day
Nini East Predicted Vs. Actual
Actual Oil Flowrate Predicted OilFlowrate
0
200
400
600
800
1000
1200
1400
1600
19.02 10.04 30.05 19.07 07.09 27.10
OilSm^3/day
Nini A Predicted Vs. Actual
Actual Oil Flowrate Predicted Oil Flowrate
Snowball effectLower production More problems

Actual Flowrates
0
50
100
150
200
250
300
350
400
450
19.02 10.04 30.05 19.07 07.09 27.10
GaskSm^3/day
ActualGas Flowrate Predicted Gas flowrate
0
50
100
150
200
19.02 10.04 30.05 19.07 07.09 27.10
GaskSm^3/day
Actual Gas Flowrate Predicted Gas Flowrate

Actual Flowrates
0
50
100
150
200
250
300
350
400
19.02 10.04 30.05 19.07 07.09 27.10
GORSm^3/Sm^3
Actual GOR Predicted GOR
0
50
100
150
200
19.02 10.04 30.05 19.07 07.09 27.10
GaskSm^3/day
Actual Gas Flowrate Predicted Gas Flowrate

Actual Flowrates
0
20
40
60
80
100
19.02 10.04 30.05 19.07 07.09 27.10
LiftGaskSm^3/day
Actual Lift Gas Flowrate Predicted LiftGas flowrate
0
500
1000
1500
2000
2500
3000
3500
4000
19.02 10.04 30.05 19.07 07.09 27.10
ProducedWaterSm^3/day
Actual Water Flowrate Predicted Water Flowrate

Temperature
0
5
10
15
20
25
30
35
40
45
50
Temperature[C]
Temperature- Predicted Vs. measured
Expected Temperature [24-04-10] Measured Temperature [24-04-10]
Expected Temperature [29-11-10] Measured Temperature [29-11-10]
NiniEast NiniArrival NiniDeparture Siri

Compressor performance
 Compressor capacity was lower than expected
 Moleweight was out of Spec.

 4 Months after Nini East production started, the compressor was
revamped with similar internals
 The replaced internals was covered in rust

 ~4 kg of deposits was found in the compressor
 65% iron oxide
 5% iron sulphide
 30% organic matter
 No chlorides or carbonates (indicating no liquid carry from the separators).

 The new internals increased capacity, but it was dropping steadily

 Corrosion happened in wet gas system - downstream LP
 Acid cleaning was carried out during the investigations
 Iron-rich water and condensate from knock-out drum was routed back to LP inlet scrubber
 TEG carry over from Glycol contactor to inlet scrubber for HP-section
 Mixture of condensate, iron-rich water and TEG entering LP inlet scrubber, provokes foam
formation -> liquid carry-over to LP-compressor

 Cleaning and chemical injection gave good results

 In January the compressor was revamped with new internals,
designed for the new mole weight.
 Compressor train does now deliver as expected

Wax issue
 During routine pigging in NiniA-Siri pipeline a 14m^3 wax plug was
formed. It was 160 meters long.

Wax issue
 Heavy wax deposits was caused by:
 Initial WAT ~30C
 Actual WAT ~34C
 Lower Nini East temperature
 Shut-in of high WC wells on Nini A

Wax issue
 The main points in the new wax strategy are:
 Special bypass pigs purchased;
 High water cut wells at Nini A restarted prior to pigging;
 Tailor-made chemicals for wax inhibiting/dispersion/dissolving;
 Mechanical removal of wax in production wells;
 Downhole injection of chemicals through chemical injection line at Nini East.
 A clean-up campaign was performed
 Semi-intelligent pigging
 17 pigs were launched – Increasing effective diameter

Wax issue – Differential pressure
172 mm
172 mm
176 mm
Pipe ID -182 mm

Wax issue
 New strategy is successful
 No shutdowns
 Example (7 Feb 2011)
 Pressure drop before pigging – 11.6 Bar
 Pressure drop after pigging – 6.7 Bar
 Pipeline capacity can be increased by ~ 30%

Slugging
 Severe Slugging is a challenge at Siri
 The introduction of Nini East resulted in increased flaring

Slugging
 Challenged by several slug types
 Terrain-induced slugging
 Riser-induced slugging
 Hydrodynamic slugging
A
B
C
D

Slugging
 Slugging solutions:
 Manual choking;
 Automatic choking;
 Slug catcher;
 Antifoam injection;
 Slug handling by slug control valve;
 Slug mitigation by slug control valve.

ISC System (Cranfield)
 Chemical Injection
 Slug mitigation (ISC system)

Conclusion
 Design basis is not the real world!
 Operation procedures has to be reviewed and updated
 Be ready for some urgent challenges
 Tieback solutions needs the right people at the right time
 In spite off challenges:
 Stable production
 Prolonged Siri lifetime
 A valuable asset to the Siri Complex

58
Thank you for your attention!

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