3 Scott Caird Improving Produced Water 110615 r3f

Improving Produced Water Quality at a North Sea FPSO Scott Caird 11th June 2015

Produced Water Challenges 

High oil in produced water during periods of bad weather  FPSO movement, and lack of internals in vessels  Slugs of high oil concentration in water



Naphthenate related oil in water issues  Oily deposits in process  Contaminates produced water separation process



Non-optimal water clarifier chemistries  Scaling issues associated with product  Pump not properly sized  Highly concentrated product

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Process overview

Crude oil cooler

1st stage sep

1,2

Crude/crude exchanger

Prod header

3

•F

Interstage heater

Oil to cargo

2nd stage sep

Test sep

Test header PW recycle pumps

•F

Reject oil •F

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Hydro cyclones

Water injection WI recycle WI booster PWFD pumps

WI pumps

Desander

1 = SI+CI 2,3 = EB 4 = Coagulant 5 = Flocculant

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Prod water overboard Prod water to slop Oil to closed drain

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Field Data 

API 21 – 23 native crude  38°API dry crude incoming  Approximately 1:1 ratio



100kbpd, 40 – 60% water cut



Process temperature 55°C

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Oil in water  1st stage outlet: several hundred ppm  Hydrocyclone outlet: ~100 ppm  Downstream degasser target < 22 mg/l



Produced water both injected and disposed of overboard 4

Removal of degasser deposits

Flotron D-1340 cleaned the oily deposits and separated the oil and solids completely 5

Optimising Clarifiers 

Replaced Ferric Sulphate coagulant  High Ba, Sr in produced water



Reformulated flocculant  High viscous, concentrated emulsion polymer  Created low viscous, fast acting, winterised product

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Improving Emulsion Breaker 

High oil in water from 1st stage separator



By reducing oil in water from 1st stage, can minimise impact during periods of turbulent seas

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Demulsifier Testing with Focus on Water Quality

New Product 8

Naphthenic Acid in crude oil Calcium naphthenate solids West Africa Soap emulsions

Tight emulsions Soap emulsion Fattty acid sludge

Deposition of calcium naphthenate

Calcium naphthenate solids Bohai Bay, China

Poor water quality

Water quality Bohai Bay, China

Refinery fouling

High Calcium in Crude On Crude TAN Calcium mgKOH/g mg/kg

Lab Ref

Free Water %vol

001-00

85

4.33

98.2

002-00

2.2

4.85

21.1

003-00

90

4.43

41.6

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Typical Produced Water pH Calculated pH as function of pressure in offshore production 9

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Atmosferic LP separator 7

pH

Riser + HP separator Flowline

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Reservoir 5

4

3 0

20

40

60

80

100

120

140

160

Pressure (bar)

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Blocked strainer in FPSO injection water pump

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Flow Assurance (Schmoo’s and Online Cleaners)

Combination deposit of scales, clay, naphthenates, FeS and possibly asphaltenes: Those deposits especially occur in effluent systems, where the pH of the water rises, due to the removal of CO₂. The higher pH causes scales and naphthenates to be formed and 12 due to their sticky character of the naphthenates, they absorb to all kind of solids.

Interesting conclusions from water analysis from 1995

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Field Trial New Demulsifier

Overboard

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Potential Further Improvements 

Targeted clarifier injection  High water cut wells

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Sub-sea co-mingling  Combine high water cut wells with low water cut wells

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Improved Vessel Internals  Baffles to minimise liquid movement in turbulent seas

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Summary 

Improved 1st stage water quality through demulsifier swap out

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Reduced oil and solids in water through formulating with a naphthenate inhibitor



Cleaned produced water degasser with chemical cleaner to remove deposits



Optimised clarifier combination

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50% reduction in overboard oil in water

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Thank You

 Questions

and further discussions

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