Post on 05-May-2022
SEAWATER INJECTION –A HOLISTIC REVIEW
Ross Macdonald
Proserv Production Chemistry Networking Event - 3rd March 20201
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SWI Presentation Outline
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Water Injection
Overview
Injection Water
Quality
Production
Impacts
• Pressure
Support
• Sweeping/EOR
• Example SWI
topside system
• Solids
• Bacteria
• Oxygen
• Downhole
Scaling
• MIC
• Reservoir
Souring
WATER INJECTION OVERVIEW
WATER INJECTION – PRESSURE SUPPORT
• To maintain fixed reservoir pressure
– Voidage of produced fluids replaced with water
• Above bubble point:
– Wi = (OP * Bo) + WP
• Water Injection provides:
– Secondary Production
– Maintains PRes > PBP
• Single HC Phase in Reservoir
• Asphaltene Stability in Reservoir
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WATERFLOOD
• Sweep
• Water front moves out from the injector
• Oil displaced towards production well
• Improved recovery factor
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• EOR
• Polymer flood
• Viscosity improves vertical sweep
• Surfactants
• Reduce residual oil saturation to improve recovery
• Microbial injection/stimulation
• Partial digestion of heavy oils
SEAWATER INJECTION
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WATER QUALITY
WATER QUALITY
• Injection water specification required to maintain:
– Injectivity to the reservoir
– Integrity of the well and injection equipment
• The main seawater quality issues
– Solids
– Marine Growth
– Bacteria
– Oxygen
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WATER QUALITY – SOLIDS
• Solids present in the injection water
– Deposit in injection equipment (efficiency/corrosion)
– Fouling of the sand face (reduced injectivity)
• Fouling tolerance dependent on well/reservoir
– Pore-throat size
• Mitigation: Filtration
– Typical Specification
• Particle Size < 50 µm
• Loading < 100 mg/l
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WATER QUALITY – SOLIDS
• Water hammer from Hard Shut-in
• Hammer induces mobilization in the well bore
– Rat hole solids
– Sand face solids
• Restart drives suspended solids into near well-bore
• Mitigation: Settling period in restart procedure
– Example: 6 hours minimum hold time
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WATER QUALITY – MARINE GROWTH
• Seawater contains diverse array of biota
– Varies by location and time of year (bloom period)
• Macro/Micro fouling
– Shell-fish build up in strainers/exchangers
– Biofilm growth in vessels/pipework
• Example: Ceratium tripos dinoflagellate
– Present in the upper water column
• Mitigation: Chlorine (Hypo/Electrochlorination)
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SEAWATER INJECTION
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WATER QUALITY - BACTERIA
• Seawater contains diverse array of microorganisms
• Issues
– MIC (vessels, pipework and tubing)
– Fouling of vessel internals
– Souring: SO42- → H2S
• Monitoring: Sessile Biofouling Monitoring Tubes (SBMTs)
– Compares with and without biocide
– ATP, qPCR, MPN serial dilution…
• Mitigation: Secondary biocide treatments (batch)
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SEAWATER INJECTION
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WATER QUALITY - OXYGEN
• Oxygen in SW induces pitting corrosion of the injector well tubing
• Dissolved O2 specification depends on required life of well
– Typically <10ppb for L80 tubing
• 13CR Steel tubing more susceptible to O2-induced pitting
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• Significant risk when converting 13CR production
wells to injectors
• 13CR tubing more susceptible to O2 pitting
• Oxygenated brines induce Cl-SCC
WATER QUALITY – ACHIEVING < 10 PPB
• O2 content of SW typically in the range 8 – 11 ppm
• Vacuum Deaeration Tower reduces to ~20 - 50 ppb
• Chemical scavenging utilised to achieve < 10 ppb
– Typically NH4HSO3 or NaHSO3
2HSO3- + O2 → 2H+ + 2SO4
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– Scavenger Catalyst can be required
• Bisulphite can promote corrosion
– Residual range: 1.28 – 2.56 ppm
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SEAWATER INJECTION
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PRODUCTION IMPACTS OF SEAWATER INJECTION
DOWNHOLE SCALING
• FW/SW incompatibility can lead to scale precipitation
– FW provides cation (Ba2+/Sr2+/Ca2+)
– SW provides the anion (SO42-)
• Deposition can block near wellbore and tubing
• Monitoring: SWBT%, ESEMs
• Mitigation: SI Squeeze Treatment, LSSW
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Formation Water Seawater
Na 13617 10933
K 105 460
Ca 596 428
Mg 130 1368
Ba 78 0
Sr 59 8
HCO3 1916 140
SO4 26 2960
Cl 22713 19766
MICROBIALLY INFLUENCED CORROSION (MIC)
• Reservoir contains a vast array of microorganisms
– Archaea: single-celled species
– SRA and Methanogens
• Sulphate ions metobolised by SRA
– Active species promote MIC in pipework/vessels
• ‘Bowl in bowl’ pits indicating MIC
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SOURING
• SRB & SRA present in injection water/reservoir
– Microbes motabilise SO42- to H2S
• Souring in SW supported fields effected by:
– Temperature
– Water Chemistry (salinity)
– Nutrients (sulphate, VFAs, phosphorous)
– Mineralogy (scavenging effects)
• Monitoring: H2S in gas phase
• Mitigation:
– Reservoir Souring Models (understand the potential)
– Nitrate Injection (promote NRPs)
– H2S Scavenger
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SUMMARY
• Water Injection required for pressure support and reservoir sweeping to maximise recovery
• Water quality specification required to maintain integrity and injectivity:
– Solids
– Bacteria
– Oxygen
• Seawater injection can pose significant risks to production
– Downhole Scaling
– Microbial Influenced Corrosion
– Reservoir Souring
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THANKS FOR LISTENING!