This document discusses wax deposition in oil and gas pipelines and presents the results of a wax deposition study for a condensate gathering system. It begins by explaining what wax is and how it deposits before discussing strategies for mitigating wax problems. It then describes a case study of a waxy condensate gathering plant where modeling was used to simulate wax deposition over the life of the field. The modeling showed that wax deposition would likely be a problem in the early years as pressure and temperature dropped but that the risk decreased over time as the wax appearance temperature also dropped. The study concluded that integrated modeling is useful for identifying real risks from wax deposition and determining the best strategy for mitigation or avoidance.

1. Proprietary Information
Theimportanceof life of
fieldin flowassurance – a
wax deposition study
KBCUsersGroupConference
London18th June2018
AlessandroSperanza
June 18, 20181

2. Proprietary Information
Outline
• What is wax and how does it deposit?
• Selecting a mitigation strategy
• A waxy condensate gathering system case
• Flow assurance issues during the life of the field
• Maximus/FloWax wax deposition study. Is wax really a problem?
• Conclusions
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3. Proprietary Information
WhatisPetroleumWax?
• Waxes are crystals consisting predominantly of n-
paraffins that precipitate out of crudes as the
temperature falls
• Waxes form because the n-paraffins are less soluble
and have higher melting points than other
hydrocarbons of the same molecular weight found in
oils
• The crystals are actually solid solutions of n-paraffins,
i.e. they are a mixture of n-paraffins of different
lengths, not a single n-paraffin
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4. Proprietary Information
Whatisthewaxdeposit?
• Wax crystals form at temperature below WAT (wax appearance
temperature)
• Typically at interface between oil and pipeline
• Temperature gradient across pipe section drives deposit formation
• Solid crystals form a large network with large amount of trapped liquid
(60 – 80%)
• Stationary deposit grows as long as conditions hold
• Temperature below WAT
• Temperature gradient across pipe section
• Aging: the deposit hardens as oil diffuses through gel back to flow
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5. Proprietary Information
Flowassurancestrategy
• Wax avoidance
• Keep away from WAT (insulation, active heating, blending….)
• Inject inhibitors to keep n-paraffins in solution
• Remediation
• Pigging (how often?)
• Periodic maintenance
• Live with it
• How much deposit can I tolerate?
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6. Proprietary Information
Selectinga mitigationstrategy
• How much a problem is a big problem?
• What does “waxy fluid” really mean?
• Is a deposit going to form? How thick? Where? When?
• Quantitative predictions
• Fluid PVT modelling (composition, wax precipitation, WAT etc.)
• Wax deposition (insulation, flow rate, choking …)
• Thermo-hydraulics (pressure drop, production profile, temperature drop…)
• Variation of producing conditions
• Need a holistic modelling approach allowing to look at various aspects of
the production (PVT, hydraulics, composition, field planning, wax
deposition etc.) 
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7. Proprietary Information
• Gas condensate field with potential issues of wax, hydrates and liquid
hold-up
• MEG injection for hydrates inhibition
• Wash water injection optimised for scales
avoidance
• 2% total wax content
Awaxycondensategatheringplant
• Wells 4, 5 brought in as per
drilling schedule
• Subsea flowline at 7ºC seabed
temperature
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8. Proprietary Information
Importanceoflifeoffield
• Bottom hole pressure decreases as reservoir is depleted
• Composition varies all the time, as different wells come into production
and conditions of producing wells change
• As pressure drops, temperature in the transport line decreases
• Difficult to select appropriate design case unless variations are
considered
• May introduce large design margins or underestimate risks
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9. Proprietary Information
Flowassuranceissues
• With insulation, temperature at
arrival below WAT and hydrates
dissociation T at beginning of
production
• Things may get worse as
temperature/pressure drop
• MEG injection takes care of hydrates
• What’s best strategy for wax avoidance?
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10. Proprietary Information
Lifeoffieldsimulation
• Wells 1 – 3 are initially in production. Wells 4 and 5 are drilled as per
schedule
• Arrival pressure at platform is set initially at 90 bar. Dropped to 60 bar
just before production drops off plateau
• Pressure/production/PI profile given by reservoir team
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11. Proprietary Information
Flowassurancemonitoring
• MEG injection takes care of hydrates
• Wax may form along the flowline and the riser during first 9 years
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WAT
Temperature at end
flowline
HDT
WAX may deposit No WAX
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12. Proprietary Information
Lifeoffieldsimulation:reservoir
• As reservoir pressure drops
• The fluid cools down and pressure in the production line decreases
• GOR at wellbore varies as pressure drops, from gas only to bi-phase production
June 18, 2018
Gas only
Two-phase
• As new wells come into production,
the fluid mix in the line varies
• Composition changes all the time
• Temperature profile changes due to
variations of heat transfer and new
wells coming in
• PVT tables based network and wax
simulation would be hopeless
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13. Proprietary Information
Lifeoffieldsimulation:transportline
• Pressure and temperature drop along the transport line
• Liquid holdup grows. Wax mass fraction peaks at year 7
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14. Proprietary Information
Iswaxgoingtobea problem?
• As temperature drops
slowly, the wax mass
fraction may increase.
• As composition varies
in the flowline
however, the WAT also
drops
• Wax problems is less
critical than one could
have thought
• Temperature is below
WAT in first 9 years
• First 7 years may be
most critical
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15. Proprietary Information
Waxdepositionstudy
• With FloWax can select the cases of interest from
within the network
• Wax deposition cases are run in sequence from
clean pipeline conditions
• Subsea flowline is the only area of the network
where T goes below WAT
• Can predict
• Required pigging frequency based on fixed criterion
• Wax deposit thickness profile
• Pressure and temperature profiles along affected pipe
segment
• Wax and other phases properties and composition
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16. Proprietary Information
Thinwaxdepositformsin4months
• Wax deposit peaks after 7 years. Never reaches 0.1 mm in 4 months
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Year0
Year7
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17. Proprietary Information
Waxdepositdisappearsatendof life
• As WAT decreases, the wax deposit disappears
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Year8
Year9
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18. Proprietary Information
Conclusions
• Wax deposition may represent a major flow assurance issue
• Costs for wax deposition avoidance or remediation may jeopardise the
economics of the project
• Correct estimation of the size of the problem is a crucial part of design
and operations management
• Sound thermodynamics and mechanistic wax deposition modelling
offers a powerful tool for design and operations
• Life of field simulations allows to pinpoint the real areas and periods of
risk during production and highlight the evolution of the problem
• Integrated wax deposition simulations, within field planning modelling,
offers a major advantage for the correct elaboration of the best
avoidance or mitigation strategy
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19. Proprietary Information June 18, 2018 19
Thankyou