Presentation given in the upstream track at the Europe Simulation Software User Conference June 2018

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
June 18, 2018 2

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
June 18, 2018 3

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
June 18, 2018 4

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?
June 18, 2018 5

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.) 
June 18, 2018 6

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
June 18, 2018 7

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
June 18, 2018 8

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?
June 18, 2018 9

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
June 18, 2018 10

11. Proprietary Information
Flowassurancemonitoring
• MEG injection takes care of hydrates
• Wax may form along the flowline and the riser during first 9 years
June 18, 2018
WAT
Temperature at end
flowline
HDT
WAX may deposit No WAX
11

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
12

13. Proprietary Information
Lifeoffieldsimulation:transportline
• Pressure and temperature drop along the transport line
• Liquid holdup grows. Wax mass fraction peaks at year 7
June 18, 2018 13

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
June 18, 2018 14

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
June 18, 2018 15

16. Proprietary Information
Thinwaxdepositformsin4months
• Wax deposit peaks after 7 years. Never reaches 0.1 mm in 4 months
June 18, 2018
Year0
Year7
16

17. Proprietary Information
Waxdepositdisappearsatendof life
• As WAT decreases, the wax deposit disappears
June 18, 2018
Year8
Year9
17

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
June 18, 2018 18

19. Proprietary Information June 18, 2018 19
Thankyou