10_ orr - phase inversion
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PDF about Phase Inversion.tells about emulsion Viscosity and inversion pointTRANSCRIPT
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Classification: Internal Status: Draft
Phase inversion in heavy crude oil production
Robert Orr
Water in oil Oil in water
Addition of water
?
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Contents
• Definitions
• What is phase inversion?
• Why phase invert
• Factors controlling phase inversion
• Studies of phase inversion in connection with separation
• Challenges
• Suggestions
• Conclusions
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Phase inversion is
unbelievably complicated
and
poorly understood
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Definitions
• Surfactant
– a chemical that is surface active
– Reduces surface/interfacial tension
– May stabilise against coalescence
• Only consider surfactant stabilised systems
• Two types of emulsions
– Bancroft’s law states that the surfactant prefers to be in the continual phase
– Surfactants in continual phase – a normal emulsion – emulsion ”stable” – slow separation
– Surfactants in the dispersed phase an abnormal emulsion – emulsion not ”stable” – rapid separation
• Demulsifier – special case – should be considered as a system without surfactants
• Phase inversion from:
– A stable to non-stable emulsion
– A non-stable to a stable emulsion
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Phase Inversion – Two types
• Transitional phase inversion
– by changing the temperature or
solvent
• Catastrophic phase inversion
– By increasing the concentration of
the dispersed phase
– By applying shear
0
20
40
60
80
100
120
140
160
27.3 27.3 29.1 35.5 39.2 43.5 47.4 48.9 50.1 52.0 52.8 53.6 54.1 54.1 47.0 37.1 33.8 32.6 29.5
Temperature (°C)
Dia
mete
r (µ
m)
0
100
200
300
400
500
600
700
800
Co
nd
ucti
vit
y (
µS
/cm
)
cold coldwarm
Heavy crude oil emulsion viscosity
@ 60 °C
0
5000
10000
15000
20000
25000
0 10 20 30 40 50 60 70 80 90 100
Water cut [%]
Vis
co
sit
y [
mP
a.s
]
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Why phase invert a heavy crude oil emulsion -
separation• Many good reasons to invert a water-in-oil heavy crude emulsion
• Separation of emulsion
– Settling of water drops
• Stokes equation
settling velocity =2r2 ρg/9
is much smaller
is significantly larger
• For a light oil settling rates approx 5000 faster than for a heavy oil
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Why phase invert a heavy crude oil emulsion - transport
• Viscosity of emulsion controlled by the
viscosity of the external phase
– Typical oil viscosity 2000cP
– For an emulsion the viscosity can be
significantly higher
– Typical water viscosity 1cP
• Water continuous emulsions have lower
viscosity
– Even after 25% dilution of oil
• Reduced rate of organic deposition
Water continuous emulsion
Salager 2001
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Factors controlling phase inversion
• Surfactants
– Surfactants strongly prefers to be in the continual phase
• Viscosity
– The viscous phase prefers to be the dispersed phase
• Shear (poorly understood)
– Both the strength and the nature of the shear
• Wettability
– The fluid that wets the walls, mixer etc prefers to be the continual phase
• Droplet size
• Free gas
• Time
– Age of emulsion, mixing times etc
• There is no unique phase inversion point
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Experience with phase inversion using recirculation of water
• Heavy North Sea oil water injected for 1st stage separator,
– No improvement on oil water separation
• Light North Sea oil water injected before control valve 2nd stage separator
– Water only increased from 15 to 23 % no effect on separation
• An API 20 oil
– Capacity problems have limited the amount of water that can be circulated
• ……….
• No documented proof of phase inversion without the addition of chemicals
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Demulsifiers
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Phase inversion in crude oilsV
isco
sity
Water cut
oil
Water droplets
oil
Water droplets
water
Water droplets
Oil drops
water
Oil drops
Normal emulsion Abnormal emulsion
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Multiple emulsions
Normal to abnormal phase inversion
Piela, 2006
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Multiple emulsions in crude oil systems
Valle, 2000
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The effect of free gas on phase inversion
Water cut regions where phase inversion occurs for a medium light oil
(crude 1), light oil (crude 2) and heavy oil (crude 4) Valle, 2000
Heavy oil
Light oils
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The effect of droplet size and distribution on viscosity
• Smaller droplets for the same water cut
give higher viscosities
• Two emulsions mean droplet size 23 m
– One emulsion monodisperse
estimated viscosity r = 400
– 50:50 mixture of 42 and 13 m
estimated viscosity r = 150
Salager, 2001
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Phase inversion in crude oils
Conditions after water addition, over a mixing device –
What happens?
Water continuous
flow of WiO emulsion
OR
Oil in water flow
w
oil
Oil continuous emulsion
Water added
choke
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Two approaches to phase inversion (consider a 30% water in oil emulsion with a phase inversion point 70% water)
• Adding more water to come over phase
inversion point
• Have to add nearly 300% the volume of
water compared to oil volume.
– Possible capacity problems?
• No stabilisation of oil droplets
• Possible problems with shut ins.
• Cheap?
• Very low viscosity
• Need large amounts of water
• Adding a little water with added
chemicals to come over phase inversion
point approx 10% of oil volume.
• Established technology -Orimulsion
• Possible problems with use of chemicals
– HSE
– Expensive?
– What can one do with extra water
(contaminated with surfactant)
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Phase inversion studies using only shear
on w/o light crude oil emulsions
Effect of water soluble surfactant (1) on in separation
of intial water from Crude 1
0
5
10
15
20
0 10 20 30 40 50 60 70 80 90 10
0
Surfactant (1) [ppm]
Fra
cti
on
wa
ter
rem
ain
ing
in
oil p
ha
se
Fraction water
remaining in oil
phase
Fraction 'old' water
remaining in oil
phase
Initial water fraction
Phase Inversion - Crude 2 - Initially 15%WC
0
2
4
6
8
10
12
Dee
mulsi
fier
Surfa
catn
t 1
Additive
Fra
cti
on
wate
r re
main
ing
in
oil p
hase
Fraction 'new '
w ater remaining in
oil phase
Fraction 'old'
w ater remaining in
oil phase
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Addition of chemicals to invert emulsion
• Demulsifier
– Produce an unstable emulsion
– Possible problems with depletion of demulsifier
• Water soluble surfactant/particles/gels
– Potential to produce a stable emulsion
– May need water
– May be expensive
• Orimulsion uses surfactant to stabilise emulsion
• Can possibly be recycled
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• Using 0.5% water soluble surfactant
Heavy oil in water emulsions stabilised by water soluble surfactant
• Using 0.5% water soluble surfactant
• Emulsions are
– Stable
– Low viscosities
– Destabilised by heating to approx
65ºC
0
0,005
0,01
0,015
0,02
0,025
0 10 20 30 40 50 60 70
% oil in the emulsionR
ela
tive
Vis
co
sit
y (
wit
h r
eg
ard
to
oil)
40°C
4°C
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Issues
• Availability of water
– “Water more valuable than oil”
• Recycling
– Water
– Chemicals
– HSE
• Effect of gas
– Can stabilise water in oil
– Can it stabilise oil in water?
– Other gases, e.g. CO2, N2, etc
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Type of shear
Commercial phase inversion equipmentAkay, 1998
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Suggestions for areas of work
• Need to know:
– Relationship between shear rate and droplet size
• Droplet sizes that can be broken by a given shear or type of shear
– Is there a point of no return?
• Droplet sizes created by a given shear (and type)
– The time when droplets are unstable
ShearTime
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Possible solution
Low shear
d ( m)
d ( m)
d ( m)
High shear
Oil
Heat
exchanger
Water surfactant solution
70% oil in water emulsion
Oil
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Conclusions
• Phase inversion of water in oil emulsions has potential for heavy crude oil
systems because:
– Ease of separation
– Ease of transport
• Most probably an additional chemical is required
• To obtain optimal benefits from phase inversion care is needed with phase
inversion
• Acknowledgements
– StatoilHydro for permission to present this paper
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Thank you for your attention
Questions?
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What is Heavy Crude Oil?
Density @ 15C > 0.993 or API gravity < 20
API = (141.5/SG) – 131.5
High Viscosity (100 to 10,000 cP)
Bitumen: API gravity <10 (SG > 1.0 g/mL) & viscosity >10,000 cP
Gravity 35 20 15 10 5
(oAPI)
Viscosity 10 100 1000 10,000 100,000
(cP)
Conventional
Crude Oil
Extra Heavy Oil
(Tar Sand Oil &
Bitumen)
Heavy Crude
Oil
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Simple Shear
Simple shear Extensional Rotational
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Reasons for failure
• No enough water added
• Testing of ”old” emulsions
– When surfactant is adsorbed at an
interface it will stay there
• Should it really be expected? Shear
Time
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The effect of droplet size on viscosity
Thompson, 1985
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Why is Phase inversion so attractive
• Water in oil emulsions are stable
• Oil in water emulsions are unstable
• Viscosity of an emulsion is mainly
controlled by the viscosity of the external
phase.
• Stokes law
– settling velocity =2r2 ρg/9
• Ease of transportationWater continuous emulsion
Salager, 2001
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Emulsification
ShearTime