Classification: Internal Status: Draft Phase inversion in heavy crude oil production Robert Orr Water in oil Oil in water Addition of water ?
Classification: Internal Status: Draft
Phase inversion in heavy crude oil production
Robert Orr
Water in oil Oil in water
Addition of water
?
2
Contents
• Definitions
• What is phase inversion?
• Why phase invert
• Factors controlling phase inversion
• Studies of phase inversion in connection with separation
• Challenges
• Suggestions
• Conclusions
3
Phase inversion is
unbelievably complicated
and
poorly understood
4
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
5
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
]
6
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
7
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
8
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
9
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
10
Demulsifiers
11
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
12
Multiple emulsions
Normal to abnormal phase inversion
Piela, 2006
13
Multiple emulsions in crude oil systems
Valle, 2000
14
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
15
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
16
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
17
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)
18
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
19
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
20
• 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
21
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
22
Type of shear
Commercial phase inversion equipmentAkay, 1998
23
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
24
Possible solution
Low shear
d ( m)
d ( m)
d ( m)
High shear
Oil
Heat
exchanger
Water surfactant solution
70% oil in water emulsion
Oil
25
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
26
Thank you for your attention
Questions?
27
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
28
Simple Shear
Simple shear Extensional Rotational
29
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
30
The effect of droplet size on viscosity
Thompson, 1985
31
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
32
Emulsification
ShearTime