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