Tekna Heavy Oil Technology for

Offshore Applications

Chemistry and Physics of Heavy Oil and other

Dispersions

Per Eivind Gramme

Special Advisor

Grenland Group ASAStavanger, 14.-15. May 2009

Factors stabilizing emulsion and slows down gas/oil/water separation

Inorganic particles

Organic precipitated particles

Napthenic acids

Asphaltenes

ResinsWax

Organic acidsEtc.

1. Surface active components stabilizing the gas/oil and oil/water interface

a) Foam

b) Emulsion

2. Large molecules (ex.: wax and asphalthenic

components) increasing the viscosity

of the crude oil

TWO MAIN FACTORS STABILIZING CRUDE OILS

Interface stabilisation by surfactants

Handeled by adding antifoam agent and de-emulsifier

Oil viscosity

Handeled by increasing the processing temperature

100 cP

Factors stabilizing emulsion

Viscosity of crude oil

Surfactants

Particles that are surface active

The emulsion stability is a function of Water Cut

The emulsion stability is a function of Water Cut

Water cut

▪ Water cut

The effect of water cut and the need for de-emulsifier

The crude oil separation properties are dependant on the system pressure!

1 10 100 1000System pressure (bar)

0

20

40

60

80

100Relative rate of separation

Bottom hole sample

Wellhead sample

Separator 1

Separator 2

Stock tank oil

Downhole Separation

Subsea Separation

Topside Separation

Oil/water separation is strongly dependent on system pressure

0 20 40 60 80 100Water cut (%)

0

20

40

60

80

100 Water separated within 4 min (%)P sep = 1 bara

Crude 1 at 245barCrude 2 at 300barCrude 3 at 180barCrude 4 364barCrude 5 at 170barCrude 6 at 1barCrude 7 at 1barCrude 8 at 1 bar

Downhole

Topside

0 20 40 60 80 100Water cut (%)

0

20

40

60

80

100 Water separated within 4 min (%)P sep = 1 bara

Crude 1 at 245barCrude 2 at 300barCrude 3 at 180barCrude 4 364barCrude 5 at 170barCrude 6 at 1barCrude 7 at 1barCrude 8 at 1 bar

Downhole

Topside

0 20 40 60 80 100Water cut (%)

0

20

40

60

80

100 Water separated within 4 min (%)

Crude 9 at 175barCrude 9 at 1bar100% sep.

Downhole

Topside

0 20 40 60 80 100Water cut (%)

0

20

40

60

80

100 Water separated within 4 min (%)

Crude 9 at 175barCrude 9 at 1bar100% sep.

Downhole

Topside

Light and medium heavy crudes Heavy crude

Sep

ara

tio

n

eff

icie

ncy

Topside and LP separation

Subsea separation

Downhole separation

The structure of oil/water interface and fluid viscosity changes with T and P

T1 and P1 T2 and P2

The important stages of destabilization

Step 1: Drainage of liquid between droplets

Step 2: Breaking the droplet surface

Surfactants

Polymerization at the interface

Action 1: Control viscosity by temperature or use diluent

Action 2: Remove surfactants from the interface using de-emulsifier or (Psys)

Step 1

Design the prosess such that the oil viscosity in the gravity separators and the electrostatic coalescer is less than 5 – 7 cP!

0

5

10

15

20

10 60 110 160 210

Temperature (deg.C)

Oil

visc

osity

(cP)

Oil continuous separation of heavy crudes is dependent on the viscosity which is controlled by the the processing temperature

0

50

100

150

200

10 15 20 25 30

API Density (-)

Tem

pera

ture

(Deg

.C)

The heavy crudes need to be heated in order to bring the viscosity below approx. 5 to 7 cP for efficient processing

Operation at higher temperatures is limited by materials and corrosion aspects, instrumentation and safety aspects!

Data from fields offshore Brasil

Naphtha as diluent may also be used to reduce the oil viscosity

1.Nafta’s high API density ensures very efficient dilution of heavy oil

2.Nafta is compatible with asphaltenes and is easily reuseable

3.Nafta has low affinity versus water ( 0,04 g/l)

Effects of viscosity and surfactants on separation

0

20

40

60

80

100

120

140

2 7 12 17 22 27 32 37

Viscosity continuous phase

Req

uire

d liq

uid

resi

denc

e tim

e

Separation limited by viscocity

Separation limited by surfactant stabilization

Oil from field A

Destabilization using de-emulsifiers

Viscosity reduction by increasing the prosessing temperature

For efficient gravity separation the viscosity of the oil should be less than 10 cP preferably below 7 cP

10 cP

Step 2

Select a de-emulsifier that is reactive towards the surfactants stabilizing the water droplet surface!1. The de-emulsifier is specific for the present crude

oil !

2. The de-emulsifier is specific for the processing temperature and pressure !

3. The way of adding the de-emulsifier and dosage control is important !

4. Multiple dispersions caused by mixing wells is a challenge !

The basic effect of a de-emulsifier

+ =Surface active

Oil soluble

+ =

Effect of de-emulsifier

What dosage of the de-emulsifier is required ….

0

20

40

60

80

100

1 10 100 1000

Dosage (mg/l)

Effic

ienc

y (%

)

Optimal dosage

The required dosage of de-emulsifier depends on:

1. The type of surfactants present

2. The concentration of surfactants at the interface

3. The droplet size distribution and the droplet concentration.

4. The flow rate of crude oil

Add de-emulsifier only once unless otherwise specified!

Dosage

The dosage of de-emulsifiers ….

0 20 40 60 80 100

Demulsifier dosage (ppm)

0

20

40

60

80

100% of water separated in 2 min.

Up Do

1. De-emulsifiers should always be added just upstream choke valves or a high shear devicein order to obtain fast mixing into the crude and to improve the access to the surface of the droplets.

2. The more viscous the crude is the longer reaction time is needed. If possible, deemulsifiers should be added at well head or ever better, down-hole.

3. The dosage of de-emulsifier is dependent on the system pressure.

Usually less de-emulsifier is required at higher system pressure

4. De-emulsifier should be eveluated at system conditions and NOT using stabilized crudes and bottle tests.

Effect of adding deemulsifier upstream a choke valve (19 API crude)

What affects separation in a gravity separator?

GAS

OIL

WATER

Free sedimentation

Break-down of foam

Free sedimentation

Hindered sedimentation

Break-down of emulsion

The important mechanisms are: 1. Droplet break-up due to shear upstream separator

2. Sedimentation (free and hindered)

3. Droplet coalescence

4. Droplet coalescence in dense packed bed

5. Gas flotation

6. Other mechanisms?

Viscosity correction factors for break-up models

( ) ⎥⎦

⎤⎢⎣

⎡

∗σ∗ρμ

∗+= 5.0smd

dµdisp D

964.002.1F

Correction factor for dispersed phase viscosity based on the Viscosity no.:

Correction factor for the continous phase (tentative):

4.0

0c

cµcontF ⎟⎟

⎠

⎞⎜⎜⎝

⎛μμ

= where µc0 = 1 cP

Effect of viscosity on droplet break-up

Continuous phase viscosity Dispersed phase viscosity

Effect of oil viscosity on coalescence and sedimentation in gravity separation

Droplet coalescence Droplet sedimentation

Effect of oil viscosity on emulsion layer break-down

Break-down of emulsion layer

Gas bubbles in emulsion band counteract break down of emulsion layer and separation

0

20

40

60

80

100

0 20 40 60 80 100

Watercut (%)

Wat

er s

epar

ated

with

in 4

min OW separation

GOW separation

Why is gas entrained into the oil/water phase?

GG

O/W

1. There is always small gas bubbles present in the G/O/W fluid entering the inlet cyclone.

2. As the oil is gas saturated and the pressure is partly released before the separator, small bubbles are formed (20 – 150 µm)

3. At higher watercuts the apparent viscosity of the liquid may be significantly higher than the pure oil.

4. The water droplets and gas bubbles move countercurrent within the cyclone. The gas bubbles is therefore hindered in reaching the gas core.

Inefficient gas/liquid separation by inlet devices / inlet cyclones due to small bubble size and high oil phase viscosity (heavy oils)

Why is gas entrained into the oil/water phase?

1. High velocities and bubble flow in upstream piping

2. Upstream inlet heater

3. Choking at manifold

4. Pressure drop across inlet device

Bubble flow in the upstream piping

Size of dispersed bubbles in bubble flow regime.

Mixing multiple wells in a manifold

Conclusions

Evaluate chemicals and required dosage level at realistic process conditions.Be careful trying to assess the separation properties of a given crude oil based on operational experience from a given gravity separator.The separability reflects the fluid itself, but also the upstream system and the actual separator design.

For more viscous crude oils both viscosity and droplet stability has to be adjusted in order to attain optimal separation.Be careful avoiding gas bubbles in dense packed droplet layer when designing the separator.Avoid or control multiple dispersions.

Thank You !