Oil/Water Emulsions
Formation Prediction and Measurement
Dr.
Dr Brendan Graham
University of Western Australia
Centre for Petroleum, Fuels & Energy
Fluid Science Division

Outline
• Introduction to Oil/Water Emulsions
– Formation, Issues, Remediation
• Measurement Techniques
– Techniques, Issues
• UWA Apparatus
– Address shortcomings
• Multi Phase Flow Meters
– Types, Issues

Production Issues
• Lost Production
– Down hole
• Transportation issues
– Viscosity
• Treatment costs
– Chemical, Electrical
• Need to know risk of formation

Relative Viscosity of Emulsions
4

Emulsion Viscosity
• Viscosity of emulsions depends on
– Viscosities of the oil & water
– The volume fraction of the dispersed water
– The droplet size distribution
– The temperature
p
– The shear rate – facilities design implications
– The amount of solids present
5

Crude Oil/Water Emulsions
• Three criteria to form an emulsion
– Two immiscible phases
p
– Agitation to disperse one liquid into droplets
– Emulsifier to stabilise droplets
• Emulsions are problem only if stable on production
time scale

Sources of shear
• Gas lift wells
– Gas injection p
j points
• Pumping wells
– Pump and tubing
• Gas evolution
– Perforations, screens, chokes, flow lines

Emulsion Stability
• Two common types of emulsifiers
– Surfactant or surface active agent
• Reduces surface tension
• Forms viscous barrier
• Repulsion of electrically charged droplets
– Fine solid particles
• Sand, silt, FeS, asphaltenes
8

Emulsifiers
• Naturally occurring
– Higher boiling point fractions – asphaltenes resins
asphaltenes, resins,
organic acids & bases
• Introduced surfactants
– Drilling fluids, stimulation chemicals, EOR
surfactants
– Injected chemicals for wax scale control
wax,
9

Minimisation Techniques
• Use downhole chokes
– Higher temperatures
g p
– Lower pressure differential
• Minimise points of flow disruption
– Smooth flow lines
– Pumps in working order
• Injected chemicals
– Minimise use
– Check for compatibility

Will an oil form an emulsion?
Will my demulsifier work?

Laboratory Techniques
• Bottle Shaker/Rocker
• Blender (D ASTM 1401)
– Originally made for non crude oil application
– Routinely modified for different applications

Case Study Results
• Looking at real report data
• Issues
– Measurement accuracy
– Reproducibility

30:70 Oil:Brine
Low Agitation

30:70 Oil:Brine
High Agitation

• Accuracy of Measurement
– Phase levels not correct
– Subjective determination of levels

Reproducibility

Current Test Conditions
• Shear conditions not representative of real world
shear experienced by oil/water
• Overestimate emulsion formation tendency
• Results quite subjective, user dependent
• Determines demulsifier choice and dosing amount
• N d more representative method
Need t ti th d

UWA solution
• Objective measurement technique
• User independent
• Based on amount of energy required for emulsion
formation

Emulsion Dynamometer
• V i bl speed rotor
Variable d t
• Measure force transmitted
through solution
• Determine energy inputted
into system

Effect of Shear Rate
orce (N)
Fo
Time (s)

Reproducibility
0.1
Sample 1
0.09 Sample 2
Sample 3
0.08
0.07
0.06
Force
0.05
0.04
0.03
0.02
0 02
0.01
0
0 10 20 30 40 50 60
Time (s)

Addition of Surfactant
Increased Energy Input
Slippage
Ons Time [(log (s)]
(
Decreased Energy Input
Increased Viscosity
set
Surfactant Concentration (mg/10mL water)

Applications of Emulsion Dynometer
• Determine energy required for emulsion formation
• Test demulsifier efficacy based on energy applied to
system
• Compare to CFD models to determine amount of
shear experienced in p
p production

Multiphase Meters
• Used to determine flow rates of oil/water in
pipelines
• Need to determine phase fractions
– Gamma rays
– Microwave
– Electrical impedance

Electrical Impedance
• Based on Bruggeman Equation
Measured 13
ε w − ε mix ⎛ ε o ⎞
⎜ ε ⎟ = 1 − φw
×⎜
ε w − ε o ⎝ mix ⎟⎠ Calculated
Assigned Values

Measure & calculate εr (= n2) for oil & emulsion
Characterization of oil
(SCN components)
℘SCN = 0.3341M SCN + 0.4208
ε −1
calculate εoil : = ρ ∑ z SCN℘SCN
ε +2
Measured εoil (Capacitor) Calculated εoil
2.44 ± 0.06 2.1

Relation of Measured to Calculated Data
Then measure εwater & εmix
for known water cuts (φw)
f k t t
to test Bruggeman eqn
Errors of 10-15% compared
to Bruggeman eqn used by
industry in MPFMs

Summary
• Current laboratory results not reproducible and
subjective
• MPFM have errors of 10-15%
• Need for careful evaluation of results

Questions ?