Oil/Water EmulsionsOil/Water EmulsionsFormation Prediction and Measurement

Dr Brendan GrahamDr. Brendan GrahamUniversity of Western AustraliaCentre for Petroleum, Fuels & EnergyFluid 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 temperaturep– The shear rate – facilities design implications– The amount of solids present

5

Crude Oil/Water Emulsions

• Three criteria to form an emulsion– Two immiscible phasesp– Agitation to disperse one liquid into droplets– Emulsifier to stabilise droplets

• Emulsions are problem only if stable on production• Emulsions are problem only if stable on production time scale

Sources of shear

• Gas lift wells– Gas injection pointsj p

• Pumping wells– Pump and tubing

• Gas evolution– Perforations, screens, chokes, flow lines

Emulsion Stability

• Two common types of emulsifiers– Surfactant or surface active agent– 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 resinsHigher boiling point fractions asphaltenes, resins,

organic acids & bases

• Introduced surfactants– Drilling fluids, stimulation chemicals, EOR

surfactantsInjected chemicals for wax scale control– Injected chemicals for wax, scale control

9

Minimisation Techniques

• Use downhole chokes– Higher temperaturesg p– Lower pressure differential

• Minimise points of flow disruption– Smooth flow lines– Pumps in working order

• Injected chemicalsInjected chemicals– Minimise use– Check for compatibility

Will an oil form an emulsion?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• Blender (D ASTM 1401)– Originally made for non crude oil application– Routinely modified for different applications– Routinely modified for different applications

Case Study Results

• Looking at real report data

• IssuesIssues– Measurement accuracy– Reproducibility

30:70 Oil:BrineLow AgitationLow Agitation

30:70 Oil:BrineHigh AgitationHigh 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 dependentResults quite subjective, user dependent

• Determines demulsifier choice and dosing amount

N d t ti th d• Need more representative method

UWA solution

• Objective measurement technique

• User independentUser independent

• Based on amount of energy required for emulsion formationformation

Emulsion Dynamometer

V i bl d t• Variable speed rotor

• Measure force transmitted through solutionthrough solution

• Determine energy inputted into systeminto system

Effect of Shear Rate

orc

e (

N)

Fo

Time (s)

Reproducibility

0.08

0.09

0.1Sample 1

Sample 2

Sample 3

0.05

0.06

0.07

rce

0 02

0.03

0.04

0.05

Fo

0

0.01

0.02

0 10 20 30 40 50 60

Time (s)

Addition of Surfactant

Increased Energy InputSlippage

(s)]

set T

ime

[(log

(

Decreased Energy InputIncreased Viscosity

Ons

Surfactant Concentration (mg/10mL water)

Applications of Emulsion Dynometer

• Determine energy required for emulsion formationDetermine energy required for emulsion formation

• Test demulsifier efficacy based on energy applied to systemsystem

• Compare to CFD models to determine amount of shear experienced in productionp p

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

Measuredomixw φεεε

=⎟⎟⎞

⎜⎜⎛

×− 1

31

Assigned ValuesCalculated

wmixow

φεεε

−=⎟⎟⎠

⎜⎜⎝

×−

1

Measure & calculate εr (= n2) for oil & emulsion

Characterization of oil Characterization of oil (SCN components)

4208.03341.0 +=℘ SCNSCN M

calculate εoil : ∑ ℘=+−

SCNSCNzρεε

21

Measured εoil (Capacitor) Calculated εoil

2.44 ± 0.06 2.1

Relation of Measured to Calculated Data

Then measure εwater & εmix

f k t t (φ ) for known water cuts (φw) to test Bruggeman eqn

Errors of 10-15% compared to Bruggeman eqn used by industry in MPFMsindustry in MPFMs

Summary

• Current laboratory results not reproducible and subjective

• MPFM have errors of 10-15%

• Need for careful evaluation of resultsNeed for careful evaluation of results

Questions ?