spe distinguished lecturer series · 2 crude oil emulsions: everything you wanted to know but were...
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SPE DISTINGUISHED LECTURER SERIESis funded principally
through a grant of the
SPE FOUNDATIONThe Society gratefully acknowledges
those companies that support the programby allowing their professionals
to participate as Lecturers.
And special thanks to The American Institute of Mining, Metallurgical,and Petroleum Engineers (AIME) for their contribution to the program.
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Crude Oil Emulsions:Everything You Wanted to Know
But Were Afraid to Ask
Sunil Kokal
Saudi Aramco
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Outline● Emulsions
What are emulsions?Types of emulsionsWhere do they form?Stability of emulsionsChallenges during oil production
● Reservoir and production aspects of emulsions
● Demulsification: oil-water separation● Emulsion treatment programs● Recommendations
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Milk Mayonnaise
Some Examples of Emulsions
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Definitions● Emulsion: An emulsion is a colloidal
dispersion of one liquid (disperse phase) in another (continuous phase)
● Types of Emulsion:Water-in-oilOil-in-waterComplex/multiple emulsions
● Macroemulsions, size > 0.1 µm● Microemulsions, size < 0.1 µm
Oil-field emulsions are water-in-oil macroemulsions
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Emulsion Photomircrographs
a) Water-in-oil emulsion b) Oil-in-water emulsion
c) Water-in-oil-in-water emulsion d) Presence of solids
10μ
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Where do they form?
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Grains
OilFlow
Emulsion
Water
Gas
Oil
Separator
Where do we encounter emulsions?
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Emulsion Stability
● Emulsions are inherently unstable● Classified based on their kinetic
stabilityloose few minutesmedium tens of minutestight hours, days
● Presence of emulsifying agents● Films act as physical barriers to
coalescence● Factors Affecting Stability
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Loose EmulsionTight Emulsion
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An example of a very tight emulsion
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Factors affecting stability
● Heavy polar material in the crude oil● Fine solids including organics
(asphaltenes, waxes) and inorganics(clays, scales, corrosion products)
● Temperature● Droplet size and and droplet size
distribution● pH of the brine● Brine composition
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Mechanism of emulsion stabilization
Water droplet Asphalteneaggregate
+
Asphaltene Stabilizedwater droplet
Droplets resist coalescence due to steric/colloidal stabilization
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Photo-micrograph of an emulsion showing interfacial films
10 μm
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Measurement of stability
● Determines the ease of separation● Most common is the bottle test● Used for
water separation over timewater separation with demulsifier dosagescreening demulsifiers
● Standard ASTM method for BS&W● Developed at Saudi Aramco: ESI or
Emulsion Separation Index
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Emulsion Challenges During Oil Production
● Negatives:Water and salt in sellable crudeOil in disposal water…injectivity concernsFlow assurance concernsProductivity decline in wellsHigher demulsifier and treatment costsEquipment trips and upsetsHigher oil production costs
● Positives:None!
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Reservoir Aspects of Emulsions
● During drilling operations● Acidization of wells● Well treatments● EOR/IOR operations
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Drilling Operations
● Drilling muds can form tight emulsions
● May cause formation damage● Incorrect estimation of reserves● Most likely to form in reservoirs
with:Lower APIs (< 25o)Lower temperatures (< 150oF)Poorer rock quality (low porosities and permeabilities)Higher amounts of asphaltenes
● Recommend compatibility studies
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Acidization Operations● pH affects emulsion stability● Severe emulsion upsets after acid
stimulation● Occurs due to solid precipitates
mainly asphaltenes● Form very stable and tight emulsion
and can kill a well● Proper design
of acid treatment is necessary to avoid emulsion upsets
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0
20
40
60
80
100
0 2 4 6 8 10 12 14pH
% W
ater
Sep
arat
ion
Effect of pH on emulsion stability
No Demulsifier(24 hr)
30 ppm Demulsifier(1 hr)
30 ppm Demulsifier(24 hr)
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EOR/IOR Operations
● Chemical (ASP) method prone to emulsion problems
● CO2 injection asphaltene precipitation tight emulsions
● Microbial sludges● Thermal heavy oil
solid stabilized emulsions
● Much higher demulsifier treatment costs
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Production Aspects of Emulsions
● High viscosities of emulsions flow assurance issues
● Productivity declines● Oil-water separation
concerns● Facilities operational
concerns● Off-spec crude and
disposal water
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0
5
10
15
20
25
0 20 40 60 80 100
Water Cut, %
Rel
ativ
e Vi
scos
ity, μ
e/ μo
Very tight emulsionTight emulsionMedium emulsionLoose emulsionVery loose emulsion
Viscosity of emulsions
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Demulsification
● Breaking of a crude oil emulsion into oil and water phases
● From a process point of view:Rate or speed of separationResidual water in oilResidual oil in water
● Oil should not contain more that 0.2% BS&W and 10 PTB salt
● Water should contain less than 100 ppm of oil
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Mechanisms Involved in Demulsification
● Two step processFlocculation (or aggregation, or agglomeration or coagulation)Coalescence
● Either of these steps can be the rate determining step
Emulsion Flocculation Coalescence
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Flocculation
● Droplets clump together forming “floccs”
● May not lose their identity● Rate of flocculation depends on
Watercut of the emulsionTemperatureViscosity of the oilDensity differenceElectrostatic field
Flocculation
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Coalescence
● Water droplets fuse or coalesce to form a larger drop
● Coalescence is enhanced byHigh rate of flocculationAbsence of mechanically strong IFFHigh interfacial tensionsHigh watercutsLow oil viscosityLow interfacial viscosityChemical demulsifiersHigher temperatures
Coalescence
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Methods of Emulsion Breaking
● Any or combination of:Thermal…providing heat Mechanical…residence time Electrical…electrostatic gridsChemical…adding demulsifiers
● Demulsification methods very application specific
● Dynamic process: emulsions and conditions change with time
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Emulsion Video
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Emulsion Treatment Program
● Very site specific● Experience and engineering
judgment● Data needed:
Laboratory studiesData from nearby wells/fieldsField trials
● Balance between chemical, thermal, mechanical and electrical
● Optimization
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Emulsion Treatment Program Questions?
● Are we using the best demulsifier?
● What is the retention time?● What type of emulsion?● What is the water cut?● System heated, or can it be?● Range of operating conditions?● Feed constant or changing?
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● Each production stream unique● Laboratory tests with actual samples● Incorporate flexibility during design● Planning early● Pilot and field trials● Re-engineering and retrofitting● Record data for diagnosis● Review periodically
Emulsion Treatment Program Guidelines
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● Fine solids management Scales: Inhibit scale formationAsphaltenes: management, dispersantsCorrosion products: inhibitors
● Acidization…review field performance● Commingling of crudes…compatibility● Mixing and shear…reduce, optimize● Check compatibility of chemicals
Emulsion Treatment Program Prevention
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● Bottle tests…representative samples● Field testing with promising demulsifiers● Proper demulsifier mixing● Demulsifier overdosing● Understanding the causes of tightness● Evaluating the process● Maintaining a database● Demulsifier usage
Less than 5 ppm to over 200 ppmGenerally between 10 to 50 ppm
Emulsion Treatment ProgramDemulsifier Selection & Optimization
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0
1
2
3
4
5
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Cos
t ($/
MB
)199619971999200020022003
Demulsifier costs at a separation plant
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● Diagnose…your emulsions and your hardware● Retrofit…your vessels…after economic analysis● Perform…field trials…periodically●Monitor…performance● Reduce…shear and fine solids…scales,
asphaltenes, clays●Maintain…records● Proactive…in using new technology…
Recommendations
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One thing to remember…
Crude Oil Emulsions:Society of Petroleum Engineers
Petroleum Engineering HandbookVolume 1, Chapter 12
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SPE DISTINGUISHED LECTURER SERIESis funded principally
through a grant of the
SPE FOUNDATIONThe Society gratefully acknowledges
those companies that support the programby allowing their professionals
to participate as Lecturers.
And special thanks to The American Institute of Mining, Metallurgical,and Petroleum Engineers (AIME) for their contribution to the program.
THANK YOU!