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Boundary Tension and Wettability. Immiscible Phases Earlier discussions have considered only a...
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Transcript of Boundary Tension and Wettability. Immiscible Phases Earlier discussions have considered only a...
![Page 1: Boundary Tension and Wettability. Immiscible Phases Earlier discussions have considered only a single fluid in the pores –porosity –permeability Saturation:](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649d1a5503460f949ef976/html5/thumbnails/1.jpg)
Boundary Tension and Wettability
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Immiscible Phases• Earlier discussions have considered only a single
fluid in the pores– porosity– permeability
• Saturation: fraction of pore space occupied by a particular fluid (immiscible phases)
– Sw+So+Sg=1
• When more than a single phase is present, the fluids interact with the rock, and with each other
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DEFINITION OF INTERFACIAL TENSION
• Interfacial (boundary) tension is the energy
per unit area (force per unit distance) at the
surface between phases
• Commonly expressed in
milli-Newtons/meter (also, dynes/cm)
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BOUNDARY (INTERFACIAL) TENSION
Modified from PETE311 Notes
• Imbalanced molecular forces at phase boundaries• Boundary contracts to minimize size• Cohesive vs. adhesion forces
LIQUID(dense phase)
MolecularInterface
(imbalanceof forces)
GASSOLID
LIQUID
GAS
SOLID
Cohesive forceAdhesion force
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DEFINITION OF WETTABILITY
• Wettability is the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids.
• Wettability refers to interaction between fluid and solid phases.
• Reservoir rocks (sandstone, limestone,
dolomite, etc.) are the solid surfaces
• Oil, water, and/or gas are the fluids
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WHY STUDY WETTABILITY?•Understand physical and chemical interactions between
• Individual fluids and reservoir rocks• Different fluids with in a reservoir• Individual fluids and reservoir rocks when multiple fluids are present
•Petroleum reservoirs commonly have 2 – 3 fluids (multiphase systems)
• When 2 or more fluids are present, there are at least 3 sets of forces acting on the fluids and affecting HC recovery
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DEFINITION OF ADHESION TENSION
• Adhesion tension is expressed as the
difference between two solid-fluid
interfacial tensions.
cosowwsosTA
• A negative adhesion tension indicates that the denser phase (water) preferentially wets the solid surface (and vice versa).
• An adhesion tension of “0” indicates that both phases have equal affinity for the solid surface
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CONTACT ANGLE
The contact angle, , measured through the denser liquid phase,defines which fluid wets the solid surface.AT = adhesion tension, milli-Newtons/m or dynes/cm)
= contact angle between the oil/water/solid interface measured through the water, degrees
os = interfacial energy between the oil and solid, milli-Newtons/m or dynes/cm
ws = interfacial energy between the water and solid, milli-Newtons/m or dynes/cm
ow = interfacial energy (interfacial tension) between the oil and water, milli-Newtons/m or dynes/cm
Solid
Water
Oil
Oil Oil
os ws
ow
os
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• Wetting phase fluid preferentially wets the solid rock surface.
• Attractive forces between rock and fluid draw the wetting phase into small pores.
• Wetting phase fluid often has low mobile.
• Attractive forces limit reduction in wetting phase saturation to an irreducible value (irreducible wetting phase saturation).
• Many hydrocarbon reservoirs are either totally or partially water-wet.
WETTING PHASE FLUID
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• Nonwetting phase does not preferentially wet the solid rock surface
• Repulsive forces between rock and fluid cause nonwetting phase to occupy largest pores
• Nonwetting phase fluid is often the most mobile fluid, especially at large nonwetting phase saturations
• Natural gas is never the wetting phase in hydrocarbon reservoirs
NONWETTING PHASE FLUID
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WATER-WET RESERVOIR ROCK
• Reservoir rock is water - wet if water preferentially wets the rock surfaces
• The rock is water- wet under the following conditions:
ws > os
• AT < 0 (i.e., the adhesion tension is negative)
• 0 < < 90
If is close to 0, the rock is considered to be “strongly water-wet”
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WATER-WET ROCK
• Adhesive tension between water and the rock surface exceeds that between oil and the rock surface.
• 0 < < 90
Solid
Water
Oil
os ws
ow
os
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OIL-WET RESERVOIR ROCK
• Reservoir rock is oil-wet if oil preferentially wets the rock surfaces.
• The rock is oil-wet under the following conditions:
os > ws
• AT > 0 (i.e., the adhesion tension is positive)
• 90 < < 180If is close to 180, the rock is considered to be “strongly oil-wet”
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OIL-WET ROCK
• 90 < < 180
• The adhesion tension between water and the rock surface is less than that between oil and the rock surface.
Solid
Water
Oil
os ws
ow
os
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From Amyx Bass and Whiting, 1960; modified from Benner and Bartel, 1941
INTERFACIAL CONTACT ANGLES,VARIOUS ORGANIC LIQUID IN
CONTACT WITH SILICA AND CALCITE
OR
GA
NIC
LIQ
UID
S
SILICA SURFACE
CALCITE SURFACE
WATER
WATER
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GENERALLY,
• Silicate minerals have acidic surfaces• Repel acidic fluids such as major polar organic compounds present in some crude oils• Attract basic compounds• Neutral to oil-wet surfaces
• Carbonate minerals have basic surfaces• Attract acidic compounds of crude oils• Neutral to oil-wet surfaces Tiab and Donaldson, 1996
Caution: these are very general statements and relationsthat are debated and disputed by petrophysicists.
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WATER-WET OIL-WET
Ayers, 2001
FREE WATER
GRAIN
SOLID (ROCK)
WATER
OIL
SOLID (ROCK)
WATER
OIL
GRAIN
BOUND WATER
FR
EE
WA
TE
R
OIL
OILRIM
< 90 > 90WATER
OilAir
WATER
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OIL-WETWATER-WET
WATER
WATERWATER
Air Oil
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From Levorsen, 1967
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Brown, G.E., 2001, Science, v. 294, p. 67-69
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From Tiab and Donaldson, 1996
n = 161 ls., dol.
CONTACT ANGLE: Triber et al.-Water-wet = 0 – 75 degrees -Intermediate-wet = 75 – 105 degrees-Oil-wet = 105 – 180 degrees
n = 30 silicate and 25 carbonates
CONTACT ANGLE:-Water-wet = 0 – 80 degrees -Intermediate-wet = 80 – 100 degrees-Oil-wet = 100 – 180 degrees
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WETTABILITY IS AFFECTED BY:
• Composition of pore-lining minerals
• Composition of the fluids
• Saturation history
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WETTABILITY CLASSIFICATION • Strongly oil- or water-wetting
• Neutral wettability – no preferential wettability to either water or oil in the pores
• Fractional wettability – reservoir that has local areas that are strongly oil-wet, whereas most of the reservoir is strongly water-wet - Occurs where reservoir rock have variable mineral composition and surface chemistry
• Mixed wettability – smaller pores area water-wet are filled with water, whereas larger pores are oil-wet and filled with oil - Residual oil saturation is low - Occurs where oil with polar organic compounds invades a water-wet rock saturated with brine
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IMBIBITION
• Imbibition is a fluid flow process in which the saturation of the wetting phase increases and the nonwetting phase saturation decreases. (e.g., waterflood of an oil reservoir that is water-wet).
• Mobility of wetting phase increases as wetting phase saturation increases
– mobility is the fraction of total flow capacity for a particular phase
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WATER-WET RESERVOIR,IMBIBITION
• Water will occupy the smallest pores
• Water will wet the circumference of most larger pores
• In pores having high oil saturation, oil rests on a water film
• Imbibition - If a water-wet rock saturated with oil is placed in water, it will imbibe water into the smallest pores, displacing oil
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OIL-WET RESERVOIR,IMBIBITION
• Oil will occupy the smallest pores
• Oil will wet the circumference of most larger pores
• In pores having high water saturation, water rests on an oil film
• Imbibition - If an oil-wet rock saturated with water is placed in oil, it will imbibe oil into the smallest pores, displacing water
e.g., Oil-wet reservoir – accumulation of oil in trap
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DRAINAGE• Fluid flow process in which the saturation of
the nonwetting phase increases
• Mobility of nonwetting fluid phase increases as nonwetting phase saturation increases– e.g., waterflood of an oil reservoir that is oil-wet
– Gas injection in an oil- or water-wet reservoir
– Pressure maintenance or gas cycling by gas injection
in a retrograde condensate reservoir
– Water-wet reservoir – accumulation of oil or gas in trap
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IMPLICATIONS OF WETTABILITY
• Primary oil recovery is affected by the
wettability of the system.
– A water-wet system will exhibit
greater primary oil recovery.
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WATER-WET OIL-WET
Ayers, 2001
FREE WATER
GRAIN
SOLID (ROCK)
WATER
OIL
SOLID (ROCK)
WATER
OIL
GRAIN
BOUND WATER
FR
EE
WA
TE
R
OIL
OILRIM
< 90 > 90WATER
OilAir
WATER
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IMPLICATIONS OF WETTABILITY
• Oil recovery under waterflooding is
affected by the wettability of the
system.
– A water-wet system will exhibit
greater oil recovery under
waterflooding.
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From Levorsen, 1967
Effect on waterflood of an oil reservoir?
Water-Wet System
Oil-Wet System
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IMPLICATIONS OF WETTABILITY
• Wettability affects the shape of the
relative permeability curves.
– Oil moves easier in water-wet rocks
than oil-wet rocks.
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IMPLICATIONS OF WETTABILITY
1 2 3 4 5 6 7 8 9 10 11 120
20
40
60
8012345
Coreno
Percentsilicone Wettability0.000.0200.2002.001.00
0.6490.176
- 0.222- 0.250- 0.333
Curves cut off at Fwd •100
1 23
45
Water injected, pore volumes
Rec
ove
ry e
ffic
ien
cy, p
erce
nt,
So
i
Modified from Tiab and Donaldson, 1996
?p. 274
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IMPLICATIONS OF WETTABILITY
Water injection, pore volumes
0
20
40
60
80
1 2 3 4 5 6 7 8 9 10
Squirrel oil - 0.10 N NaCl - Torpedo core ( • 33 O W • 663, K • 0945, Swi • 21.20%)
Squirrel oil - 0.10 N NaCl • Torpedo Sandstone core, after remaining in oil for 84 days ( • 33.0 W • 663, K • 0.925, Swi • 23.28%)
Rec
ove
ry e
ffic
ien
cy, p
erce
nt
Sp
i
Modified from NExT, 1999
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WETTABILITY AFFECTS:
• Capillary Pressure
• Irreducible water saturation
• Residual oil and water saturations
• Relative permeability
• Electrical properties
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LABORATORY MEASUREMENT OF WETTABILITY
Most common measurement techniques
– Contact angle measurement method
– Amott method
– United States Bureau of Mines (USBM) Method
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NOMENCLATURE
AT = adhesion tension, milli-Newtons/m or dynes/cm)
= contact angle between the oil/water/solid interface measured through the water (more dense phase), degrees
os = interfacial tension between the oil and solid, milli-Newtons/m or dynes/cm
ws = interfacial tension between the water and solid, milli-Newtons/m or dynes/cm
ow = interfacial tension between the oil and water, milli-Newtons/m or dynes/cm
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References
1. Amyx, J.W., Bass, D.M., and Whiting, R.L.: Petroleum Reservoir Engineering, McGrow-Hill Book Company New York, 1960.
2. Tiab, D. and Donaldson, E.C.: Petrophysics, Gulf Publishing Company, Houston, TX. 1996.
3. Core Laboratories, Inc. “A course in the fundamentals of Core analysis, 1982.
4. Donaldson, E.C., Thomas, R.D., and Lorenz, P.B.: “Wettability Determination and Its Effect
on Recovery Efficiency,” SPEJ (March 1969) 13-20.