An Introduction to Wettability of Oil...
Transcript of An Introduction to Wettability of Oil...
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An Introduction toWettability of Oil Reservoirs
Petrophysics and Surface Chemistry Group
Petroleum Recovery Research Center
New Mexico Tech
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Outline
• The big picture
• Microscopic view of oil reservoirs
• Capillary phenomena
• Surface chemistry in oil reservoirs
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Outline
• The big picture
• Microscopic view of oil reservoirs
• Capillary phenomena
• Surface chemistry in oil reservoirs
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Geologic scale
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Structural trap
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Outline
• The big picture
• Microscopic view of oil reservoirs
• Capillary phenomena
• Surface chemistry in oil reservoirs
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Microscopic view of an oil reservoir
Blue color is epoxy in interconnected pore spaces.
Typical sandstone.
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Less porous or less permeable?
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More complicated sandstoneEarly diagenetic spheroids in a fine-to medium-grained subarkose,showing variations in internalpatterns and typical radial-fibroustexture.St Bees Sandstone Formation(Triassic), Cumbria, UK.White - quartz; yellow - stained K-feldspar; brown - iron oxide;blue - stained porosity.Scale bar: 100 microns.
from: STRONG, G. E. & PEARCE, J. M. 1995. Carbonate spheroids in Permo-Triassic sandstones ofthe Sellafield area, Cumbria. Proceedings of the Yorkshire Geological Society Vol. 50, Pt 3, 209-211.
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Kaolinite (clay)
Kugler, R.L. and Pashin, J.C., 1994,Reservoir heterogeneity in Carter sandstone,North Blowhorn Creek oil unit and vicinity,Black Warrior basin, Alabama: GeologicalSurvey of Alabama Circular 159, 91 p.
Authigenic kaolinite, Cartersandstone, Black Warrior
basin, Alabama
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Illite (clay)
http://www.creationresearch.org/vacrc/sem02.html
"Hairy" illite clay found in the Coconino sandstone - 2000X — Thefine hair-like structure is actually crystalline mineral and is adiagenetic alteration product of other minerals in the subsurface.
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Outline
• The big picture
• Microscopic view of oil reservoirs
• Capillary phenomena
• Surface chemistry in oil reservoirs
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Common characteristics of oil-bearing rocks
• Pores in which oil is found are small
d < 100µ
• Surface area is high
>> 1 m2/g
• Fluid-fluid interfaces coexist.
• Capillary forces hold oil in place.
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Capillary phenomena
• Capillary rise
• Capillary pressure
• Interfacial tension
• Contact angles
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Capillary rise
0 1,000 2,000 3,0000.001
0.01
0.1
1
10
100
tube radius (microns)
heig
ht o
f ris
e (m
eter
s)
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Capillary pressure
h
Pc = ∆ρ∆ρ g h
Pc = Pnw - Pw
Pw
Pnw
Pc = 2γγ / rr
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Interfacial tension, γ
Liquid 1
Liquid 2
γγ11
γγ22
γγ11d γγ22
d
γγ11d γγ22
d
γγ11d γγ22
dγγ11γγ1212 γγ22= + − 2
F.M. Fowkes, “Attractive Forces at Interfaces,”Ind. Eng. Chem. (Dec 1964) 56, 40-52.
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Why is this interface curved?
Pw
Pnw
θθ
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Water-wet (oil is non-wetting)
water
oil
θθ = 0°
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Oil-wet (oil is spreading)
water
θθ = 180°
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Partial wetting: 0° < θ < 180°
γγos = γγws + γγow cos θθ
water
oilθ
γγos
γγow
γγws
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Crude oil contacting a clean surface
mica
brine
crude oil
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A fresh drop of crudeoil under water doesnot wet the surface.
After it contacts thesurface, the area underthe drop can becomeoil-wet.
If so, a drop of crudeoil remains adheringto the surface.
Adhesion of crude oil under brine
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AFM shows adsorption
clean mica A-93 treated mica
PB brine + A-93, 3 weeks, 80°C, wash with cyclohexane
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Contact angle on treated surface
decane
mica
water
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Brine mediates crude oil/solid interactions
A-93 crude oil aged at 80°C
0 10 20 30 40 500
30
60
90
120
150
180
Aging time in oil (days)
Dec
ane/
wat
er c
onta
ct a
ngle
(de
g)
0.01
0.1
1.0
pH 4
pH 6
pH 8
NaCl (M)
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Wettability affects oil recovery
0 2 4 6 8 10 12 140
20
40
60
80
100
Pore Volumes Injected
Oil
Rec
over
y (%
OO
IP)
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Wettability of an oil reservoir?
• There is not one simple answer.
• Measure properties of reservoir cores– preserved in original condition
– restored to original condition
• Consider the underlying surface chemistry.
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Outline
• The big picture
• Microscopic view of oil reservoirs
• Capillary phenomena
• Surface chemistry in oil reservoirs
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Crude oil fractions
Crude oil
Asphaltenes
Maltenes
Saturates Aromatics Resins
dilute with n-alkane
solution precipitate
adsorb on silicaelute with:
(2) toluene (3) toluene/methanol(1) alkane
no direct effect on wetting can adsorb -> alter wetting
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Mechanisms of interaction
• Polar (water absent)
• Ionic (water present)– acid/base– ion binding
• Surface precipitation
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Mechanisms of interaction
• Polar (water absent)
• Ionic (water present)– acid/base– ion binding
• Surface precipitation
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Basic oil components
low pH high pH
N
R
H+++N
R
H
oilBase
- - - - - - - - -glass / mica
water4
6
8
10
pH0.01 M
0.10 M
1.0 M
2.0 M
[NaCl]
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Acidic oil components
low pH high pH
H++C
OO
R
-COHO
R
oil
Acid
- - - - - - - - -glass / mica
water4
6
8
10
pH0.01 M
0.10 M
1.0 M
2.0 M
[NaCl]
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Examples of acid/base interactions
A-93 crude oil aged at 80°C
0 10 20 30 40 500
30
60
90
120
150
180
Aging time in oil (days)
Dec
ane/
wat
er c
onta
ct a
ngle
(de
g)
0.01
0.1
1.0
pH 4
pH 6
pH 8
NaCl (M)
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Mechanisms of interaction
• Polar (water absent)
• Ionic (water present)– acid/base– ion binding
• Surface precipitation
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Ion binding
H++C
OO
R
-COHO
R
oil
water
- - - - - - - - -Ca2+
Ca2+
Ca2+
glass / mica
Acid:
slow interactionscan be very strongnot very predictable
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Mechanisms of interaction
• Polar (water absent)
• Ionic (water present)– acid/base– ion binding
• Surface precipitation
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One asphaltene molecule?
SS
S
S
S
N
N
N
O
O
S
S
S
S
S
S
S
S= O
NVO
N
N
S
C: 81.0%H: 8.0%N: 1.4%O: 1.0%S: 7.3%V: 0.8%
Mol. Wt.: 6191
H/C: 1.18
Strausz et al., 1991
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Asphaltene aggregation
PRI
volume fraction of oil
RI oil
heptane
colloids
precipitate
macromolecules
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Effects of asphaltenes on wetting
unstable
0 0.2 0.6 0.8 10
30
60
90
120
150
180
Oil Volume Fraction
Ad
van
cin
g C
on
tact
An
gle
(deg
)
Prudhoe Bay(A-93)
plus n-heptane
0.4
Al-Maamari and Buckley, SPE 59292
pH 4
pH 8
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More examples
180
0 0.2 0.4 0.6 0.80
30
60
90
120
150
Ad
van
cin
g a
ng
le (
deg
)
Oil volume fraction (f )
A-93
Lagrave
Mars-Pink
Mars-Yellow
Tensleep
v,oil
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High contact angles at onset
Lagrave
180
0
30
60
90
120
150
Ad
van
cin
g a
ng
le (
deg
)
A-93
Mars-Pink
Mars-Yellow
Tensleep
-0.04 0 0.04 0.08 0.12RI = RI - PRI
∆∆
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Summary
• Oil is found in the small pore spaces in rockswhere it coexists with water (and possibly a gasphase).
• Capillary forces can hold oil in place.• Magnitude of capillary forces depends on
– pore size– IFT– wettability (contact angles)
• Wettability is determined by surface chemistry