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These powerpoint files were produced for the Earth History class at the Free University Berlin, Department of Geological Sciences
The copyright for texts, graphical elements, and images lies with C. Heubeck, unless otherwise specified.
Download, reproduction and redistribution of theses pages in any form is hereby permitted for private, personal, non-commercial, and class-related purposes use as long as the source is identified.
Despite of my efforts, I cannot guarantee the completeness, correctness and actuality of the material.
Prof. Christoph HeubeckInstitut für Geologische WissenschaftenFreie Universität BerlinMalteserstr. 74-10012249 BerlinGERMANY
ph: ++49-(0)30-83870695 fax: ++49-(0)[email protected] http://userpage.fu-berlin.de/~cheubeck/
Reservoir Petrophysics
Today’s Lecture
Pressure Distribution in a ReservoirBuoyancy / DisplacementOil and water distribution in a reservoirPorosimetryCapillarity
2
Pressure, arbitrary units
Hei
g ht b
elo w
wa t
er s
urfa
c e, f
t
40 50 60 70 80 90
-15
-10
-5
0
5
-20
Wood density = 0.6Water density = 1.00
The longer the wooden beam, the greater the buoyant force at the top of the board
In general:∆p = δh*∆ρ
∆p
Free water surface
Buoyancy
Pressure, arbitrary units
Hei
g ht a
bove
fre e
wat
e r, f
t
40 50 60 70 80 90
0
5
10
15
20
- 5
ρ gas = 0.3
ρ water = 1.00
∆p = 10
ρ light oil = 0.7
ρ heavy oil = 0.9
contact
contact
contact
shale seal
sandstonereservoir
Reservoir Pressure Gradients
Pressure, arbitrary units
Hei
g ht a
bove
fre e
wat
e r, f
t
40 50 60 70 80 90
0
5
10
15
20
- 5
ρga
s =
0.3
ρ water = 1.00
ρlig
ht o
il =
0.7
ρhe
avy
oil =
0.9
shale seal
sandstonereservoir
Reservoir Pressure Gradients Repeat Formation Tester
Pressure, arbitrary unitsde
pth
40 50 60 70 80 90
80
70
60
50
40
90
ρ water = 1.00
sandstonereservoir
shale seal
ρ heavy oil = 0.9
contact
3
The Concept of Displacement Pressure
how to get the oil in the rock !
The Concept of Displacement Pressure
Capillary water
Types of Water in the Reservoir
Structural water (chemically bound)
Hydration water (chemically bound)
Bound water, immobile water, irreducible water
Bound to the grain by capillary force
Capillary water
Water … and what to do about it !
Structural water (chemically bound)
Hydration water (chemically bound)
Bound water, immobile water, irreducible water(“Haftwasser”)
Can’t do much about them !
Displace as much as possible !
4
Capillarity: Definition
Capillarity ...
... is the tendency of wettingliquids to ascend minute openings(< 0.5 mm diameter) through theagency of a molecular surfaceforce, and (possibly) actingagainst the force of gravity.
Observations
• sponge sucking up liquid• sponge on kitchen counter staying wet• water rising through plants
The Concept of Capillary Pressure
Hydrocarbon
The capillary pressure of a rock is a function of 3 variables :
water
rock rock
• hydrocarbon-water interfacial
tension γ, • wettability (expressed as the
contact angle θ), and • radius of of the pore throat r
The Concept of Capillary Pressure
Hydrocarbon
The capillary pressure of a rock is a function of 3 variables :
water
rock rock
r
θ
• hydrocarbon-water interfacial
tension γ, • wettability (expressed as the
contact angle θ), and • radius of of the pore throat r
γ
The Concept of Capillary Pressure
Hydrocarbon
The capillary pressure of a rock is a function of 3 variables :
water
rock rock
r
θ
• hydrocarbon-water interfacial
tension γ, • wettability (expressed as the
contact angle θ), and • radius of of the pore throat
wherePc = displacement pressureγ = oil-water interfacial tension
(„surface tension“)θ = contact angle of wetting fluid
against the solid („wettability“)r = radius of the pore throat
2γ cos θr Pc =
γ
5
Extreme Example of VERY LOW Capillary Pressure
water
rock rock
θ
wherePc = displacement pressureγ = oil-water interfacial tension
(„surface tension“)θ = contact angle of wetting fluid
against the solid („wettability“)r = radius of the pore throat
2γ cos θr Pc =
As γ , Pc
As θ , Pc
As r , Pc
γ
Hydrocarbon
r
Extreme Example of VERY HIGH Capillary Pressure
water
rock rock
θ
wherePc = displacement pressureγ = oil-water interfacial tension
(„surface tension“)θ = contact angle of wetting fluid
against the solid („wettability“)r = radius of the pore throat
2γ cos θr Pc =
As γ , Pc
As θ , Pc
As r , Pc
γ
r
Hydro-carbon
A closer look at these three factors
•Interfacial tension(„surface tension“)
•Wettability
•Radius of the porethroat
1. Interfacial Tension (“Surface Tension”)
The surface tension of a fluid is• a measure of the cohesion of the molecules at a fluid‘s surface• a function of density r and area of cross section
... is an experimentally determined constant:
All values against air; x 10-3 Nm-1
Pure water, 20 deg C 72.25 Brines higherLight crude oils 20-30 Heavy crudes 35 Mercury 500
Surface tension declines with increasing temperature (and shows a complex behavior with pressure)
6
2. Wettability
calcite
oil
quartz
oil
water
water Wetting Liquid
Non-wetting LiquidContact
angle θ
A water-wet system
Water-wet vs. oil-wet
less mobile
mobile
So
100
0
High initial SoRapid declineHigh recovery rate
Time
An oil-wet system
Water-wet vs. oil-wet
Time
So
100
0
Low initial SoLong slow declineLow recovery
less mobile
mobile
Reservoir Wettability
Initially, all reservoirs are thought to be water-wet
Only after migration, reservoirs may change to oil-wet – why ?Complex chemical and physical interactions of HC with mineral surfaces
Rule of thumb:Carbonate reservoirs are generally oil-wet;Siliciclastic reservoirs are generally water-wet
7
Proportions of oil and water in a reservoir
After finding a reservoir, need to estimate the volumeof oil in it
To what degree has oil beencapable of entering thereservoir pore space, displacingthe capillary water ?
Displacement Pressure vs. Buoyancy Pressure
Capillary Pressure and Buoyancy Pressure: Migration
Capillary pressure measures the forcenecessary to displace capillary water from apore space
Buoyancy pressure is the additional force by which water is displaced by lighter oil from a given volume
For a given reservoir and fluid, it is afunction of reservoir height
For a given reservoir and fluid, it is afunction of pore size
Pw
Pnw
Remember ? Pressure Distribution in a Reservoir
4050 4060 4070 4080 4090
Hei
ght a
bove
fre e
wat
e r, f
t
4040
0
50
100
150
200
-50
Oil density = 0.77Water density = 1.00
∆p = 100*(0.433-0.333)=10 psi
∆p = 150*(0.433-0.333)=15 psi
In general:∆p = dh*(ρbrine-ρhc)
Buoyancy pressureOil pressure gradient
slope = 0.333 psi / ftWater pressure gradient
slope = 0.433 psi / ft
Pressure
Pressure Distribution in a Reservoir
4050 4060 4070 4080 4090
Hei
ght a
bove
fre e
wat
e r, f
t
4040
0
50
100
150
200
-50
Pressure
Available buoyancy pressure
Necessary capillary pressure
8
Force Balance in a Reservoir: Saturation Sw, So
Pressure
4050 4060 4070 4080 4090
Heig
ht
ab
ove f
ree w
at e
r , f
t
4040
0
50
100
150
200
-50
Available buoyancy pressure
Necessary capillary pressure
No HC entry into pore space
Beginning HC entry into pore space
Moderate entry into pore space
Strong entry into pore space
SaturationSo <>
Oil saturation(% of pore volume)
100 80 60 40 20 0
10
50
100
200
500
0
20
Oil-water contact
Seal
Sandstone reservoir
Saturation Sw, So as a function of Pressure
Theoretical curve for perfectly sorted pore
space
Seal
Oil-
wat
er c
apill
a ry
P res
sure
(o
il co
lum
n i n
feet
)Oil saturation
(% of pore volume)
Oil-
wat
er c
apill
a ry
P res
sure
(o
il co
lum
n i n
feet
)
100 80 60 40 20 0
10
50
100
200
500
0
20
Oil-water contact
Sandstone reservoir
Saturation Sw, So as a function of Pressure
Actual curve for perfectly sorted pore
space
Seal
Seal
Irreducible Sw
Entry Pressure
Pore space geometry
1 2
3
3 Shuaiba ls; f=11.9%; k=0.163mD Source: Core Lab
2 Sierra Chata ss; f=7.9%; k=0.399 mD Source: Core Lab
1 http://energy.usgs.gov/ factsheets/Petroleum/SEM.html
9
Pore space geometry
1 2
3
Small pores: ~ 100 µ diameter
Large surface area: >>1m2/g
Una pausa ?
To Repeat
The reservoir must be permeable and porous
Oil displaces pore water completely or partially, depending on capillary pressure
Buoyancy helps
Both determine water saturation
Capillary Pressure and Buoyancy Pressure: Migration
Capillary pressure measures the force necessary to displace capillary water from a pore space
Buoyancy pressure is the additional force by which water is displaced by lighter oilfrom a given volume
For a given reservoir and fluid, it is a function of reservoir height
For a given reservoir and fluid, it is a function of pore size
Pw
Pnw
10
How is the largest connected pore throatdiameter estimated ?
Best:•Injection of a known volume of
non-wetting fluid into sample•Measure pressure necessary to
increase saturation•Measure saturation through
resistivity of rock+fluid
Advantages:•Measure capillary properties of pore size
distribution•Quick and easy with Hg
Porosity, permeability, and capillary pressure
Mercury-injection capillary pressure curve
•Place core plugsample in chamber
•Surround withknown volumeof Hg
•Increasepressure in steps, displacewater (or air)
•Measure Hg saturation aftereach pressureincrease
Mercury saturation (% of pore volume)
Mer
c ury
Pr e
ssur
e ( p
s i)
100 80 60 40 20 0
100
500
1000
2000
5000
0
Entrypressure
200
Plateau
Swi
A Test
Mercury saturation (% of pore volume)
Mer
c ury
Pr e
ssur
e ( p
s i)
100 80 60 40 20 0
100
500
1000
2000
5000
0
200
decreasing reservoir quality !
Your Reservoir – how much oil is in it ?
Mercury saturation (% of pore volume)
Mer
c ury
Pr e
ssur
e ( p
s i)
100 80 60 40 20 0
100
500
1000
2000
5000
0
200
Oil saturation (% of pore volume)
Hei
g ht a
bove
OW
C (f
t)
Res
e rvo
ir
OWC
11
Rock Type 1
0
2
4
6
8
10
12
1.82
20
0.71
69
0.28
21
0.11
10
0.04
37
0.01
72
0.00
68
0.00
27
0.00
10
0.00
04
Particle Size, mm
Incr
emen
tal V
olum
e %
0
10
20
30
40
50
60
70
80
90
100
-0.9
-0.5
-0.1
0.35
0.75
1.15
1.56
1.96
2.36
2.77
3.17
3.58
3.98
4.38
4.79
5.19
5.59 6
6.4
6.8
7.21
7.61
8.02
8.42
8.82
9.23
9.63 10
10.4
10.8
11.2
Particle Size, Phi
Cum
ulat
ive
Vol
ume
%
Porosity vs. Permeabiliy, Cap. Pressure Samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30porosi ty (v/v)
per
m (m
D)
RT 1 > 3500 k/ phiRT 2 450 - 3500RT 3 150 - 450RT 4 6.32 - 150RT 5 > 6.32
0.1 µ
0.25µ
0.5 µ
5 µ
2 µ
1 µ
2 0 µ
10 µ
3R
XRD Rock Type 1
Quartz75%
llli te/M ica1%
Ferroan Dolomite
4%
Plag Feldspar
4%K-Feldspar
15%
50µ
125µ
1
10
100
1000
10000
100000
0 10 20 30 40 50 60 70 80 90 100
Pseudo-Water Saturation (%)
Hg
Inje
ctio
n Pr
essu
re (p
si)
Hg Capillary Pressure
Particle Size
50µ
Rock Type 2Porosity vs. Permeabiliy, Cap. Pressure Samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30porosity (v/v)
perm
(m
D)
RT 1 > 3500 k/ phiRT 2 450 - 3500
RT 3 150 - 450R T 4 6.32 - 150R T 5 > 6.32
0.1 µ
0.25µ
0.5µ
5 µ
2 µ
1 µ
20 µ
1 0 µ
0
2
4
6
8
10
12
1.82
20
0.71
69
0.28
21
0.11
10
0.04
37
0.01
72
0.00
68
0.00
27
0.00
10
0.00
04
Particle Size, mm
Incr
emen
tal V
olum
e %
0
10
20
30
40
50
60
70
80
90
100
-0.87
0.48
1.83
3.17
4.52
5.86
7.21
8.55
9.90
11.25
Laser Particle S ize, Rock Type 2 (phi )
Cum
ulat
ive
Volu
me
%
High-Pressure Hg-Inject ion Capillary Pressure Curves, RT 2
1
10
100
1000
10000
100000
0 10 20 30 40 50 60 70 80 90 100Pseudo-Water Saturation (%)
Hg
Inje
ctio
n P
ress
ure
(psi
)
XRD Rock Type 2
K- Fel dspar14%
P lag Fel dspar
4%
Ferroan Dol omite
5%lll ite/Mica
3% Quartz67%
50µ
125µ
Hg Capillary Pressure
Particle Size
50µ
High-Pressur e Hg-Injecti on Capilla ry Pressure Curves, RT 3
1
10
100
1000
10000
100000
0 10 20 30 40 50 60 70 80 90 100Pse udo-Water Satur ation (%)
Hg
Inje
ctio
n Pre
ssur
e (p
si)
0
2
4
6
8
10
12
1.82
20
0.71
69
0.28
21
0.11
10
0.04
37
0.01
72
0.00
68
0.00
27
0.00
10
0.00
04
Part icle S ize, mm
Incr
emen
tal V
olum
e %
0
10
20
30
40
50
60
70
80
90
100
-0.87
0.48
1.83
3.17
4.52
5.86
7.21
8.55
9.90
11.25
Laser Particle Si ze, Rock Type 3 (phi)
Cum
ulat
ive
Volu
me
%
Rock Type 3Po rosity vs. Permeabiliy, Cap. Pressure Samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30porosi ty (v/v)
perm
(mD)
RT 1 > 3500 k/ phiRT 2 450 - 3500RT 3 150 - 450RT 4 6 .32 - 150
RT 5 > 6.32
0.1µ
0.25µ
0.5 µ
5 µ
2 µ
1 µ
20 µ
10 µ
XRD Rock Type 3
Quartz66 %
lllite/Mica4 %
Ferroan Dolomite
7 %
Plag Feldspar
7 %K-Feldspar
11 %
50µ
125µ
Hg Capillary Pressure
Particle Size
50µ
Rock Type 4
0
2
4
6
8
10
12
1.82
20
0.71
69
0.28
21
0.11
10
0.04
37
0.01
72
0.00
68
0.00
27
0.00
10
0.00
04
Particle Siz e, mm
Incr
emen
tal V
olu
me %
0
10
20
30
40
50
60
70
80
90
1 00
-0.87
0.48
1.83
3.17
4.52
5.86
7.21
8.55
9.90
11.25
Laser P article Size, Rock Type 4 (phi)
Cum
ulat
ive
Volu
me %
High-Pressure Hg-Inje ction Capillary Pressure Curves, RT 4
1
10
100
1000
1 0000
10 0000
0 10 20 30 40 50 60 70 80 90 100Pseudo-Water Saturation (%)
Hg
Inje
ctio
n Pr
essu
re (p
si)
Porosity vs. Permeab iliy, Cap . Pressure Samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30porosity (v/v)
perm
(mD)
RT 1 > 3500 k/ phiRT 2 450 - 3500RT 3 150 - 450R T 4 6.32 - 150
R T 5 > 6.32
0.1 µ
0.25µ
0.5 µ
5 µ
2 µ
1 µ
20 µ
1 0 µ
XRD Rock Type 4
K-Feldspar6%
Plag Feldspar
8%
Ferroan Dolomite
6%lllite/M ica
7% Quartz65%
50µ
125µ
Hg Capillary Pressure
Particle Size
50µ
12
0
1
2
3
4
5
6
1.82
20
0.71
69
0.28
21
0.11
10
0.04
37
0.01
72
0.00
68
0.00
27
0.00
10
0.00
04
Partic le S ize, mm
Incr
emen
tal V
olum
e %
0
10
20
30
40
50
60
70
80
90
1 00
-0.87
0.48
1.83
3.17
4.52
5.86
7.21
8.55
9.90
11.25
Particle Size, Phi
Cum
ulat
ive V
olum
e %
Porosity vs. Permeabiliy, C ap. Pre ssure Samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30po rosit y (v/v)
per
m (m
D)
RT 1 > 3500 k/phiRT 2 450 - 3500RT 3 150 - 450RT 4 6.32 - 150RT 5 > 6.32
0.1µ
0.25µ
0.5µ
5 µ
2 µ
1 µ
20 µ
10 µ
High-Pres sure Hg -Inject io n C apillary Pre ssure C urves, RT 5
1
10
100
1000
10000
100000
0 10 20 30 40 50 60 70 80 90 100Pseudo-Water Saturation (%)
Inje
ctio
n Pr
essu
re (p
si)
Rock Type 5XRD Rock Type 5
Quart z51 %
ll lite/M ica13 %
Ferroan Dolomite
6 %
Pl ag Fe ldspar
7 %K-Feldspa r
5 %
50µ
125µ
Hg Capillary Pressure
Particle Size
50µ
Petrophysics - Literaure
• Tiab, D., and C. Donaldson, 1996, Petrophysics – Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties: Gulf Publishing Co., 706 p.
• Various skripts, available as downloadable pdfs from the internet and compiled in the class archive
In what types of large-scale geometric bodies do these conditions exist in the
subsurface ?
Next Lecture
Reservoirs
Petrophysics Links
• http://www.micromeritics.de/ and http://www.micromeritics.com/: Homepages of the leading producer of pore-analytical hardware; gooddownloadable pdf script; link to a visualisation-software company www.pore-cor.com.
• http://www.petrophysics.net/index.htm: “The Petrophysics Portal: The science of measuring rock properties and the realtionship between those. Maintained by Mark Deakin, a consultant. Many links to organizations, companies etc.
• http://www.hendersonpetrophysics.com/ Similar but not as good.
• http://www.mines.edu/~golhoeft/research/petro.html : An article describing the essence of Petrophysics; by Gary R. Olhoeft, Prof. at Colorado School of Mines.
• http://iva.uni-ulm.de/PHYSIK/VORLESUNG/fluidemedien/node46.html