pc_lab_measurements
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Lab Measurements of Capillary Pressure
All Roads Lead to Rome: Water Saturation atCapillary Equilibrium in the Core
Carlos A Grattoni
London Petrophysical Society - One day Seminar
14 December 2009
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Slide 2®
A proper understanding of capillary pressure behaviour is
crucial for reservoir characterisation and hydrocarbonproduction
Capillary pressure play a role in:
Saturation-height models for determination of hydrocarbon in place
Calculating original saturations through depleted zones
Thin bedded zones that resistivity logs cannot resolve
Checking irreducible water saturations calculated from logs
Residual oil saturation determination
Derivation of free water level from formation pressure data
Explaining differences in contacts between wells
Sealing capacity
….
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Slide 3®
Capillary PressureControlling factors
Pc = ∆ρ g h Fluids density, height
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Slide 4®
Capillary Pressure Definitions
Entry pressure
Threshold,
Breakthrough,Bubbling Pressure Water blocking
Snap-off
Saturation: Fraction of the pore space occupied by a given fluid
⎟⎟⎠
⎞⎜⎜⎝
⎛ +=21
11
RRPc σ
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Slide 5®
Capillary Equilibrium (water-wet)
Sw
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Slide 6®
Static Water Saturation Distribution
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Slide 7®
Quantitative Measurement Saturation on Cores
For core cut in water based mud,Retort Method is used toidentify potential oil and gasreservoirs
For core cut in oil based mud,Retort Method and Dean-Starkwater saturation can provideaccurate measurement of
connate water saturation
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Slide 8®
• Pc
(Sw) depends on thesaturation history. Thiseffect is known ashysteresis
• Drainage: the wettingphase saturation decreases
• Imbibition: the wetting
phase saturation increases
Capillary Pressure Cycles (water-wet)
Swi
Sor
Pc
0 1
Imbibition
Primary Drainage
Secondary Drainage
Water-wet system
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Slide 10®
POROUS DIAPHRAGM METHOD
Scale
Brine
Ultra-finefrittedglass disk
OilSeal
Saran tube
Crude oil
Nitrogenpressure
Neoprenestopper
Spring-
Kleenexpaper
Core
Modified from Welge and Bruce, 1947
Restored State Cell
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Slide 11®
POROUS DIAPHRAGM METHOD
Laboratory procedure
•Begin with core and porous disksaturated with wetting fluid
•Use non-wetting fluid pressure to forceinto core, thus displacing wetting fluidthrough the porous disk
•The pressure difference between the fluids
equals the capillary pressure
•Wait until equilibrium is reached (i.e., nomore wetting fluid is displaced)
•Measure/ determine wetting phase saturation
in core at each pressure increment
• Repeat at successive higher pressures
Unconfined Confined stress
Water
Saturated
diaphragm
Air or Gas Gas or Oil
Water
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Slide 12®
POROUS DIAPHRAGM- example
Data
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Slide 13®
MERCURY INJECTION METHOD
Lucite window
Lucite window
To
0-2,000 psi pressuregauge
Regulating valve
atmosphere
U-tube monometer
Cylinder
0-200 psi pressure gauge
From Purcell, 1949
Lucite window
Lucite window
To
0-2,000 psi pressuregauge
Regulating valve
atmosphere
U-tube monometer
Cylinder
0-200 psi pressure gauge
From Purcell, 1949
Sample Chamber
Mercury Pump
Mercury
DisplacementReading
Sample
Up to 60000 psi
Fully automatic:vacuum, volume
injected, low-high
pressure
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Slide 14®
MERCURY INJECTION, examples
Incremental Intrusion (mL/g)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.0010.1101000Pore Diameter (m icrometers)
Capillary Press ure (psi)
1
10
100
1000
10000
100000
0 20 40 60 80 100% Hg Saturation
Pore Size Distribution,Inference of porenetwork characteristics
Needs converting toOther fluid systems
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Slide 15®
Data conversion to reservoir conditions
( ) ( )labawaw
owowyac PcPc
−−
−−=θ γ θ γ
coscos
Typically
In the lab
γa-w ≈ 70 dynes / cm
θa-w ≈ 0o
In the reservoir
γo-w ≈ 28 dynes / cm
θo-w ≈ 33 a 55o
( ) ( ) labowyacow Pcx
Pc / / 70
70.028−− =
( )( ) 43
1
/
/
aPc
Pc
labow
resow ≈−
−
Pc Conversion
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Slide 16®
Typical Values ofγ , θ
PC ratio
5
8.7
1
15
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Slide 17®
CENTRIFUGE METHOD
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Slide 18®
Schematic drawing of the centrifuge set-up
Malla
SEALING SCREW
SCALE
CORE PLUGMESH
CENTRIFUGE TUBE
CALIBRATE
D SCALE
ROTATION VELOCITY
1500-20000 r.p.m
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Slide 19®
Analysis and Calculations
LL
r nP einlet c ⎟⎠
⎞⎜⎝
⎛ −∆=2
2ρ
0
5000
10000
15000
20000
25000
30000
35000
0.00 0.20 0.40 0.60 0.80 1.00
Capillary pressure PC
Saturation
Mean saturation
n: number of revolutions per minute
L: sample lengthRe: distance from sample to rotor
Sw
Hagoort, SPEJ 1980
Reality?
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Slide 20®
Combined methods (CT scans, NMR)
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Slide 21®
Comparison of Main Capillary Pressure Methods
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Slide 22®
Vapour equilibrium (desorption) method
• Thompson (1870) showed that the vapour pressure above a liquidsurface is a function of its curvature.
• Capillary pressure is therefore related to vapour pressure for porous
media containing water in equilibrium with its vapour.
whereP c = capillary pressure,R = universal gas constant,R H = relative humidity,
T = absolute temperature,V m = molar volume of water (0.018016).
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Slide 23®
Vapour equilibrium methodPlugs placed in constant humidity chambers until weight/saturation stabilises
Saturated solutions of different salts
Very high pressures, simple and cheap technique, very slow (months)
Other systems: Glycerol - water
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Slide 24®
Comparison Vapour desorption- centrifuge
Newsham et al., SPE 89866
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Slide 26®
Phyllosilicate-frame analogue
(converted to Hg)
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Slide 27®
Heterogeneous samples
0.1
1
10
100
1000
10000
100000
0 20 40 60 80 100
Gas Saturation
Capillary
Pressure (psi)
Sample F Sample H
Sample M Break T 2
Break T 1PcHg converted to gas-brine
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Slide 28®
Capillary pressure of combined rocks
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Slide 29®
Fault rocks- sealing capacity
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Slide 30®
Water Saturation at Capillary Equilibrium
Do all Roads Lead to Rome?