1. Laboratory Measurement of Capillary Pressure

2. LABORATORY METHODS FOR MEASURING CAPILLARY PRESSURE
Determination of Pc(Sw) function
Porous diaphragm method
Mercury injection method
Centrifuge method
Dynamic method

3. POROUS DIAPHRAGM METHOD FOR CAPILLARY PRESSURE
Scale of
Brine
Ultra-fine
fritted
glass disk
Seal of
red oil
squared
paper
Saran tube
Crude oil
Nitrogen
pressure
Neoprene
stopper
Nickel-
plated
spring
Kleenex
Core
Porous diaphragm method of
measuring capillary pressure
Laboratory procedure
Begin with core saturated with wetting fluid. In addition, saturate the porous disk with same wetting fluid
Use pressure to force nonwetting fluid (usually air) into core, thus displacing wetting fluid through the porous disk
The pressure difference between the pressure in the nonwetting fluid and the pressure in the wetting fluid equals the capillary pressure
Repeat at successively higher pressures until equilibrium is reached (i.e., no more wetting fluid is displaced)
Measure wetting phase saturation in core at each pressure increment
Modified from Welge and Bruce, 1947

4. CAPILLARY PRESSURE USING POROUS DIAPHRAGM METHOD
Measured
data points
Capillary pressure, psia
Irreducible
Wetting Phase
Saturation
Displacement
pressure
Wetting phase saturation, %
100

5. COMMENTS ON POROUS DIAPHRAGM METHOD
Capillary Pressure 5
COMMENTS ON POROUS DIAPHRAGM METHOD
Advantages
Very accurate
Can use reservoir fluids
Disadvantages
Very slow (days, weeks, months)
Range of capillary pressure is limited by “displacement pressure” of porous disk
Wetting phase of disk should be same as core sample
Holes in porous disk act as capillaries, allowing only wetting to flow out until displacement pressure is exceeded

6. MERCURY INJECTION METHOD FOR CAPILLARY PRESSURE
0-200 psi pressure gauge
0-2,000 psi pressure
gauge
Regulating valve To
Lucite window
atmosphere
Cylinder
U-tube monometer
Lucite window
Laboratory procedure
Uses mercury as the nonwetting fluid and air (usually under vacuum) as the wetting phase
Force mercury into core
Measure pressure required to force additional mercury volume into core
Calculate mercury saturation (i.e., nonwetting phase saturation) from known injection volumes and known pore volume of core sample
From Purcell, 1949

7. COMMENTS ON MERCURY INJECTION METHOD
Capillary Pressure 7
COMMENTS ON MERCURY INJECTION METHOD
Advantages
Results obtained quickly (minutes,hours)
Method is reasonably accurate
Very high range of capillary pressures
Disadvantages
Ruins core / mercury disposal
Hazardous testing material (mercury)
Conversion required between mercury/air capillary data to reservoir fluid systems

8. CENTRIFUGE METHOD FOR DETERMINING CAPILLARY PRESSURE
Seal Cap
Core holder body
Window
Tube body
Support disk
O - Ring
Laboratory procedure
Similar to porous disk method except centrifugal force (rather than pressure) is applied to fluids in core
Pressure (force per unit area) is computed from centrifugal force (which is related to rotational speed of centrifuge)
Saturation is computed from fluid removed
From Slobod and others,
1951

9. COMMENTS ON CENTRIFUGE METHOD
Capillary Pressure 9
COMMENTS ON CENTRIFUGE METHOD
Advantages
Results can be obtained fairly quickly (hours, days, weeks)
Reasonably accurate
Can use reservoir fluids
Disadvantages
Complex analysis required can lead to calculation errors

10. DYNAMIC METHOD OF MEASURING CAPILLARY PRESSURETo
atmosphere
Oil burette
Porcelain
plate
Oil inlet
Po
Pg Pc
Gas
inlet
outlet
Core
Laboratory procedure
Establish simultaneous steady-state flow of two fluids through core
Measure pressures of the two fluids in core using special wetted disks (one porous diaphram wet by core’s wetting phase, and one porous diaphram wet by core’s non-wetting phase).
Difference between the pressure between phases is capillary pressure
Saturation is varied by regulating quantity of each fluid entering core
From Brown, 1951

11. COMMENTS ON DYNAMIC METHOD
Capillary Pressure 11
COMMENTS ON DYNAMIC METHOD
Advantages
Simulates reservoir flow conditions
Can use reservoir fluids
Disadvantages
Very tedious to perform (weeks, months)
High cost

12. AVERAGING CAPILLARY PRESSURE DATA USING THE LEVERETT J-FUNCTION
The Leverett J-function was originally an attempt to convert all capillary pressure data to a universal curve
A universal capillary pressure curve does not exist because the rock properties affecting capillary pressures in the reservoir have extreme variation with lithology (rock type)
BUT, Leverett’s J-function has proven valuable for correlating capillary pressure data within a lithology (see ABW Fig 3-23).

13. EXAMPLE J-FUNCTION FOR WEST TEXAS CARBONATE
Capillary Pressure 13
Black data are from an original capillary pressure experiments. The blue, red, and green data were for three new experiments, performed to determine the reliability of the original data.
The black line represents an average J-function that was initially used in a reservoir simulation study for the field. Ultimately, the rock type was broken into smaller units, and five different capillary pressure relationships were used to represent the ranges of carbonate rock quality observed in the reservoir.

14. DEFINITION OF LEVERETT J-FUNCTION
Capillary Pressure 14
DEFINITION OF LEVERETT J-FUNCTION
C Pc k ( ) = J S w s q f
cos
J-Function is DIMENSIONLESS, for a particular rock type:
Same value of J at same wetting phase saturation for any unit system, any two fluids, any values of k,f
(k/f)1/2 is proportional to size of typical pore throat radius (remember k can have units of length2)
C is unit conversion factor (to make J(Sw) dimensionless)
J(Sw) = Leverett J-function, dimensionless
Sw = water saturation, fraction
Pc = capillary pressure, psia
 = interfacial tension, dynes/cm
 = contact angle, degrees
k = formation permeability, md
 = porosity, fraction

15. Pc(Sw) Depends on k,f High Quality
Capillary Pressure 15
Core
Pore
Petrophysical
Gamma Ray
Flow
Core
Lithofacies
Plugs
Types
Data
Log
Units
Capillary f
vs k
Pressure
High Quality 5 4 3
Function moves up and right, and becomes less “L” shaped as reservoir quality decreases 2
Low Quality 1

16. LEVERETT J-FUNCTION FOR CONVERSION OF Pc DATA
Capillary Pressure 16
LEVERETT J-FUNCTION FOR CONVERSION OF Pc DATA
J(Sw) = Leverett J-function, dimensionless
Sw = water saturation, fraction
Pc = capillary pressure, psia
 = interfacial tension, dynes/cm
 = contact angle, degrees
k = formation permeability, md
 = porosity, fraction

17. USE OF LEVERETT J-FUNCTION
Capillary Pressure 17
J-function is useful for averaging capillary pressure data from a given rock type from a given reservoir
J-function can sometimes be extended to different reservoirs having same lithologies
Use extreme caution in assuming this can be done
J-function usually not accurate correlation for different lithologies
If J-functions are not successful in reducing the scatter in a given set of data, then this suggests that we are dealing variation in rock type