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1/12/2006

Capillary Pressure From Logs

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PredictPredict SwSw distributiondistribution in reservoirin reservoir

(compare with log data, initialize simulator)(compare with log data, initialize simulator)

PredictPredict free water levelfree water level

Predict Rock Type, Quality and Pore geometryPredict Rock Type, Quality and Pore geometry

Assist in interpretation/calculation ofAssist in interpretation/calculation of relativerelative

permeabilitypermeability

CalculateCalculate pore size distributionpore size distribution

Applications of CapillaryApplications of Capillary

Pressure DataPressure Data

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r

Cos

Cos

Capillary pressureCapillary pressure exists whenever twoexists whenever twoimmiscible phases are present in a fineimmiscible phases are present in a fine

tube, andtube, and is defined as the pressure dropis defined as the pressure drop

across the curved liquid interfaceacross the curved liquid interface..

r

Cos2Pc

=

hgPc =

Capillary pressure in a tube can beCapillary pressure in a tube can becalculated if the fluidcalculated if the fluid interfacial tensioninterfacial tension,,

rockrock--fluidfluid contact anglecontact angle, and the tube, and the tube

radiusradius are known.are known. Capillary pressure can also be expressedCapillary pressure can also be expressed

as a hydrostatic head. It is equal to theas a hydrostatic head. It is equal to the

product of theproduct of the heightheight of the liquid rise, theof the liquid rise, the

density differencedensity difference of the two liquids, andof the two liquids, and

thethe gravitational constant.gravitational constant.

Pw-PnwPc =

CAPILLARY PRESSURE THEORYCAPILLARY PRESSURE THEORY

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0 1Water Saturation

HeightAboveWaterLevel

B

A

AARockRock--typetype BBRockRock--typetype

Pore size and d istr ibut ion inf luence the magnitu de of ir reduciblewater and the height of th e transit ion zone. Smaller pores and pore throats mean low er permeabi l i ty and

high er Sw

Effect of Pore Geometry

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As h ydro carbon s accumulate, the largest pores are drained f irst . Smaller po res are drained as the HC co lumn (height or pressure)

increases

A

B

Effect of Pore Geometry

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0 100%Sw

IrreducibleWa

terSaturation

Swir

WellWell

Top Transition Zone

Transition Zone

Free Water Level

(Pc = 0)

HC and

Mobile Water

Observed HC-WC

(Pc = Pce)

HC, water-free

D

E

PT

H

Fluid Distribution in a HC

Reservoir

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A

Rock type B

Rock type A

B

Capillary PropertiesCapillary Properties

Calibrated Log ResponseCalibrated Log Response

CAPILLARYPRESSURE

HEIGHTINRESERVOIRABOVEFWL

0 Sw 1

Sealing Fault

A

A

B

FWL

OWC

OWC OWC

Relationship of Reservoir Saturations to:

Logged Interval

Rt

Sw Profile in Wellbore

Rt = F Rw / Swn

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0 1

Sw

Cap

illaryPressureorH

eightAboveFWL

OWC

OWC

OWC

FWL

SedimentarySequence

A B CRock Type

0 1

Sw

Sw from Wireline

B

A

C

B

A

B

A

C Sw trace

Sw Distribution by

CAPILLARY PRESSURE Model

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Capillary Pressure Curves from NMR

- 1

10 -4 10 -3 10 -2 10 -1 10 0 10 1

T2 (s)

Cumulative

T2

Distribution

951211-02

T2 distributions are normally displayed as incremental porosity

distributions. Integrating from left to right gives us cumulative porosity

distributions

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Capillary Pressure Summary

Primary Uses

Determine pore throat size distribution

Determine vertical wetting phase

saturation distribution

Help separate rock types (quality)