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RESERVOIR PETROPHYSICS. LABORATORY DETERMINATION OF POROSITY. POROSITY DEFINITION. Porosity : The fraction of a rock that is occupied by pores. Porosity is a static property – it can be measured in the absence of flow

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Reservoir petrophysics 1335964

RESERVOIR PETROPHYSICS

LABORATORY DETERMINATIONOF POROSITY


Porosity definition
POROSITY DEFINITION

Porosity: The fraction of a rock that is occupied by pores

  • Porosity is a static property – it can be measured in the absence of flow

  • Determining effective porosity requires fluid flow to determine if pores are interconnected


Rock matrix and pore space

matrix

pore space

ROCK MATRIX AND PORE SPACE


Measurement of porosity
MEASUREMENT OF POROSITY

  • Core samples(measure two of: Vb, Vp, or Vm)

  • Openhole wireline logs


Laboratory determination of porosity

LABORATORY DETERMINATIONOF POROSITY

  • Most methods use small samples (core plugs)

    • multiple samples must be analyzed to get statistically representative results

    • sampling technique is important

      • often all samples are taken from “sweet spots” skewing analysis

  • To determine porosity, measure 2 of 3

  • volumetric parameters:

    • Bulk volume, Vb

    • Matrix volume, Vm (also called grain volume)

    • Pore volume, Vp


Reservoir petrophysics 1335964

Volume is an extensive property

Fraction of volume consisting of

pores or voids

Fraction of volume consisting

of matrix


Matrix densities m of typical pure components of reservoir rock
MATRIX DENSITIES (m) OF TYPICAL PURE COMPONENTS OF RESERVOIR ROCK


Laboratory methods of porosity determination

LABORATORY METHODS OFPOROSITY DETERMINATION

  • Bulk volumedeterminations

  • Direct calculation

  • Fluid displacement methods

    • Gravimetric

    • Volumetric – mercury pycnometer ( a precisely calibrated bottle)


Bulk volume by direct measurement
BULK VOLUME BY DIRECT MEASUREMENT

  • Applicable for regularly shaped cores or core plugs

  • Calculate from core dimensions

  • For example; volume of right circular cylinder


Laboratory methods of porosity determination1

LABORATORY METHODS OFPOROSITY DETERMINATION

  • Bulk volumedeterminations

  • Direct calculation

  • Fluid displacement methods

    • Gravimetric (Archimedes) methods

    • Volumetric – in pycnometer


Archimedes method

Wdry

Wsat

Wsub

Vp =

Wsat - Wdry

fluid

Vm =

Vb =

Wdry - Wsub

fluid

=

Wsat - Wdry

Wsat - Wsub

Wsat - Wsub

fluid

ARCHIMEDES METHOD


Example 1 bulk volume calculated by displacement
EXAMPLE 1Bulk Volume Calculated by Displacement

A core sample coated with paraffin immersed in a container of liquid displaced 10.9 cm3 of the liquid. The weight of the dry core sample was 20.0 g, while the weight of the dry sample coated with paraffin was 20.9 g. Assume the density of the solid paraffin is 0.9 g/cm3.

Calculate the bulk volume of the sample.


Reservoir petrophysics 1335964

SOLUTION - Example 1

Weight of paraffin coating, Wparaffin =

Weight of dry core sample coated with paraffin - Weight of dry core sampleWparaffin = 20.9 g = 20.0 g = 0.9 g

Volume of paraffin coating = Weight of paraffin / density of paraffin

Vparaffin = 0.9 g / 0.9 g/cm3 = 1.0 cm3

Bulk volume of core sample = (Bulk volume of core coated with paraffin) – (volume of paraffin)

Vb= 10.9 cm3 – 1.0 cm3 = 9.9 cm3

(V = m/ρ)


Laboratory methods of porosity determination2

(Vb)

(Vm)

(Vp)

LABORATORY METHODS OF POROSITY DETERMINATION

  • To determine porosity, measure 2 of 3

  • basic parameters:

    • Bulk volume

    • Matrix volume

      • Assume matrix (grain) density

      • Displacement method

      • Boyles Law

    • Pore volume


Laboratory methods of porosity determination3

LABORATORY METHODS OFPOROSITY DETERMINATION

  • Matrix(Vm)

  • Assume rock density based on lithology and measure dry mass

  • Displacement methods

    • volumetric

    • gravimetric (see previous description)

  • Boyle’s Law:


Matrix volume from matrix density
MATRIX VOLUME FROM MATRIX DENSITY

  • Known or assumed matrix density


Applicability and accuracy of matrix measurement techniques
APPLICABILITY AND ACCURACY OF MATRIX MEASUREMENT TECHNIQUES

  • Known or assumed matrix density

    • Accurate only if matrix density is known and not assumed

    • Core samples are often mixtures of several components with varying matrix densities, so density must be measured


Laboratory methods of porosity determination4

(Vb)

(Vm)

(Vp)

LABORATORY METHODS OF POROSITY DETERMINATION

  • To determine porosity, measure 2 of 3

  • basic parameters:

    • Bulk volume

    • 2. Matrix volume

    • Assumed matrix (grain) density

    • Displacement method

    • Boyles Law

    • 3. Pore volume


Matrix volume from displacement method
MATRIX VOLUME FROM DISPLACEMENT METHOD

  • Reduce sample to particle size

  • Measure matrix volume of particles by

    • Volumetric method

    • Archimedes method (gravimetric measurement)


Reservoir petrophysics 1335964
EXAMPLE 2SOLUTIONCalculating the Matrix Volume and Porosity of a Core Sample Using the Displacement Method


Reservoir petrophysics 1335964

9.9 cm3 – 7.7 cm3

=

9.9 cm3

SOLUTION - Example 2Calculate the Porosity of a Core Sample Using the Displacement Method and Matrix Volume

The core sample from Example 1 was stripped of the paraffin coat, crushed to grain size, and immersed in a container with liquid. The volume of liquid displaced by the grains was 7.7 cm3.

Calculate the matrix volume and the core porosity. Is this effective porosity or total porosity? (It is total porosity)

Bulk Volume, Vb = 9.9 cm3

Matrix Volume, Vma = 7.7 cm3

= 0.22 or 22%


Laboratory methods of porosity determination5

(Vb)

(Vm)

(Vp)

LABORATORY METHODS OF POROSITY DETERMINATION

  • To determine porosity, measure 2 of 3

  • basic parameters:

    • Bulk volume

    • 2. Matrix volume

    • Assumed matrix (grain) density

    • Displacement method

    • Boyles Law (Gas Expansion)

    • 3. Pore volume


Matrix volume from gas expansion method
MATRIX VOLUME FROM GAS EXPANSION METHOD

  • Involves compression of gas into pores

  • Uses Boyle’s law


Gas expansion method to calculate v ma
GAS EXPANSION METHOD TO CALCULATE Vma

  • Initial conditions, with volumes of 2 cells known

  • Place core in second cell, evacuate gas (air) from second cell

  • Open valve


Gas expansion method to calculate v ma1
GAS EXPANSION METHOD TO CALCULATE Vma

P1

Initial conditions

Core

V1

Valve

closed

Evacuate

Cell 2

Cell 1


Gas expansion method to calculate v ma2
GAS EXPANSION METHOD TO CALCULATE Vma

Final conditions

P1

P2

Core

Valve

open

Cell 1

Cell 2


Gas expansion method to calculate v ma3
GAS EXPANSION METHOD TO CALCULATE Vma

  • Vf = Volume of Cell 1 + Volume of Cell 2 - Matrix Volume of Core

  • Vt = Volume of Cell 1 + Volume of Cell 2

  • Vm = Vt - Vf


Applicability and accuracy of matrix measurement techniques1
APPLICABILITY AND ACCURACY OF MATRIX MEASUREMENT TECHNIQUES

  • Displacement method - Very accurate when core sample is crushed without destroying individual matrix grains

  • Gas expansion method - Very accurate, especially for samples with low porosities

    Neither method requires a prior knowledge of core properties


Laboratory methods of porosity determination6

LABORATORY METHODS OF POROSITY DETERMINATION

  • To determine porosity, measure 2 of 3

  • basic parameters:

    • Bulk volume

    • Matrix volume

    • Pore volume

(Vb)

(Vm)

(Vp)


Laboratory methods of porosity determination7

LABORATORY METHODS OF POROSITY DETERMINATION

  • Pore volume determination (Effective)

  • Gravimetric (Archimedes)

  • Wsat - Wdry

  • fluid

  • 2. Boyle’s Law:

  • (Gas expansion)

Vp =


Pore volume from saturation method
PORE VOLUME FROM SATURATION METHOD

  • Measures the difference between the weight of a core sample saturated with a single fluid and the dry weight of the core

  • Pore volume,


Example 3 archimedes method of calculating porosity a core sample
EXAMPLE 3Archimedes MethodofCalculatingPorosity a Core Sample

Using the gravimetric method with the following data, calculate the pore and bulk volumes and the porosity. Is this porosity total or effective?

Dry weight of sample, Wdry = 427.3 g

Weight of sample saturated with water, Wsat = 448.6 g

Density of water (f ) = 1.0 g/cm3

Weight of saturated sample submerged in water, Wsub = 269.6 g


Example 3 solution archimedes method of calculating porosity a core sample

Wsat – Wdry =

f

448.6 – 427.3 g

1.0 g/cm3

Vp =

= 21.3 cm3

Wsat – Wsub =

f

448.6 – 269.6 g

1.0 g/cm3

Vb =

= 179.0 cm3

21.3 cm3

=

=

0.12 or 12%

179.0 cm3

EXAMPLE 3SolutionArchimedes MethodofCalculatingPorosity a Core Sample


Applicability and accuracy of pore volume measurement techniques
Applicability and Accuracy of Pore Volume Measurement Techniques

  • Saturation (Archimedes) method

    • Accurate in better quality rocks if effective pore spaces can be completely saturated

    • In poorer quality rocks, difficult to completely saturate sample

    • Saturating fluid may react with minerals in the core (e.g., swelling clays)


Laboratory methods of porosity determination8

LABORATORY METHODS OF POROSITY DETERMINATION Techniques

  • Pore volume determination (Effective)

  • Gravimetric (Archimedes)

  • Wsat - Wdry

  • fluid

  • 2. Boyle’s Law:

  • (Gas expansion)

Vp =


Pore volume from gas expansion method
PORE VOLUME FROM GAS TechniquesEXPANSION METHOD

Initial conditions

P1

Core

V1

Valve

closed

Cell 1

Cell 2


Pore volume from gas expansion method1
PORE VOLUME FROM GAS TechniquesEXPANSION METHOD

Final conditions

P1

P2

Core

Valve

open

Cell 1

Cell 2


Pore volume from gas expansion method2
PORE VOLUME FROM GAS EXPANSION METHOD Techniques

  • Very accurate for both high-quality (high ) and low-quality (low ) core samples

  • Should use low-molecular-weight inert gases (e.g., helium)

  • Measures effective (connected) pore volume


Reservoir petrophysics 1335964

SUMMARY Techniques

To determine porosity, measure 2 of 3

basic parameters:

  • Bulk volume

  • Matrix volume

  • Pore volume


Cores
CORES Techniques

  • Allow direct measurement of reservoir properties

  • Used to correlate indirect measurements, such as wireline/LWD logs

  • Used to test compatibility of injection fluids

  • Used to predict borehole stability

  • Used to estimate probability of formation failure and sand production


Reservoir petrophysics 1335964

SOME KEY FORMULAS Techniques