RESERVOIR PETROPHYSICS

1 / 42

RESERVOIR PETROPHYSICS - PowerPoint PPT Presentation

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

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

PowerPoint Slideshow about 'RESERVOIR PETROPHYSICS' - calixte

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

RESERVOIR PETROPHYSICS

LABORATORY DETERMINATIONOF 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
• Determining effective porosity requires fluid flow to determine if pores are interconnected
MEASUREMENT OF POROSITY
• Core samples(measure two of: Vb, Vp, or Vm)
• Openhole wireline logs

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

Volume is an extensive property

Fraction of volume consisting of

pores or voids

Fraction of volume consisting

of matrix

LABORATORY METHODS OFPOROSITY DETERMINATION

• Bulk volumedeterminations
• Direct calculation
• Fluid displacement methods
• Gravimetric
• Volumetric – mercury pycnometer ( a precisely calibrated bottle)
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 OFPOROSITY DETERMINATION

• Bulk volumedeterminations
• Direct calculation
• Fluid displacement methods
• Gravimetric (Archimedes) methods
• Volumetric – in pycnometer

Wdry

Wsat

Wsub

Vp =

Wsat - Wdry

fluid

Vm =

Vb =

Wdry - Wsub

fluid

=

Wsat - Wdry

Wsat - Wsub

Wsat - Wsub

fluid

ARCHIMEDES METHOD
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.

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)

(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 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
• Known or assumed matrix density
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

(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
• Reduce sample to particle size
• Measure matrix volume of particles by
• Volumetric method
• Archimedes method (gravimetric measurement)
EXAMPLE 2SOLUTIONCalculating the Matrix Volume and Porosity of a Core Sample Using the Displacement Method

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%

(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
• Involves compression of gas into pores
• Uses Boyle’s law
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 Vma

P1

Initial conditions

Core

V1

Valve

closed

Evacuate

Cell 2

Cell 1

GAS EXPANSION METHOD TO CALCULATE Vma

Final conditions

P1

P2

Core

Valve

open

Cell 1

Cell 2

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 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 DETERMINATION

• To determine porosity, measure 2 of 3
• basic parameters:
• Bulk volume
• Matrix volume
• Pore volume

(Vb)

(Vm)

(Vp)

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

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

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

• 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 DETERMINATION

• Pore volume determination (Effective)
• Gravimetric (Archimedes)
• Wsat - Wdry
• fluid
• 2. Boyle’s Law:
• (Gas expansion)

Vp =

PORE VOLUME FROM GASEXPANSION METHOD

Initial conditions

P1

Core

V1

Valve

closed

Cell 1

Cell 2

PORE VOLUME FROM GASEXPANSION METHOD

Final conditions

P1

P2

Core

Valve

open

Cell 1

Cell 2

PORE VOLUME FROM GAS EXPANSION METHOD
• 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

SUMMARY

To determine porosity, measure 2 of 3

basic parameters:

• Bulk volume
• Matrix volume
• Pore volume
CORES
• 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