This document summarizes a presentation on porosity and methods for measuring it. It discusses both direct methods that measure volume, such as mercury injection and gas expansion, and indirect well logging methods like neutron, density, NMR, and acoustic logs. The various methods are based on different measurement principles and assumptions, so perfect agreement is not expected. Choosing a method requires considering the sample properties and intended application.

1. Presentation of petrophysics
•Presenter:
•ZEESHAN AHMED (K-19PG-01)
•SHAIQ ALI (K-19PG-05)
•YOUNIS SATTAR (K-19PG06)

2. TOPIC: POROSITY
AND ITS
MEASUREMENT
AUTHOR : LAURA
ESPINAL
Material Measurement
Laboratory, National Institute
of Standards and Technology,
Gaithersburg, MD, USA

3. ABSTRACT:
A core sample porosity-check program is
described. A number of laboratories
participated in the investigation, which
comprised measuring the porosities. Each
laboratory employed its own method (or
methods) of measurement. These included
direct methods and indirect methods.
Brief descriptions of each method employed are
given.
The results of these measurements are compiled
and presented in graphical form

4.  INTRODUCTION:
• Porosity is one of the factors that influences
the physical interactions and chemical
reactivity of solids with gases and liquids for
many industrial applications.
• The examples of industrially important
porous materials include (i.e) oil and gas
bearing strata and rocks.
• Porosity in rocks can also be induced by
natural geological processes following
deposition, such as weathering or dissolution
and formation of fractures .

5. • A great many methods have been developed for determining porosity, mainly of consolidated
rocks having intergranular porosity (encountered in oil reservoir). Most of the methods
developed have been designed for small samples. From the definition of porosity it is obvious
that common to all methods is the need to determine two of three volumes: total or bulk volume
of the sample, its pore volume, and/or the volume of its solid matrix. The various methods
based on such volume determination, called “direct methods”, differ from each other in the way
these volumes are determined. Other methods are available, called “indirect methods” based on
the measurement of some properties of the void space. Examples of such properties are the
electrical conductivity of electrically conducting fluid filling the void space of the sample, or the
absorption of radioactive particles by a fluid filling the void space of the sample. The porosity of
the larger portion of rock is determined statistically from the results obtained on numerous small
samples
 TECHNIQUES:

6.  Direct
Methods:
Mercury injection method:
• Mercury intrusion porosimetry (MIP) is a
powerful technique utilized for the evaluation of
porosity, pore size distribution, and pore volume
(among others) to characterize a wide variety of
solid and powder materials. The instrument,
known as a porosimeter, employs a pressurized
chamber to force mercury to intrude into the
voids in a porous substrate. As pressure is
applied, mercury fills the larger pores first. As
pressure increases, the filling proceeds to smaller
and smaller pores. Both the inter-particle pores
(between the individual particles) and the intra-
particle pores (within the particle itself) can be
characterized using this technique.

7.  Gas
expansion
method:
• Gas expansion method.
• A sample of known bulk volume is enclosed
in a container of known volume. It is
connected to another container with a known
volume which is evacuated (i.e., near vacuum
pressure). When a valve connecting the two
containers is opened, gas passes from the first
container to the second until a uniform
pressure distribution is attained.

9.  Imbibition
method:
• Reservoir rocks have the ability of imbibe
water spontaneously. This property is used to
determine effective porosity of the rock. In
this method the weight of a dry sample is
measured and then the sample is immersed
under vacuum in water or any other fluid that
rock has the tendency to imbibe. After
enough time, up to several days, the saturated
sample is weighted. Utilizing the density of
the liquid we can find the imbibed fluid
volume and subsequently the effective
porosity of the sample.

10.  Indirect
Methods:
Indirect methods are based on well logging
data:
Neutron log
Density log
NMR(Nuclear Magnetic Resonance) log
Acoustic (Sonic) log

11.  Compensated
Neutron log:
• CNL (compensated neutron) logs also called
neutron logs, determine porosity by assuming
that the reservoir pore spaces are filled with
either water or oil and then measuring the
amount of hydrogen atoms (neutrons) in the
pores. These logs underestimate the porosity
of rocks that contain ga

12. Application
of Neutron
log:
• It measured the porosity
• Gas detection
• Shale volume determination
• Lithology indication

13. formation
density
compensated
log:
• formation density compensated logs also
called density logs, is a porosity log that
measures electron density of a formation and
determine porosity by evaluating the density
of the rocks. Because these logs overestimate
the porosity of rocks that contain gas they
result in “crossover” of the log curves when
paired with Neutron logs

14. Application
of Density
log:
• Identify the evaporate mineral
• Detect gas bearing zone
• Determine hydrocarbon density
• Evaluate shaly sand reservoir

15. Nuclear
Magnetic
Resonance
log:
• Nuclear Magnetic Resonance logs may be the
well logs of the future. These logs measure
the magnetic response of fluids present in the
pore spaces of the reservoir rocks. In so
doing, these logs measure porosity and
permeability, as well as the types of fluids
present in the pore spaces

16. Acoustic
log:
• Acoustic log also called as sonic log that emits
sounds waves which start at the source, ravel
through the formation and return back to
receiver . Its main use to provide information
to support and calibrate the seismic data and
to drive the porosity of the formation.

17. Application
of
Acoustic
log:
• It measured the speed of sound waves in
subsurface formation.
• It determine the porosity of formation and
lithology.
• Correlation with other well .
• Detecting the over pressure.
• Evaluate the secondary porosity.

18. Conclusion:
Due to the inherent difference in the physical principles for each method, perfect agreement between the
values of total porosity, surface area, average pore size, and distribution obtained for all techniques is not
possible.
Similarly, a perfect agreement between two techniques will not necessarily validate the values obtained.
Within a given technique, the postsynthesis history of the sample should be taken into account as many
material applications require
postsynthesis treatments (e.g., annealing and mechanical forming), which can lead to different porosity. All
techniques have advantages and disadvantages, in particular with respect to the assumptions made to
derive the results. An approach to understand how these techniques differ from each other could involve
the evaluation of a reference model porous material using the techniques under consideration. The
selection criteria should extend beyond the expected pore-size range and take into account the suitability
of sample preparation, material property, and sample geometry requirements for every technique as well
as the intended material’s applicationA

19. • https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910393