Reservoir Porosity; Porosity Definition; Types Porosity; Origins of Porosity in Clastics and Carbonates; Primary (Original) Porosity; Secondary (Induced) Porosity; Pore Space Porosity Classification; Absolute (or Total) Porosity; Effective Porosity; Porosity Calculated; Porosity Values; Porosity in Sandstone; Sandstones Porosity Types; Factors That Affect Porosity in Sandstones ; Grain Packing in Sandstone; Progressive Destruction of Bedding Through Bioturbation; Dual Porosity in Sandstone; Dissolution Porosity in Sandstone; Porosity in Carbonate; Carbonates Porosity Types; Idealized Carbonate Porosity Types; Comparison of Total and Effective Porosities; Reservoir Average Porosity; MEASUREMENT OF POROSITY

1. @Hassan Z. Harraz 2019
Reservoir Porosity
Prof. Dr. Hassan Z. Harraz
Geology Department, Faculty of Science, Tanta University
hharraz2006@yahoo.com
Spring 2019
Many slides contain more detailed notes that
may be shown using the “Notes Page View”
1

2. OBJECTIVES
❑To provide an understanding of
❖The concepts of rock matrix and porosity
❖The difference between original (primary) and
induced (secondary) porosity
❖The difference between Total and Effective Porosity
❖Laboratory methods of porosity determination
❖Determination of porosity from well logs
❖Discussion Topics:
• Origins and descriptions
• Factors that effect porosity
• Methods of determination
2

3. Outlines
1) Porosity in Sandstone:
▪ Major Components of Sandstone
▪ Sandstone Classification
▪ Sandstones Porosity Types
▪ Factors That Affect Porosity in Sandstones
▪ Grain-Size Sorting in Sandstone
▪ Grain Packing in Sandstone
▪ Types of Textural Changes Sensed by the Naked Eye as
Bedding
▪ Progressive Destruction of Bedding Through Bioturbation
▪ Diagenesis
▪ Dual Porosity in Sandstone
▪ Dissolution Porosity in Sandstone
▪ The role of Rock Texture
2) Porosity in Carbonate:
▪ Carbonate Rock Classification
▪ Carbonates Porosity Types
▪ Idealized Carbonate Porosity Types
❑ Comparison of Total and Effective Porosities
❑ Reservoir Average Porosity
❑ MEASUREMENT OF POROSITY:
▪ Core samples (Laboratory)
▪ Openhole wireline logs
3
❑ Introduction
❑ Reservoir Porosity
❑ Porosity Definition
❑ A Pore space
❑ Rock Matrix and Pore Space
❑ Classification of Rocks
❑ Sedimentary Rock Types
❑ Grain-Size Classification for Clastic Sediments
❑ Comparison of Compositions of Clastic and Carbonate Rocks
❑ Types Porosity:
I) Origins of Porosity in Clastics and Carbonates:
1) Primary (Original) Porosity
2) Secondary (Induced) Porosity
II) Pore Space Porosity Classification:
1) Absolute (or Total) Porosity
2) Effective Porosity
❑ Porosity Calculated
❑ Porosity Values

4. Introduction
❑Reservoir rocks may range from very loose and unconsolidated
sand to a very hard and dense sandstone, limestone, and dolomite.
❑Knowing the physical properties of the rock and the existing
interactions between the hydrocarbon system and the formation is
essential in understanding and evaluating the performance of a
given reservoir
❑Rock properties are determined by performing laboratory analysis on
cores from the reservoirs.
❑These laboratory core analysis are divided in to:
➢routine (porosity, permeability, and saturation) and
➢special tests (overburden pressure, capillary pressure, relative
permeability, wettability, and surface and interfacial tension)
❑The rock properties data are essential for reservoir engineering
calculations as they affect both the quantity and the distribution of
HC and with the fluid properties, control flow of existing phases
within the reservoir.
4

5. Definition:
▪ Porosity is the fraction of a rock that is occupied by voids (pores).
▪ Ratio of the volume of space to the total volume of a rock.
▪ Porosity is expressed as a percentage (%) of the total rock which is
taken up by pore space.
▪ Porosity units are fraction or %
▪ Quantitatively
➢ Example: a sandstone may have 8% porosity……This means
92 % is solid rock and 8 % is open space containing oil, gas,
or water.
❖ The porosity is a measure of the storage capacity (pore volume)
that is capable of holding fluids
❖ Porosity of a rock is a measure of its ability to hold a fluid.
❖ Porosity is an intensive property describing the fluid storage
capacity of rock.
Reservoir Porosity
5

6. A Pore
• The texture of a rock
consists of it's grain or
mineral crystal size, the
arrangement of the
grains or crystals, and
the degree of uniformity
of the grains or crystals.
6
Elements of Pore Throat:
• Size & frequency distribution-uncorrelated,
Correlated
• Connectivity of pores and throat-No of pore
throat connecting to pores
• Spatial arrangement-Arrangement of pores of
different sizes w.r.t each other

7. Rock Matrix and Pore Space
Note different use of “matrix” by geologists and engineers
7
• Water often exists as a thin film
coating the rock grain surface.
• Oil and gas occupy the larger pore
spaces with a film of water between
the rock surface and the
hydrocarbons.
• Geologist - Rock matrix is the grains of
sandstone, limestone, dolomite, and/or
shale that do not make up the supporting
structure.
• Engineer - Matrix is the non-pore space
• Pore space is filled with fluids (water, oil,
natural gas)

8. Classification of Rocks
Sedimentary
Rock-forming
process
Sourceof
material
Igneous Metamorphic
Molten materials in
deep crust and
upper mantle
Crystallization
(Solidification of melt)
Weathering and
erosion of rocks
exposed at surface
Sedimentation, burial
and lithification
Rocks under high
temperatures
and pressures in
deep crust
Recrystallization due to
heat, pressure, or
chemically active fluids
8

9. 9

10. Relative Abundances
Sedimentary Rock Types
Clastic and Carbonate Rocks
10

11. Grain-Size Classification for Clastic Sediments
11

12. Comparison of Compositions of Clastic and
Carbonate Rocks
12

13. 13
Genetic Porosity
Classification
(Origins of Porosity in
Clastics and Carbonates)
1) Primary
(Original) Porosity
2) Secondary
(Induced) Porosity
Pore Space
Porosity
Classification
(In Terms of Fluid
Properties)
1) Absolute (or
Total) Porosity
2) Effective Porosity
Types Porosity

14. 1) Primary (Original) Porosity
❑ Porosity of the rock that formed at the time of its deposition.
❑ Primary porosity of a sediment or rock consists of the spaces between the grains.
❑ Primary porosity decrease due compaction and packing of grains.
❑ Primary porosity less than one percent in crystalline rocks like granite.
❑ Developed during the deposition of the rock material (e.g., intergranular porosity of sandstone
and intercrystalline porosity of limestone).
❑ Typified by:
➢ Intergranular pores of clastics or carbonates
➢ Intercrystalline and fenestral pores of carbonates
❑ Rocks with the original porosity are more uniform in their characteristics
❑ Usually more uniform than induced porosity
❑ more than 55% in some soils
I) Origins of Porosity in Clastics and Carbonates
(Genetic Porosity Classification)
14

15. 2) Secondary (Induced) Porosity
❑ develops after deposition of the rock.
❑Developed by some geologic processes after deposition of
the rock (diagenetic processes)
❑Examples:
➢Grain dissolution in sandstones or carbonates
❑ Vugs and solution cavities in carbonate rocks created by the
chemical process of leaching.
❑ Fracture: Fracture development in some sandstones, shales,
and carbonates (Examples of geologic processes include
faulting and uplifting).
15

16. II) Pore Space Porosity Classification
(In Terms of Fluid Properties)
❑Some void spaces become isolated due to excessive
cementation, thus many void spaces are interconnected
and others are isolated. This leads to the following
classification:
1) Absolute (abs) [or Total (t)] Porosity is the ratio between
the total pore volume (interconnected pores and
isolated ones) and the bulk volume of material (i.e., the
ratio of the entire pore space in a rock to its bulk
volume).
2) Effective Porosity (e)
➢is the ratio between the interconnected pore space volume and the
bulk volume,
➢indicates the percentage of the total volume of reservoir rock where
the void space is connected by flow channels.
16

17. Porosity Calculated
Vp is pore volume, ft3
Vb is bulk volume (Vb= Vg + Vp) or Bulk
volume of reservoir rock, ft3
Vg is grain volume, ft3
17

18. Absolute (φabs ) or
Total (t) Porosity
VolumeBulk
Pore VolumeTotal
VolumeBulk
Pore SpacectedInterconne
❖ Effective porosity: of great importance; contains the
mobile fluid.
❖ Production only occurs from the interconnected pore space
Effective Porosity (e) =
=
18

19. Porosity Values
❑Porosity Values:
• 0-5% - Negligible
• 5-10%- Poor
• 10-15%- Fair
• 15-20%- Good
• 20 -25% - Very good
• >25% Excellent
19
What is good porosity?
❑Practical Scale for cut-off for Oil:
• Sandstone ~8%
• Limestone ~5%
❑For Natural Gas the cut off is lower
Net pay: the fraction of the reservoir that has porosity above a minimum
threshold (this is the sum of the productive zones)

20. 1) Porosity in Sandstone
• Sandstone usually has
regular grains; and is
referred to as a grain-stone.
• Porosity (): Determined
mainly by the packing and
mixing of grains.
• Fractures may be present.
20
➢ The porosity of a sandstone depends
on the packing arrangement of its
grains.

21. Sandstone Classification
21

22. 1) Framework: Sand (and Silt) Size Detrital Grains
2) Matrix: Silt and Clay Size Detrital Material
3) Cement: Material Precipitated Post-depositionally, During Burial. Cements
Fill Pores and Replace Framework Grains
4) Pores: Voids Among the Above Components
Four Major Components of Sandstone
 Note different use of “matrix”
by geologists and engineers
1. Framework
2. Matrix
3. Cement
4. Pores
Engineering
“matrix”
Geologist’s Classification
22

23. Sandstones Porosity Types
i) Intergranular (Primary):
Interstitial Void Space
between Framework
Grains.
ii) Micropores: Small Pores
Mainly Between detrital
Framework Grains or
Cement.
iii) Dissolution: Partial or
Complete Dissolution of or
Authigenic Grains (Can
Also Occur Within Grains)
iv) Fractures: Breakage Due
to Earth Stresses.
23

24. Factors That Affect Porosity in Sandstones:
i) Primary Factors:
➢ Particle sphericity and angularity
➢ Packing
➢ Sorting (variable grain sizes)
ii) Secondary (Diagenetic):
➢ Cementing materials
➢ Overburden stress (compaction)
➢ Vugs, dissolution, and fractures
24

25. Factors which influence clastic depositional systems
25

26. Grain-Size Sorting in Sandstone
Roundness and Sphericity of Clastic Grains
26

27. Line of Traverse
(using microscope)
Cement
Matrix
(clays, etc.)
Tangential Contact
Sutured Contact
Long Contact
Concavo-Convex
Contact
Grain Packing in Sandstone
(modified from Blatt, 1982)
This Example
Packing Proximity = 40%
Packing Density = 0.8
4 Types of Grain Contacts
Packing Proximity
Packing Density
A measure of the extent to
which sedimentary particles
are in contact with their
neighbors
A measure of the extent to
which sedimentary particles
occupy the rock volume
27

28. CUBIC PACKING OF SPHERES
Porosity = 48%
RHOMBIC PACKING OF SPHERES
Porosity = 27 %
Note that for uniform-sized
spheres with cubic packing,
porosity is independent of grain
size.
( )
%6.47
32
1
r8
r3/4r8
VolumeBulk
VolumeMatrixVolumeBulk
VolumeBulk
VolumePore
Porosity
3
33
=

−=
−
=
−
=
=
28

29. Porosity Calculations - Uniform Spheres
• Bulk volume = (2r)3 = 8r3
• Matrix volume =
• Pore volume = bulk volume - matrix volume
3
r4
3

29

30. Packing of Two Sizes of Spheres
Porosity = 14%
Porosity increases as the range of particle size decreases
Mixing of larger and smaller
particles clearly has a significant
affect on porosity, reducing the
original porosity of 47.6% to 14%.
Real formations do not consist of
these perfectly shaped spheres,
but these theoretical packing
models help us understand the
effects of particle size and
distribution on porosity.
30

31. Types of Textural Changes Sensed by the Naked
Eye as Bedding
31

32. Progressive Destruction of
Bedding Through Bioturbation
32

33. Diagenesis
Diagenesis is the Post-
Depositional Chemical and
Mechanical Changes that
Occur in Sedimentary Rocks
Some Diagenetic Effects Include
Compaction
Precipitation of Cement
Dissolution of Framework
Grains and Cement
The Effects of Diagenesis May
Enhance or Degrade Reservoir
Quality
Whole Core
Misoa Formation, Venezuela Photo by W. Ayers
33

34. Dual Porosity in Sandstone
Note different use of “matrix”
by geologists and engineers
Dual porosity is comprised of two entirely different types of void space,
intergranular pore space, and voids in fractures:
1) Primary and secondary “matrix” porosity system
2) Fracture porosity system1. Framework
2. Matrix
3. Cement
4. Pores
Engineering
“matrix”
Geologist’s Classification
34

35. Sandstone Composition,
Framework Grains
Average Detrital Mineral Composition of
Shale and Sandstone
35

36. Porosity in Sandstone
Photomicrograph by R.L. Kugler
36

37. Secondary Electron Micrograph
Clay Minerals in Sandstone Reservoirs,
Authigenic Chlorite
Jurassic Norphlet Sandstone
Offshore Alabama, USA (Photograph by R.L. Kugler)
Occurs as Thin
Coats on Detrital
Grain Surfaces
Occurs in Several
Deeply Buried
Sandstones With
High Reservoir
Quality
Iron-Rich
Varieties React
With Acid
~ 10 mm
37

38. Electron Photomicrograph
Clay Minerals in Sandstone Reservoirs,
Fibrous Authigenic Illite
Jurassic Norphlet Sandstone
Hatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)
Illite
Significant
Permeability
Reduction
Negligible
Porosity
Reduction
Migration of
Fines Problem
High Irreducible
Water Saturation
38

39. Intergranular Pore and Microporosity
Intergranular Pores
Contain Hydrocarbon
Fluids
Micropores Contain
Irreducible Water
Backscattered Electron Micrograph
Carter Sandstone, Black Warrior Basin,
Alabama, USA (Photograph by R.L. Kugler)
39

40. Clay Minerals in Sandstone Reservoirs,
Authigenic Kaolinite
Secondary Electron Micrograph
Carter Sandstone
North Blowhorn Creek Oil Unit
Black Warrior Basin, Alabama, USA
Significant Permeability
Reduction
High Irreducible Water
Saturation
Migration of Fines
Problem
(Photograph by R.L. Kugler)
40

41. Dissolution Porosity in Sandstones
41

42. The role of Rock Texture…
Soi=(1-Swi) high
Soi=(1-Swi) low
42

43. Poor Reservoir Rock
(Isolated Void Space)
• This sandstone would not be an
acceptable reservoir rock, regardless
of the value of its porosity and the
hydrocarbon saturations, because
each void space is isolated from the
other void spaces.
• This sandstone has a high absolute
porosity but a zero effective porosity
Good Reservoir Rock
(Interconnected Void Space)
• This is sandstone would be an
acceptable reservoir rock
because of the interconnected
pore spaces and hydrocarbon
saturation.
• This sandstone has a high
absolute porosity and a high
effective porosity
43

44. Pore Network-Reconstructed using thin section
IMAGE Analysis
Porosity intergranular- 0.23
Porosity total- 0.28
Absolute Permeability- 426md
Porosity intergranular- 0.37
Porosity total- 0.39
Absolute Permeability- 5600md
44

45. 2) Porosity in Carbonates
45
Folk Carbonate Rock Classification

46. Dunham Carbonate Rock Classification
• Carbonate rocks are often subjected to early cementation, so reservoir
quality depends very strongly on dissolution, fracturing and dolomitization.
➢Most carbonate reservoirs are due to secondary porosity.
• Reefs sometimes preserve primary porosity.
46

47. Carbonates Porosity Types
i) Interparticle porosity: Each grain
is separated, giving a similar pore
space arrangement as sandstone.
ii) Intergranular porosity: Pore
space is created inside the
individual grains which are
interconnected.
iii) Intercrystalline porosity:
Produced by spaces between
carbonate crystals.
iv) Mouldic porosity: Pores created
by the dissolution of shells, etc.
v) Fractured porosity: Pore spacing
created by the cracking of the rock
fabric.
vi) Channel porosity: Similar to
fracture porosity but larger.
vii) Vuggy porosity: Created by the
dissolution of fragments, but
unconnected.
47

48. Carbonates Porosity Types
Interparticle
Intraparticle
Intercrystal
Moldic
Pores Between Particles or Grains
Pores Within Individual Particles or Grains
Pores Between Crystals
Pores Formed by Dissolution of an
Individual Grain or Crystal in the Rock
Fenestral
Fracture
Vug
Primary Pores Larger Than Grain-Supported
Interstices
Formed by a Planar Break in the Rock
Large Pores Formed by Indiscriminate
Dissolution of Cements and Grains
48

49. Idealized Carbonate Porosity Types
(modified from Choquette and Pray, 1970)
49

50. Carbonate Porosity - Example
50

51. 51

53. Comparison of Total and Effective Porosities
• Very clean sandstones : e → t
• Poorly to moderately well -cemented
intergranular materials: t  e
• Highly cemented materials and most
carbonates: e < t
▪ Effective porosity (e) → of great importance;
contains the mobile fluid
➢Production only occurs from the interconnected
pore space.
53

54. In the geology section, we show core photographs with examples of
porosity.
For now, it is useful to note these effects:
❖ Secondary (induced) porosity are more complex than primary (Original) porosity.
❖ Porosity increases as angularity of particles increases.
❖ Porosity increases as the range of particle size decreases.
❖ In contrast, porosity decreases as the volume of interstitial and cementing material increases.
❖ Porosity decreases as the compaction increases (greater depth generally means higher
overburden stresses, higher compaction forces, and lower porosity)
❖ Vugs and fractures will contribute to porosity, but to understand their affect on effective
porosity requires careful study of cores and special logging measurements.
❖ A Total Porosity less the fraction of the pore space occupied by shale or clay
❖ In very clean sands, Total Porosity is equal to Effective Porosity.
❖ Effective porosity – of great importance; contains the mobile fluid
❖ Production only occurs from the interconnected pore space.
54

55. Reservoir Average Porosity
• In case of large variation in the porosity vertically
and no or small variation horizontally or parallel
to the planes, then the arithmetic average or
thickness-weighted average porosity is used:
55
Due to the change in sedimentation or depositional conditions can
cause porosity in one portion of the reservoir to be greatly different
from that in another area, so the areal-weighted average or the
volume-weight average can be used:

56. MEASUREMENT OF POROSITY
• Core samples (Laboratory)
• Openhole wireline logs
56

57. Sandstone Porosity Measured by
Various Techniques
57

58. Information From Cores*
• Porosity
• Horizontal permeability to
air
• Grain density
• Vertical permeability to air
• Relative permeability
• Capillary pressure
• Cementation exponent (m)
and saturation exponent (n)
Standard Analysis Special Core Analysis
*Allows calibration of wireline log results
58

59. Coring Assembly and Core Bit
59

60. Coming Out of Hole
With Core Barrel
60

61. Whole Core Photograph,
Misoa “C” Sandstone,
Venezuela
Whole Core
Photo by W. Ayers
61

62. Sidewall Sampling Gun
Core bullets
Core sample
Formation rock
62

63. Sidewall Coring Tool
Coring bit
Samples
63

64. Whole Core Analysis vs. Plugs or Sidewall Cores
Whole Core
• Provides larger samples
• Better and more
consistent representation
of formation
• Better for heterogeneous
rocks or for more
complex lithologies
64
Plugs or Sidewall Cores
• Smaller samples
• Less representative of
heterogeneous formations
• Within 1 to 2% of whole cores
for medium-to high-porosity
formation
• In low-porosity formations, 
from core plugs tends to be
much greater than  from
whole cores
• Scalar effects in fractured
reservoirs

65. Sparks and Ayers, unpublished
CORE PLUG
65

66. Student Questions / Answers
• intraparticle porosity in carbonates (JC1):
• vugs and fractures
• why are clays important (JC1):
• one major reason is that clays conduct electricity, this can
effect water saturation calculations if not accounted for
• fines (ABW):
• solid particles so small that they can flow with fluids through
pores - but they can also plug pore throats
• tortuousity (ABW):
• the indirect curvy flow path through the pore system to get
from point A to point B
• holocene:
• referring to the Holocene Epoch (geology) or in general
meaning about the last 10,000 years.
66

67. REFERENCES:
• Bradley, H.: “Petroleum engineering handbook-chapter 26
properties of reservoir rocks”, 1987
• Ursin, J. and Zolotukhin, A.B.: “Introduction to reservoir
engineering-Fundamentals-4-fundamentals of rock
properties”, Stavanger,1997.
• Folk, R.L. (1974). Petrology of Sedimentary Rocks, 2nd edn.,
Hemphill Publication Company, Texas, 182pp. ISBN:
0914696033, 9780914696032
• Folk, R.L., Ward, W.C. (1957). Brazos River bar: A study in the
significance of grain size parameters. J
• Pettijohn, F.J. (1975). Sedimentary Rocks. 2nd edition, Harper
and Row, New York, 183 pp.
• Pettijohn, F.J.; Potter, P.E., Siever, R. (1987). Sand and
Sandstones. Springer, New York, 553 pp.
67