My seminar At Periyar University Salem I'm Thomas chinnappan Keeranur Pudukkottai tamilnadu India @tcoftheworld @tcorganization

1. Porosity and types
BY:
THOMAS CHINNAPPAN .A ,
M.SC.APPLIED GEOLOGY,
PERIYAR UNIVERSITY,
SALEM.

2. Porosity :
Defination: The ratio of the pore volume in a rock to
the bulk volume of that rock.
Denoted by φ.
Express in Percent.
Mathematical Form: φ = Vp/Vb

3. Types of porosity :
There are two types of porosity
1) Primary porosity
2) Secondry porosity

4. 1) Primary porosity :
• The porosity of the rock that formed at the time of
its deposition.
• Two basic stages
• Predeposition and depositional stage
Predeposition stage :
• begins when individual sedimentary particles form and
includes intragranular porosity such as is seen
• in forams, pellets, ooids, and other nonskeletal grains.

5. Depositional stage :
• time involved in final deposition
• burial of a sediment or a growing organic
framework
• total volume of carbonate porosity
observed in carbonate rocks and sediments

6. Secondary porosity :
• developed at any time after final deposition
• time interval may be divided into stages
• porosity-modifying processes occurring in
shallow surficial diagenetic environments
• stages: eogenet, telogenetic, and
mesogenetic

7. Further Types of porosity :
They are further subdivided into :
1) Total porosity
2) Effective porosity
3) Microporosity
4) Mesoporosity
5) Macroporosity

8. Total porosity :
The ratio of the entire pore space in a rock
to its bulk volume.
Effective porosity :
The measure of the void space that is filled by
recoverable oil and gas φ = Vol. of interconnected
pores + Vol. of deadend Total or bulk vol. of
reservoir rock In very pure sandstone Total porosity
is equal to Effective porosity

9. Macroporosity :
Macroporosity In solids , the term
'macroporosity' refers to pores greater than 50
nm in diameter.

10. Microporosity :
the term 'microporosity' refers to pores smaller
than 2 nm in diameter.
Mesoporosity :
Mesoporosity In solids , the term
'mesoporosity' refers to pores greater than 2
nm and less than 50 nm in diameter.

11. Fabric selectivity :
• solid depositional and diagenetic constituents of a
sediment or rock are defined as its fabric.
• solid constituents consist of :primary grains, such as
ooids and bioclast
• later-formed diagenetic constituents calcite,
dolomite, and sulfate cements
• recrystallization or replacement components,
such as dolomite and sulfate crystals

12. FABRIC SELECTIVE :
• Interpartical
• Intrapartical
• Fenestral
• Shelter
• Framework
• Intercrystal
• Moldic
NOT FABRIC SELECTIVE :
• Fracture
• Channel
• Vug
• Cevaron
Basic porosity types

13. Interpartical porosity :
Porosity between particles
Fabric selective
Intrapartical porosity :
Porosity within individual particles
or grains

14. Fenestral :
Pores larger than grain-
supported interstices
(interparticle)
Growth framework :
Porosity created by in-
place growth of a
carbonate rock
framework

15. Shelter :
Porosity created by the
sheltering effect of large
sedimentary particles
Porosity formed by selective
removal of an individual
constituent of the rock
Modlic porosity :

16. Not fabic selective
Fracture porosity :
Porosity formed by fracturing
Channel porosity :
Markedly elongate pores

17. Vuggy porosity :
Pores larger than 1/16
mm in diameter and
somewhat equant in
shape
Cavern :
Very large channel or vug

18. Fabric selective or not
Breccia :
Interparticle porosity in breccia
Boring :
Porosity created by boring organism
Burrow :
Porosity created by organism burrowing
Shrinkage :
Porosity produced by sediment shrinkage

19. Determination of Porosity :
1) Direct method
2) Water evaporation method
There are two types :

20. Direct method :
Determining the bulk volume of the porous
sample, and then determining the volume of the
skeletal material with no pores .
pore volume = total volume − material volume.
Water evaporation method :
pore volume = weight of saturated sample −
weight of dried sample)/density of water

21. Interparticle porosity :
• Mud-free carbonate sediments, like their
siliciclastic counterparts
• dominated by intergranular porosity at the
time of deposition.
• sediments exhibit porosities from 40- 50% &
near the upper limit of 48%
Primary porosity

22. • wide variability of particle shape seen in
carbonates
• excess porosity over the 27-30% expected in
spherical particles
• maximum packing and commonly observed in
siliciclastic sediments

23. • This shape variation seems to be a function of
their biological origin
• the common presence of intraparticle
porosity that may occupy a significant
percentage of the bulk volume of the
sediment

24. Intrapartical porosity :
• one of the fundamental differences between
• carbonate and siliciclastic porosity originate in a
variety of ways.
• living chambers of various organisms such as
Foraminifera, gastropods, Rudists, and
brachiopods

25. • ultrastructure of some abiotic grains, such
as ooids, and composite grains
• such as pelloids, which consist of packed,
needle-shaped crystals

26. • lead to significant intraparticle porosity
• activity of microboring algae and fungi
may significantly
• increase the intraparticle porosity of
carbonate grains
• ultrastructure of the tests and skeletons
of organisms

27. Depositional porosity of mud- bearing
sediments :
• Carbonate sediments containing mud range in
porosity from 44 to over 75%
• Grain-supported muddy sediments such as
packstones show the lowest porosity range

28. • deep marine oozes can have porosities of up to
80%
• high porosities seen in the mud-supported shelf
sediments are surely the effect of shape and fabric

29. • perhaps the effect of oriented sheaths of
water molecules responding to the strongly
polar aragonite crystals
• high porosities reported for deep marine
oozes
• high intragranular porosity found in the
dominant organic components

30. Framework and fenestral porosity
• activity of reef-building organisms, can be
depositional porosity type in the reef
environment.
• Framebuilders, such as scleractinian corals,
can construct an open reef framework
• volumes of pore space during the
development of the reef

31. • construct an open framework reef, coralline
• algae, and in the past
• stromatoporoids, and sponges have tended to
erect a more closed framework structure with
significantly less framework porosity

32. • associated with supratidal, algal-
• related, mud-dominated sediments can be
locally important
• opening communication between the larger
• fenestral pores through the intercrystalline
porosity developed in the matrix dolomite.

33. Secondary porosity
Formation by dissolution :
• Dissolution of limestones and sediments
• change in the chemistry of the pore fluid
• change in salinity, temperature, or partial
pressure of CO2.
• development of a meteoric water system in a
shallow shelf sequence

34. • hydrocarbon maturation or shale dewatering may
provide aggressive fluids
• meteoric waters early in the burial history of a
carbonate sequence

35. Associated with dolomitization :
• Intercrystalline porosity associated with
dolomites
• form a reservoir type in a no.of setting ranging
from supratidal/sabkha to normal marine
sequences

36. • role of dolomitization in porosity
development and destruction
• close relationship between percentage of
dolomite and porosity

37. Associated with breccias :
• Brecciation of carbonate rock sequence no.of
situations including:
• evaporite solution collapse,
• limestone solutioncollapse
• faulting, and
• soil formation

38. • Limestone breccias, particularly those
associated with evaporite or limestone solution
collapse,
• Reservoir for hydrocarbons or a host for
mineralization.

39. Associated with fractures :
• Fracturing is particularly effective and
common in carbonate reservoirs
• brittle nature of carbonates relative to the
more ductile fine-grained siliciclastics
• Associated with Faulting, folding, differential
compaction, salt dome movement, and
hydraulic fracturing within overpressured
zone

40. • Fractures in carbonates are commonly filled
with a variety of mineral species
• including, calcite, dolomite, anhydrite, galena,
sphalerite, celestite, strontianite, and fluorite

41. Summary
Carbonate sediments and rocks generally have a
much more complex pore system
than do siliciclastics because of the wide variety of
grain shapes common in carbonates,
the presence of intragranular, framework, and
fenestral porosity in carbonates, and the
potential for the development of moldic and highly
irregular dissolution-related porosity
in carbonates.