3.2 POROSITY AND PERMEABILITY
65
100
Saturation by fluid "B"
~
0%
l
(1)
c/)
(/)
rl
Displacement
pressure
I
I
I
0
I ~
Saturation by fluid "A'L--~ - 100%
I
Irreducible
saturation
of fluid "A"
Fig. 3.17. Graph showing the basic parameters of a capillary pressure curve for a rock sample. The sample is
initially totally saturated by fluid A. This is gradually displaced by fluid B as pressure is increased.
3.2.2 Pore Morphology
3.2.2.1 Introduction and Classification
Any petrophysical study of a reservoir rock necessitates a detailed description of the
amount, type, size distribution, and genesis of its porosity. The classification of the main
types of porosity is discussed next, followed by a description of the more common varieties of pores. A large number of adjectives have been used to describe the different
types of porosity present in sediments. Choquette and Pray (1970, pp. 244-250) provide
a useful glossary of pore terminology.
The pores themselves may be studied by a variety of methods ranging from examination of rough or polished rock surfaces by hand-lens or stereoscopic microscope,
through study of thin sections using a petrological microscope, to the use of the scanning electron microscope. Another effective technique of studying pore fabric is to impregnate the rock with a suitable plastic resin and then dissolve the rock itself with an
appropriate solvent. Examination of the residue gives some indication, not only of the
size and shape of the pores themselves, but also of the throat passages that connect
pores (e.g., Wardlaw, 1976). The minimum size of throats and the tortuosity of pore systems are closely related to the permeability of the rock.
These different observational methods show that there are many different types of
pore systems. Various attempts have been made to classify porosity types. These range
from essentially descriptive schemes, to those which combine descriptive and genetic
criteria (e.g., Choquette and Pray, 1970), and those which relate the porosity type to the
65
100
Saturation by fluid "B"
~
0%
l
(1)
c/)
(/)
rl
Displacement
pressure
I
I
I
0
I ~
Saturation by fluid "A'L--~ - 100%
I
Irreducible
saturation
of fluid "A"
Fig. 3.17. Graph showing the basic parameters of a capillary pressure curve for a rock sample. The sample is
initially totally saturated by fluid A. This is gradually displaced by fluid B as pressure is increased.
3.2.2 Pore Morphology
3.2.2.1 Introduction and Classification
Any petrophysical study of a reservoir rock necessitates a detailed description of the
amount, type, size distribution, and genesis of its porosity. The classification of the main
types of porosity is discussed next, followed by a description of the more common varieties of pores. A large number of adjectives have been used to describe the different
types of porosity present in sediments. Choquette and Pray (1970, pp. 244-250) provide
a useful glossary of pore terminology.
The pores themselves may be studied by a variety of methods ranging from examination of rough or polished rock surfaces by hand-lens or stereoscopic microscope,
through study of thin sections using a petrological microscope, to the use of the scanning electron microscope. Another effective technique of studying pore fabric is to impregnate the rock with a suitable plastic resin and then dissolve the rock itself with an
appropriate solvent. Examination of the residue gives some indication, not only of the
size and shape of the pores themselves, but also of the throat passages that connect
pores (e.g., Wardlaw, 1976). The minimum size of throats and the tortuosity of pore systems are closely related to the permeability of the rock.
These different observational methods show that there are many different types of
pore systems. Various attempts have been made to classify porosity types. These range
from essentially descriptive schemes, to those which combine descriptive and genetic
criteria (e.g., Choquette and Pray, 1970), and those which relate the porosity type to the