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92 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
Ellison, is based on the time of origin, mode of origin, and distribution
relationships of pores spaces [3].
Primary Porosity
1. Intercrystalline: voids between cleavage planes of crystals, voids
between individual crystals, and voids in crystal lattices. Many of
these voids are sub-capillary, i.e., pores less than 0.002 mm in
diameter. The porosity found in crystal lattices and between mud-sized
particles has been called “micro-porosity” by Pittman, as shown in
Figure 3.2 [4]. Unusually high recovery of water in some productive
carbonate reservoirs may be due to the presence of large quantities of
microporosity .
2. Intergranular or interparticle: voids between grains, i.e., interstitial
voids of all kinds in all types of rocks. These openings range from
sub-capillary through super-capillary size (voids greater than 0.5 mm in
diameter).
3. Beddingplanes: voids of many varieties are concentrated parallel to
bedding planes. The larger geometry of many petroleum reservoirs is
controlled by such bedding planes. Differences of sediments deposited,
of particle sizes and arrangements, and of the environments of deposition
are causes of bedding plane voids.
4. Miscellaneous sedimentary voids: (1) voids resulting from the
accumulation of detrital fragments of fossils, (2) voids resulting from
the packing of oolites, (3) vuggy and cavernous voids of irregular and
variable sizes for at the time of deposition, and (4) voids created by living
organisms at the time of deposition.
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Fi#yre 3.2. Types of porosity found in sandstone reservoirs (courtesy of Core
Laboratories).
