Page 154 - The Petroleum System From Source to Trap

7. Carbonate Reservoir Rocks 147

LE B P X -
FA R I C SELECTIVE NOT FA R I C SELECTIVE
B
B

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xD I N TERPARTI C F R AC U R E FR

X� INTRAPARTICLE W P � C H ANNEL C H

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X 2:�:�:f�:X. I N TERCRYSTAL BC V U G VUG
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CA E R N cv
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�ES� KEYSTO N E KV
VUG

FA R I C S E LECTIVE OR NOT
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BRECCIA BOR I N G B U R R OW S H R I N K AGE
BR BO B U SK

Figure 7.5. Porosity classification of carbonate rocks. Large X's indicate the most significant porosity types in carbonate
reservoirs; black areas are porosity. (After Choquette and Pray, 1970).

and depositional environment is shown in Figure 7.8. High porosity and low permeability associated with
These two plots together show that the highest average basinal and, to a lesser extent, slope deposits can be
porosity and permeability values are in lithofacies associ­ accounted for in a number of ways: (1) ineffective but
ated with shoal environments, the second highest with abundant WP porosity within tests of planktonic
reef environments, and the next highest with tidal flat foraminifera that make up nearly 90% of certain deep
environments. Granted, with only one field contributing water ooze deposits; (2) microcrystalline BC porosity
to slope facies (i.e., Poza Rica), adequate statistical between clay-sized coccolith fragments in true chalk
treatment is not possible. deposits; or (3) microcrystalline BC porosity (also