Page 153 - The Petroleum System From Source to Trap

146 Jordan and Wilson

large voids between branching or platy elements of a
M ),w ),p 0G 08 D
colonial organism. Claims that this is a common and
significant type of porosity, especially in reefal facies, are
•M � w ;,.p •G '1'8 Mo
refuted by the nearly universal filling of such voids by
reef-derived sediments, either coarse-grained skeletal
OM •W •P ),G 't' 8 ), W o
�rainstones (),G) or skeletal wackestones-mudstones
(,, W /M). Four additional pore types (fractures plus three
EBM � G 178 0G0
types of dissolution pores) are listed as nonfabric
()G (s\8 selective, indicating that they can be produced in any
carbonate rock type. Finally, there are four unusual and
*G 1TT8 less important pore types listed at the bottom of Figure
7.5 that may or may not be associated with rock fabric.
From this complete listing of every possible pore type,
Figure 7.4. Common carbonate lithofacies, shown as six
families of carbonate textures. six are recognized as being of major importance to
reservoir facies development in carbonate rocks: inter­
particle (BP), intraparticle (WP), intercrystalline (BC),
PORE TYPES moldic (MO), fracture (FRt and vuggy (VUG). The fact
that only two of these (BP and WP) are primary in origin
Porosity is best described by the system of Choquette emphasizes the role of diagenesis in porosity develop­
and Pray (1970t which is reproduced in Figure 7.5. The ment in carbonate reservoirs.
only modification from the original is the addition of A direct relationship exists between the most common
"keystone vugs." Certain types of porosity in carbonate pore types observed in carbonate rocks (Choquette and
rocks occur as a function of a rock's fabric (i.e., its Pray, 1970) and carbonate textures (Figure 7.6). The
Dunham texture); these are the eight porosity types listed strong association of BC porosity with dolomites,
as fabric selective. The terms interparticle and intraparticle growth-framework (GF) porosity with boundstones, and
are abbreviated as BP (for between particle) and WP (for BP and keystone vug (KV) porosity with grainstones
within particlet respectively, to avoid confusion with the further demonstrates that a rock's composition and
similar sounds of "inter-" and "intra-." The terms used texture control (or at least limit) the types of porosity that
are descriptive, although it helps to realize that f e nestra may be developed. Figure 7.7 shows the average
(Latin for "window") refers to rectangular voids porosity of carbonate reservoirs plotted against the envi­
arranged in a rectilinear pattern and that shelter refers to ronment of deposition, using as a data set all fields
an umbrella effect provided by shell fragments or other described in Carbonate Petroleum Reserooirs by Roehl and
large platy biodasts. Grmuth-framework porosity refers to Choquette (1985). The relationship between permeability

Table 7.2 Compilation of 24 Standard Microfaciesa

Depositional
Environment Carbonate Facies Remarks
JISA�IN 1 . SPICUUTE
and 2. MICROBIOCLASTIC CALCISILTITE � gv:, silt-sized; cross-bedded
LOWER SLOPE 3. PELAGIC LIME MUDSTONE & W/M+� Halobia common· mav have graptolites
MIDDLE 4. MICROBRECCIA of BIOCLASTIC LITHOCLASTIC PACKSTONE P J\B P
and UPPER 5. BIOCLASTIC GRAINSTONE/PACKSTONE >. GIP
SLOPE 6. REEF RUDSTONE 0 R PR 't'.k'R
REEF or OUTER SHELF 7. BOUNDSTONE B a BA, Bl, or FR
e .a. � OS �B UF PBI
MIDDLE 8. WHOLE-FOSSIL WACKESTONE
SHELF 9. BIOCLASTIC WACKESTONE � � W+O
1 0 . COATED WORN BIOCLASTS IN MICRITE (P&W'S) @ P /W
1 1 . COATED BIOCLASTS IN SPARITE (GRAINSTONE$) @ OG
1 2 . COQUINA, SHELL HASH, BIOCLASTIC GRAINSTONE OR RUDSTONE (\) G >.GIR may have dasyclads
SHOALS 1 3 . ONKOID BIOSPARITE; GRAINSTONE � G
14. LAG O >..G+B iron-staining common
1 5 . OOLITE· OOID GRAINSTONE X 0G
RESTRICTED MARINE 1 6 . PELSPARITE, PELOIDAL GRAINSTONE, LOFERITE O G may have ostracods and/ or forams
SHOALS 1 7 . GRAPESTONE PELSPARITE or GRAINSTONE l O G OBG
Inner Shelf) 1 8 . FORAMINIFERA or DASYCLAD GRAINSTONE � O G
1 9 . PELLETED LIME MUDSTONE/WACKESTONE or a LOFERITE
RESTRICTED MARINE (which is a PELSPARITE WITH FENESTRAL POROSITY) O M /W o>.w may have ostracods and gastropods
SHELF LAGOONS 20. ALGAL STROMATOLITE MUDSTONE -m B
(Inner Shelf) 2 1 . SPONGIOSTROME MUDSTONE -m O B
22. MICRITE WITH LARGE ONKOIOS @ W IF
23. UNLAMINATEO HOMOGENEOUS UNFOSSILIFEROUS PURE MICRITE M may have selenite crystals
24. COARSE LITHOCLASTIC BIOCLASTIC RUDSTONE or FLOATSTONE 8 M/F B : M cross-bedded
•After Wilson (1980a,b).