Carbonates versus clastics

1. Carbonate sedimentology/1
• Interpretation techniques applied to clastic
reservoirs can also be applied to carbonate
depositional systems.
• Carbonates however, differ from clastics due to
the importance of biogenic processes and their
susceptibility to diagenetic modifications.
Carbonates versus clastics

2. Carbonate sedimentology/2
Tucker (1985)
Shelf marginal reef
Shelf
Shelf marginal reef
Mud
Tidal flats
Skeletal
pellet mud
Lagoon
Shelf
Skeletal
sand
Patch reefs
Slope
Oolite sand bodies
Pelagic ooze
Basin
Re-sedimented
carbonates
Shoreline
Depositional environments

3. Carbonate sedimentology/3
Carbonate grain types

4. Carbonate sedimentology/4
Dunham (1962)
Carbonate classification

5. Carbonate sedimentology/5
Folk (1962)
Carbonate classification

6. Carbonate sedimentology/7
• All primary sedimentary structures recognised in
siliciclastic rocks can occur in carbonates
(e.g. cross-bedding in ooid shoals, slumps etc.)
• In addition there may be:
– Biogenic structures (reefs etc.)
– Diagenetic structures unique to carbonates
Sedimentary structures

7. Carbonate sedimentology/8
Sedimentary structures

8. Carbonate sedimentology/9
Carbonate lithofacies – core calibration
Vertical well
Boundary between FMI facies FMI7 and FMI4. The
burrowed surface is clearly visible (arrowed) as are the
packstone-filled burrows below.
Burrowed contact (dashed line)
between FMIF7 and FMIF4. Burrows
(squares) are filled with packstone.
Possible hardground.
FMIF7
FMIF4
Static image Dynamic image Slabbed core

9. Carbonate sedimentology/10
Carbonate lithofacies – core calibration
Vertical well
Thin, very resistive horizon (FMIF11) corresponding to a
subtle lithological change in a mudstone-wackestone
succession (FMIF2). The resistivity contrast may be due
to differential cementation.
Thin mudstone unit with
matrix-supported
intraclasts (possible debris
deposit) within a
mudstone-wackestone
succession
FMIF11
FMIF2
FMIF2
Static image Dynamic image
Slabbed core

10. Carbonate sedimentology/11
Carbonate lithofacies
FMI image facies associations vs Ka
0.01
0.10
1.00
10.00
100.00
1000.00
0 1 2 3 4 5 6
FMI image facies association
Ka
(mD)
FMIA1
FMIA2
FMIA3
FMIA4
FMIA5

11. Carbonate sedimentology/12
• Fractures occur in carbonates in the same
manner as in clastics.
• However tension gashes associated with
stylolite bands are a common feature in
carbonates.
• The interpretation techniques used for clastic
sediment fractures are applied to carbonate
fractures.
Fractures in carbonates

12. Carbonate sedimentology/13
Conductive fracture
Resistive fracture
Fractures in carbonates
Vertical well

13. Carbonate sedimentology/14
Bedding
Fractures
Fractures in carbonates
Vertical well

14. Carbonate sedimentology/15
The ultimate goal