1. CaCO3 Its characteristics and geological application
Kyung Sik Woo Department of Geology Kangwon National Uninersity

2. CaCO3?

3. Limestone CaCO3 Caves Hydrocarbon Climate Change Gas Hydrates
Sea level
change
Release
of GH
Reservoir
quality
Limestone
CaCO3
Caves
Gas
Hydrates

4. Limestone? Fossiliferous rock Beautiful coral reef regions
Brachiopod-rich Ordovician limestone, USA

5. Contents Carbonate rocks Carbonates & hydrocarbon
My carbonate research related to HC

6. What is a carbonate rock?
Aragonite
Calcite
- High Mg-calcite
(>5 mole % MgCO3)
- Low Mg-calcite
(< 5 mole % MgCO3)
Dolomite
Others
Carbonate minerals
Limestone
calcite (CaCO3)
Dolomite
dolomite [CaMg(CO3)2]
Most ancient carbonate rocks are mostly composed of calcite and dolomite.
Dolomitic limestone

7. Three characteristics of carbonate sediments
Biological in origin
Local in origin
Susceptible to post-depositional diagenesis

8. Sediment are born, not made….
Biological in origin
Organisms are main producers.
Sediment are born, not made….

9. Various carbonate producers

10. Carbonates are like Shakespeare!
Actors have changed,
but the stages are the same!
(After Horowitz and Potter, 1971)

11. Local in origin
Geographic distribution
Local distribution

12. Grain size and skeletal architecture
(After Folk and Robles, 1964)

13. Beach sediments in U Island
Study Area
7~10 cm
4~7 cm
1~4 cm
0.5~1 cm

14. Very susceptible to diagenesis
Pleistocene limestone in Florida, USA

15. Rapid change after sea-level drop!
(From James and Choquette, 1990)
Glacial vs. Interglacial Settings

16. Warm- vs. cool-water carbonates
Tropical carbonates
Chuurk atoll, Micronesia
Temperate carbonates
Dok Island
Important to understand carbonates around the Korean Peninsula!

17. Limestone vs. Clastic rocks
CARBONATE SEDIMENTS, ROCKS SILICICLASTIC SEDIMENTS, ROCKS
Most occur in tropics Climate, water depth no constraint
Most are marine May be marine or non-marine
Organisms erect structure No analogous process
Sediment texture controlled by growth form Sediment texture reflects hydraulic energy in
and ultrastructure of organisms environment of deposition
Grain composition directly reflects Grains related to provenance of sediment
environments of deposition climate and tectonics of source
Shelf limestones often consist of numerous Shelf clastics do not generally show cyclicity
stacked shoaling upward sequences
Shelf undergoes predictable evolution in Shelf evolution in response to sealevel more complex
response to sea level because rate of because of potential changes in sediment availability
carbonate production constant across shelf through tectonism and climate at the source
Often cemented in marine environment Seldom cemented marine environment
Muds and grains may be formed by chemical Muds and grains formed by breakdown of pre-existing
precipitation rocks
Susceptible to early diagenetic overprint, Less susceptible to early diagenesis, porosity
porosity difficult to predict related to depositional environment, predictable
More susceptible to burial diagenesis, Less susceptible to burial diagenesis, porosity
porosity basement relatively shallow basement relatively deep

18. Carbonates vs. Clastics
Local in origin vs. transported for a long distance
Clastics
Carbonates

19. Carbonates vs. Clastics
Carbonates contain different constituents throughout geologic time
Clastics
Carbonates
Ordovician limestone, China
Carboniferous limestone, Korea

20. Carbonates vs. Clastics
Diagenetic changes due to sea-level fluctuations
Carbonates: Diagenetic changes due to sea-leval fluctuations
Clastics: Only subjected to deep burial diagenesis
2 cm
A mini cave with mini stalagmites

21. Carbonates vs. Clastics
Porosity & permeability for HC exploration in clastic rocks are more or less predictable.
Porosity & permeability for HC exploration in carbonates are difficult to predict

22. Carbonates and hydrocarbon exploration
Moldic pore

23. Carbonates in the world

24. Carbonates Oil Province
Map showing the worldwide distribution that produce hydrocarbons from carbonate reservoirs (After St. John, 1980)

25. Carbonate complexity
(After Al-Marzouqi et al., 2010)

26. Porosity types
(After Choquette and Pray, 1970)

27. Porosity related to depositional environments
Depositional texture related to porosity

28. Carbonate depositional models
Reef
Lagoon

29. Reconstruction of depositional environments is critical for hydrocarbon exploration.
(From Jordan and Wilson, 1994)

30. Recently developed integrated concept
Depositional setting
SL change
Sequence
stratigraphy
(From James and Kendall, 1992)

31. Porosity controlled by diagenesis
1mm

32. Diagenetic environments

33. Diagenetic pores (Woo et al. 2009, Geoscience Journal)
Vuggy pores by vadose diagenesis
Halimeda moldic pores
2 cm
2 cm
2 cm

34. Importance of dolomite as a result of diagenesis
2CaCO3 + Mg2+ → CaMg(CO3)2 + Ca2+
Limestone
Dolomite
Dolomite
Bitumen
1 cm

35. Porosity increase due to dolomitization during diagenesis
(From Massulo, 2004)

36. Compiled data are necessary!
Understanding depositional environments and diagenesis are critical to predict and evaluate HC reservoir quality thorough these techniques.
(After Al-Hanai et al., 2000)

37. Cretaceous limestone: the Stuart City Trend (Texas) and the Golden Land and Poza Rica Trend (Mexico)

38. One million dollar question: Why is it much more productive in Mexico?
Mexico vs. Texas
Stuart City Trend, Texas
El Abra Limestone, Mexico
One million dollar question: Why is it much more productive in Mexico?
2 cm
2 cm
(Woo et al., 1992, Journal of Sedimentary Research)

39. Different diagenetic history due to different tectonic history…
Karst landform
Caves
Rio Secreto Cave in Yucatan
(From Massulo, 2004)

40. Paleocenographic conditions responsible for hydrocarbon source
Black Sea
(Woo et al., 1993, Paleoceanography)