CaCO3 Its characteristics and geological application Kyung Sik Woo Department of Geology Kangwon National Uninersity wooks@kangwon.ac.kr

CaCO3?

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

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

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

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

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

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

Various carbonate producers

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

Local in origin Geographic distribution Local distribution

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

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

Very susceptible to diagenesis Pleistocene limestone in Florida, USA

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

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

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

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

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

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

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

Carbonates and hydrocarbon exploration Moldic pore

Carbonates in the world

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

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

Porosity types (After Choquette and Pray, 1970)

Porosity related to depositional environments Depositional texture related to porosity

Carbonate depositional models Reef Lagoon

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

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

Porosity controlled by diagenesis 1mm

Diagenetic environments

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

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

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

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)

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

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)

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

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