FE 02-16I Carbonate Description

Nội dung text: FE 02-16I Carbonate Description

1. Describing Carbonate Rocks • Carbonate rocks are difficult to classify because of the complexity of sources and types of their occurrences
2. Aids to Carbonate Rock Determination • Calcimeter • Alizarin Red S – Limestone will turn deep red – Dolomite is unaffected
3. Dunham: Mudstone
4. Dunham: Packstone
5. Dunham: Boundstone
6. Carbonate Rocks: Grain Size • Describe the size of physically transported particles (oolites, interclasts, fossils, pellets) and chemically precipitated minerals (either as pore-filling cement, primary ooze, or products of recrystallization and replacement)
7. Grain Type Categories Grain Type Example Detrital Grains Rock fragments, intraclasts Skeletal Grains Crinoidal, Molluscan, Algal Pellets Fecal Pellets, grains of mud Lumps Composite grains, Algal lumps Coated Grains Oolites, Pisolites, Encrusted grains
8. Carbonate Rocks: Hardness or Induration • Same as those for clastics
9. Carbonate Rocks: Cement or Matrix • Cementation is a result of crystallization from an aqueous solution with unimpeded growth into a void • Lime mud/clay matrix is an integral part of the deposited sediment • Matrix recrystallization occurs at the lattice level in the solid phase
10. Micrite and Sparite • Micrite – abbreviation of “microcrystalline ooze”; a precipitate formed within the basin of deformation and showing no or little evidence of transport; consists of crystals 1-4 μm diameter occuring as matrix (dull and opaque ultra fine- grained material that forms the bulk of limestones and the matrix of chalk) • Sparite cement consists of clean calcite crystals, generally longer than micrite, forming pore filling cement between grains and within cavities
11. Carbonate Rocks: Visual Structure • Most significant structural features are postlithification voids (fractures, fissures, joints, vugs) because they have a major impact on rock strength, porosity and permeability and are significant in terms of reservoir potential and lost circulation problems • Other less prominent features: slickensides and staining
12. Porosity Classification of Carbonate Rocks • Intergranular – pore space between grains or particles of a rock • Intercrystal – pore space between crystals of a rock • Vuggy – pore space between grains or crystals of a rock wherein the space is equal or larger than the size of the individual grains or crystals. It usually has the form of irregular voids. • Moldic – due to the leaching of soluble grains • Fracture
13. Carbonate Rocks: Secondary Porosity • Secondary porosity is porosity formed secondary to the rock fabric. This type is usually not seen in cuttings, but may be inferred. – Ex: fractures, fissures, vugs
14. End of Topic