Carbonate Diagenesis From soft sediment to hard rock M.Geo.136b: Beckenanalyse 2 A Presentation by: Falko Malis Stephan Sarner Maximilian Schaidt Johannes Sucke
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Carbonate classification after Folk Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Carbonate classification after Dunham Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Carbonate classification after Dunham Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Diagenetic factors: Dolomitization Physical compaction Chemical processes Cementation Chemical compaction Dissolution Inversion Recrystallization Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Dolomitization Two basic models for dolomitization are discussed: Primary production of dolomite: Microrganisms break down MgSO4, dolomite is produced Only produces small amounts of dolomite Secondary transformation of calcite or aragonite: Calcite or aragonite comes in contact with Mg rich fluids and reacts with them Applies to most of global dolomites 6 (or more) different types can be distiguished
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Coroong lagoon type: Flügel, 2004 Lagoons are filled with marine water and Mg rich groundwaters Water in the lagoons evaporates The Mg rich brine seeps through the porous carbonates and reacts with them
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Sabkha evaporation type: The areas behind the shore lines become hit by storms Flügel, 2004 The marine water is evaporated and a brine is formed The brine reacts with the upper layers of the carbonates Associated with saltflats
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Seepage reflux type: Tides fill up lagoons behind the shore line Flügel, 2004 This water is evaporated and poduces a brine that seeps back to the ocean Associated with evaporites
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Burial compaction type: Flügel, 2004 Some carbonates are compacted and by this can loose some of their porewater Clayminerals transform and Mg is expulsed Porewater is rich in Mg and reacts with carbonates in higher areas
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Mixing formation type: Marine water and fresh water are mixed in the underground Flügel, 2004 Can be located more landward than the other forms of dolomitization
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Models for secondary poduction: Seawater dolomitization type: Ocean current and Tides press seawater into the underground Flügel, 2004 Geothermal heat warms up the water and makes it rise The warm water produces dolomite
Physical Compaction Two phases: Carbonates Diagenetic Mechanisms Environments Hydrocarbon No contact point contact tangential contact sutured +concave convex contact 1. Deposition of sediments, change of packing density, dewatering Reduction to about 75% of original porosity Often happens within the burial depth of just one meter 2. Deformation of grains Reduction to 50% of porosity at several 100m Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Dynamic factors: Overburden Temperature Pressure Duration of burial stress Pore pressure Pore water chemistry Inheritited factors Sedimentary fabric Skeletal architecture and mineralogy Clay content Grain size, sorting, shape Cementation Preburial dolomitization
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Chemical compaction Result of rock fluid interaction Most important process: Pressure solution Driving force: Porespace fluid pressure Choquette, James; 19
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Pressure solution Riekesche Prinzip Pressure solution process Dissolution of minerals at contact Diffusion towards pore space Precipitation at less stressed faces of the grains wikipedia.org
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Stylolites Dissoluted mineral material from pressure solution Typically alongside layer surfaces (vertical by tectonic avtivity) Insoluble minerals (clays, pyrite and oxides) remain within the stylolites and make them visible Chemical dissolution/ formation of stylolites Pressure solution forms Scholle, 2003 Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Stylolite classification stylolitized ooids Scholle, 2003 Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Diagenetic changes Example of physical and chemical processes on an octacoral A D: cementation of vugs inside the coral E & F: deep burial compaction resulting in grain breakage G: refilling with clasts and cementation Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Types of diagenesis 1) Meteoric 2) Marine 3) Burial Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon 1) Meteoric vadose environment Above water table Pores filled with freshwater & air Two processes: a) extensive dissolution of unstable minerals (aragonite & high Mg calcite) b) reprecipitation of stable carbonate (low Mg calcite) Strong effect on permeability Cement fabrics reflect selective dissolution of water environment Karstic features (sinkholes, caves, collapse breccias) steady state Flügel, 2004
Low Mg needle Carbonates Diagenetic Mechanisms Environments Hydrocarbon Dissolution of ooids & meniscus fabric Microstalactitic cement Scholle, 2003 Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Flügel, 2004
Complete filling of primary porosity & high dissolution of Carbonates Diagenetic Mechanisms Environments Hydrocarbon 1) Meteoric phreatic environment Isopachous low Mg calcite cementation Scholle, 2003 Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Flügel, 2004
Botryo cemen Carbonates Diagenetic Mechanisms Environments Hydrocarbon 2) Marine phreatic environment Early stage cementa microcrystalline gra Thick micrite enve & aragonitic need Scholle, 2003 Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Flügel, 2004
Carbonates Diagenetic Mechanisms Environments Hydrocarbon 3) Burial environment Physical compaction & reorientation of grains Brittle defo Scholle, 2003 Scholle, 2003
Physica compa Carbonates Diagenetic Mechanisms Environments Hydrocarbon 3) Burial environment Chemical dissolution/ formation of stylolites Scholle, 2003 Scholle, 2003
Carbonates Diagenetic Mechanisms Environments Hydrocarbon Hydrocarbon in carbonates Carbonates are typical reservoir rocks large porespace and high fissuring especially Dolomite (highly stable) ~50% of world s oil and gas are stored in carbonate rocks https://sofia.usgs.gov/
sepmstrata.or Carbonates Diagenetic Mechanisms Environments Hydrocarbon Fluid migration from source rock due to lower density of hydrocarbon (0,5 1,2 g/cm³) Accumulation of hydrocarbons under impermeabel caprock (seal)
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References Flügel, E.: Microfacies of Carbonate Rocks; Berlin, Heidelberg; 2004 Scholle, S.; Ulmer Scholle, D.: A Color Guide to the Petrography of Carbonate Rocks; Tulsa; 2003