Changes

There are five basic carbonate depositional environments. From shore to basin, they are ''[[peritidal]]'' (tidal flat), ''[[shallow shelf interior]], [[shelf margin complex]], [[slope]]'', and ''[[basin]]'' ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]). (For more information on carbonate depositional environments, see Scholle et al.<ref name=Scholleetal_1983>Scholle, P. A., D. G. Bebout, and C. H. Moore, eds., 1983, [http://store.aapg.org/detail.aspx?id=656 Carbonate depositional environments]: AAPG Memoir 33, 708 p.</ref>)

There are five basic carbonate depositional environments. From shore to basin, they are ''[[peritidal]]'' (tidal flat), ''[[shallow shelf interior]], [[shelf margin complex]], [[slope]]'', and ''[[basin]]'' ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]). (For more information on carbonate depositional environments, see Scholle et al.<ref name=Scholleetal_1983>Scholle, P. A., D. G. Bebout, and C. H. Moore, eds., 1983, [http://store.aapg.org/detail.aspx?id=656 Carbonate depositional environments]: AAPG Memoir 33, 708 p.</ref>)

The peritidal depositional environment is complex ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]). Sediments deposited between mean high and mean low tide are called ''[[intertidal]] sediments'', sediments deposited above mean high tide are called ''[[supratidal]] sediments'', and sediments deposited below mean low tide are called ''[[subtidal]] sediments''. In arid and semi-arid climates, evaporite flats ([http://www.crienterprises.com/Edu_Evap_Coastal_Sabkha.html sabkhas]) are present from which [[gypsum]] and [[halite]] are deposited. [[Sand dune|Eolian sand dunes]] composed of siliciclastic or carbonate grains may form on the supratidal surface.

The peritidal depositional environment is complex ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]). Sediments deposited between mean high and mean low tide are called ''[[intertidal]] sediments'', sediments deposited above mean high tide are called ''[[supratidal]] sediments'', and sediments deposited below mean low tide are called ''[[subtidal]] sediments''. In arid and semi-arid climates, [[evaporite]] flats ([http://www.crienterprises.com/Edu_Evap_Coastal_Sabkha.html sabkhas]) are present from which [[gypsum]] and [[halite]] are deposited. [[Sand dune|Eolian sand dunes]] composed of siliciclastic or carbonate grains may form on the supratidal surface.

The shallow shelf interior environment ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]) is dominated by low-energy waters that allow lime mud to accumulate. [[Storm deposits and currents|Storms]], however, churn the sediment into [[suspension]], winnowing out the fine-sized material and concentrating the coarse material. Near shorelines, the shelf environment may be composed of offshore [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars] and [[spit]]s oriented parallel to shoreline. Shorelines that face heavy wave action accumulate [[carbonate sand]] or gravel. [[Tidal current]]s are concentrated in channels between islands and produce [[tidal delta]]s on the lee side of the island.

The shallow shelf interior environment ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig2.png|Figure 2]]) is dominated by low-energy waters that allow lime mud to accumulate. [[Storm deposits and currents|Storms]], however, churn the sediment into [[suspension]], winnowing out the fine-sized material and concentrating the coarse material. Near shorelines, the shelf environment may be composed of offshore [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars] and [[spit]]s oriented parallel to shoreline. Shorelines that face heavy wave action accumulate [[carbonate sand]] or gravel. [[Tidal current]]s are concentrated in channels between islands and produce [[tidal delta]]s on the lee side of the island.

===Dolomitization===

===Dolomitization===

''Dolomitization'' is a diagenetic process that converts [[limestone]]s to [[dolostones]] through a microchemical process of calcium carbonate dissolution and dolomite precipitation. Dolomitization can change the rock fabric and the petrophysical properties significantly because the dolomite [[Crystallization|crystal]]s are commonly larger than the replaced limestone particles. Dolomite [[cement]] systematically grows on the dolomite crystal faces, reducing reservoir quality. Dolomitization requires the addition of large quantities of magnesium through [[Fluid flow fundamentals|fluid flow]].

''Dolomitization'' is a diagenetic process that converts [[limestone]]s to [[dolostones]] through a microchemical process of calcium carbonate dissolution and [[dolomite]] precipitation. Dolomitization can change the rock fabric and the petrophysical properties significantly because the dolomite [[Crystallization|crystal]]s are commonly larger than the replaced limestone particles. Dolomite [[cement]] systematically grows on the dolomite crystal faces, reducing reservoir quality. Dolomitization requires the addition of large quantities of magnesium through [[Fluid flow fundamentals|fluid flow]].

===Evaporite mineralization===

===Evaporite mineralization===

The most common evaporite mineral found with carbonate rocks is [[anhydrite]] and its hydrous form, [[gypsum]]. Gypsum is the common form at shallow depths, but it converts to anhydrite at depth in response to higher temperatures. Bedded anhydrite is commonly found in tidal flat environments and is an effective reservoir seal. Diagenetic anhydrite is found in reservoir rocks as nodules and [[poikilotopic crystal]]s, which have little effect on reservoir properties, and as pore-filling crystals, which reduce [[reservoir quality]].

The most common [[evaporite]] mineral found with carbonate rocks is [[anhydrite]] and its hydrous form, [[gypsum]]. Gypsum is the common form at shallow depths, but it converts to anhydrite at depth in response to higher temperatures. Bedded anhydrite is commonly found in tidal flat environments and is an effective reservoir seal. Diagenetic anhydrite is found in reservoir rocks as nodules and [[poikilotopic crystal]]s, which have little effect on reservoir properties, and as pore-filling crystals, which reduce [[reservoir quality]].

===Dissolution and associated processes===

===Dissolution and associated processes===

''Dissolution'' is the diagenetic process by which [[carbonate]] and [[Evaporites|evaporite]] minerals are dissolved and removed, thus creating and modifying pore space in reservoir rocks (see [[Reservoir quality]]). The effect of this process on [[permeability]] depends upon the geometry and location of the resulting voids relative to the rock fabric. In some cases, dissolution is [[Fabric selective disslution|fabric selective]] and results in formation of isolated [http://wiki.seg.org/wiki/Dictionary:Vug vugs]. In other cases, dissolution enlarges [[fracture]]s and [[Porosity#Carbonate pore systems|interparticle pores]] resulting in large, connected [[vug]]s. If the vugs are large enough, the roof may collapse, forming a floor [http://geology.com/rocks/breccia.shtml breccia] and fractured roof.

''Dissolution'' is the diagenetic process by which [[carbonate]] and evaporite minerals are dissolved and removed, thus creating and modifying pore space in reservoir rocks (see [[Reservoir quality]]). The effect of this process on [[permeability]] depends upon the geometry and location of the resulting voids relative to the rock fabric. In some cases, dissolution is [[Fabric selective disslution|fabric selective]] and results in formation of isolated [http://wiki.seg.org/wiki/Dictionary:Vug vugs]. In other cases, dissolution enlarges [[fracture]]s and [[Porosity#Carbonate pore systems|interparticle pores]] resulting in large, connected [[vug]]s. If the vugs are large enough, the roof may collapse, forming a floor [http://geology.com/rocks/breccia.shtml breccia] and fractured roof.

==Carbonate rock fabric and petrophysical relationships==

==Carbonate rock fabric and petrophysical relationships==

[[Category:Sedimentology and stratigraphy – Carbonates]]

[[Category:Sedimentology and stratigraphy – Carbonates]]

[[Category:Depositional environments]]

[[Category:Depositional environments]]