Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting reservoir system quality and performance

  | chapter = Predicting reservoir system quality and performance

  | frompg  = 9-1

  | frompg  = 9-101

  | topg    = 9-156

  | topg    = 9-102

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

==Stages affect porosity==

==Stages affect porosity==

Three major geologic stages determine the [[porosity]] of carbonate rocks:<ref name=ch09r10>Choquette, P., W., Pray, L., C., 1970, Geologic nomenclature and classification of porosity in sedimentary carbonates: AAPG Bulletin, vol. 54, no. 2, p. 207–250. Classic reference for basic concepts regarding carbonate porosity.</ref>

Three major geologic stages determine the [[porosity]] of carbonate rocks:<ref name=ch09r10>Choquette, P. W., and L. C. Pray, 1970, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0054/0002/0200/0207.htm Geologic nomenclature and classification of porosity in sedimentary carbonates]: AAPG Bulletin, vol. 54, no. 2, p. 207–250. Classic reference for basic concepts regarding carbonate porosity.</ref>

* Predepositional

* Predepositional

The '''postdepositional stage''' is the time after final deposition. All the porosity that forms during this stage is diagenetic or secondary in origin. Diagenetic processes are related to changes in water chemistry, temperature, pressure, and water movement.

The '''postdepositional stage''' is the time after final deposition. All the porosity that forms during this stage is diagenetic or secondary in origin. Diagenetic processes are related to changes in water chemistry, temperature, pressure, and water movement.

[[file:predicting-reservoir-system-quality-and-performance_fig9-68.png|thumb|{{figure number|1}}After .<ref name=ch09r10 />]]

==Time-porosity table==

==Time-porosity table==

[[file:predicting-reservoir-system-quality-and-performance_fig9-68.png|thumb|400px|{{figure number|1}}Time–porosity terminology and relationships.<ref name=ch09r10 />]]

The following table and chart in [[:file:predicting-reservoir-system-quality-and-performance_fig9-68.png|Figure 1]] list time–porosity terminology and relationships.

 

The table and chart in [[:file:predicting-reservoir-system-quality-and-performance_fig9-68.png|Figure 1]] list time–porosity terminology and relationships.

==Postdepositional substages==

==Postdepositional substages==

* Telogenetic (late)

* Telogenetic (late)

The '''eogenetic substage''' (early diagenetic period) is the time from final deposition to the time when the sediment is buried below the zone of influence from surface processes. The eogenetic zone extends from the surface to the base of the zone of influence of surface processes. Even though the eogenetic substage may be geologically brief and the zone thin, the diagenesis that occurs is more varied and generally more significant than any other substage. Eogenetic processes are generally fabric selective. The major porosity change is reduction through carbonate or evaporite mineral precipitation. Internal sedimentation also reduces porosity. Although minor in comparison, the most important porosity creation process is selective solution of aragonite.<ref name=ch09r10 />

The '''eogenetic substage''' (early diagenetic period) is the time from final deposition to the time when the sediment is buried below the zone of influence from surface processes. The eogenetic zone extends from the surface to the base of the zone of influence of surface processes. Even though the eogenetic substage may be geologically brief and the zone thin, the [[diagenesis]] that occurs is more varied and generally more significant than any other substage. Eogenetic processes are generally fabric selective. The major porosity change is reduction through carbonate or [[evaporite]] mineral precipitation. Internal sedimentation also reduces porosity. Although minor in comparison, the most important porosity creation process is selective solution of aragonite.<ref name=ch09r10 />

 

The '''mesogenetic substage''' (middle diagenetic) encompasses the time when the sediment is out of the influence of surface diagenetic processes. Cementation is the major process. [[Porosity]] obliteration occurs when mosaics of coarsely crystalline calcite precipitate in large pores. Pressure solution occurs at higher pressures.

The '''mesogenetic substage''' (middle diagenetic) encompasses the time when the sediment is out of the influence of surface diagenetic processes. Cementation is the major process. [[Porosity]] obliteration occurs when mosaics of coarsely crystalline calcite precipitate in large pores. Pressure solution occurs at higher pressures.

The '''telogenetic substage''' (late diagenetic) occurs when sedimentary carbonates are raised to the surface and erosion occurs along [[Unconformity|unconformities]]. The telogenetic zone extends from the surface to the point where surface processes no longer influence diagenesis. Solution by meteoric water creates porosity. Internal sedimentation and cementation by precipitation from solution destroy porosity.

 

The '''telogenetic substage''' (late diagenetic) occurs when sedimentary carbonates are raised to the surface and erosion occurs along unconformities. The telogenetic zone extends from the surface to the point where surface processes no longer influence diagenesis. Solution by meteoric water creates porosity. Internal sedimentation and cementation by precipitation from solution destroy porosity.

==Path of diagenesis==

==Path of diagenesis==

The parts of the path of diagenesis that a carbonate sediment follows determine the evolution of its porosity. [[:file:predicting-reservoir-system-quality-and-performance_fig9-69.png|Figure 1]]summarizes the diagenesis that occurs along the path.

The parts of the path of [[diagenesis]] that a carbonate sediment follows determine the evolution of its porosity. [[:file:predicting-reservoir-system-quality-and-performance_fig9-69.png|Figure 2]] summarizes the diagenesis that occurs along the path.

==See also==

==See also==

* [[Predicting carbonate porosity and permeability]]

* [[Predicting carbonate porosity and permeability]]

* [[Carbonate facies]]

* [[Carbonate facies]]

* [[Early carbonate diagenesis]]

* [[Early carbonate diagenesis]]

* [[Basics of carbonate porosity formation and preservation]]

* [[Basics of carbonate porosity formation and preservation]]

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]