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  = 9-107

  | topg    = 9-156

  | topg    = 9-108

  | 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

==Early influences==

==Early influences==

How much influence does the original fabric of a carbonate rock (grains, mud, and pore space) have on with the pore space in the rock now? Which has more impact on [[reservoir quality]] of carbonates: early or late diagenesis? The interaction of early diagenesis with original fabric elements determines, in many cases, the ultimate reservoir quality of a carbonate. A rock that begins with good [[porosity]] and [[permeability]], either from depositional or early diagenetic processes, has a better chance of retaining those qualities than an initially poor-quality rock becoming a good-quality rock. [[Porosity]] can be created late in a rock's life; however, concentrating on the early history of a carbonate rock is generally more rewarding when searching for reservoir-quality rocks.

How much influence does the original fabric of a carbonate rock (grains, mud, and pore space) have on with the pore space in the rock now? Which has more impact on [[reservoir quality]] of carbonates: early or late [[diagenesis]]? The interaction of early diagenesis with original fabric elements determines, in many cases, the ultimate reservoir quality of a carbonate. A rock that begins with good [[porosity]] and [[permeability]], either from depositional or early diagenetic processes, has a better chance of retaining those qualities than an initially poor-quality rock becoming a good-quality rock. [[Porosity]] can be created late in a rock's life; however, concentrating on the early history of a carbonate rock is generally more rewarding when searching for reservoir-quality rocks.

==Diagenesis and rock fabric==

==Diagenesis and rock fabric==

[[file:predicting-reservoir-system-quality-and-performance_fig9-74.png|thumb|300px|{{figure number|1}}Fabric and nonfabric pore geometries and processes that create them.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-74.png|thumb|400px|{{figure number|1}}Fabric and nonfabric pore geometries and processes that create them. Modified from Choquette and Pray;<ref name=ch09r10 /> courtesy AAPG.]]

The initial solid constituents of a carbonate rock normally determine its initial pore type and geometry and strongly influence diagenesis. Early pore space in carbonate rocks generally has fabric-selective characteristics; creation of late pore space does not.<ref name=ch09r10>Choquette, P., W., Pray, L., C., 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> Surface and shallow diagenesis mainly occurs in fabric-selective pore geometries that allow the greatest fluid flow (mostly interparticle or intercrystalline). Late-stage shallow diagenesis mainly occurs in nonfabric-selective pore geometries that allow the greatest fluid flow (mostly fracture related). Deep diagenetic processes can be both fabric selective (fluid flow through interparticle or intercrystalline pores) or nonfabric selective (compaction).

The initial solid constituents of a carbonate rock normally determine its initial pore type and geometry and strongly influence [[diagenesis]]. Early pore space in carbonate rocks generally has fabric-selective characteristics; creation of late pore space does not.<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> Surface and shallow diagenesis mainly occurs in fabric-selective pore geometries that allow the greatest fluid flow (mostly interparticle or intercrystalline). Late-stage shallow diagenesis mainly occurs in nonfabric-selective pore geometries that allow the greatest fluid flow (mostly [[fracture]] related). Deep diagenetic processes can be both fabric selective (fluid flow through interparticle or intercrystalline pores) or nonfabric selective (compaction).

==Fabric and nonfabric selection porosity==

==Fabric and nonfabric selection porosity==

[[:file:predicting-reservoir-system-quality-and-performance_fig9-74.png|Figure 1]] shows fabric and nonfabric pore geometries and processes that create them.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-74.png|Figure 1]] shows fabric and nonfabric pore geometries and processes that create them.

[[file:predicting-reservoir-system-quality-and-performance_fig9-75.png|thumb|{{figure number|2}}General pathways that different carbonate rock types might take during early diagenesis as their pore systems evolve.]]

==Early diagenesis and pore-system quality==

==Early diagenesis and pore-system quality==

[[file:predicting-reservoir-system-quality-and-performance_fig9-75.png|400px|thumb|{{figure number|2}}General pathways that different carbonate rock types might take during early diagenesis as their pore systems evolve.]]

[[:file:predicting-reservoir-system-quality-and-performance_fig9-75.png|Figure 2]] shows the general pathways that different carbonate rock types might take during early diagenesis as their pore systems evolve. The parallel lines are contours of equal pore throat size. In terms of quality, points plotting along the contours represent rocks with equal flow characteristics (''see'' [[Characterizing rock quality]]). With the exception of the creation of connected vugs and dolomitized mudstone, carbonate rocks generally lose porosity and permeability as a result of diagenesis.

 

[[:file:predicting-reservoir-system-quality-and-performance_fig9-75.png|Figure 2]] shows the general pathways that different carbonate rock types might take during early diagenesis as their pore systems evolve. The parallel lines are contours of equal pore throat size. In terms of quality, points plotting along the contours represent rocks with equal flow characteristics (''see'' [[Characterizing rock quality]]). With the exception of the creation of connected vugs and dolomitized [[mudstone]], carbonate rocks generally lose porosity and permeability as a result of diagenesis.

==Preserving pore systems==

==Preserving pore systems==

Some pore systems gain quality as a result of diagenesis. The general trend of pore system quality with time and burial, however, is toward destruction. Certain processes can temporarily interrupt this trend. These are “preserved” pore systems. Some of the processes that preserve pore systems are as follows:<ref name=ch09r18>Feazel, C., T., Schatzinger, R., A., 1985, Prevention of carbonate cementation in petroleum reservoirs, in Schneidermann, N., Harris, P., M., eds., Carbonate Cements: SEPM Special Publication 36, p. 97–106.</ref>

Some pore systems gain quality as a result of [[diagenesis]]. The general trend of pore system quality with time and burial, however, is toward destruction. Certain processes can temporarily interrupt this trend. These are “preserved” pore systems. Some of the processes that preserve pore systems are as follows:<ref name=ch09r18>Feazel, C. T., and R. A. Schatzinger, 1985, Prevention of carbonate cementation in petroleum reservoirs, in Schneidermann, N., Harris, P., M., eds., Carbonate Cements: SEPM Special Publication 36, p. 97–106.</ref>

* Reduced burial stress from overpressuring

* Reduced burial stress from overpressuring

* [[Predicting carbonate porosity and permeability]]

* [[Predicting carbonate porosity and permeability]]

* [[Carbonate facies]]

* [[Carbonate facies]]

* [[Carbonate diagenetic stages]]

* [[Carbonate diagenetic stages]]

* [[Early carbonate diagenesis]]

* [[Early carbonate diagenesis]]

[[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]]