Changes

The amount of organic carbon present in a rock is a determining factor in a rock's ability to generate hydrocarbons.

The amount of organic carbon present in a rock is a determining factor in a rock's ability to generate hydrocarbons.

==Effect of depositional environment==

==Effect of depositional environment==

[[Depositional environment]] controls the amount of organic carbon contained in a rock. [[Source rock]]s are generally associated with areas where high organic productivity is combined with (1) deposition in poorly oxygenated environments ([[anoxic]] to [[dysaerobic]]), (2) upwelling, and (3) rapid sedimentation.<ref name=ch06r3>Chinn, E., W., 1991, The role of organic geochemistry in petroleum exploration: Basin Research Institute Bulletin, Louisiana State University, Baton Rouge, LA, p. 15–23. ''Short paper that summarizes petroleum geochemistry and its analytical techniques.''</ref>, because these processes preserve organic matter.

[[Depositional environments|Depositional environment]] controls the amount of organic carbon contained in a rock. [[Source rock]]s are generally associated with areas where high organic productivity is combined with (1) deposition in poorly oxygenated environments ([[anoxic]] to [[dysaerobic]]), (2) upwelling, and (3) rapid sedimentation,<ref name=ch06r3>Chinn, E., W., 1991, The role of organic geochemistry in petroleum exploration: Basin Research Institute Bulletin, Louisiana State University, Baton Rouge, LA, p. 15–23. ''Short paper that summarizes petroleum geochemistry and its analytical techniques.''</ref> because these processes preserve organic matter.

==Average TOCs==

==Average TOCs==

The table below (from <ref name=ch06r3 />) shows average TOC values for different sedimentary rock types.

The table below<ref name=ch06r3 /> shows average TOC values for different sedimentary rock types.

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! Rock type

! Rock type || TOC value, %

! TOC value, %

|-

|-

| Average for all shales

| Average for all shales || 0.8

| 0.8

|-

|-

| Average for shale source rocks

| Average for shale source rocks || 2.2

| 2.2

|-

|-

| Average for calcareous shale source rocks

| Average for calcareous shale source rocks || 1.8

| 1.8

|-

|-

| Average for carbonate source rocks

| Average for carbonate source rocks || 0.7

| 0.7

|-

|-

| Average for all source rocks

| Average for all source rocks || 1.8

| 1.8

|}

|}

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! Generation potential

! [[Petroleum generation|Generation]] potential || Wt % TOC, shales || Wt % TOC, carbonates

! Wt % TOC, shales

! Wt % TOC, carbonates

|-

|-

| Poor

| Poor || 0.0-0.5 || 0.0-0.2

| 0.0-0.5

| 0.0-0.2

|-

|-

| Fair

| Fair || 0.5-1.0 || 0.2-0.5

| 0.5-1.0

| 0.2-0.5

|-

|-

| Good

| Good || 1.0-2.0 || 0.5-1.0

| 1.0-2.0

| 0.5-1.0

|-

|-

| Very Good

| Very Good || 2.0-5.0 || 1.0-2.0

| 2.0-5.0

| 1.0-2.0

|-

|-

| Excellent

| Excellent || > 5.0 || > 2.0

| > 5.0

| > 2.0

|}

|}

==References==

==References==

{{reflist}}

{{reflist}}