Editing Connate fluids

{{short description|Liquids that were trapped in the pores of sedimentary rocks}}
{{more citations needed|date=June 2024}}
In [[geology]] and [[sedimentology]], '''connate fluids''' are liquids that were trapped in the pores of [[sedimentary rock]]s as they were deposited.  These liquids are largely composed of [[water]], but also contain many [[mineral]] components as [[Ion|ions]] in [[Solution (chemistry)|solution]].<ref>{{cite web |url=http://www.glossary.oilfield.slb.com/Display.cfm?Term=connate%20water |title=Connate water |archive-url=https://web.archive.org/web/20110718164016/http://www.glossary.oilfield.slb.com/Display.cfm?Term=connate%20water |archive-date=July 18, 2011 |website=Schlumberger Oilfield Glossary}}</ref>

As rocks are buried, they undergo [[lithification]] and the connate fluids are usually expelled.  If the escape route for these fluids is blocked, the pore fluid [[pressure]] can build up, leading to [[overpressure (geology)|overpressure]].

== Significance ==

An understanding of the [[geochemistry]] of connate fluids is important if the [[diagenesis]] of the rock is to be quantified.  The solutes in the connate fluids often precipitate and reduce the [[porosity]] and [[Permeability (fluid)|permeability]] of the host rock, which can have important implications for its [[hydrocarbon]] [[wikt:prospectivity |prospectivity]].  The chemical components of the connate fluid can also yield information on the provenance of aquifers and of the thermal history of the host rock. Minute bubbles of fluid are often trapped within the [[crystal]]s of the cementing material. These [[fluid inclusions]] provide direct information about the composition of the fluid and the pressure-temperature conditions that existed during diagenesis of the sediments.

'''Some analyses of connate water samples from Louisiana (USA) compared to seawater'''
{| class="wikitable" 
! style="background:#DDDDFF;"  | 
! style="background:#DDDDFF;"  | 
! style="background:#DDDDFF;" colspan=2 | Average of samples from Tertiary formations
! style="background:#DDDDFF;" colspan=2 | Average of samples from Cretaceous formations
|-
! style="background:#DDDDFF;"  | Constituent
! style="background:#DDDDFF;"  | Seawater mg/l
! style="background:#DDDDFF;"  | Connate water mg/l
! style="background:#DDDDFF;"  | Ratio Connate/Sea Water
! style="background:#DDDDFF;"  | Connate water mg/l
! style="background:#DDDDFF;"  | Ratio Connate/Sea Water
|-
| align=center | Lithium
| align=center | 0.2
| align=center | 3
| align=center | '''15'''
| align=center | 4
| align=center | '''20'''
|-
| align=center | Sodium
| align=center | 10,600
| align=center | 37,539
| align=center | 3.5
| align=center | 28,462
| align=center | 2.7
|-
| align=center | Potassium
| align=center | 380
| align=center | 226
| align=center | 0.59
| align=center | 193
| align=center | 0.51
|-
| align=center | Calcium
| align=center | 400
| align=center | 2,077
| align=center | 5.2
| align=center | 4,999
| align=center | '''12'''
|-
| align=center | Magnesium
| align=center | 1,300
| align=center | 686
| align=center | 0.53
| align=center | 606
| align=center | 0.47
|-
| align=center | Strontium
| align=center | 8
| align=center | 148
| align=center | '''19'''
| align=center | 346
| align=center | '''43'''
|-
| align=center | Barium
| align=center | 0.03
| align=center | 73
| align=center | '''2,430'''
| align=center | 48.3
| align=center | '''1,608'''
|-
| align=center | Boron
| align=center | 4.8
| align=center | 20
| align=center | 4.1
| align=center | 27.5
| align=center | 5.7
|-
| align=center | Chloride
| align=center | 19,000
| align=center | 63,992
| align=center | 3.4
| align=center | 54,910
| align=center | 2.9
|-
| align=center | Bromide
| align=center | 65
| align=center | 79
| align=center | 1.2
| align=center | 287
| align=center | 4.4
|-
| align=center | Iodide
| align=center | 0.05
| align=center | 21
| align=center | '''420'''
| align=center | 37
| align=center | '''740'''
|-
| align=center | Sulphate
| align=center | 2,690
| align=center | 104
| align=center | 0.039
| align=center | 206
| align=center | 0.077
|-
| style="background:#DDDDFF;" colspan=6| Source:  A. Gene Collins, "Geochemistry of some petroleum-associated waters from Louisiana," US Bureau of Mines, Rept. of Investigations 7326, January 1970.
|}

Similar, but different in origin, is the concept of [[fossil water]], which is used to describe very old [[groundwater]] found in deep [[aquifer]]s or bedrock. Typically it was recharged during a different climatic period (e.g., the last [[ice age]]) so is also very old, but possibly not of the same genesis as the rock.

== See also ==
* [[Petroleum geology]]

==References==
{{Reflist}}

[[Category:Petroleum]]
[[Category:Sedimentology]]
[[Category:Soil mechanics]]