Connate fluids explained

In geology and sedimentology, connate fluids are liquids that were trapped in the pores of sedimentary rocks as they were deposited. These liquids are largely composed of water, but also contain many mineral components as ions in solution.[1]

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.

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 of the host rock, which can have important implications for its hydrocarbon 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 crystals 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

Average of samples from Tertiary formationsAverage of samples from Cretaceous formations
ConstituentSeawater mg/lConnate water mg/lRatio Connate/Sea WaterConnate water mg/lRatio Connate/Sea Water
align=center Lithiumalign=center 0.2align=center 3align=center 15align=center 4align=center 20
align=center Sodiumalign=center 10,600align=center 37,539align=center 3.5align=center 28,462align=center 2.7
align=center Potassiumalign=center 380align=center 226align=center 0.59align=center 193align=center 0.51
align=center Calciumalign=center 400align=center 2,077align=center 5.2align=center 4,999align=center 12
align=center Magnesiumalign=center 1,300align=center 686align=center 0.53align=center 606align=center 0.47
align=center Strontiumalign=center 8align=center 148align=center 19align=center 346align=center 43
align=center Bariumalign=center 0.03align=center 73align=center 2,430align=center 48.3align=center 1,608
align=center Boronalign=center 4.8align=center 20align=center 4.1align=center 27.5align=center 5.7
align=center Chloridealign=center 19,000align=center 63,992align=center 3.4align=center 54,910align=center 2.9
align=center Bromidealign=center 65align=center 79align=center 1.2align=center 287align=center 4.4
align=center Iodidealign=center 0.05align=center 21align=center 420align=center 37align=center 740
align=center Sulphatealign=center 2,690align=center 104align=center 0.039align=center 206align=center 0.077
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 aquifers 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

Notes and References

  1. Web site: Connate water . https://web.archive.org/web/20110718164016/http://www.glossary.oilfield.slb.com/Display.cfm?Term=connate%20water . July 18, 2011 . Schlumberger Oilfield Glossary.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Connate fluids".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.