The term connate fluids in the context of geology, and of sedimentology in particular, refers to the liquids that fill the pore-space of sedimentary rocks. These liquids are largely composed of water, but also contain many mineral components as ions in solution.

As rocks are buried, they undergo lithification and the connate fluids are 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.

See also: petroleum geology.