Application of formation water geochemistry to assess seal integrity of the Gotnia Formation, Kuwait

Abstract

A very large database of formation water geochemistry has been acquired for the Kuwait petroleum system. This database makes it possible to explore the geological history of Kuwait’s formation and ground waters in a way that is not possible by other means. Working at this regional scale spatial and formational variation in groundwater chemistry in Kuwait identifies lithostratigraphy and physical barriers to flow that can be explored in the context of Kuwait’s geological history. Cretaceous oil reservoirs in north Kuwait have formation water saturated with Na (>50%) that is anomalously abnormal in salinity for its depth. The most likely subsurface source of such saline water is the Upper Jurassic Gotnia Formation which comprises beds of evaporite halite, and/or pre-Gotnia formations of deeper reservoirs. To reach their current location, both parts of the Gotnia and Hith formations must have been breached. To date, this is the only evidence to show that the sealing capacity of the Gotnia Formation has been overcome, implying that the formation, and therefore units beneath, are capable of sourcing fluids to younger and shallower reservoirs. Given the ubiquity of samples of formation water in many other regions, applying formation water geochemistry to other petroleum systems would appear a good method for evaluating basin models and understanding of fluid migration in mature petroleum provenances.