For example Ba, and SO4 concentrations are affected by equilibrium with barite and what is likely to be sulphate reduction. Changes occur in the concentrations of many water components through time that cannot be explained by linear mixing between formation water and injected water and require dissolution or precipitation reactions to have occurred between injection and production The time series of produced waters from Miller enabled detailed study of fluid mixing in the field and the physical, chemical and thermodynamic response of the system to the The geochemistry of San Juan waters is controlled by the introduction of bicarbonate through carbonate dissolution and methane/coal oxidation leading to leaching of Na-bearing clay minerals, and by ion exchange on clay minerals and dilution by meteoric waters in certain locations. In particular, the detailed study of two very different hydrocarbon reservoir case studies (the Central US coalbed methane reservoir, the San Juan Basin and the North Sea oilfield Miller) provided an insight not only into the fundamental controls on formation water composition, but also into the effects of active oilfield development on systems that are very sensitive to change on rapid timescales. This information, together with local mineralogy, depth and temperature relations provided a sound basis from which to investigate the most important controls on formation water composition. Abundant water chemistry analyses from nine different locations (predominantly petroleum reservoirs) on five continents were evaluated.

Petroleum reservoirs