Formation water data are the key to understand in-situ hydrogeochemical conditions and to retrace petroleum-water-rock-gas interactions. In most cases, oil field operators chemically analyze produced water which compositionally differs from in-situ formation water. As water is often sampled at the surface under reduced temperature and pressure conditions, the resulting hydrochemical data may lead to misinterpretations.
Scale mineral formation and outgassing of CH4(g) and CO2(g) are two such sampling consequences besides pH increase. Moreover, metal corrosion may also change the water composition with regard to pH and concentrations of iron, sulfate, and total sulfide sulfur, among many other components. Nevertheless, taken these considerations into account, production water data store important signals. Hydrogeochemical modelling and the resulting data allow the reconstruction of the original formation water and the original, in-situ hydrogeochemical reservoir conditions.