Dariusz Dobrzyński

Interactions between Microorganisms, Crude Oil and Formation Waters

Crude oil and formation waters surrounding oil deposits constitute two environments that harbor various groups of microorganisms, such as sulphate-reducing bacteria, iron-reducing bacteria, fermenting bacteria and methanogenic archaea. Microorganisms occurring in crude oil and formation waters, which are usually mineral waters or brines, can modify the chemical composition of both oil and aqueous solution, affect dissolution/precipitation reactions of mineral phases, and consequently may influence the hydraulic properties of reservoir rocks and the conditions for hydrocarbon migration. This paper describes the potential biogeochemical reactions, which can take place in oil deposits and formation waters with the participation of microorganisms and the results of their activity. The results of geochemical modelling of formation waters based on hydrochemical data (obtained from Polish Oil & Gas Company) are discussed in terms of carbonate mineral stability. The modelling confirms theoretical predictions of the formation of the mineral phases through abiotic and biotic processes in the formation waters.