Microbial activity in crude oils under reservoir and storage conditions has been known to exist for a long time. Such activity can cause deleterious effects in the quality and subsequent processing of crudes. In the past ten to fifteen years, however, a considerable research effort has shown that there are beneficial microbial systems which can be used in microbial enhanced oil recovery (MEOR), a promising process and the resulting biotechnology may be deliverable. In this laboratory, systematic studies are being conducted which deal with the effects of thermophilic, temperature adapted, acidophilic and chemotrophic microorganisms on the chemical and physical properties of selected types of crude oils over a wide range of temperatures, pressures and salt concentrations. Current studies indicate that during the biotreatment several properties of crude oils are affected. The oils are (1) emulsified, (2) acidified, (3) there is a qualitative and quantitative change in light and heavy fraction of crudes, (4) there are chemical changes in fractions containing sulfur compounds, (5) there is an apparent solubilization of trace metals and (6) the qualitative and quantitative chemical and physical changes appear to be microbial species dependent. In this paper, recent work with Boscan crude, a high sulfur, heavy crude oil from Venezuela will be discussed.

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