Induced biochemical conversions of heavy crude oils

Abstract

Products formed during multiple interactions of microorganisms with oils fall into two major categories: those formed due to the action of indigenous microorganisms under reservoir conditions over geological periods of time and those products which are generated by the action of introduced organisms. The extreme end product of the first category is the production of heavy `biodegraded' crudes. The extreme end product of the second category is the production of reduced sulfates due to the introduction of sulfate-reducing bacteria which may lead to the souring of a field. There is, however, a select group of microorganisms whose action on the crudes is beneficial. The interactions between such microorganisms and different crude oils occur through complex biochemical and chemical reactions. These reactions depend on multiple variables within and at the interface of a multicomponent system consisting of organic, aqueous, and inorganic components. Studies, carried out in this laboratory (BNL) of biochemical and chemical reactions in crude oils which involve extremophilic organisms (organisms which thrive in extreme environments), have shown that the reactions are not random and follow distinct trends. These trends can be categorized. The use of a group of characteristic chemical markers, such as mass spectrometric fragmentation patterns of light and heavy hydrocarbons, heterocyclic and organometallic compounds, as well as total trace metal and heteroatom contents of crude oils before and after the biochemical treatment allows to follow the type and the extent of chemical changes which occur during the biochemical conversion of heavy crude oils by microorganisms. The bioconversion involves multiple, simultaneous, and/or concurrent chemical reactions in which the microorganisms serve as biocatalysts. In this sense, the biocatalysts are active in a reaction medium which depends on the chemical composition of the crude and the selectivity of the biocatalyst. Thus, the bioconversion of the crude depends on the relative distribution of saturates, aromatics, resins, and asphaltenes and the distribution of polar compounds containing the heteroatoms (N, S, O) and trace metals. The role of these constituents in the bioconversion of crudes will be briefly reviewed in this paper.