Induced biochemical conversions of heavy crude oils

Products formed during multiple interactions of microorganisms with oils fa ll into two major categories: those formed due to the action of indigenous microorganisms under reservoir conditions over geological periods of time a nd 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 se lect group of microorganisms whose action on the crudes is beneficial. The interactions between such microorganisms and different crude oils occur thr ough complex biochemical and chemical reactions. These reactions depend on multiple variables within and at the interface of a multicomponent system c onsisting of organic, aqueous, and inorganic components. Studies, carried o ut in this laboratory (BNL) of biochemical and chemical reactions in crude oils which involve extremophilic organisms (organisms which thrive in extre me environments), have shown that the reactions are not random and follow d istinct trends. These trends can be categorized. The use of a group of char acteristic chemical markers, such as mass spectrometric fragmentation patte rns of light and heavy hydrocarbons, heterocyclic and organometallic compou nds, as well as total trace metal and heteroatom contents of crude oils bef ore and after the biochemical treatment allows to follow the type and the e xtent of chemical changes which occur during the biochemical conversion of heavy crude oils by microorganisms. The bioconversion involves multiple, si multaneous, and/or concurrent chemical reactions in which the microorganism s serve as biocatalysts. In this sense, the biocatalysts are active in a re action medium which depends on the chemical composition of the crude and th e selectivity of the biocatalyst. Thus, the bioconversion of the crude depe nds on the relative distribution of saturates, aromatics, resins, and aspha ltenes and the distribution of polar compounds containing the heteroatoms(N , S, O) and trace metals. The role of these constituents in the bioconversi on of crudes will be briefly reviewed in this paper. (C) 1999 Published by Elsevier Science B.V. Ail rights reserved.