ABSTRACT
Crude oil reservoirs are inhabited by diverse microorganisms, including sulfate-reducing prokaryotes (SRP) and methanogenic consortia, many of which are involved in crude oil biodegradation and/or can utilize other compounds found in situ, such as volatile fatty acids (VFAs). While it is known that these metabolic activities readily occur at relatively low salinities and temperatures, less is understood about these processes when reservoirs are characterized by higher salinities (>0.6 M NaCl), higher temperatures (>50°C), or a combination of both conditions. Here we overview the current state of knowledge related to crude oil metabolism under high-temperature and/or high-salinity conditions that characterize many subsurface reservoirs. We highlight some case studies on this topic, including a study wherein we investigated the potential for sulfate reduction and methanogenesis using oilfield produced water (PW) samples characterized by salinities ranging from 0.9 to 2.5 M and in situ temperatures up to 70°C. At 30°C, enrichment cultures of SRP were readily established up to 2.5 M NaCl. At 50°C, SRP cultures could be established at all salinities, while establishing enrichments at 70°C was unsuccessful. Halanaerobium, Desulfovermiculus, and unclassified Clostridiales dominated the 30°C and 50°C enrichments. Temperatures of >60°C at all salinities tested impeded the successful enrichment of SRP, with similar trends observed under methanogenic conditions. While these results suggest that a combination of high salinity and high temperatures characterizing some reservoirs may naturally control detrimental microbial effects such as souring, a better understanding of the effects of these more extreme conditions on in situ microbial metabolism is warranted for future study.
