Conversion of petroleum to methane by the indigenous methanogenic consortia for oil recovery in heavy oil reservoir

[Display omitted] •Heavy oil was degraded by the enriched methanogenic consortia.•Methane production during the biodegradation of heavy oil.•Viscosity of the degraded heavy oil was reduced with the dissolution of methane.•In-situ bioconversion of heavy oil to methane has great potential on EOR. Microbial enhanced oil recovery has been well acknowledged and becoming an advanced technology for oil recovery. Compared with current techniques, a newly technical strategy of the in-situ heavy oil gasification to methane for oil viscosity reduction was proposed and successfully proved via enriching the methanogenic consortia from the brine of oil reservoir with heavy oil as carbon source. During 200days anaerobic culturing, 2.34g of heavy oil was degraded coupling with 1514μmol of methane production. Phylogenetic diversity analysis showed that the enriched consortia composed with sequences affiliated with the Firmicutes, Proteobacteria, Deferribacteres and Bacteroidetes. The recovered archaeal phylotypes were close to the Methanobacteriales and Methanosarcinales, which could convert the produced small molecules (formic acid and acetic acids) to methane. The viscosity of the degraded heavy oil was reduced by 72.45% at 20MPa after the dissolution of the produced methane. Core flooding tests finally showed that the oil degradation and methane production by the enriched methanogenic consortia made 14.7% of the tertiary enhanced oil recovery. These results demonstrated a promising and practical strategy of microbial technology on oil recovery by activating the methanogens in heavy oil reservoir.