Development of a microbial process for the recovery of petroleum oil from depleted reservoirs at 91–96°C

•Hyperthermophilic, alkalophilic, halophilic bacteria enriched from oil well.•Bacterial consortium enhanced oil recovery at 96°C in core flood studies.•96°C is the highest temperature reported for Microbial Enhanced Oil Recovery.•Microbial metabolites aiding oil recovery at 96°C were identified. A consortium of bacteria growing at 91°C and above (optimally at 96°C) was developed for the recovery of crude oil from declining/depleted oil reservoirs having temperature of more than 91°C. PCR-DGGE-Sequencing analysis of 16S rRNA gene fragments of NJS-4 consortium revealed the presence of four strains identified as members of the genus Clostridium. The metabolites produced by NJS-4 consortium included volatile fatty acids, organic acids, surfactants, exopolysaccarides and CO2, which reduced viscosity, emulsified crude oil and increased the pressure that facilitated displacement of emulsified oil towards the surface. NJS-4 enhanced oil recovery by 26.7% and 10.1% in sand pack trials and core flood studies respectively in optimized nutrient medium comprised of sucrose and sodium acetate as carbon/energy source and urea as nitrogen source (pH 7–9, 96°C, and 4% salinity). Nutrient medium for MEOR was constituted using commercial grade cheap nutrients to improve the economic viability of MEOR process.