Microbiological investigations of high-temperature horizons of the Kongdian petroleum reservoir in connection with field trial of a biotechnology for enhancement of oil recovery

The physicochemical conditions and microbiological characteristics of the formation waters of the Kongdian oilfield of the Dagang oilfield (China) were studied. It was demonstrated that this oilfield is a high-temperature ecosystem with formation waters characterized by low mineralization. The concentrations of nitrogen and phosphorus compounds, as well as of electron acceptors, are low. Oil and oil gas are the main organic matter sources. The oilfield is exploited with water-flooding. The oil stratum was inhabited mostly by anaerobic thermophilic microorganisms, including fermentative (10²–10⁵ cells/ml), sulfate-reducing (0–10² cells/ml), and methanogenic (0–10³ cells/ml) microorganisms. Aerobic bacteria were detected mainly in the near-bottom zone of injection wells. The rate of sulfate reduction varied from 0.002 to 18.940 μg S^2? l^?1 day^?1 and the rate of methanogenesis from 0.012 to 16.235 μg CH₄ l^?1 day^?1. Microorganisms with great biotechnological potential inhabited the oilfield. Aerobic thermophilic bacteria were capable of oxidizing oil with formation of biomass, the products of partial oxidation of oil (volatile acids), and surfactants. During growth on the culture liquid of oil-oxidizing bacteria, methanogenic communities produced methane and carbon dioxide, which also had oil-releasing capabilities. Using various labeled tracers, the primary filtration flows of injected solutions at the test site were studied. Our comprehensive investigations allowed us to conclude that the method for microbial enhancement of oil recovery based on the activation of the stratal microflora can be applied in the Kongdian oilfield.