Simulation of in situ oil reservoir conditions in a laboratory bioreactor testing for methanogenic conversion of crude oil and analysis of the microbial community

Abstract

A bioreactor was designed and established to simulate in situ oil reservoir conditions for investigating methanogenic conversion of crude oil by microbial community derived from production water of a high-temperature oilfield. The continuous incubation and culturing were divided into two phases (Phase I, day 0–341; and Phase II, day 341–520) to allow sampling and supplement of fresh culture medium on day 341 and 520, respectively. The average methane production rate was 4.9 and 20.8 mmol CH4·day−1 m−3 pore volume during the Phase I and Phase II, respectively. Degradation intermediates of fatty acids were detected in the culture fluids indicating the transformation of crude oil. The 16S rRNA gene sequence analysis revealed that the major bacterial community shifted from Deferribacteres to Aminicenantes and unclassified Bacteria, as well as Thermotogae and Synergistetes. The predominant methanogenic community shifted from methylotrophic methanogen (Methanolobus) to hydrogenotrophic methanogens (Methanothermobacter and Methanocalculus) and acetoclastic methanogen (Methanothrix) after 341 days of incubation, and was subsequently dominated by hydrogenotrophic methanogen (Methanothermobacter) after 520 days of incubation. This study expanded our understandings of methanogenic oil-degrading processes and the key microorganisms involved in laboratory simulation bioreactor over time of incubation. In addition, it further provides valuable insights on the microbial conversion of hydrocarbons to methane for enhancing the energy recovery from residual oil in petroleum reservoirs.