Microbial diversity of long-duration gas injection oil reservoir based on next generation sequencing in south of Iran

Recent studies have shown that oilfield harbours diverse microbial communities. Water-flooding is believed to be the main contaminating factor of oil reservoirs, however, less attempts have been made to study the effect of natural gas injection on microbial community of oilfields. Molecular methods were used to evaluate the microbial diversity of Haftkel (HK) and Lali (LA) petroleum reservoirs in the south of Iran. The HK oilfield has been injected with natural gas for long duration, but LA oilfield had no enhanced oil recovery (EOR) process. Next generation sequencing (NGS) of 16S rRNA archaeal genes indicated that the genus Methanofollis was observed with high presence in 89.7% and 92.6% frequency in the HK and LA oilfields, respectively. Most abundant phyla in HK oilfield were Synergistes (58.1%), Firmicutes (17%), Proteobacteria (Betaproteobacteria) 12.8% and unclassified bacteria (5.2%), while Thermotogae (78%), Firmicutes (10.8%), Synergistes (4%) and unclassified bacteria (3.8%) were observed in LA oilfield. The comparison of the results indicated that the injection of natural gas could increase bacterial diversity and most probable cause to increase frequency of bacterial genus Anaerobaculum belonging to the Synergistes.