Abstract
The microbial communities in alkali-surfactant-polyacrylamide-flooded (ASP-flooded) oil reservoirs have rarely been investigated compared to those in water-flooded oil reservoirs. Here, the bacterial and archaeal communities in an ASP-flooded reservoir and the adjacent water-flooded block, and responses of the microbial communities in microcosms to nutrients were investigated by 16S rRNA gene sequencing and cultivation. Compared with the water-flooded block, both the bacterial and archaeal communities inhabiting the ASP-flooded block had lower Sobs indices (91:232 and 34:55, respectively), lower Shannon indices (1.296:2.256 and 0.845:1.627, respectively) and higher Simpson indices (0.391:0.248 and 0.678:0.315, respectively). Halomonas (58.4–82.1%) and Anoxynatronum (14.5–18.2%) predominated in the ASP-flooded production wells, and were less than 0.05% in the bacterial communities of the adjacent water-flooded production wells, which were dominated by Pseudomonas and Thauera. Methanobacterium accounted for 65.0–94.5% of the archaeal communities inhabiting the ASP-flooded production wells, and Methanosaeta (36.7–94.5%) dominated the adjacent water-flooded production wells. After nutrients stimulation, the quantity of cultivable microorganisms increased from 103/mL to 107/mL. Community analysis indicated that the relative abundances of some species that belonged to Halomonas and Pseudomonas obviously increased, yet there were no oil emulsification or dispersion and changes of surface tension of the water-oil mixture. In addition, 6 alkali-tolerating strains showing 98% similarity of 16S rRNA genes with those of Halomonas alkalicola and Halomonas desiderata and 2 strains with 99% similarity with Pseudomonas stutzeri gene were isolated from the nutrients stimulated brines. In summary, this study indicated that Halomonas, Anoxynatronum, and Methanobacterium were dominant populations in the ASP-flooded reservoir, the extreme environment decreased microbial diversity, and restricted microbial growth and metabolisms.
Highlights
Water-flooding is an efficient secondary oil recovery process with pressurized water being pumped into oil-bearing strata to push oil out of reservoirs, and has been employing worldwide (Lenchi et al, 2013; Cai et al, 2015)
The results indicated that ASP-flooding decreased microbial diversity, and a number of bacterial and archaeal populations still survived in the ASPflooded reservoir
The results indicated that the microbial communities showed significant responses to nutrients addition: the number of cultivable microorganisms increased from 103/mL to 107/mL, the relative abundances of some OTUs that belonged to Halomonas and Pseudomonas obviously increased
Summary
Water-flooding is an efficient secondary oil recovery process with pressurized water being pumped into oil-bearing strata to push oil out of reservoirs, and has been employing worldwide (Lenchi et al, 2013; Cai et al, 2015). Polymer-flooding is considered a most successful chemical EOR method, and has achieved large-scale field application (Gao, 2013) This technique generally employs hydrolyzed polyacrylamide to recovery the residual oil underground through sealing mainstream channels and increasing viscosity of the displacing phase (Nasr-El-Din et al, 1991; Goodyear et al, 1995). Alkali-surfactant-polyacrylamide-flooding (ASP-flooding) is another EOR method, and has been used to exploit the residual oil underground in high water-cut and depleted oil reservoirs (Carrero et al, 2007; Shen et al, 2009) This technique can effectively improve the sweep efficiency of displacing phase through generating ultralow interfacial tension of water-oil mixture, improving oil mobility, and sealing mainstream channels. Our knowledge about microbial communities in ASP-flooded reservoirs is lacking
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
