Abstract
Alkaline-surfactant-polymer (ASP) flooding technology is used to maximize crude oil recovery. However, the extensive use of alkaline materials makes it difficult to treat the water used. Here, an improved multi-zone anaerobic baffled reactor (ABR) using FeSO4 as electron acceptor was employed to treat the wastewater from ASP flooding technology, and the effects on major pollutants (hydrolyzed polyacrylamide, petroleum substances, surfactants suspended solids) and associated parameters (chemical oxygen demand, viscosity) were evaluated. Gas chromatography-mass spectrometry (GC-MS) was used to follow the degradation and evolution of organic compounds while high-throughput DNA sequencing was used to determine the bacterial diversity in the ABR. The results obtained after 90 d of operation showed decreases in all parameters measured and the highest mean removal rates were obtained for petroleum substances (98.8%) and suspended solids (77.0%). Amounts of petroleum substances in the ABR effluent could meet the requirements of a national standard for oilfield reinjection water. GC-MS analysis showed that a wide range of chemicals (e.g. aromatic hydrocarbons, esters, alcohols, ketones) could be sequentially removed from the influent by each zone of ABR. The high-throughput DNA sequencing showed that the bacteria Micropruina, Saccharibacteria and Synergistaceae were involved in the degradation of pollutants in the anaerobic and anoxic reaction zones, while Rhodobacteraceae and Aliihoeflea were the main functional microorganisms in the aerobic reaction zones. The results demonstrated that the improved ABR reactor had the potential for the treatment of wastewater from ASP flooding technology.
Highlights
Alkaline-surfactant-polymer (ASP) flooding is an efficient tertiary recovery technique used for the extraction of crude oil which cannot be recovered during the second stage [1]
The results demonstrated that the improved anaerobic baffled reactor (ABR) reactor had the potential for the treatment of wastewater from ASP flooding technology
The content of petroleum substances in the wastewater treated by the ABR could meet the requirements of a national standard ( 5 mg/L) for reinjection of the water at the Daqing Oilfield in China
Summary
Alkaline-surfactant-polymer (ASP) flooding is an efficient tertiary recovery technique used for the extraction of crude oil which cannot be recovered during the second stage [1]. ASP flooding technology uses alkali, surfactant and polymer agents to displace crude oil [2], and the mean recovery is significantly improved compared with the water flooding method [3]. ASP flooding technology has greatly improved the recovery rate of crude oil, remediation of the process water is an inevitable issue [5,6] limiting further development of the technology. The composition of the ASP flooding process water is complex since the use of alkali, surfactants and polymers results in many pollutants including polymers and surfactants. The Daqing oilfield in Heilongjiang province is the largest oilfield in China where ASP flooding technology is widely used in the recovery of crude oil. The reinjected water is required to meet a national standard for the use of reinjection water for high permeability reservoirs with oil and suspended solids contents of < 20 mg/L each (Oil and gas development Standardization Technical Committee, 2012)
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