title: Toluene depletion in produced oil contributes to souring control in a field subjected to nitrate injection.
abstract: Souring in the Medicine Hat Glauconitic C field, which has a low bottom-hole temperature (30 °C), results from the presence of 0.8 mM sulfate in the injection water. Inclusion of 2 mM nitrate to decrease souring results in zones of nitrate-reduction, sulfate-reduction, and methanogenesis along the injection water flow path. Microbial community analysis by pyrosequencing indicated dominant community members in each of these zones. Nitrate breakthrough was observed in 2-PW, a major water- and sulfide-producing well, after 4 years of injection. Sulfide concentrations at four other production wells (PWs) also reached zero, causing the average sulfide concentration in 14 PWs to decrease significantly. Interestingly, oil produced by 2-PW was depleted of toluene, the preferred electron donor for nitrate reduction. 2-PW and other PWs with zero sulfide produced 95% water and 5% oil. At 2 mM nitrate and 5 mM toluene, respectively, this represents an excess of electron acceptor over electron donor. Hence, continuous nitrate injection can change the composition of produced oil and nitrate breakthrough is expected first in PWs with a low oil to water ratio, because oil from these wells is treated on average with more nitrate than is oil from PWs with a high oil to water ratio.
authors.affiliation: Petroleum Microbiology Research Group, Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada.
authors.forename: Akhil
authors.initials: A
authors.lastname: Agrawal
authors.forename: Hyung Soo
authors.initials: HS
authors.lastname: Park
authors.forename: Safia
authors.initials: S
authors.lastname: Nathoo
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Gieg
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Jack
authors.forename: Kirk
authors.initials: K
authors.lastname: Miner
authors.forename: Ryan
authors.initials: R
authors.lastname: Ertmoed
authors.forename: Aaron
authors.initials: A
authors.lastname: Benko
authors.forename: Gerrit
authors.initials: G
authors.lastname: Voordouw
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D019652:Extraction and Processing Industry / Q000379:methods*; D009566:Nitrates / Q000737:chemistry*; D010578:Petroleum / Q000032:analysis*; D013431:Sulfates; D013440:Sulfides; D013997:Time Factors; D014050:Toluene / Q000737:chemistry*
chemical_list: D009566:Nitrates; D010578:Petroleum; D013431:Sulfates; D013440:Sulfides; D014050:Toluene