The Effectiveness of Nitrate-Mediated Control of the Oil Field Sulfur Cycle Depends on the Toluene Content of the Oil

Abstract

The injection of nitrate is one of the most commonly used technologies to impact the sulfur cycle in subsurface oil fields. Nitrate injection enhances the activity of nitrate-reducing bacteria, which produce nitrite inhibiting sulfate-reducing bacteria (SRB). Subsequent reduction of nitrate to di-nitrogen (N2) alleviates the inhibition of SRB by nitrite. It has been shown for the Medicine Hat Glauconitic C (MHGC) field, that alkylbenzenes especially toluene are important electron donors for the reduction of nitrate to nitrite and N2. However, the rate and extent of reduction of nitrate to nitrite and of nitrite to nitrogen have not been studied for multiple oil fields. Samples of light oil (PNG, CPM, and Tundra), light/heavy oil (Gryphon and Obigbo), and of heavy oil (MHGC) were collected from locations around the world. The maximum concentration of nitrate in the aqueous phase, which could be reduced in microcosms inoculated with MHGC produced water, increased with the toluene concentration in the oil phase. PNG, Gryphon, CPM, Obigbo, MHGC, and Tundra oils had 77, 17, 5.9, 4.0, 2.6, and 0.8 mM toluene, respectively. In incubations with 49 ml of aqueous phase and 1 ml of oil these were able to reduce 22.2, 12.3, 7.9, 4.6, 4.0, and 1.4 mM of nitrate, respectively. Nitrate reduced increased to 35 ± 4 mM upon amendment of all these oils with 570 mM toluene prior to incubation. Souring control by nitrate injection requires that the nitrate is directed toward oxidation of sulfide, not toluene. Hence, the success of nitrate injections will be inversely proportional to the toluene content of the oil. Oil composition is therefore an important determinant of the success of nitrate injection to control souring in a particular field.

Comparison of Nitrate and Perchlorate in Controlling Sulfidogenesis in Heavy Oil-Containing Bioreactors

“…Experiments with batch cultures and bioreactors in which heavy MHGC oil was the only available electron donor indicated absence of PRB capable of coupling the reduction of perchlorate to the oxidation of oil components ( Figures 3 , 5 and Supplementary Figure S1 ). Nitrate was reduced to nitrite and dinitrogen under these conditions, which resulted in removal of alkylbenzenes from the oil ( Supplementary Figure S1 ), as found previously ( Lambo et al, 2008 ; Agrawal et al, 2012 ; Suri et al, 2017 ). Because perchlorate was not reduced it was inert, i.e., no high-potential electron transport pathways were operating, and sulfide production was observed both in enrichment cultures and bioreactors containing sulfate and perchlorate.…”

“…Studies on the control of sulfide production with nitrate in heavy oil-containing bioreactor columns as well as in the field have shown that alkylbenzenes (toluene, ethylbenzene, and m - and p -xylene) were utilized as electron donors for nitrate reduction ( Lambo et al, 2008 ; Agrawal et al, 2012 ; Suri et al, 2017 ), whereas alkylbenzenes and alkanes were used as electron donors for sulfate reduction ( Agrawal et al, 2012 ). Acetate accumulated transiently as an intermediate in the metabolism of these oil components under sulfate-reducing, but not under nitrate-reducing conditions ( Callbeck et al, 2013 ).…”

Time Course-Dependent Methanogenic Crude Oil Biodegradation: Dynamics of Fumarate Addition Metabolites, Biodegradative Genes, and Microbial Community Composition

“…To prepare the inoculum for this study, produced water was obtained from five production wells (PW; 4-PW, 7-PW, 18-PW, 32-PW, 33-PW; Figure S1 ) in the Medicine Hat Glauconitic C (MHGC) field (Voordouw et al, 2009 ). Although this oilfield has been used as a study site for nitrate treatment of souring for 10 years (Suri et al, 2017 ), previous investigations of this oilfield have reported chemical and functional evidence of nitrate-free “zones” harboring active methanogenic archaea (Agrawal et al, 2012 ), from which all PW samples were collected for this study. Berdugo-Clavijo and Gieg ( 2014 ) also demonstrated that methanogenic crude oil biodegradation could be established from these produced waters.…”

Mitigating Sulfidogenesis With Simultaneous Perchlorate and Nitrate Treatments

“…Nitrate has been used as a biological treatment in oil reservoir systems since the 1990s ( Coates et al, 1993 ; Hubert et al, 2003 ; Arensdorf et al, 2009 ; Gieg et al, 2011 ). This treatment has direct and indirect effects on sulfate reduction but is not always predictable ( Hubert and Voordouw, 2007 ; Voordouw et al, 2009 ; Gieg et al, 2011 ; Carlson et al, 2015a ; An et al, 2017 ; Okpala et al, 2017 ; Suri et al, 2017 ; Engelbrektson et al, 2018 ). Nitrate has multiple mechanisms of action to control sulfate reduction.…”