Calcium nitrate for oilfield souring and sulfide control: how nitrate injection works, what doses are reported, and where it fails
Nitrate injection controls reservoir souring, the microbial production of H2S in waterflooded oil fields, by stimulating nitrate-reducing bacteria that compete with sulfate-reducing bacteria (SRB) for degradable organics and that oxidise sulfide directly.[1] The nitrite they produce is a strong SRB inhibitor.[4] Calcium nitrate has documented North Sea field use: on the Gullfaks field it replaced 240,000 litres per year of biocide and had run for more than three years by 2005.[21] Reported doses are system-specific: a patent background cites roughly 25–500 ppm nitrate plus nitrite in injection water,[13] lab bioreactors needed 4–10 mM nitrate (about 250–620 mg/L),[1][4] and field failures are documented when the oil, salinity or nitrogen supply is wrong.[3][7] For biogas digesters, calcium nitrate dosing is reported to cut H2S, but the evidence is thin and partly vendor-linked.[19]
Key facts at a glance
| Item | Value / answer |
|---|---|
| What it controls | Biogenic H2S from sulfate reduction in waterflooded reservoirs, produced-water systems and storage ponds[1][9] |
| Core mechanism | Nitrate-reducing, sulfide-oxidising bacteria (NR-SOB) and heterotrophic nitrate reducers (hNRB) compete with SRB for organics[1] |
| Inhibitor produced | Nitrite, formed by nitrate reduction, strongly inhibits SRB[4]; modelling work ranks nitrite inhibition as the major mechanism[10] |
| Largest field example | Gullfaks (Statoil): calcium nitrate replaced 240,000 L/yr of biocide; in use over 3 years by Dec 2005[21] |
| Dose range cited in patent background | Generally under about 3,000 ppm total nitrate + nitrite, more particularly about 25–500 ppm in injected water[13] |
| Bioreactor dose example (full control) | 4 mM nitrate (about 250 mg/L as NO3) completely stopped sulfide in heavy-oil columns; 1–2 mM gave only transient partial control[4] |
| Dose that failed | Up to 25 mg/L nitrate for 90 days did not stop souring in a Brazilian offshore-field column study with 150 mg/L VFA[7] |
| Why oil composition matters | Toluene in the oil consumes nitrate; nitrate reduced in microcosms ranged from 1.4 to 22.2 mM across six oils[3] |
| Salinity effect | Nitrite accumulated and inhibited SRB at 2.5 M NaCl but not at 0.5 M in Bakken shale-oil bioreactors[2] |
| Main corrosion caution | Nitrite breakthrough gave the highest pitting density in FPSO topside microcosms[8] |
| Calcium salt use in injection water | Calcium nitrate is named among salts that can act as fines stabiliser and souring control in waterflood injection water (patent description)[14] |
| Biogas digester evidence | Calcium nitrate dosing reported (conference paper, industry co-authored) to raise methane yield and lower H2S[19]; a separate WEF nitrate-recycle sludge process reported at least 90% H2S reduction in biogas[20] |
What is reservoir souring and why does nitrate stop it?
Seawater and many produced waters carry sulfate. Once injected into a warm, organic-rich reservoir, sulfate-reducing bacteria turn it into sulfide, souring the oil, water and gas, corroding steel and raising treating costs.[5][23] Nitrate treatment works through three overlapping routes: biocompetitive exclusion (heterotrophic nitrate reducers use the same organic electron donors as SRB), direct sulfide oxidation by NR-SOB, and nitrite inhibition of SRB.[1][4] A 2019 modelling study concluded that nitrite inhibition was the major mechanism whether nitrate reduction was autotrophic or heterotrophic, and that the nitrite-to-nitrate reduction-rate ratio can indicate how well a treatment will work.[10] Field data suggest the dominant nitrate pathway varies: in one mesothermic field, ammonium in produced water did not rise under nitrate injection, pointing to denitrification rather than reduction to ammonium.[6]
This page covers oilfield and biogas use. For municipal sewers, force mains and lift stations, see calcium nitrate for H₂S odour control in wastewater; the biology is shared but the dosing points, targets and risks differ.
Where is nitrate used in oil and gas?
- Waterflood injection water. Continuous low-level dosing into seawater or produced-water injection. A patent description notes that calcium, magnesium or potassium nitrate can be added during the main waterflood phase for souring control, and that calcium nitrate can double as a fines stabiliser during well commissioning.[14]
- Reservoir treatment of an already soured field. Nitrate and/or nitrite solutions injected into an injection well in contact with a producer to cut sulfide in production fluids.[13]
- Produced-water storage ponds. A 2025 trial added nitrate directly to a high-salinity storage pond in a hydraulic-fracturing setting; sulfate stayed stable over 4 weeks while the SRB share fell and nitrate and nitrite fluctuated after dosing; the study reports no measured sulfide in the pond.[9]
- Topsides and produced-water reinjection. Here the main question is corrosion rather than souring (see risks below).[8]
What case studies exist for calcium nitrate?
The best-known is the North Sea. Statoil used calcium nitrate on Gullfaks, where it replaced an annual 240,000 litres of biocide; the company reported more than three years of operation by December 2005, with the same approach on Veslefrikk (replacing biocides to reduce pipe corrosion) and Statfjord.[21] In Canada, the Medicine Hat Glauconitic C heavy-oil field is injected with nitrate and has served as a research field for how oil composition controls nitrate use.[3][4] A Saskatchewan Bakken shale-oil study found that nitrate injection can prevent souring if salinity stays high, suggesting nitrate-amended reinjection of saline produced water may be cost effective.[2] Publicly available field dose records are sparse, so most numbers below come from bioreactors, patents and modelling.
How much nitrate is dosed? Reported ranges
| System | Reported nitrate figure | Outcome / note | Source |
|---|---|---|---|
| Injection water (patent background) | ~25–500 ppm nitrate + nitrite; generally <3,000 ppm | Prior-art range, not a specification | [13] |
| Electron balance (patent example) | ~93 ppm nitrate per 50 ppm glucose | Nitrate demand scales with available organics | [13] |
| Bioreactor, heavy oil, 2 mM sulfate | 4 mM (full); 1 and 2 mM only transient partial control | 4 mM stopped sulfide in sand-packed columns | [4] |
| Bioreactor, lactate-fed | 10 mM at 0.013–6 mM sulfate | Needed regardless of sulfate level | [1] |
| Column, 150 mg/L VFA | up to 25 mg/L for 90 days | Did not stop souring; nitrogen-limited, SRB-group growth rose | [7] |
| Bioreactor + biocide, 3 mM VFA | 2 mM continuous | Alone ineffective; synergy only with long-low biocide pulses | [5] |
| Corfu sewer, NH4NO3, 500 m³/h, 3–27 mg S/L | 6.9 / 15 / 27.7 kg/h | 84% / 98% / 99% sulfide removal; about 30 g/m³ at 15 kg/h (calculated) | [16] |
Conversion note: 1 mM nitrate is about 62 mg/L as NO3−. A single “mg nitrate per mg sulfide” ratio is not a reliable design figure from these sources: the demand depends on the organics, the oil (toluene soaks up nitrate),[3] the nitrate pathway, and whether the aim is prevention or removal of existing sulfide. Nitrate demand is better set by a treatability or bioreactor test on the actual water and oil, then tuned by monitoring. A common field failure is under-dosing: too little nitrate can leave SRB growing.[22]
Is calcium nitrate better than sodium or ammonium nitrate?
The sources here do not contain a head-to-head field trial of nitrate salts, so any ranking would be speculation. What can be said:
- Calcium nitrate has North Sea field precedent[21] and is named in a patent among injection-water salts that serve souring control and fines stabilisation.[14] It is also the salt in the digester work discussed below.[19]
- Ammonium nitrate was used for sewer sulfide control in Corfu, where the authors judged the added ammonia load tolerable at about 10 kg/h.[16] In reservoirs the extra ammonium is a nitrogen source for microbes; in a nitrogen-limited column, nitrate addition even stimulated SRB-containing groups.[7]
- Calcium as a cation is a check item in sulfate-rich water, where calcium sulfate scaling is a general oilfield concern. This is basic water chemistry, not tested in the cited sources, so run a scaling check on the mixed water.
- Handling: calcium nitrate dissolves readily and is supplied as a concentrate; a patent notes a concentrate tank may sit at the injection site.[14][24]
What are the risks and how does nitrate treatment fail?
- Corrosion and pitting. In microcosms of produced fluids from two FPSOs held at 54 °C, untreated live replicates had the highest general corrosion (up to 0.48 mm/year), nitrate- or nitrite-treated fluids were below 0.12 mm/year, but nitrite breakthrough showed the highest pitting density.[8] Laboratory and field results on corrosion are not uniform.
- Nitrate consumed by the oil, not the sulfide. Success is inversely related to toluene content, because nitrate reduced on toluene is not available to suppress SRB.[3]
- Salinity and temperature. High salinity favoured nitrite accumulation and SRB inhibition in Bakken cultures; at low salinity nitrite did not accumulate.[2]
- Nitrogen supply and electron-donor excess. Where organic acids exceeded nitrate demand and nitrogen was limiting, 25 mg/L nitrate did not control souring.[7]
- Mixed systems. Different platforms respond differently: one FPSO responded as expected while nitrate was less effective on the other.[8] Treat each system separately.
- Nitrogen species in produced water. Monitor nitrate, nitrite and ammonium: in one mesothermic field, ammonium in producing wells fell on average from 0.3 to 0.2 mM over 2 years of nitrate injection, but that is one field and may not transfer.[6]
Does calcium nitrate work in biogas digesters and industrial effluents?
The same biology applies in anaerobic digesters: denitrifiers outcompete SRB for substrate and nitrite inhibits sulfate reduction. Proceedings by authors from the University of Kaiserslautern and Yara Industrial report that calcium nitrate dosing gave higher methane yield, lower H2S, substrate savings, better viscosity and a more robust plant, with enhanced denitrification and methanogenesis and less sulfate reduction.[19] A separate WEF proceedings abstract describes a sludge-digestion process with a nitrate recycle loop (not calcium nitrate dosing) in which pilot H2S in biogas was consistently cut by at least 90% without ferric chloride, which shows the nitrate route works at pilot scale.[20] Treat this as promising but limited and partly vendor-linked evidence: a 2021 critical review of digester H2S management centred on iron salts, microaeration and post-treatment rather than nitrate.[15] For industrial effluents the closest published evidence is from sewers, where nitrate dosing of sewer biofilms is reported to reduce methane formation as well as sulfide,[17] and where nitrite-derived free nitrous acid has been shown to damage the SRB Desulfovibrio vulgaris in lab work.[18] Trial on your own effluent before committing.
How is a nitrate souring-control programme run?
- Characterise the water and oil. Sulfate, organic acids (VFA), temperature, salinity, toluene or alkylbenzene content, existing sulfide.[3][4]
- Test in a bioreactor or batch microcosm with field water and oil; record nitrate required to stop sulfide.[1][4]
- Choose a dosing strategy. Continuous low-level injection is the common approach; the patent route for existing souring injects nitrate/nitrite solution at an injector.[13]
- Set up a concentrate tank and metering with fully dissolved, particle-free solution.[14]
- Monitor sulfide, sulfate, nitrate, nitrite and ammonium at producers and topsides; watch for nitrite or nitrate breakthrough.[2][6][8]
- Adjust. Raise dose if sulfide rebounds; cut or add inhibitors if nitrite breakthrough and pitting rise.[8]
What should be monitored?
The cited studies track sulfide and sulfate, nitrate and nitrite (by ion chromatography),[9] ammonium to see the nitrate pathway,[6] microbial community by DNA sequencing,[9] and corrosion by general rate and pitting density rather than rate alone.[8] Nitrite appearing in produced fluids is a signal to check both souring control (good) and pitting risk (bad).
What are the alternatives to nitrate?
| Option | How it works | Evidence / limits | Source |
|---|---|---|---|
| Biocides (glutaraldehyde, THPS, quaternary ammoniums) | Kill or damage microbes | Glutaraldehyde acts on DNA, RNA and protein synthesis; THPS raises membrane permeability. Long-low pulses plus nitrate gave synergy in bioreactors; reservoir biocide injection is not commonly done | [5][22] |
| Perchlorate / chlorate | Reduced to chlorite, toxic to SRB; also reacts with sulfide | Worked in sediment columns, but perchlorate was not reduced and did not stop sulfate reduction in heavy-oil incubations | [4][11][12] |
| H2S scavengers | End-of-pipe chemical removal | Treats symptoms, not sulfide generation | [22] |
| Iron salts (digesters) | Precipitate sulfide as FeS | 88–100% H2S removal at 1.2–2.5:1 iron-to-sulfide w/w; chemical cost is a disadvantage | [15] |
| Microaeration (digesters) | Oxygen sets redox near −250 mV | >95% H2S reduction at pilot and full scale; over-aeration risk | [15] |
| Biogas post-treatment | Biotrickling filters, scrubbers | >95% removal, but does not protect methanogens inside the digester | [15] |
When calcium nitrate is NOT the right choice
- Systems with high toluene or other nitrate-consuming organics, or nitrogen-limited and electron-donor-rich waters, where nitrate can be consumed before it suppresses SRB or can even stimulate them.[3][7]
- Topsides and produced-water systems with corrosion sensitivity unless pitting is monitored; nitrite breakthrough raised pitting density.[8]
- Anyone expecting a universal dose. Reported nitrate figures span more than two orders of magnitude between systems; test your own water and oil.[1][4][13]
- Reservoir injection with an off-the-shelf fertilizer product. Injection water needs particle-free, specified solution; confirm injectivity, chloride, metals and scaling compatibility first.[14]
What HRSU supplies — and what it does not
HRSU Indore supplies fertilizer-grade calcium nitrate powder: 18.5–19% calcium, 15.5% minimum nitrogen, 100% water-soluble with 0% insoluble residue, in 25 kg and 50 kg bags with batch COA, for bulk and export, with TDS and SDS available. A fully soluble product suits concentrate-tank make-up, because undissolved particles can block metering lines and reduce injectivity. HRSU does not claim any oilfield-chemical, API, offshore-approved, or biogas-additive grade, and has no field data of its own on souring control. If you are evaluating calcium nitrate for injection water or a digester, send your solution specification (insolubles, chloride, heavy metals, sulfate compatibility), request the TDS and a sample, and validate it in your own trial.
Request a calcium nitrate sample and COA for your souring trial
100% water-soluble · 0% insoluble residue · 25 kg & 50 kg bags · bulk/export available.
Buy online WhatsApp usFrequently asked questions
How does nitrate injection control H2S in oil reservoirs?
What nitrate dose is used for reservoir souring control?
Has calcium nitrate been used in a real oil field?
Yes. Statoil used calcium nitrate on Gullfaks, where it replaced 240,000 litres per year of biocide and had run for more than three years by December 2005; Veslefrikk and Statfjord also switched.[21]
Why does nitrate sometimes fail to stop souring?
Does nitrate treatment cause corrosion?
Not always, but there is risk. In FPSO topside microcosms nitrate and nitrite treatment lowered general corrosion rates, but nitrite breakthrough gave the highest pitting density.[8]
Can calcium nitrate be dosed into biogas digesters to cut H2S?
Proceedings report higher methane yield and lower H2S with calcium nitrate dosing,[19] and a separate WEF nitrate-recycle sludge process reports at least 90% H2S reduction (not calcium nitrate dosing).[20] Evidence is limited and partly vendor-linked; iron salts and microaeration are the better-documented options.[15]
What are the alternatives to nitrate for sulfide control?
Can HRSU calcium nitrate be used for oilfield injection?
HRSU supplies 100% water-soluble, 0%-insoluble-residue fertilizer-grade powder with batch COAs. It makes no oilfield-grade claim, so confirm your injection-water specification and run a trial first.
Related guides
- Calcium nitrate for H2S odour control in wastewater
- Calcium nitrate as a corrosion inhibitor
- Calcium nitrate for lake sediment remediation
- Calcium nitrate safety, handling and storage
References
- Oil field souring control by nitrate-reducing Sulfurospirillum spp. that outcompete sulfate-reducing bacteria for organic electron donors (Hubert & Voordouw) — Applied and Environmental Microbiology, 2007. Peer-reviewed
- Control of sulfide production in high salinity Bakken shale oil reservoirs by halophilic bacteria reducing nitrate to nitrite (An, Shen & Voordouw), University of Calgary — Frontiers in Microbiology, 2017. Peer-reviewed
- The effectiveness of nitrate-mediated control of the oil field sulfur cycle depends on the toluene content of the oil (Suri, Voordouw & Voordouw) — Frontiers in Microbiology, 2017. Peer-reviewed
- Comparison of nitrate and perchlorate in controlling sulfidogenesis in heavy oil-containing bioreactors (Okpala & Voordouw), University of Calgary — Frontiers in Microbiology, 2018. Peer-reviewed
- Control of microbial sulfide production with biocides and nitrate in oil reservoir simulating bioreactors (Xue & Voordouw), University of Calgary — Frontiers in Microbiology, 2015. Peer-reviewed
- Ammonium concentrations in produced waters from a mesothermic oil field subjected to nitrate injection decrease through formation of denitrifying biomass and anammox activity (Shartau et al.) — Applied and Environmental Microbiology, 2010. Peer-reviewed
- Effects of nitrate injection on microbial enhanced oil recovery and oilfield reservoir souring (da Silva et al.), Embrapa / UFSC — Applied Biochemistry and Biotechnology, 2014. Peer-reviewed
- Assessing microbial corrosion risk on offshore crude oil production topsides under conditions of nitrate and nitrite treatment for souring — Microorganisms, 2022. Peer-reviewed
- Nitrate-reducing microorganisms prevent souring of an oil field produced water storage pond — FEMS Microbiology Ecology, 2025. Peer-reviewed
- A sulfur and nitrogen cycle informed model to simulate nitrate treatment of reservoir souring — Scientific Reports, 2019. Peer-reviewed
- Inhibition of microbial sulfate reduction in a flow-through column system by (per)chlorate treatment (Engelbrektson et al.), UC Berkeley / Lawrence Berkeley National Laboratory — Frontiers in Microbiology, 2014. Peer-reviewed / national lab
- Attenuating sulfidogenesis in a soured continuous flow column system with perchlorate treatment (Engelbrektson et al.), UC Berkeley / Lawrence Berkeley National Laboratory — Frontiers in Microbiology, 2018. Peer-reviewed / national lab
- US 8,573,300 B2 — Reducing sulfide in oil reservoir production fluids (BP) — U.S. Patent and Trademark Office, via Google Patents. Patent
- US 11,162,311 B2 — Method of controlling salinity of an injection water during commissioning of an injection well (BP) — U.S. Patent and Trademark Office, via Google Patents. Patent
- Hydrogen sulphide management in anaerobic digestion: a critical review on input control, process regulation, and post-treatment (Vu et al.), University of Technology Sydney — Bioresource Technology, 2021 (accepted manuscript). Peer-reviewed review
- Addition of nitrate for sulphide control in a sewer network (Mathioudakis et al., Corfu) — Global NEST Journal, 2006. Peer-reviewed
- Effects of nitrate dosing on methanogenic activity in a sulfide-producing sewer biofilm reactor — Water Research, 2013 (PubMed 23352490). Peer-reviewed (PubMed record)
- Antimicrobial effects of free nitrous acid on Desulfovibrio vulgaris: implications for sulfide-induced corrosion of concrete — Applied and Environmental Microbiology, 2016. Peer-reviewed
- Calcium nitrate dosage results in improved biogas quality in anaerobic digesters (Stoeck, Filker, Breiner, Ettl, Doppelbauer; Univ. of Kaiserslautern and Yara Industrial) — Aqua Enviro conference proceedings. Conference proceedings (industry co-authored)
- Follow the nitrate pathway to cleaner digestion and more biogas — Water Environment Federation (Access Water) proceedings. Conference proceedings
- Using fewer harmful chemicals (Gullfaks calcium nitrate) — Equinor (formerly Statoil), 29 Dec 2005. Operator news release
- Microbiological oilfield souring and chemical treatment strategies (L. Walker, Rawwater Engineering) — Processing Magazine, 31 Oct 2019. Trade article
- Sulfate-reducing microorganism — Wikipedia. Encyclopedia
- Calcium nitrate — Wikipedia. Encyclopedia