he study in this article presents the outcomes of an extended pressurised bioreactor investigation evaluating the long-term souring control efficacy of Vink Chemicals’ biocide, grotan® OX, against a mixed oilfield microbial consortium.
Reservoir souring, driven by microbial activity, particularly sulfate- reducing prokaryotes (SRP) and other anaerobes, poses a persistent challenge in oilfield operations. The evolution of biogenic hydrogen sulfide (H2S) not only contributes to asset corrosion and health, safety,and environment (HS&E) hazards but also affects crude quality and processing economics. Traditional short-term kill prevention strategies often fail under long-residence-time conditions prevalent in deep injection systems. There is a growing need for long-acting, broad- spectrum biocides capable of metabolic suppression over months, not just hours.
Case studies have been reported where a conventional biocide was applied over several months in a high salinity, low flow offshore waterflood system. Initial H2S levels decreased after dosing but increased again within a few days, indicating a resurgence of microbes. This suggested that conventional biocide chemistries were unable to provide any remedial capacity and therefore could not persist long enough to cause any significant prevention through metabolic suppression. This is not an isolated example.
These experiences underscore the need for next-generation biocide strategies, those that go beyond microbial kill and instead aim for long-term metabolic inhibition, biofilm disruption, or even quorum sensing interference.
This article presents a rigorous comparative study of grotan OX, Vink Chemicals’ high-stability oxazolidine biocide, under simulated field conditions over 17 weeks.
Materials and methods
Bioreactor setup
12 water-saturated bioreactors were constructed and operated at the Rawwater UK laboratories. The columns operated in parallel under pressurised, anoxic conditions at 1000 psig and 30°C to simulate common downhole near wellbore environments. All bioreactors were packed with a pre-established sand matrix, populated with a mature, diverse, sessile oilfield microbial community.
During each weekly batch injection cycle, a baseline injection water consisting of anoxic synthetic seawater supplemented with 120 mg/L mixed VFAs (at a ratio of 100:10:10 of acetate, propionate, and butyrate respectively) was injected as a carbon source typically available in an oil-bearing reservoir to support microbial activity at an injection flow rate of 5.0 mL/min.
Two biological replicates were run for each of the following treatments:
- Industry incumbent – glutaraldehyde (A1/A2).
- Industry incumbent – THPS (B1/B2).
- In-house candidate – confidential (C1/C2).
- grotan OX (D1/D2).
- Controls (PC1/PC2).
Injection scenario and dosing strategy
During each of the first three injection cycles, one third of the measured swept volume was replaced in each bioreactor using the baseline injection water. In week 4, the entire swept volume of each bioreactor column was replaced in preparation for the week 5 biocide dosing campaign.
Biocides were dosed at concentrations reflecting typical field-use levels. All biocides were applied across the full swept volume of all treated bioreactors at 750 ppm/v product. Following biocide dosing in week 5, the bioreactors received a one-third swept volume injection between weeks 6 and 17, allowing for a real-time evaluation of biocide performance and long-term persistence.
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