2015 SPE Produced Water Symposium
Title: Chloramine: An Effective Biocide for Produced Waters
Objective/Scope: Produced waters containing high levels of oxidant demanding chemicals such as ammonia, hydrogen sulfide, iron, and manganese are often thought to be difficult to disinfect using oxidizing biocides such as hypochlorite. It is the goal of this paper to present evidence that chloramines generated in situ through the reaction of ammonia present in produced water with hypochlorite added as a disinfectant can effectively control microbial populations in produced water.
Methods, Procedures, Processes: Testing was accomplished by treating produced waters being held in retention ponds with a hypochlorite-based disinfectant solution produced at the pond location using a mobile on-site generation (OSG) system. OSG in this treatment scenario involves the electrolysis of sodium chloride brines to yield a hypochlorite-based oxidizing biocide solution. This solution is then injected into the produced water at a rate to ensure that the Oxidation-Reduction Potential (ORP) of the treated water is around 450 mV. Samples of both the raw and treated water were analyzed for both chemical composition as well as microbial populations.
Results, Observations, Conclusions: Raw water in this study was found to consistently have relatively high ammonia content in the range of 58 to 68 mg/L along with an ORP in the range of -87 to 190 mV. Populations of Acid Producing Bacteria (APB) and Sulfate Reducing Bacteria (SRB) were found to be 1010 and 1011 MPN/mL, respectively. Treatment also resulted in a clear visual difference in the produced water, with the raw water being black in color with the treated water having a muddy brown coloration. On site analysis of the treated water fond that the ORP after oxidant injection was between 464-543 mV, a value consistent with the presence of chloramines and not free chlorine which is supported by the measurement of a free chlorine residual of only 1.1 mg/L but a total chlorine residual of 55 mg/L. Populations of APBs and SRBs in the treated water were found to be 1 and 10 MPN/mL, respectively, representing substantial reductions in the initial populations. Overall, this data clearly demonstrates that chloramines generated in situ through the treatment of high ammonia waters with OSG produced hypochlorite can effectively control the populations of key microbes in produced waters.
Novel/Additive Information: Effectively controlling microbial populations using chloramines generated in situ through the reaction of hypochlorite with ammonia often present in produced water offers the ability to achieve required disinfection with oxidizing biocides without meeting the total oxidant demand of the water being treated.