No abstract

An increased awareness of the environmental impact and operational cost associated with freshwater usage in energy production has shifted industry interest towards replacing freshwater sources with produced water in oilfield stimulation applications. Produced water often contains high concentrations of bacterial assemblages, which can cause operational challenges such as corrosion, slime formation, and souring. Microbial control agents are subsequently necessary to manage the poor water quality of most produced water sources. However, such chemicals are highly reactive and relatively unspecific, making their toxicity both a performance metric and an ecological, human health, and disposal concern. Given the advantageous biological activity of microbial control agents, controlled detoxification following use is a pertinent factor in responsible hazard management. Formaldehyde-releasing agents are a widely used category of microbial control additives which slowly and continuously release small amounts of formaldehyde, a toxic environmental pollutant and known human carcinogen. This research evaluated the acute (short-term) aquatic toxicity of two liquid formaldehyde-releasing microbial control additives, identified necessary parameters for their detoxification, and measured the resulting change in their toxicity over time, using a light-based acute toxicity test. The additives investigated were a tetrakis(hydroxymethyl)phosphonium sulfate (THPS)-based product (approximately 75% active by weight), and a 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH)-based product (approximately 70% active by weight). Laboratory results suggest that the THPS-based additive was three times more toxic than the DMDMH-based additive on a percent volume basis, and pH was an important factor in THPS toxicity. Data were consistent with a maximum sixfold decrease in DMDMH toxicity for a 0.05% (v/v) solution following eight days of aeration at 0.15±0.05 liters per minute (LPM) (corresponding to a total of 172.8 L Air /mL Sample ), and more than a twelvefold decrease in THPS toxicity for a 0.05% (v/v) solution following a pH increase and eight days of aeration at 0.15±0.05 LPM (corresponding to a total of 172.8 L Air /mL Sample ). Aeration alone decreased the toxicity of DMDMH over the course of eight days, while a combination of aeration and pH increase were necessary to decrease the toxicity of THPS over the same time period. This work presents a proof of concept for a relatively simple and cost effective detoxification of the evaluated additives and highlights the key parameters for this process.

Summary An increased awareness of the environmental impact and operational costs associated with freshwater usage and wastewater disposal in energy production has shifted industry interest toward replacing freshwater sources with lower-quality or recycled water in oilfield applications, and has highlighted the importance of addressing toxicity as part of a successful waste-management plan. Poor-quality and recycled waters often contain high concentrations of bacterial assemblages, which can cause operational challenges such as corrosion, slime formation, and souring. Microbial-control agents, such as biocides, are subsequently necessary to manage bacteriological problems. However, these chemicals are highly reactive and can react indiscriminately with biological targets, making their toxicity both a performance metric and an ecological, human-health, and disposal concern. The luminescent-bacteria toxicity test presented in this work, for instance, is a key regulatory parameter in the pumpoff and landspray disposal of drilling fluids in Alberta, Canada. Considering the necessary toxicity of biocides, controlled detoxification following use is a pertinent factor in responsible hazard management. Formaldehyde-releasing agents are the most widely used category of microbial-control additives that slowly and continuously release small amounts of formaldehyde, a toxic environmental pollutant and known human carcinogen. This research evaluated the acute (short-term) aquatic toxicity of two liquid formaldehyde-releasing biocides, identified necessary parameters for their detoxification, measured the resulting change in their toxicity over time, and used regulatory requirements for toxicity testing set by the Alberta Energy Regulator (AER) for drilling-waste management to evaluate the practical relevance of this detoxification to waste-management practices. The additives investigated were a tetrakis(hydroxymethyl)phosphonium sulfate (THPS)-based product, and a 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH)-based product. Laboratory results suggest that the THPS-based additive was more toxic than the DMDMH-based additive on a percent volume basis, and pH was an important factor in THPS toxicity. Aeration alone decreased the toxicity of DMDMH over the course of the experiment, while a combination of aeration and pH increase were necessary to decrease the toxicity of THPS over the same time period. This work presents a proof of concept for a relatively simple and cost-effective detoxification of the evaluated additives, highlights the key parameters for this process, and uses toxicity-threshold levels referenced by the AER drilling-waste-management directive to evaluate their application in waste-assessment practices.