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UBC Theses and Dissertations

An accidental release of flowback water from storage system : a risk assessment study Gandhi, Himani Rajiv


In the last decade, extraction of unconventional oil and gas (UOG) has rapidly increased in Canada. One of the major concerns related to UOG extraction is the risk of accidental releases during wastewater management. UOG extraction uses technologies of horizontal drilling and hydraulic fracturing. Flowback and produced water are generated as wastewater and may contain high concentrations of salts, metals, oil, grease, and organic compounds. Flowback water is stored on site before being transported for treatment, reuse or disposal. It is stored in containment pond, above ground walled storage systems (AWSS) or storage tanks. A comprehensive risk assessment has been carried out for the accidental release of flowback water during the storage. Two components of risk namely probability of failure and consequence assessment on the ecology have been examined using the frameworks of Backward Integrated Analysis (BIA) and Ecological Risk Assessment (ERA), respectively. In BIA, failure modes were identified for an uncontrolled release of flowback water due to AWSS failure by developing a fault tree. The probability of failure of the system was calculated and its failure modes were ranked by assigning risk priority number (RPN). To assess the consequence of the accidental release, the toxicity and exposure of the flowback water components to the aquatic ecology were examined through ERA. Toxicity of each constituent of flowback water was assessed by developing species sensitivity distribution curves. An exposure model using dilution factor and adsorption coefficient of the flowback water constituents is proposed and risk quotient was used to characterize ecological risk. To demonstrate the methodology, a case study in Montney unconventional play in Northern BC was carried out. The risk to the aquatic ecology was found to be very low, however, scenario analysis and uncertainty analysis prove that the risk cannot be completely overlooked. A review of the regulations for storage systems was carried out and they were assessed in light of the results of the study. Enforcing regulations pertaining to the quality of water stored, citing of the storage system with respect to the water body and making secondary system mandatory were realized to be the most beneficial.

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