Facilities: Carleton University Vertical Flare Facility
Hydro-fracturing, i.e. the process of stimulating well-production by injecting mixtures of water, proprietary chemicals, and particles into boreholes to create fractures in oil- and gas-bearing formations, has become the dominant method of extracting unconventional natural gas sources such as tight gas and coal-bed methane. Once a well is fractured, prior to the start of production, the injected liquids must be cleared from the well. This “flowback’” process may extend for several days to weeks, during which time the liquids (water, and fracturing, and formation fluid) are ideally separated from the released gases, and this gas stream is commonly directed to a flare system. In Alberta, flare volumes during flowback average 113,200 m3 but may be more than 8 times higher than this at individual wells.
The basic composition of injected fluids is a water-based mixture of sand, acids, biocides, surfactants, corrosion and scale inhibitors, and a variety of chemicals used to alter fluid properties. Additionally, it is common to flush wells with high-pressure hydrochloric acid (3%-28% solution) prior to the injection of fracturing fluids. Limited data suggest chloride (Cl-) is by far the most common anion in flowback liquids, and is an accurate predictor for the total amount of dissolved solids . Concerns arise if flowback fluids become vaporized or aerosolized during the separation process and mix with the gas being directed to a flare, where, in addition to impacts on flare efficiency and formation of BC, there is the special concern regarding the potential emission of chlorinated hydrocarbon species (e.g., dioxins and furans).