Chemical Technology July 2015

at equilibrium in the connate waters. After fracture treating shale, the recovered water volume peaks in a few days (5 to 15 days is common) and then sharply declines. This short- lived burst of water recovery describes a rapidly changing flow environment. When the salinity profile is compared, the produced water quickly moves from: a base frac fluid to a mixture of base fracturing fluid and connate water to a rich leachate and then sharply decreases in volume, salt and mineral content to a purer connate composition with very low recovered volumes. Our data highlights a few issues that should be taken into account when developing treatment strategies for frac and produced waters to allow for their reuse. The first issue is that unlike coal bed methane produced wa- ters, no polyaromatic hydrocarbons (PAH) are observed, meaning that the general toxicity of the produced (frac flowback) water is potentially lower for shale plays. This is important since many PAHs have serious health effects in the >0,2 µg L -1 level. The second issue is that while many of the chemicals used in the frac process are identified as being present in the produced water, they are lower in concentration than those that were naturally present in the connate waters within the shale. Thus, subsequent treatment of shale produced (and flowback) water should concentrate on the removal of saturates rather than the remaining aromatic, resin and asphaltene groupings. This analysis should also be used as a guide for creating a ‘standard’ or ‘idealised’ shale produced water so that the efficacy of any treatment may be measured. The presence of chlorocarbons and organobromides is, we believe, most probably due to the interactions of produced water with the salts used in hydraulic fracturing and drilling or the chemical treatments (and pre-treatment) of produced water. At present, due to the high bacteriological content of natural waters (and also produced water upon standing in ponds which is blended with ‘fresh’ water), chemical treat-

Figure 3 The relative saturate, aromatic, resin and asphaltene (SARA) composition for produced water: (a) neutral and (b) acid extraction.

since chlorocarbons are considered an environmental pol- lutant. As with chlorocarbons, the presence of quantities of organobromides has a potential health effect since they cause malfunctioning of the nervous system and cause damage to organs such as liver, kidneys, lungs, and cause stomach and gastrointestinal issues [30]. Conclusions What are the implications for shale gas produced water treatment? In presenting the variation in composition and particular chemicals analysed, we can make a number of statements about produced water from shale gas wells with regard to re-use and disposal, as well as guide research- ers in future treatment efforts. In particular, given the salt content correlates with the concentration of hydrocarbon, it will be important to determine if the salt content and ion ratios within actual shale connate waters (water trapped in rock pores containing mineral ions) provide a link to explaining the presence of higher concentrations of some of the organics that are observed. The low permeability nature of shale means that when they are introduced to under-saturated water, solubilisation will occur of salts, organics and other minerals that were

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Chemical Technology • July 2015