Chemical Technology July 2015

WATER TREATMENT

be toxic to marine organisms [10, 11] and hence it is illegal for recovered waters from shales to be released into rivers or groundwaters. However, concerns still linger with regard to accidental spillage and exposure. In an attempt to eliminate exposure of waste produced water to the environment, companies use enclosed fluid capture systems. One common disposal practice in the Barnett Shale production area of Texas involves re-injecting the wastewater fluids back into the ground. Unfortunately, this is not a long-term solution, and it will be necessary to clean produced water for reuse in hydraulic fracturing. The chemical and physical characteristics of produced water from conventional and unconventional oil and gas reservoirs worldwide and the potential treatment options for the waters have been reported [12–14]. However, in most cases the organic content has been described by the total organic content (TOC) rather than the individual species present. A detailed study by Orem et al has investigated the identity of organic compounds in produced water for coalbed gas wells [15] but this source presents different issues to those

and the well begins to produce hydrocarbons, the water that comes to the surface is now called ‘produced water’. Generally this water has far lower or no amounts of the engineered components that were added to the frac water initially. However, the chemical make-up of the production water may still include quantities of chemicals and materi- als, such as inorganic salts, bacteria and organic molecules, with the organic molecules being either naturally occurring or a residue from the added components. Shale gas wells produce most of their water within the first few weeks of production. Subsequently, a few barrels a day are com- monly produced. Given that projections of cumulative net water used in all shale plays during the next 50 years totals 4 350 Mm³, there is an incentive to reuse frac flowback and produced water for hydraulic fracturing. Unfortunately, produced water is often unsuitable for reuse in frac fluids due to high dissolved salts and high organic content, including: hydrocarbons, greases, and biological matter. Furthermore, produced water discharges offshore have been shown to

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Chemical Technology • July 2015