Hydraulic fracturing (also fracking) is a well stimulation technique in which rock is fractured by a pressurized liquid. The process involves the high-pressure injection of 'fracking fluid' (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely.
Hydraulic fracturing began in 1947 as an experiment and the first commercially successful application followed in 1950. As of 2012, 2.5 million "frac jobs" had been performed worldwide on oil and gas wells; over one million of those within the U.S. Such treatment is generally necessary to achieve adequate flow rates in shale gas, tight gas, tight oil, and coal seam gas wells. Some hydraulic fractures can form naturally in certain veins or dikes.
Hydraulic fracturing is highly controversial in many countries. Its proponents advocate the economic benefits of more extensively accessible hydrocarbons. Opponents argue that these are outweighed by the potential environmental impacts, which include risks of ground and surface water contamination, air and noise pollution, and the triggering of earthquakes, along with the consequential hazards to public health and the environment.
Suspended solids removal is typically the first step in the treatment of the flow back water and can employ a number of chemical, physical and/or biological methodologies including, but not limited to settling, filtration, electro-coagulation and precipitation. Electro-coagulation results in a combination of solids that can be skimmed from the water surface and heavier solids that can be filtered or centrifuged off. Chlorine dioxide oxidation is utilized to breakdown oil/grease emulsions, destroy various chemical additives, kill bacteria and oxidize reduced compounds like iron to form non-soluble compounds. Chemical precipitation/clarification removes inorganic scale forming compound like barium, strontium, metals, etc. Controllers are being used at a number of sites to control electro-coagulation systems and chlorine dioxide generators and are also utilized as part of an overall system for chemical precipitation/clarification processes along with metering pumps for maintaining pH, ORP and feed coagulants/flocculants to the system at various stages of the process.
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