By David Yoxtheimer
Hydraulic fracturing is necessary for development of the Marcellus shale natural gas as this process opens up fractures in the shale which allows the natural gas to flow to the well.
This operation involves injecting 5 to 10 or more million gallons of water, sand, and a small addition of chemical additives into the formation at high pressure.
After the injection is completed, approximately 5-10 percent of the fluids (known as flowback) initially return to the surface via the well prior to producing hydrocarbons. Therefore, a 5-million gallon hydraulic fracture stimulation might return 250,000 to 500,000 gallons of brine initially, but the wells will continue to produce 5-10 barrels of brine (known as production fluids) with every million cubic feet of gas for the productive life of the well.
The reuse of these return fluids by the drilling industry for subsequent hydraulic fracture treatments significantly reduces the volume of wastewater being generated by hydraulic fracturing. This brine can be treated and blended with fresh water and reused, which is what many companies are now doing to minimize the amount of water that would otherwise be potentially discharged to streams or rivers once treated. Greater than 90% of the return fluids are being reused in hydraulic fracturing operations, and the recycled fluids make up approximately 20% of the fluids used to fracture a well.
Currently, Pennsylvania Department of Environmental Protection standards dictate that any return brine must be treated to have a total dissolved solids (TDS) concentration of 500 parts per million prior to discharge into a stream or river via a permitted discharge, which occurs with about 5% of the fluids generated on a statewide basis. This treatment level is consistent with drinking water standards and currently only two treatment plants in Pennsylvania are designed to meet these standards, therefore TDS levels should not increase in surface waters to unacceptable levels through treatment and discharge practices.