Hydraulic Fracturing and Waste Water Treatment - Part 1
The US Energy Information Administration estimates that US potential natural gas resources total 2543 trillion cubic feet (tcf), with shale gas deposits contributing 862 tcf (34 percent) of this total. At 2010 consumption rates (about 24.1 tcf), the estimated reserve could supply more than 100 years of use. In the eastern US, the Marcellus shale formation extends from New York through Pennsylvania, western Maryland, virtually all of West Virginia, and includes portions of western Virginia and eastern Ohio, and is generally 4000-8500 ft below ground surface. This is far below the aquifers that supply well-water for drinking. It is estimated by researchers Terry Englander, a geoscience professor at Pennsylvania State University, and Gary Lash, a geology professor at the State University of New York, to contain about 50 tcf of recoverable natural gas.
As with any resource extraction activity, concerns have been expressed regarding the procedures used and their actual or potential environmental impacts. In the case of shale gas production, a major concern is related to the hydraulic fracturing used to open cracks in the shale which allow the natural gas to be more efficiently collected. A central focus is on both the volume of water needed for the “fracing” process, the chemicals used, and the potential for groundwater contamination and spills of the waste water water to surface streams and rivers.
The hydraulic fracturing process injects water, sand, and other ingredients at very high pressure into the well. The high pressure creates small fractures in the rock that extend out as far as 1,000 feet away from the well. After the fractures are created, the pressure is reduced. Water from the well returns to the surface (known as flowback), but the sand grains remain in the rock fractures, effectively propping the fractures open and allowing the gas to move. Most frac fluid used in shale gas wells consists of water, a proppant (generally sand), a friction reducing agent (to help the flow-back water return from the well at the end of the frac job), and other chemicals used to protect the well and to optimize performance.
The US Department of Energy estimates that for a typical well in the Marcellus formation, 80,000 gallons of water are needed for well drilling, and 3.8 million gallons for fracturing. Water and sand comprise more than 98 percent of the fracing fluid. 30-70 percent of the fracing fluid returns to the surface as flowback. Thus, there is a large volume of contaminated water from each natural gas well that must be treated in some fashion.
In my next post, we’ll review recent innovations found in Way Better Patents Water Index that apply to the water used in hydraulic fracturing operations.