Some of the fluid coats the fractures, or is lost into the natural fracture network of the rock. The fluids used in hydraulic fracturing vary from pure water to gummy gels. Other frac treatments contain various substances to improve the fluid's flow characteristics and effectiveness in fracturing the rock formation. While some additives may not be suitable for treatments in active aquifers, most are not toxic. All fracture treatments are designed such that the fluids are limited to the hydrocarbon zone being treated.
Fracture treatments vary from small to large.
Fluid volumes introduced range from a few hundred to over 100,000 gallons, and fractures may extend outward from the well for tens to over a thousand feet, and vertically over tens to hundreds of feet. Very few cases of lost fracturing fluid showing up in other wells have been reported. The Alabama case rested entirely on one or two claims of slight contamination in wells that have always yielded low-quality water. These wells were producing water directly from the coal seam that was the target of fracturing for coalbed methane production. Water wells in this area typically produce methane as an unwanted and potentially dangerous byproduct, regardless of hydraulic fracturing.