One facet of the US drive to seek energy independence is to increase oil and gas production in the states. The US has large reserves of oil and gas contained in geologic formations (shales, tight sands and coalbed methane). However they are hard to extract because of their poor flow rate caused by low permeability. One approach to converting these reserves to production is the expanded use of the fracking (induced hydraulic fracturing) technique. This technique propagates fractures in a rock layer by the use of a pressurized fluid. The fractures allow the trapped gases to flow to the wellbore and be extracted in a profitable manner .
The fracking process utilizes a well casing perforated in the zone that contains an oil or gas formation (zone of interest, ZOI). A fracking fluid, primarily water, is injected into the well and eventually builds pressure in the ZOI, thus cracking/fracturing the formation.
Naturally occurring sand grains, man-made or specially engineered proppants, such as resin-coated sand or high-strength ceramic materials like sintered bauxite, may to be used as part of the fracking fluid. These components remain in the ZOI to keep the fractures open. Some of the fracturing fluids are returned to the surface where they are stored in open pits or tanks for treatment or reuse. The amount of fluid that remains in a well vary depending on ZOI geology. This can be as much as 75% of the fluid.
The EPA has seen data that suggest that in fracking related situations enhanced migration of gas has occurred within ground water at depths used for domestic water supply and to domestic wells.
In a study of the Pavilion aquifer in Wyoming, constituents associated with hydraulic fracturing have been released into the Wind River drinking water aquifer at depths above the current production zone.
The study also detected high concentrations of benzene, xylenes, gasoline range organics, diesel range organics, and total purgeable hydrocarbons in ground water samples from shallow monitoring wells near pits. Thus indicating that pits are a source of shallow ground water contamination in the area of investigation. Pits were used for disposal of drilling cuttings, flowback, and produced water. Pits also represent potential broader contamination of shallow ground water.
The May 9, 2011 issue of “Proceedings of the National Academy of Sciences” discusses systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well.
While the above studies are significant, they raise many questions that need further investigation before appropriate mitigation can be successfully implemented. EPA is working with states and other key stakeholders to help ensure that natural gas extraction does not come at the expense of public health and the environment. Learn more here.
ProPublica is an independent, non-profit newsroom that produces investigative journalism in the public interest.Their work focuses exclusively on important stories that may affect the general public. They have conducted an on going investigation into FRACKING. Below is one of the stories in this instegative series.
Fluids From Marcellus Shale