In Kentucky, most gas wells are drilled using pressurized air circulated through the drill pipe (not water) and hydraulic fracture stimulation of natural gas wells is accomplished using nitrogen as the main ingredient. The nitrogen is mixed with a relatively small amounts of water (i.e., several thousands of gallons and not millions) to create a foam that is more efficient in delivering sand to prop open the induced fractures than is straight nitrogen. Most of the water issues associated with natural gas development have to do with hydraulic fracturing (using water) of shale gas wells. Kentucky is pretty much an exception to the general case outlined as follows.
There are two primary water issues in natural gas development: water supply and water quality. In drilling for natural gas (or oil) there is often a surface disturbance similar to a construction site during active drilling and completion. Existing laws cover such things as management of surface runoff and the protection of underground sources of drinking water (USDWs). In most states, USDWs are protected by requiring the installation of pipe in the well (“casing”) that is cemented back to surface specifically for this purpose. Additional strings of casing are installed, each one nested within the previous string, as the well deepens and is required to seal the well from unwanted fluid (brines) entry, maintain integrity of the bore hole, and facilitate isolating the producing zone. Where water-based frac fluids are used, treatment volumes are typically 3 to 5 million gallons per well and can be greater. This can be burdensome on many rural water systems as you generally need treated water; raw water withdrawn from local creeks and ponds contains too much bacteria and other potential pollutants to be effective (too many uncontrolled variables). Fracture stimulation treatment volumes are typically 95.5% water, 4% sand, and the rest additives. Typical additives are used to prevent scale and corrosion of the pipe in the well, reduce friction, increase viscosity (carry sand more effectively), prevent bacterial growth, and acids to help open the induced fractures (brick cleaner/muriatic acid).
Now we get to the meat of the controversy. The first is what are these chemicals? If you google “what’s in frac fluid” you’ll find lists of these chemicals posted by Halliburton, Chesapeake, EQT, and other companies. And, yes, a check of the MSDS shows some are pretty nasty. This brings up the second part of the controversy which is that this is somehow unregulated. The injection of this fluid mixture for the purpose of inducing fractures in an oil or gas reservoir to stimulate production is not regulated under the Underground Injection Control (UIC) provisions of the Safe Drinking Water Act. This is mainly because, especially in a gas well, the fluid is injected, and then as much as possible is removed from the underground reservoir so that gas may be produced. What is regulated under the Clean Water Act and Amendments is the treatment and disposal of the used frac fluid when it is brought back to the surface. The spent frac fluid must either be treated, a potential burden to local waste water treatment facilities, or it must be disposed of in a permitted disposal well (i.e., permitted as an EPA Class I UIC disposal well).
Problems with this fluid can occur if there is a spill, the induced fractures could communicate with pre-existing wellbores, fractures, or faults and reach shallower USDWs, or the stimulation could “go out of zone”, fracture the reservoir seal, and propagate upward to USDWs. It is also possible that the casing in the well could be poorly cemented and the fluids under pressure could migrate upward along the wellbore itself. There are several tools for the simulation and design of fracture stimulation treatments and tools for realtime monitoring of the progress of the stimulation while it is being pumped.
Information provided by the Kentucky Geological Survey.