In a hydraulic fracturing job, "fracturing fluids" or "pumping fluids" consisting primarily of water and sand are injected under high pressure into the producing formation, creating fissures that allow resources to move freely from rock pores where it is trapped.
Typically, steel pipe known as surface casing is cemented into place at the uppermost portion of a well for the explicit purpose of protecting the groundwater. The depth of the surface casing is generally determined based on groundwater protection, among other factors. As the well is drilled deeper, additional casing is installed to isolate the formation(s) from which oil or natural gas is to be produced, which further protects groundwater from the producing formations in the well.
Casing and cementing are critical parts of the well construction that not only protect any water zones, but are also important to successful oil or natural gas production from hydrocarbon bearing zones. Industry well design practices protect sources of drinking water from the other geologic zone of an oil and natural gas well with multiple layers of impervious rock.
While 99.5 percent of the fluids used consist of water and sand, some chemicals are added to improve the flow. The composition of the chemical mixes varies from well to well.