Many oil and natural gas deposits are trapped in environments alongside water, and wells that are constructed to exploit these resources require techniques to handle the wastewater, also known as “saltwater,” “oilfield brine,” and “produced water,” that the extraction process brings up to the surface. Generally, the resources are mixed with the water and must be extracted. The remaining saltwater has to be carefully managed, and the Environmental Protection Agency places strict limits on its disposal. While companies are increasingly turning to injection wells, where the saltwater is recycled for use in extracting further natural gas or oil through hydraulic fracturing, the management of these fluids still requires care, and saltwater disposal wells have been designed specifically to contain them.
Generally, the goal of a saltwater disposal well is to ensure that the saltwater never interacts with the groundwater or the outside environment. In one state, Texas, the requirement for these kinds of wells states that three layers must be used: surface casing, production casing, and protection casing. The outermost layer, the surface casing, is steel and concrete that starts at the surface and descends all the way to the deepest groundwater layer. Next, the production casing takes the form of a pipe cemented to the wellbore, followed by the protection layer, with its injection tubing string. These components bring the water underground, where it remains safely stored in underground geologic formations.