Wells
Wells are structures created by boring holes into the ground to extract or inject fluids, playing a crucial role in accessing resources beneath the Earth's surface. Historically utilized primarily for extracting groundwater, wells now serve a variety of functions, including the production of oil, gas, and even the disposal of hazardous waste. The construction process of wells has evolved from manual excavation to sophisticated mechanical methods, with the choice of machinery dependent on the required depth and geological conditions. Wells are typically lined with casing materials—plastic for shallow wells and steel for deeper ones—to prevent structural collapse and contamination. The perforated section of the casing, known as the screen, facilitates fluid exchange with surrounding rock, while gravel pack and impermeable grout are used to protect the well from surface pollutants. The significance of groundwater sourced from wells is substantial, as it supports domestic, agricultural, and industrial needs, although it is vulnerable to contamination from various sources like pesticides and industrial waste. Overall, wells are essential for resource extraction, but their construction and use must be carefully managed to mitigate environmental impacts.
On this Page
Subject Terms
Wells
DEFINITION: Holes bored into the ground to extract or inject fluid
Wells serve an important purpose in enabling the extraction of fluids from beneath the earth’s surface, but sometimes the processes involved in boring wells can contribute to environmental degradation, such as through habitat destruction and water pollution.
The earliest wells were excavated by hand, and over time various mechanical methods have been developed for boring into the ground. The machinery used to create wells in the modern world depends on the depth desired and the types of rock through which the drill must bore. The borehole is cased with plastic pipe in shallow wells and steel pipe in deep wells to prevent caving of the walls. The casing is perforated at the depth from which production occurs. This section, called a screen, allows an exchange of fluid between the casing and surrounding rock. The space between the screen and the surrounding rock is filled with gravel to allow fluid to flow freely between the well and the aquifer. The space between the casing and the exposed rock in the upper part of the well is tightly sealed with impermeable grout to prevent contaminants from entering the bore from the surface.
Wells were originally used only to extract underground water. Today they serve many purposes, including extraction, injection, and of fluid below the surface. Water wells and oil wells are examples of producing wells that extract fluids from the subsurface. A typical draws water either from the surface or from deeper, confined aquifers. Oil and gas wells produce from deep rock strata. Wells are also used to remove contaminated and dewater saturated zones in which construction or other activity extends below the water table.
Injection wells are used to introduce fluids into the subsurface. They are used as a way to store water that could otherwise be lost to high evaporation rates or runoff. Oil is occasionally pumped into subsurface, impermeable salt caverns for storage. To increase production in an oil well, water or gas may be pumped into oil-bearing strata to displace the oil. One means of disposal of hazardous wastes is to inject them into deep levels of the earth’s crust. Monitoring wells are used to determine variations in depth to the and to provide early warning of the migration of hazardous fluids. Frequent tests of monitoring wells are required around sites of potential groundwater contamination.
Groundwater is a major source of water for domestic, agricultural, and industrial use. It exists in the subsurface, filling pores and cracks in consolidated rocks and loose, unconsolidated sand, gravel, clays, and mixtures of these materials. The surface aquifer is the saturated zone that receives water by down from the surface. This is the zone most susceptible to contamination by toxic substances from industrial and municipal wastes, feedlots, septic tanks, crop fertilizers, pesticides, and herbicides. Confined aquifers are less susceptible to contamination because they are sealed from surface percolation by overlying impermeable beds. Confined aquifers can be contaminated when they are exposed to direct recharge or by boreholes that reach them from the surface. Disposal wells with corroded casings may serve as conduits for into subsurface water supplies. Improperly grouted wells may allow surface contamination to infiltrate water supplies through along the outside of the casing.
Bibliography
"Learn About Private Water Wells." US Environmental Protection Agency (EPA), 22 Feb. 2024, www.epa.gov/privatewells/learn-about-private-water-wells. Accessed 24 July 2024.
Leys, Tony. "Millions of Americans Rely on Private Wells. Few Test Their Water." KFF Health News, 24 Oct. 2023, kffhealthnews.org/news/article/rural-america-private-water-wells-bacteria-nitrates-pfas-testing/. Accessed 24 July 2024.
Misstear, Bruce, David Banks, and Lewis Clark. Water Wells and Boreholes. Hoboken, N.J.: John Wiley & Sons, 2006.
Sipes, James L. Sustainable Solutions for Water Resources: Policies, Planning, Design, and Implementation. Hoboken, N.J.: John Wiley & Sons, 2010.