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A wellbore is a hole drilled to access natural resources below the surface of the earth. Also known as a borehole, the hole can be dug by hand or with the use of mechanized equipment. Most are dug with drilling rigs, allowing people to drill deeply and quickly, as hand digging can be time consuming and very expensive.
One reason to create a wellbore is for the purpose of exploration. When people are looking for deposits of natural resources, they may have to sink an array of wellbores in order to find a reliable deposit. These holes are small and probes can be sunk to collect samples for analysis. Once exploration is complete, holes that did not bear useful deposits can be abandoned and covered or filled, depending on the policy preferred by the drilling company.
Other wellbores are used for active resource extraction. A water well is a classic example. After sinking several test wells to find the right spot, a permanent wellbore can be sunk to provide access to underground deposits of water. A pump is installed to pull the water up. Oil and gas wells are also widespread around the world, and people can use wells to access deposits of other kinds of underground resources as well.
Typically, some steps must be taken to make a wellbore safe and stable. As the hole is dug, casing is advanced to line the walls of the wellbore. This casing will keep the walls from collapsing, preventing damage to equipment, as well as human injuries to people who may be lowered into the hole to inspect it, clean it, or collect samples. Casing can include anything from concrete rings to simple tubing to house a drill, depending on the size and type of hole being dug. The location is also carefully chosen to avoid unstable pockets underground that might cause problems for personnel working on the wellbore.
For safety reasons, in many regions of the world, wellbores must be appropriately capped. For a well in active use, a drilling array or pump will include a covering housing. This prevents people and animals from falling in and will also control the release of gases and fumes in an emergency. For wells no longer in use, permanent capping or filling may be required, along with signage to warn people about the presence of a well so they can avoid it. Failure to secure a well can subject people to fines and other penalties, especially if someone is injured.