DTI defines a well to be a borehole drilled into the earth from a single surface or subsurface location to a single subsurface location. If the surface location changes but the target location stays the same then a new well is regarded as a respud of the first well. If the target location changes but the surface location stays the same the new well is called a geological sidetrack. If a sidetrack is made to bypass an obstruction while the surface and target locations remain the same this is called a mechanical sidetrack. A well may be drilled intentionally into an existing well. Wells include finder wells (cheap wells designed to gather minimum essential data), exploration wells, production wells, sidetrack wells, multi lateral wells.