]> A borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes including the extraction of water or fluid (such as oil) or gases (such as natural gas or methane), as part of a geotechnical investigation or environmental site assessment, for mineral exploration, or as a pilot hole for installing piers or underground utilities. A bored, drilled or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension. The subsurface emplacement of "fluids" through a bored, drilled, or driven "well", or through a dug well, where the depth of the dug well is greater than the largest surface dimension.