When we hear the word ‘’Borehole’’ what comes to peoples mind most of the time is water. But the word Borehole is used by Engineers and environmental consultants to collectively describe all of the various types of holes drilled as part of a geotechnical investigation or environmental site assessment. This includes holes advanced to collect soil samples, water samples or rock cores, to advance in situ sampling equipment or to install monitoring wells.

The Kola Superdeep Borehole was the longest and deepest borehole in the world for nearly 20 years. In May 2008, a new record for borehole length was established by the extended reach drilling (ERD) well BD-04A, which was drilled by Transocean for Maersk Oil in the Al Shaheen Oil Field in Qatar. Transocean drilled a total length of 12,289 m (40,318 ft), with a record horizontal reach of 10,902 m (35,768 ft) in only 36 days.

On 28 January 2011, Exxon Neftegas Ltd., operator of the Sakhalin-I project, drilled the world’s longest extended-reach well offshore on the Russian island of Sakhalin. It has surpassed the length of both the Al Shaheen well and the Kola borehole. The Odoptu OP-11 well reached a measured total length of 12,345 m (40,502 ft) and a horizontal displacement of 11,475 m (37,648 ft). Exxon Neftegas completed the well in 60 days.

On 27 August 2012, Exxon Neftegas Ltd beat its own record by completing the Z-44 Chayvo well. This ERD well reached a measured total length of 12,376 metres (40,604 ft).

In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) in 1989 and is still the deepest artificial point on Earth.