1. n. [Drilling]

An inexact term describing a borehole (and associated casing program) significantly smaller than a standard approach, commonly a wellbore less than 6 in. in diameter. The slimhole concept has its roots in the observed correlation between well costs and volume of rock extracted. If one can extract less rock, then well costs should fall. One form of slimhole work involves using more or less conventional equipment and procedures, but simply reducing the hole and casing sizes for each hole interval. A second form involves technology used for exploration boreholes in the hard rock mining industry. In the mining rig operations, the drillstem serves a dual purpose. After the hole is drilled, the drillstem remains in the hole and is cemented in place. Then a new drillstem is used for the new hole section, and also cemented in place. The drillstring for mining rig operations is rotated like that for conventional oilfield rotary rig operations, but typically at a much higher speed.