Highly Deviated and Horizontal Wells

The tools and techniques discussed in earlier chapters are normally used to drill directional wells whose maximum inclination is about 60°. Highly deviated wells may be described as those wells whose inclination exceeds 60° for most of their length. It is possible to extend directional drilling techniques to increase the inclination to 60–90°, although alterations may have to be made to drilling practices. Modifications to standard rig equipment may also be necessary to drill these high-angled wells successfully. A horizontal well may be defined as a well which is drilled to an inclination of 90°, and maintains this inclination for a significant distance. Owing to the need for special equipment and the longer drilling times that must be expected, horizontal wells are considerably more expensive than conventional deviated wells.