The term \u201cdrilling\u201d related to a well indicates the sequence of operations, tools and materials required to construct a circular borehole in the subsoil for geological exploration purposes or for the production of underground fluids such as hydrocarbons, groundwater, geothermal fluids, etc. A well is drilled by applying technologies not requiring direct access by man at the bottom of the borehole. Any drilling technology is based on the application of the following basic actions: a) overcoming the resistance of the rock at the bottom hole, crushing it into millimeter or sub-millimeter particles (cuttings); b) removing the cuttings from the bottom hole; c) ensuring the mechanical stability of the borehole walls; d) preventing the underground fluids contained in the drilled formations from entering the well.
The above actions can be achieved by various drilling technologies, developed throughout the last two centuries. However, this study illustrates the principles of rotary drilling, so far the most developed technology and the only one utilized in the field of oil and gas exploration and production. In particular, this chapter illustrates the operations, tools and materials employed in rotary drilling rigs utilized on shore. The drilling rigs used on shore are modular equipment which can be moved from a drill site to another in a reasonable short time, from a few days to weeks. Offshore drilling follows the same basic principles, tools and materials deployed on shore, but they are configured with a number of different drilling systems to suit operations in the marine environment. Normally these rigs are self contained aboard of a floating vessel
