The principle of rotary screw air compression is really no different than reciprocating (piston) compression. Both are positive displacement machines that take in a fixed volume of air at atmospheric press.
[pdf] An automated drill rig (ADR) is an automated full-sized walking land-based drill rig that drills long lateral sections in horizontal wells for the oil and gas industry. ADRs are agile rigs that can move from pad to pad to new well sites faster than other full-sized drilling rigs. Each rig costs about $25 million. ADR is used extensively in the . According to the "Oil Patch Daily News", "Each rig will generate 50,000 man-hours of work during the construction phase and up. The oil rig count is currently 411 rigs, compared to 438 in June and 483 one year ago. The gas rig count is 122, compared to 111 in June and 97 last August. In the major plays, the Permian Basin rig count is at 255 rigs, 16 fewer than June’s count.
[pdf] Stand-alone, information-packed chapters of the 12th edition of the definitive rig operations manual, the new IADC Drilling Manual, are now available in convenient electronic form. More than 100 renowned technical experts contributed to the first major rewrite of the IADC Drilling Manual in 22 years.
[pdf] 
