The need for more compact, safer, more efficient, more flexible drilling rigs, with reduced costs in hole-making, has produced a number of approaches to the solution of these problems. One approach is a hydraulic semiautomatic drilling rig using a hydraulic power swivel mounted on a special mast fitted with tracks for a travelling block and the swivel, along with hydraulic power tongs and back-up tool, air slips, and hydraulic pipe-handling equipment. This rig, which can be operated by two men, has been field tested and it has proven to be highly flexible, mobile and efficient in the drilling and coring of medium-depth and shallow holes and in workover operations.


As in the case with much other oil and gas industry equipment, the semi-automatic rig discussed in this paper did not have its beginnings as a drilling rig. However, the principal elements - the hydraulic power swivel and hydraulic hoist - were developed initially as drilling tools.

Current development of the hydraulic power swivel, plus the combination of it with both standard automated rig equipment and specially fabricated equipment for pipe handling, all mounted in compact unit fashion, has provided the drilling industry with a new drilling tool and a new concept—a semi-automatic rig for medium depth drilling with a two-man crew.


The initial development work on the hydraulic power swivel and hydraulic hoist was done in 1955 by Paul Scott in Michigan. By late-1958, the PS-200 model swivel, a predecessor to current and more efficient models, was designed.

Initial use of the power swivel was in coring operations on holes drilled with cable tools in Michigan, with uses expanding to some drilling operations in those holes. Power swivel use progressed to the drilling of up to 15-in. diameter surface holes in glacial drift formations.

During field testing on 30 different wells in North Louisiana, a power swivel drilled some 75,000 ft of 6-1/4-in. and 7-7/8-in. diameter holes to maximum depth of 3,700 ft with no stuck drill stem or twist-offs experienced. Drilling rates, under a variety of conditions over a wide area, averaged 37 ft/hr on a number of the holes with the low experienced of 16.4 ft/hr and the high 100 ft/hr.

Equipment used in the 30-well field test program included a Model 100 power swivel, an Emsco D-175 slush pump, 2-7/8-in. drill pipe, and a Woodfield [H-25] drawworks mounted on a Leland well service unit truck.

Still another field test was a 4-3/4-in. diameter slim-hole test drilled to 4,800 ft in South Texas using a trailer-mounted Model 100 power swivel for rotation.

During development of the hydraulic semi-automatic rig, two trailer-mounted hydraulic power swivel rigs, capable of drilling holes at as high as 30 degrees from the vertical, were assembled, tested and delivered to the Atomic Energy Commission. Used in post-shot operations for rapid recovery of sub-surface samples as soon as possible following underground nuclear test explosions, the two rigs presently are rated as the most efficient found for that purpose.


Reduction of operating costs was one of the primary considerations in the development of the hydraulic semi-automatic rig, with particular consideration of reduction of rig-crew size, weight of drilling equipment, and of rig-up and tear-down time.

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