New Life For The Fishtail: The Diamond Drag Bit
Authors: Combes J.D. 
Published: December 2007

This paper is to be presented at the 39th Annual Fall Meeting to be held in Houston, Tex., on Oct. 11–14, 1964, and is considered property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Engineers or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in JOURNAL OF PETROLEUM TECHNOLOGY or SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted on request, providing proper credit is given that publication and the original presentation of the paper.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
Since late 1962 intensive field trials of the diamond drag bit have been conducted in the delta area of South Louisiana. Considerable experimentation has been done, principally in 9-7/8 in. hole sizes, and some excellent results have been obtained. Drag bit runs in the depth interval from 1,800 ft to 11,000 ft are compared to rock bit runs in the same interval and area. Best results seem to occur below the 6,500–7,000-ft range although some excel-lent shallower runs have been recorded. Bit weights of 10,000–15,000 lbs. with rotary speed of around 250 rpm appear to provide the best drilling performance. Hole deviation has not been a significant problem although several instances of hole deviation have been noted. This is similar to the hole deviation experiences with rock bits in this area.
Comparative drilling costs per foot for drag bits and rock bits have been compiled and plotted; the costs include bit cost and rig operating cost while rotating, tripping and circulating for trips. The resultant curves indicate that the average drag bit costs are significantly less than the average rock bit costs in the wells reviewed. Cost curves drawn using only the best recent rock bit runs and the average bit runs fell very closely together indicating the excellent overall performance of the drag bit. Further trials are in progress to ascertain the potentialities of this bit in deeper sections where some favorable runs have been recorded.
In addition to the cost reductions already cited, the drag bit offers the advantage of fewer bit runs, which is a significant factor in hazardous drilling areas.

Introduction
Since its introduction in late 1962 some 44 runs have been made using the diamond drag bit in the delta area of South Louisiana. Considerable savings have been effected in this program of cost reduction using both drag and rock bits. Early successes with the drag bit encouraged further trials to more fully evaluate its capabilities. Although additional experimentation will be required to fully explore the potential of the drag bit in this area, sufficient data is available for some conclusions to be drawn.

Summary
1. Drag bits are generally not competitive with rock bits in this area at depths shallower than 7500 ft.2. Hole deviation has not been a major problem with these bits although some difficulties have been experienced.3. Rotary speeds of 200 to 250 RPM are most advantageous.4. Bit weights of 10,000 to 15,000 lb were generally found best. Several excellent runs below 9,000 ft using 25,000-lb weight on bit were encouraging and further trials with this increased weight are in progress.