The Effect of Circulating Media and Nozzle Design on Rock Bit Performance
- L.L. Payne (Hughes Tool Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1952
- Document Type
- Journal Paper
- 9 - 13
- 1952. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
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In an attempt to discover the effect of various circulating media and nozzledesigns on rock bit performance, a series of laboratory and field tests havebeen conducted. Although it is possible to conduct experiments in thelaboratory, actual conditions existing in the bored hole cannot be duplicated.Consequently, most laboratory results require confirmation from fieldapplication. However, notwithstanding the limitations, interesting andinformative results obtained from laboratory tests may aid in planning futureinvestigations.
Circulation of Air or Gas
Laboratory experiments conducted over several years proved that this type ofmedium was superior to a drilling fluid insofar as rock bit performance isconsidered. A special bit, mounted on a drill press and used for testingformation cores received from various fields, consistently indicated higherdrillability than actually obtained in practice. In the laboratory, air wasused to cool the cutters and to remove cuttings. Drilling was conducted underatmospheric pressure and this no doubt had a partial effect upon the morefavorable drilling rate obtained in the laboratory.
Extensive field tests were conducted in the fall of 1949 to determine therelative merits of circulating air compared to water while drilling a softlimestone encountered in a Michigan limestone quarry. The initial test ofcirculating air confirmed previous laboratory indications. On-bottom drillingtime per foot of hole was reduced 50 per cent compared to previous resultsobtained while circulating water. Bearing life materially increased whilecirculating air and the footage per bit was doubled over the results obtainedwith water. The on-bottom drilling cost per foot of hole was reduced byhalf.
A second field test was conducted in a Michigan dolomite quarry. On-bottomdrilling time per foot of hole was reduced by 20 per cent and the amount ofhole drilled per bit was doubled. A substantial reduction in total drillingcost per foot of hole resulted. The holes drilled vary in depth from 50 ft to120 ft. At these depths pressure on the formation differed only slightly whiledrilling with water or air. The results proved rather conclusively that whendrilling in the absence of sub-surface water flow a rock bit will performbetter with air used in the circulating system.
During 1950 a major operator became interested in circulating air onseismograph, rigs. Considerable difficulty had been encountered in Canadaduring the winter months because of the extreme cold freezing the circulatingfluid. Furthermore, in many areas a ready source of water is not available andmust be trucked to the rigs.
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