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PublisherAmerican Petroleum InstituteLanguageEnglish
Document ID 50-061
Content TypeConference Paper
TitleFactors Affecting the Rate of Penetration of Bits
AuthorsW.J. Bielstrein and George E. Cannon, Humble Oil and Refining Co.
SourceDrilling and Production Practice, 1950
Copyright1950. American Petroleum Institute
PreviewABSTRACT

Preliminary tests to determine the effect of various factors affecting the rate of penetration of rock bits are recorded. The importance of the number and design of cutting elements in rate of penetration is established in the limited tests. Findings also indicate that the magnitude of the various effects on the rate of penetration varies with changes in the type of formation drilled. The effect of hydraulic factors affecting the rate of penetration is explored with definite advantages determined for increased circulation rate, high fluid-velocity nozzles directed to the bottom of the hole, and the utilization of these nozzles to produce high nozzle-fluid velocities at the bit. A nozzle design for increasing the efficiency of nozzles has been established to provide for allocating more of the available hydraulic horsepower to increasing penetration rates. Effects of rotary speed and bit weight were investigated, and it was found that the rate of penetration increased with increasing rotary speed and bit weight, with the rate of change in the two factors being principally a function of the formation being drilled.

In a series of papers1,2,3 resented by members of the staff of the Petroleum Engineering Division of the Humble Oil and Refining Co. during 1948 and 1949, it was shown that the rate of penetration with two-way drag-type bits was related to certain hydraulic factors. A mathematical analysis of these hydraulic factors showed that their effects on drilling rate could be reduced to generalized equations. Several excellent articles4,5 on the factors affecting the rate of penetration of rock bits have been presented during the past Few years. In general, however, the data presented were based on laboratory studies, using either full-scale or miniature bits to drill either a few inches or a few feet of hole.

The tests described herein were conducted in drilling wells. Every effort was made to select formations of uniform drill ability and to evaluate only one variable at a time. Because of the wide variation in the hardness or drill ability of the formations normally drilled with rock bits, it probably will be impossible to reduce the factors affecting the rate of penetration to one set of generalized equations. However, laboratory data published in the past4,5 and the data in this paper show that the operator can take advantage of numerous physical and hydraulic factors to increase the rate of penetration obtained with rock bits.

This investigation of the factors affecting the rate of penetration of rock bits was divided into three parts: 1, the effect of bit design from the standpoint of number of cutting elements and distribution of fluid with respect to the cutting elements and the bottom of the hole; 2, the evaluation of the hydraulic factors affecting the rate of penetration: and 3, the effect of rotary speed and bit weight on the rate of penetration. To date tests, have been confined to formations which might be classified as the softer rocks which, in most cases, cannot be economically drilled with drag bits, and to formations classed as medium hard and nonabrasive. In tests where other factors were investigated, the tooth design of the bit cutting elements was the same as for conventional bits used in drilling the particular types of formations.

BIT DESIGN

Investigations of bit design were confined essentially to bits having various numbers of cutting elements and to modifications to change the distribution of circulating fluid at the bit. Several tooth designs of the cutting elements were investigated to determine their relative merits.
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