This report develops a simple method for determining the combination of weight-on-bit, rotary speed and hydraulic horsepower which produces minimum drilling cost. Empirical relationships are developed to show the influence on penetration rate of weight-on-bit, rotary speed and hydraulic horsepower. Optimum weight-on-bit is shown in relation to formation drill ability, and optimum rotary speed is related to weight-on-bit. These five relationships are then combined into a chart for determining optimum drilling techniques from a minimum of field test data.

Secondary issues discussed are: Advantages of the jet bit over the regular bit and minimum nozzle fluid velocity requirements for jet bit use relative to formation drill ability; and distribution of pump horsepower into nozzle fluid velocity and circulating volume.


The wide variations in drilling conditions encountered in oilfield work make it difficult to develop general rules of operation for obtaining maximum drilling efficiency. Field experience and test data usually provide the basis for operations in a particular locale, but testing often is too costly and experience too late. Consequently, a method for determining optimum drilling techniques for any particular drilling condition, with a minimum of engineering effort and drilling experience, is greatly needed.

To assist in developing such a method is the purpose of this report. It is recognized that sufficient drilling information has not been accumulated to accomplish this ambitious job without some shortcomings along the way. It is believed, however, that the method proposed is flexible to improvements which are sure to be made, and that ultimately the purpose of the report will be accomplished more comprehensively through a combined effort of interested parties.

Controllable Factors That Affect Bit Performance

Drill bit performance depends primarily on five controllable factors:

  1. Weight-on-bit,

  2. rate of rotation,

  3. hydraulic horsepower,

  4. type of bit, and

  5. properties of the circulating medium.

Although each parameter contributes individually to bit performance, they are closely interrelated and their combined influence governs the degree of drilling efficiency obtained. The influences of circulating media have been covered in literature and will not be discussed herein.

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