No hydraulic system, however large, can be effective unless it ensures delivery of sufficient horsepower at the bit, where it can perform useful work. perform useful work. A numerical relationship is developed and computer plots presented, showing the critical dependence of bit hydraulic horsepower on pump operating pressure for selected combinations of variables.

The need for raising pressures is indicated for deeper wells, where the bit is remote from its source of hydraulic supply. Other factors shown to be of prime importance in determining pressures levels are pipe size, mud density and hole size.

The choice of nozzle diameter combination is less critical than is often supposed. A simple method of choice., due to Goins, is discussed and recommended. With this method, choice virtually depends only upon hole size and pump operating pressure, and the selection remains unchanged until one or another of these criteria is changed. Validity can be readily checked at the rig. A simple tabulation is available to the driller or the tool pusher. Results are proven to be within 96 to 100 percent of absolute optimum. percent of absolute optimum


A hydraulic system in a rotary drilling rig is relatively wasteful of power. For example, it would not be unusual for a pump receiving mechanical energy at the rate of 1,000 hp to deliver not more than 750 hp to the hydraulic system, of which only about 400 hp is actually being used in hydraulic jetting action at the bit.

If such a system, normally wasteful of power, is also operated inefficiently and power, is also operated inefficiently and without proper engineering foresight, it would not be surprising to find the bit action starved of hydraulic power, and the drilling capabilities of the rig seriously curtailed.

This paper will examine the important factors controlling efficiency of the rig hydraulic system, and indicate how these factors should be adjusted to provide reasonably high efficiency with a reasonable economy of engineering effort.

Survey of the System

Fig. 1 shows the rig hydraulic system in diagrammatic form.


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