A new computer technique has been developed for providing information on rotary drilling hydraulics. The computer program determines the proper bit nozzle size and pump operating conditions for all combinations of depth and mud density for a given hole size. By performing the calculations for all hole sizes used, the program completely defines optimum hydraulics for a given rig, making repetitive calculations for each well unnecessary.

The computer program presented was used to compare various published optimization procedures over a typical range of field conditions. The optimization procedures studied were

  1. establishment of maximum jet impact force,

  2. establishment of maximum bit horsepower,

  3. establishment of maximum nozzle velocity,

  4. establishment of known cleaning needs with the least pump horsepower expenditure, and

  5. pump horsepower expenditure, and

  6. establishment of optimum bit horsepower using the Economy Method.

The comparison includes differences among the procedures in pump cost as well as the differences in the hydraulic horsepower, jet impact, and nozzle velocity of the bit.


The development of the jet bit has been one of the most significant improvements in drilling technology. The main advantage of the jet bit is its higher efficiency in removing rock cuttings from the hole. Cuttings remaining on the bottom of the borehole will impede further penetration by the bit until they are removed. Wasteful regrinding is prevented if the fluid circulating past the bit removes cuttings as rapidly as they are formed.

In order to utilize the full potential of the jet bit, the proper potential of the jet bit, the proper nozzle size and pump pressure must be used. Figure 1, after Kendall and Goins, illustrates the large increase in bit hydraulic horsepower that can be achieved by the selection of a proper hydraulics program of bit nozzle proper hydraulics program of bit nozzle size and pump operating conditions.

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