John D. Deane & Harold H. Doiron, Reed Rock Bit Co.
A method is presented for optimizing roller cone bit hydraulics programs to provide minimum cost per foot drilled. The method differs from traditional optimization techniques in that optimum pump operating conditions are determined rather than being arbitrarily imposed as a constraint on the optimization process. The method considers rate of penetration (ROP) response to increased bit hydraulic horsepower (BHHP) as well as increased fuel and pump maintenance costs to provide increased BHHP. Optimum conditions may be determined through a parametric analysis or by imposing simple relationships between pump fuel and maintenance costs and ROP response to increased BHHP. Full scale laboratory drilling data under various overbalance pressure conditions are presented to demonstrate the relationship between ROP and BHHP. Laboratory and field results with blanked nozzles and asymmetric three nozzle configurations are also presented.