Two conventional 7-7/8 inch diameter natural stone surface set diamond bits were instrumented and used to drill shale in controlled laboratory tests at simulated conditions. The designations assigned to these bits in accordance to the International Association of Drilling Contractors are D333 and D323. The D333 bit is recommended for soft to medium formations whereas the D323 bit is recommended for medium to medium hard formations. Each bit has a different hydraulic design. The D333 is a radial flow design, whereas the D323 has a forced flow or "feeder-collector" hydraulic design.

Miniature pressure transducers were mounted at different locations on the bit crowns. While drilling under a wide range of simulated conditions, output from these transducers were recorded. From this data, an understanding of the magnitude and distribution of pressures at the bit face was obtained. An analysis of the data showed that a substantial amount of hydraulic energy is expended at or near the crowfoot or center of the bits. Also, an estimate of pump-off force (or hydraulic lift) as a function of pressure drop was obtained from the pressure distribution data. The work presented in this paper was sponsored by the Department of Energy, Office of Fossil Energy, Bartlesville Energy Technology Center in Bartlesville, Oklahoma.

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