Deep-well drilling costs can be reduced substantially by using higher mud pump pressures. This has been demonstrated during the drilling of 1267 m (4166 ft) of 12 1/4-in. and 8 1/2-in. hole with a land rig, using pump pressures approaching 35 MPa (5000 psi) over a period of six weeks. Drilling costs were reduced by 25 percent (approximately $134,000) in the test well as a result of the higher pressures. The tests used drilling bits which combined mechanical and jet action, viz., extended-nozzle bits and a diamond bit designed to withstand the increased mud velocities. Both types of bits gave significantly improved performance when used at the higher pressure. Further tests were made with standard downhole turbines driving conventional bits. Improved performance was achieved at the higher pressure, provided the correct bit was selected for the formation encountered. In these cases the increase in penetration rate was due to the higher mechanical power developed by the turbine rather than increased jet action at the bit. Of the four turbine runs, two were found to be more economic than rotary runs made in similar formations in the reference well. The high-pressure mud pumps and other conventional equipment used in the tests performed well at the 35 MPa (5000 psi) pump pressure. Two standard triplex mud pumps were provided with fluid ends of an Exxon Production Research design and manufactured in Germany under Shell supervision. No failures occurred during six months of operation and in general, the equipment performed with the same downtime at the high pressure as the conventional equipment used in the reference well at the usual operating pressure (21 MPa (3000 psi)).

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