| 摘要 |
A drillstring pressure-modulation valve is disclosed which is usable in combination with a downhole drilling motor and a drillstring thruster to compensate for changes in pressure drop through the drilling motor which normally occur during drillin g. When conditions chnage during drilling, which in turn changes the pressure drop through the drilling motor, the drillstring pressure-modulation valve compensates for su ch changes to minimize the effect of such changes on the operation of the thruster and the resulting WOB created by the thruster. The modulation valve has a feature which allows it to find automatically a balanced preload condition for the main needle valve, the primary functional element within the modulation valve, each time the rig pumps are turned off and then turned on. The modulation valve is fully self-contained, and is assembl ed as part of the bottomhole assembly. The device senses the no-load pressure drop in the system and sets itself each time the rig pumps are turned on to compensate for any change in the no-load pressure drop experienced below the device which could be attributab le to such things as motor wear, bit nozzle plugging, or changes in the flow rate. Accordingly, the hydraulic thrusting force remains constant over a wide range of drilling environments. As thedrilling conditions change and the pressure drop in the downhole motor increases, the needle valve shifts to compensate for such additional pressure drop with a resultant small or no effect on the thruster and the resulting WOB created by the thruster located upstream of this modulation valve.
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