| 摘要 |
Multistate mud pulsing is achieved by generating both positive and negative pulses within a drill string by means of a plurality of selectively operable bypass passages around a restriction to primary mud flow within a drill string or by venting to outside of the drill string. A fraction of the hydraulic mud is drawn from a location upstream from the restriction into a valve manifold. The removed fraction of hydraulic mud is selectively communicated from the valve manifold either to a point inside a drill string downstream from the restriction or to a point exterior to the drill string in annulus between the outside of the drill string in the borehole. Mud reinjected downstream from the restriction creates a positive pressure pulse within the drill string. Mud which is diverted to the annulus outside of the drill string creates a negative mud pulse within the drill string. Selective activation of valving for distributing the mud downstream from the restriction or to the exterior drill string annulus allows the apparatus to used as a simple positive pressure pulse telemetry system, a simple negative pressure telemetry system or a multistate mud pulse telemetry system. A system capable of three or four state telemetry is comprised of a single bypass passage for diverting a portion of hydraulic mud from the main flow in the drill string, and a single bypass passage for recombining it with the main flow downstream from the restriction within the drill string. Depending upon nonsimultaneous or simultaneous operation of the passages, a three or four state telemetry system is provided.
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