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Abstract

A method and apparatus for communicating with a device downhole in a well, such as a bottom hole assembly in a drill string. Pressure pulses, such as those generated by the pistons of the mud pump, are transmitted through the drilling mud to a pressure pulsation sensor in the bottom hole assembly. The pressure pulsation sensor features a piezoceramic element that generates a varying voltage signal in response to the received pressure pulsations. The pressure pulsation sensor also has electronic components that allow it to analyze a characteristic of the pressure pulsations, such as their frequency. Based on its analysis of the pressure pulsations, the sensor can decipher a command from the surface, for example, that directs the steering of a steerable drill string, or that can determine whether the mud pumps are operating. If the mud pumps are not operating the sensor directs a microprocessor to reduce power to the bottom hole assembly electrical components, such as a measurement while drilling tool, thereby conserving battery power. The method and apparatus can also be used to control the operation of flow control valves in a multilateral well.

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First Claim