Active reduction of tool borne noise in a sonic logging tool

Abstract From the Canadian patent

A sonic logging tool that can be positioned within a fluid-filled borehole includes an axially distributed active vibration control system to reduce tool borne noise. The tool includes an acoustic transmitter an axial array of acoustic receivers, and actuator assemblies that are coupled to cancel tool mode vibrations at stations along the receiver section of the tool. In a preferred embodiment force is applied in feedback mode based on tool mode vibrations sensed at each station. The force at each station is applied by a real-time computational algorithm using feedback. The feedback includes weighting to accommodate monopole or dipole tool mode vibration. The computational algorithm …