Acoustic formation logging tool with improved transmitter

Abstract

An acoustic formation logging tool includes a transmitter, a receiver, a tube wave absorber, and a digital signal processing section. The transmitter includes an electromagnetic actuator based on capacitive discharge through a coil, producing an intense magnetic pressure which causes an actuator to move into an oil-filled acoustic waveguide. The actuator includes a pusher plate with holes that reduces cavitation and is capable of operation at great depths commonly encountered in oil well logging. Pulse power and spectrum of the acoustic transmitter are sufficient to measure either reflections from distant geological structures or waves propagating through the formation near the borehole. A positive acoustic pulse and a symmetric negative acoustic pulse are generated by action of the actuator on the acoustic waveguide. By directing and diverting the positive and negative pulses, a plurality of acoustic transmitters in a tool provide for operation in a multiplicity of modes: monopole, dipole, quadrupole, and a new unipole mode. The tube wave absorber is provided for attenuating tube wave energy that is propagated in the borehole fluid.