Acoustic isolation for a telemetry system on a drill string

A system for the transmission of acoustic signals representative of down hole drilling parameters encountered during operation of a drilling apparatus that includes a rotating table, a drill string coupled thereto, and a drill bit, driven through said drill string, wherein said acoustic signals are caused to propagate along said drill string on which acoustic noise exists that extends over an acoustic frequency spectrum having a lower acoustic frequency band and an upper acoustic frequency band, said system comprising:

• an acoustic receiver coupled to said drill string to receive signals in an acoustic frequency passband within said upper acoustic frequency band of said acoustic noise frequency spectrum;
• an acoustic transmitter coupled to said drill string at a predetermined distance from said acoustic receiver for transmitting an acoustic signal within said acoustic frequency passband of said receiver;
• instrumentation means coupled to said acoustic transmitter for modulating said transmitted acoustic signal, said modulation representative of said downhole drilling parameters;
• a first lowpass acoustic filter coupled between said instrumentation means and said drill bit comprising a first mass section, a second mass section, a compliance element, shaped in cross-section as an elongated S, circumferentially therebetween, and first and second coupling sections for coupling said first and second mass sections between sections of said drill string, said first and second coupling sections circumferentially coupled respectively to said first and second mass sections via first and second damping elements both having longitudinal and transverse sections, whereby noise generated during the drilling operation at acoustic frequencies within said passband of said receiver are attenuated for longitudinal, transverse and torsional modes;
• and
• a second lowpass acoustic filter coupled between said acoustic receiver and said rotating platform comprising a first mass section, a second mass section, a compliance element, shaped in cross-section as an elongated S, circumferentially therebetween, and first and second coupling sections for coupling said first and second mass sections between sections of said drill string, said first and second coupling sections circumferentially coupled respectively to said first and second mass sections via first and second damping elements both having longitudinal and transverse sections, whereby noise at acoustic frequencies within said passband of said receiver, generated by the rotation of said platform and the operation of equipment thereabove are attenuated for longitudinal, transverse and torsional acoustic modes.