At present,the MWD systems continuous wave mud pulse telemetry transmit is not faster than 1or 2bits/s from deep wells containing highly attenuative mud,because positive pulsers create strong signals but large axial flow forces impede fast reciprocation while mud sirens provide high data rates without higher signal strength.A high-data-rate system providing 10bits/s and operable up to30 000 ft is described,which creates strong source signals by using downhole constructive wave interference in two novel ways.Telemetry schemes,frequencies and pulser locations in the MWD drill collar are selected for positive wave phasing,and sirens-in-series are used to create additive signals——both without incurring power and erosion penalties.The positions normally occupied by pulsers and turbines are reversed to minimize times required for constructive interference and modulation.A system design approach is undertaken,e.g.,strong source signals are augmented with new multiple-transducer surface signal processing methods to remove mudpump noise and signal reflections at both pump and desurger,and mud,bottomhole assembly and drill pipe properties,to the extent possible in practice,are controlled to reduce signal attenuation.The results of detailed acoustic modeling in realistic drilling telemetry channels are described,and short and long wind tunnels for signal strength,torque,erosion and jamming testing,and telemetry and signal processing evaluation,respectively,are introduced.Special scaling methods are developed to extrapolate cost-effective wind tunnel test results to real muds flowing at any downhole speed.New siren concept prototype hardware and also typical acoustic test results are also given.
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