Simulation of stress waves in attenuating drill strings, including piezoelectric sources and sensors

A key element in drill steering and prediction of lithology ahead-of-the-bi t is the transmission of while-drilling information from the bottom of the well to the rig operator and the geophysicists. Mud-pulse telemetry, based on pressure pulses along the drilling mud and extensional waves through the drill string, is the most used technique. The last method, properly design ed, could transmit data rates up to 100 bits per second, against the 1 or 2 bits per second achieved with pressure pulses. In this work, a time-domain algorithm is developed for the propagation of one-dimensional axial, torsi onal, and flexural stress waves, including transducer sources and sensors. In addition, the equations include relaxation mechanisms simulating the vis coelastic behavior of the steel, dielectric losses, and any other losses, s uch as those produced by the presence of the drilling mud, the casing, and the formation. Moreover, the algorithm simulates the passbands and stopband s due to the presence of the coupling joints and pulse distortion and delay due to nonuniform cross-section areas. Acoustic and electric pulses, gener ated at one location in the string, can be propagated and detected at any o ther location by piezoelectric and acoustic sensors, such as PCB accelerome ters, clamp-on ammeters, force, and strain transducers. (C) 2000 Acoustical Society of America. [S0001-4966(00)02907-6].