Acoustical properties of drill strings: Theory

Abstract

Drill strings are assembled from 30‐ft sections of steel pipe and used to drill wells to recover petrochemical and geothermal resources. The ability to transmit data by acoustic carrier waves generated within the drill string would have significant economic impact on the drilling industry. This poses an unusual waveguide problem. The string, which may be up to 30 000 ft long, forms a periodic structure of slender pipe threaded together with large‐diameter tool joints. Classical analysis methods along with numerical algorithms can be used to study the behavior of both periodic and transient acoustic waves in this structure. Stress waves that propagate along this waveguide exhibit all of the phenomena associated with Brillouin scattering theory. The results show a comb filter structure with passbands that produce significant wave dispersion. In addition, the acoustic impedance that determines the design of sending and receiving transducers is a strong function of position as well as frequency. [This work wa...