Influence factors of acoustic transmission in drill strings

Using the finite difference method, the transmission characteristics of the acoustic wave in the passband transmitting through the drill string were researched, and the influences of the viscous damping of the drill fluid, the formation damping coefficient and elastic coefficient, the number of drill pipes and the existence of the drill collar were analyzed. The wave time domain and frequency domain distributions were analyzed. The results show that the drilling fluid viscous damping has effect on acoustic wave time domain distribution, and has little effect on the acoustic wave signal amplitude and frequency domain distribution. Formation damping coefficient has effect on amplitude of the large amplitude acoustic wave and time domain of small amplitude acoustic wave. The amplitude of large amplitude acoustic wave is slightly smaller when the formation damping coefficient is big, and vibration of small amplitude acoustic signal becomes messy when the formation damping coefficient is small. Formation elastic coefficient has effect on vibration amplitude of acoustic wave, and the vibration amplitude of acoustic wave increases with the formation elastic coefficient increasing. Drill pipe quantity has effect on acoustic wave time domain distribution, but has no effect on the frequency domain distribution. With the drill pipe quantity increasing, the received acoustic wave amplitude reduces. The drill collar has no effect on acoustic transmission properties in drill string without considering the attenuation. The drill string structure plays a major role for the selected carrier frequency, and the other factors and drill string structure have effect on the distribution of relay device.