Analysis of Echo Cancellation Method Using Two Acoustic Receivers in Drillstring Channel
LI Cheng1, JING Zhong-wu1, LIU Zhao1, FAN Shang-chun1, DING Tian-huai2
1. School of Instrumentation Science and Opto-electronics Engineering, Beihang University, Beijing 100191, China2. Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China
Abstract：With regard to the reduction of transmission performance caused by downlink echoes resulting from the surface noise and the periodic structure of drillstring in logging while drilling, an acoustic signal detection method using dual acoustic receivers is provided in this paper. Based on the analysis of noises existing in drillstring, the proposed method establishes theoretical suppression model of echo noises by using the transient pulse responses in uplink and downlink channels. Then the unit sinusoidal pulse signal and the phase shift keying modulated data are respectively imposed on the drillstring at the excitation end as well as an additive white Gaussian noise applied at the receiving end. By applying a finite-differential algorithm for the one-dimensional propagation of longitudinal waves along the drill string, the transmission characteristics of acoustic signals in the periodic pipe structure transmission channel are analyzed in one-receiver mode and dual-receiver mode by the time and frequency domain simulation. The simulation results prove the validity of the signal detection method using two acoustic receivers to extract original data information from acoustic waves propagating along the drillstring. This method will contribute to the echo cancellation and downhole noise reduction, resulting in the improvement of signal-to-noise ratio and the increase of transmission rate, which provides the methodological foundation for the optimal design of acoustic telemetry system.
2013, Vol. 32 
