Research On Modulation And Demodulation Algorithm Of High Data Rate Mud Pulse Telemetry System

L/MWD (logging/measurement while drilling) system transmits orientation data, formation data and drilling parameter to the surface in real-time, in which the technology of mud pulse telemetry (MPT) is wide used for data uploading. The realization of high-speed mud pulse telemetry (MPT) system is one of the tough industry problems, which is an almost unknown field in our country. This paper aims to establish a high-speed MPT system with a transfer rate up to 12bps. This paper mainly solves five aspects such as the selection of signal modulation, removal of noise, signal synchronization, signal equalization and decision and the experimental verification.On selection modulation, the paper first analyzes the generation mechanism of pulse signal and signal transmission characteristics of which in the mud channel. Then, to reduce signal attenuation as well as the difficulty of signal gereration, the baseband pulse amplitude modulation is selected as one of the modulation scheme of the system, and to improve anti-noise performance and avoid the pump noise, the PSK modulation is used as the other modulation scheme of the system. On the noise elimination, the paper analyzes the composition of the system noise and model the noise as quasi-periodic noise with Gaussian noise superimposed. Using a finite impulse response filter, the noise out of signal band is filtered out, which shows the adaptive notch filter may be a perfect method to filter out single frequency noise or narrow-band noise; the experience-based time-domain waveform noise cancellation algorithm is applied to eliminate stable complex noise in signal band. The dual sensor adaptive noise cancellation algorithm can make uses of the phase difference generated by noise and signal propagating in the opposite direction and theoretically it can completely remove all the noise (including the signal echoes) propagating in direction opposite with mud pulse signal.Signal synchronization includes frame synchronization and carrier synchronization. On frame synchronization, we obtain two schemes, namely the use of system-specific features of mud pressure lifting and m sequences and the use of good autocorrelation characteristics of Chirp signal; for carrier synchronization, we use a decision feedback carrier synchronization loop which is carried in communication system widely. On equalizing and decision, in the paper we analyze the communications environment of mud pulse telemetry systems from starting and points out that the mud pulse channel is frequency-selective channel, the channel delay spread is large, inter-symbol interference is serious, and there is varying feature. The article utilizes a fractionally-spaced decision feedback equalizer based on RLS adaptive algorithm to process the received signal.Finally, the high-speed mud pulse telemetry system is tested in a 3000m water circulation line. The experiment results reveal that PAM modulation data transmission rate in the absence of data compression can be achieved to 12bps, a similar performance of the high-speed mud pulse telemetry systems developed by some leading companies su as Schlumberger and Baker Hughes.