Research On Mud Pulser Signal Processing Technology

Mud pulse transmission technology is of stable transmission rate and high reliability and is widely used in the oilfield,so it is an important research direction of MWD/LWD.After measured data is encoded,the mud pulse generates a modulated pressure wave,which is transmitted from downhole to the surface by mud channel.Signal detection,acquisition,processing,demodulation and decoding processes are carried out on the surface system.The mathematical model of drilling fluid channel was studied in this thesis in order to obtain the properties of mud pulse signal propagating and some improved methods were proposed based on present demodulation and decoding system of the research group,which laid the foundation for future works.Firstly,the research status of measurement while drilling,characteristics of mud channel and positive pulse pressure signal processing methods are introduced,and the necessity of research in mud channel and positive pulse signal processing software with independent intellectual property rights is proposed.Secondly,based on the theory of water hammer and conservation law of mass,the fluctuation equations of mud pressure and flow in the pipeline are established;the transfer function of the mud pulse has been obtained,by which the transmission characteristics of mud channel was analyzed.The focus is the property of the dynamic viscosity function N(s),and the frequency characteristics and influencing factors of the transfer function were analyzed.The single pipeline was taken as a four-port model with two inputs and two outputs,and the matrix transfer model has been obtained.Based on the model of a single pipeline,the matrix transfer model of the series pipeline was derived,which simplifies the method to analyze the transmission characteristics of surface system and provides theoretical guidance for subsequent signal processing and decoding methods.For the Pulse Location Management(PLM)encoding positive pulse signal,the filtering effects of cross-correlation and Savitzky-Golay(S-G)filter were compared,and the applicability of S-G filter for positive pulse signal processing was studied.The causes of signal delay were analyzed and processing methods were proposed.Different signal processing methods,such as signal differential,moving average filtering,Butterworth low-pass filter,sampling median filtering and adaptive cross-correlation were analyzed and compared,and the existing positive pulse signal demodulation and decoding system was improved.The signal processing procedure was adjusted for the mud pulse signal with baseline drift,and the differential processing to remove baseline drift was placed first in the signal processing procedure.The cross-correlation signal was normalized and the decoding threshold was modified.The fixed threshold was adjusted to the adaptive threshold according to the amplitude of mud pulse.Independent translating software has been designed for a specific downhole data transmission format,the basic functions of MWD has been obtained.