Research And Implementation Of MWD Mud Pulse Codec Technology

Measurement While Drilling(MWD)is an important technical measure for obtaining downhole data parameters in oil drilling activities,and is applied on a large scale to oil exploration in various complex wellbores.The MWD system is equipped with a measuring device in the drilling tool near the drill bit,which can transmit the collected data information to the ground in real time while not affecting the drilling work.The continuous pressure wave signal transmission mode has a high transmission rate,can carry a large amount of data information,and has strong anti-interference ability,and is a mainstream technology of a high-speed wireless MWD mud pulse remote transmission system.Due to the harsh environment of the mud channel,the pulse signal will attenuate rapidly as the transmission distance increases.In order to improve the transmission performance of the system,it is necessary to conduct in-depth research on the coding and decoding technology of the mud pulse signal.In this paper,mud pulse is taken as the research object.For the encoding and decoding technology of MWD mud pulse,three aspects are studied: the characteristics of mud pulse transmission,the enhancement of pulse signal filtering,and the method of grid coding pulse interval modulation.And based on C language on VS2013 platform,a signal codec module was developed.The main research content is as follows:1.The transmission characteristics of mud pulse signal were studied,including the pulse transmission speed and attenuation characteristics,and the noise components of the channel.Combining the working principle of the APS oscillating shear valve type continuous wave pulser,the continuous pressure wave is mathematically modeled.Using the channels measured by the 3,000-meter water circulating pipeline of COSL,the mud pulse signal was simulated and the pulse interval modulation signal was subjected to spectrum analysis.2.For the identification and detection of pulse signals,the MSSNR pulse truncation algorithm for pulse signal processing is studied.Using the pulse accumulation method to obtain a higher signal-to-noise ratio pulse signal,and using the obtained pulse signal to perform pulse truncation filter training.The mathematical calculation process of the training algorithm was deduced,the algorithm software design flow was explained,and the effect of the signal sample processed by the pulse truncation software module is given.3.For the problem of poor transmission performance of the current pulse interval modulation method,a grid coding pulse interval modulation method is studied.Using the TC-PIM good code search method,the best encoder structure of TC-PIM is obtained.The best subset of 5-bit PIM symbols is divided to verify the feasibility of the algorithm.The software design of the convolutional code mapping module and the Viterbi decoding module is completed,and the system simulation environment is built using MATLAB to verify the function of the software module.