Continuous Wave Slurry Pulse Transmission System Design

Measurement while drilling is a technology that can continuously acquire and transmit information about geology or drill bits to the ground while the rig is drilling.It can be used by field engineers to optimize drilling strategies and adjust drilling parameters,which is useful for reducing drilling costs and improving drilling efficiency.It is of great significance.Continuous mud pulse communication is a commonly used wireless communication method in the field of measurement while drilling.At present,the contradiction between a large amount of downhole information and inefficient communication rate is the main problem of the mud pulse transmission method.The purpose of this thesis is to improve the transmission rate and reliability of mud pulse communication.Under the MATLAB simulation environment,research is carried out on the signal modulation method,mud channel noise and transmission characteristics,noise elimination and decoding method of the receiving end in the system.Firstly,the modulation of the mud pulse signal is a mechanical modulation.Based on the classical modulation method of the pulser,an 8PSK modulation method suitable for continuous wave signals is proposed.Through the analysis of the 8PSK single pulse sequence,the continuous pressure wave is derived by Fourier transform.8PSK signal mathematical model,and use MATLAB to get the simulation waveform.The effectiveness and reliability of QPSK signal and 8PSK signal are compared based on the analysis of time domain and frequency domain characteristics.The results show that continuous wave 8PSK modulation can double the information transmission rate under the same carrier frequency and bandwidth compared to the existing 2PSK or even QPSK modulation.Secondly,the noise of the mud channel is analyzed and modeled,and the channel transmission characteristics are numerically analyzed.The mud channel noise components are complex,and the important components are the strong periodic pump noise signal and the nonperiodic Gaussian noise signal.At the same time,the speed transmission model and the channel attenuation model are used to simulate the channel characteristics.The results show that the signal frequency and transmission distance are important factors that affect the signal attenuation.Finally,by establishing a wellhead pressure wave model,combined with noise and channel attenuation characteristics,the wellhead continuous pressure wave signal is simulated.Use the time domain averaging method based on the characteristics of the mud pump to remove the pump noise,and use the improved layered threshold wavelet denoising method to remove the remaining noise;use the zero demodulation method and the phase demodulation method for joint demodulation to obtain the original data,The practicability of the 8PSK modulation scheme for continuous mud pulse signals is verified.Use actual downhole engineering values for comprehensive simulation,set simulation parameters,and change the noise intensity until the demodulation error occurs,and the noise boundary that can be correctly demodulated is obtained.The scheme is reliable and effective under the condition of high signal-to-noise ratio.In short,this system is suitable for applications under conditions such as large downhole information demand and high environmental noise signal-to-noise ratio.It can successfully identify downhole information when the noise intensity does not exceed-10 db.It is suitable for horizontal wells and extended reach wells at the early stage of drilling.Under the conditions of complex geological environment and high demand for underground information,it can provide new ideas for improving signal transmission rate and adapting to diversified environmental transmission strategies.