Study On Characteristics Of Variable-amplitude Drilling Fluid Pressure Phase Shift Keying Signals

The measurement while drilling(MWD)is a modern drilling technique that measures downhole formation information and telemetry drilling in real time during drilling.It measures the downhole information related to the drilling process near the drill bit,and can transfer the downhole information obtained to the ground without interrupting the drilling operation,so that field technicians can perform real-time analysis and guide drilling operations.At present,continuous pressure transmission methods for drilling fluids in telemetry systems used at home and abroad have been widely used because of its strong anti-interference ability and fast data transmission.Variable amplitude drilling fluid pressure phase shift keying(PSK)signals are generated by momentarily changing the rotary valve speed.Studies have shown that changing the rotary valve speed affects the amplitude of the carrier signal.This paper starts with the working principle of the rotary valve type drilling fluid pressure signal generator and analyzes the law of the amplitude of the rotary valve speed and DPSK differential signal phase shift(DPSK)signal and variable amplitude drilling fluid quadrature phase shift(QPSK)signal.The time-domain mathematical model of varying-range drilling fluid pressure PSK signal is constructed,and the frequency domain expression of variable-range drilling fluid pressure PSK signal is obtained by Fourier transform.Theoretical and numerical analysis methods were used to study the amplitude transmission characteristics of the drilling fluid pressure PSK signal through the drilling fluid.The research results show that the carrier signal will be distorted by the phase shift modu lation and the transmitted signal waveform in the drilling fluid.The signal distortion in the dril ling fluid is related to the signal transmission distance,drilling fluid viscosity and gas content,and the internal diameter of the drill string.After the signal is modulated by the variable ampli tude drilling fluid PSK phase shift keying modulation,the distortion of the signal is large.Bec ause the modulation signals have different attenuation levels of the high and low frequency co mponents of the transmission signal in the drill string,the high frequency part is attenuated to a greater degree,so the modulation signal is drilled.The distortion of the transmission signal in the column is reduced,but as the transmission distance increases,the distortion decreases gr adually to a certain value and gradually increases.Drilling fluid viscosity and gas content hav e a significant effect on the reduction of the modulation signal distortion.In order to reduce th e distortion of the signal to make the measurement information more accurate and effective,th rough the theoretical analysis of the distorted signal,the low-pass filter with the cut-off freque ncy of 6 Hz is selected to filter out the noise signal,and the amplitude-distortion signal is proc essed by the method of multiplicative compensation.Distortion compensation.The compensati on results show that the multiplicative compensation method can effectively reduce the amplit ude distortion of the modulated signal.