Research On Continuous Wave Transmission Characteristics And Signal Processing Of Logging While Drilling

In the oil drilling engineering, electromagnetic resistivity LWD (Logging-While-Drilling) can detect underground geological conditions around the drill bit, which is of great value in the well drilling and geological survey. This paper comes from the research of resistivity LWD systerm MPR, which belongs to the Drilling technology research institute of Shengli Oil (SLDTI). The main research of this paper is about the wireless communication of downhole measurement information, which is one of the key technologies of LWD. Currently, the Positive-Drilling-Fluid-Pulse is the main way to send the measurement data from downhole, however, the transmission rate is lower, which limits the MPR’s ability to acquire (non) compensation resistivity curves. In this paper, our focus is on the continuous sinusoidal pressure wave communication technology, because of the concentration of spectrum energy, long-distance transmission and high throughput, which can effectively solve the issue of low data rates. The encoded continuous pressure wave is the main study object, this dissertation analyzed the transmission characteristics of the signal in drill pipe through theoretical calculation and simulation, designed new continuous pressure wave transmission, and studied the signal processing method and algorithm by using MATLAB.The dissertation is focus on the continuous pressure wave communication technology of MPR, the main works are as follows:First of all, the research studied the transmission characteristics of continuous wave signal using microwave transmission line theory, and obtained the laws of propagation speed and attenuation, then compared the laws with experimental results.Secondly, the LWD’s system-noise and signal modulation schemes were analyzed. Combined with signal transmission characteristics, quaternary MPSK modulation was selected as the optimum way to carry encoded data from the downhole, and met the high transfer rate needs of MPR. The experiments were carried out by simulating pressure wave propagating through the noised channel.Finally, we studied the processing method of telemetry signal that collected by ground pressure sensors. According to the characteristics of the pump noise, the pump noise reduction method was proposed based on the Fourier fitting. Furthermore, the new left-signal noise filtering algorithm based on wavelet transform, improved signal processing capabilities. The algorithms were realized by MATLAB and passed the tests, which proved its abilities to deal with the noised continuous wave signal.Above all the findings and simulation algorithms, can effectively improve the wireless transmission rate of MPR’s measurement information, solve the crucial problem of low signal rate in LWD, and make it apply practically.