Nonlinear method for filtering noise and interference of pulse signal in measurement while drilling

Limited by drilling conditions, it's difficult to transmit signal between ground and down-hole by wire, so at present wireless transmission style which is based on the modulation of drilling fluid pulse is used in practice. However, the channel transmission of drilling fluid pressure, well depth and pump pressure have serious effect on the sampled signal in the measurement while drilling (MWD) system. The sampled signal contains some strong noises and interference, which would affect the measurement precision and the reliability. The mode of wireless communication by drilling fluid pulse and the characteristics of noise were analyzed. The linear filtering method was used to recover the pulse signal. Considering the characteristics of the noise, a new nonlinear method based on digital filtering was applied to the sampled signal processing. The filtering result of the nonlinear method is better than that of the linear method. All the pump noise and interference can be wiped off efficiently. Field application shows that this method has little impact on position and is characterized by simple decoding process, high reliability and low error rate.