Abstract
Wireless measure while drilling (MWD) transmits data by using mud pulse signal ; the ground decoding system collects the mud pulse signal and then decodes and displays the parameters under the down-hole according to the designed encoding rules and the correct detection and recognition of the ground decoding system towards the received mud pulse signal is one kind of the key technology of MWD. This paper introduces digit of Manchester encoding that transmits data and the format of the wireless transmission of data under the down-hole and develops a set of ground decoding systems. The ground decoding algorithm uses FIR (Finite impulse response) digital filtering to make de-noising on the mud pulse signal, then adopts the related base value modulating algorithm to eliminate the pump pulse base value of the denoised mud pulse signal, finally analyzes the mud pulse signal waveform shape of the selected Manchester encoding in three bits cycles, and applies the pattern similarity recognition algorithm to the mud pulse signal recognition. The field experiment results show that the developed device can make correctly extraction and recognition for the mud pulse signal with simple and practical decoding process and meet the requirements of engineering application.
Highlights
Data transmission under down-hole and data receiving on the ground are the key techniques in the wireless measure while drilling
At present the signal transmission manners used in measure while drilling (MWD) mainly include the electromagnetic wave and mud drilling fluid pressure wave [1]
The signal attenuation degree of the electromagnetic wave transmission signal becomes serious with the increase of the depth of the stratum, and the difference of the geological structure leads to different attenuation extent of signal amplitude, the signal transmission rate can only be send with a low frequency and in a short transmission distance [2]
Summary
Data transmission under down-hole and data receiving on the ground are the key techniques in the wireless measure while drilling. DSP under the down-hole collects parameters of gravity acceleration, magnetic field component and temperature, and based on the data to be transmitted to implement Manchester encoding and at the same time controls actions of the corresponding pulse generator. Process the acquired and received data with Manchester encoding and send mud pulse signal. Down-hole data transmission principle When down-hole instruments begin to work, the mud pulse signal is the Run-in pulse signal sent out 30s after the pump opens. Run-in pulse is used to ensure MWD measured in the stable voltage condition so as to ensure the accuracy of the measurement data, and Run-in pulse is a time window for ground and down-hole communications, by opening or closing the pump, it can change the speed of data transmission of underground exploring tube. FLAG signal is a synchronous mark signal,as for continuous sending of eight pulses, the binary code is “01111110”, in any
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