CN101525998B - Ground signal receiving device for electromagnetic measurement while drilling system and receiving method thereof - Google Patents
Ground signal receiving device for electromagnetic measurement while drilling system and receiving method thereof Download PDFInfo
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Abstract
The invention relates to a device in an electromagnetic measurement while drilling system for receiving an electromagnetic signal with measurement data information sent underground on the ground and transmitting the signal to a data processing computer, and a method thereof. The device uses two antennas in a well field to receive an electromagnetic signal sent underground and a well field noise signal respectively; and the two signals enter a program controlled low noise preamplifier to be amplified through the coupling of an impedance converter, then enter a signal conditioning module for processing, and then enter a digital signal processing module through analog-to-digital conversion, and finally data is transmitted to a computer terminal through an interface module. The device is matched with a downhole electromagnetic signal transmitter to form the electromagnetic measurement while drilling system to form the information communication between underground and ground. The electromagnetic measurement while drilling system is not affected by drilling fluid medium, can perform data transmission without circulating a drilling fluid under any working condition, and can solve the measurement while drilling problem in gas drilling and aerated drilling.
Description
Technical Field
The invention belongs to a measurement while drilling instrument used in mineral and petroleum resource exploration and development, such as a Measurement While Drilling (MWD) instrument, a Logging While Drilling (LWD) instrument and the like. In particular to a device and a method for receiving electromagnetic signals carrying measurement data information sent from a well underground on the ground in an electromagnetic measurement while drilling system and transmitting the electromagnetic signals to a data processing computer.
Background
In drilling projects such as petroleum, mines, geological exploration and the like, geological and engineering data need to be measured in time in order to accurately grasp formation information and enable a borehole trajectory to drill according to engineering design requirements. In addition, the data collected by the various sensors also needs to be transmitted to the surface in real time. This real-time data measurement and transmission technique is known as Measurement While Drilling (MWD).
At present, drilling fluid pulses are generally adopted at home and abroad to transmit underground and ground information, however, for gas and various gas-filled drilling fluids, because of strong fluid compressibility, drilling fluid pulse signals are very weak or even can not generate effective pulse signals, so that drilling fluid pulse MWD can not work normally. Electromagnetic measurement while drilling (EM-MWD) is a new technology which enters industrial application in the 80 th century, and can solve the difficult problem of measurement while drilling which is difficult to overcome by a drilling fluid pulse MWD system.
The research of the electromagnetic measurement while drilling technology can trace back to 30 years in the 20 th century, and practical EM-MWD systems are developed in the first 70 years in the 20 th century. In the mid-80's of the 20 th century, commercial production and use of EM-MWD systems began. In particular, since the 90's of the 20 th century, a series of commercial EM-MWD products were introduced by various overseas petroleum companies, and this technology was rapidly popularized and applied in europe, canada, south america, russia, and the like.
During the seven-five period, along with the research and the localization work of drilling fluid pulse MWD, China has conducted feasibility research on the EM-MWD technology. The units such as China radio wave propagation research institute and Harbin university of industry mainly adopt theoretical research and functional tests, explore transmission channels and characteristics of underground electromagnetic signals, analyze the influence rule of signal frequency and formation resistivity on signal attenuation, and test system power consumption and noise interference. The research conclusion is as follows: under the conditions that the formation resistivity is larger than 5 omega-m, the signal frequency is 5-20Hz, and the signal-to-noise ratio of zero decibel, the electromagnetic signal is feasible to be transmitted by 3000m underground. In the early 2006, the China Petroleum exploration and development research institute successfully developed a CGDS-I near-bit geosteering drilling system, and realized the measurement while drilling of near-bit geological parameters and engineering parameters. The measurement and transmission motor subsystem adopts an electromagnetic signal short transmission technology and is used for transmitting measurement data of a near drill bit to MWD (measurement while drilling) above a downhole motor and transmitting the measurement data to the ground through the MWD. The signal transmission rate of the electromagnetic signal short transmission technology is greater than 200bit/s, and the signal transmission distance generally does not exceed 10 m.
An electromagnetic measurement-while-drilling system for downhole and surface communication requires a downhole electromagnetic signal transmitting device that modulates measurement data onto a carrier signal, transmits it as an electromagnetic signal, and transmits it to the surface via an electromagnetic channel formed by the drill string, the wellbore, and the formation. The ground receiving device is used for receiving the electromagnetic signals transmitted from the underground, reducing underground measurement data through signal processing technologies such as filtering and demodulation and transmitting the underground measurement data to the data processing computer.
The surface receiving device is an important component of the electromagnetic measurement while drilling system. Because the electromagnetic signals are attenuated quickly in the transmission process and are interfered by factors such as noise, echo and the like, the electromagnetic signals received on the ground are sometimes very weak, and therefore, high requirements are put forward on the signal receiving and detecting technology. At present, the research of domestic electromagnetic measurement while drilling systems is still in the initial stage, and no commercial product is formed.
As in the prior art, in the reference document of application No. DE4135708A, first, the noise detection antenna and the noise reception antenna in the present invention use antennas of two different principles and structures; the two methods for eliminating noise are different, and the received noise signal and the electromagnetic wave signal are amplified in the comparison file and then enter a noise eliminator of an analog signal for noise cancellation, namely, a hardware method, an adder or a subtracter method of the analog signal are adopted for canceling the noise signal in the electromagnetic wave. After the received noise signals and electromagnetic wave signals are subjected to certain amplification, hardware filtering and signal conditioning, the two paths of signals are converted into digital signals through the A/D converter for noise elimination. The noise in the signal can be eliminated more accurately and flexibly by adopting a digital mode to carry out noise elimination processing; in addition, because the interference noise is different in different regions and well sites, different algorithms can be adopted in the digital processing mode according to the characteristics of noise signals, so that the optimal noise elimination effect is achieved, and the self-adaptive processing can be realized.
In addition, although both the reference and the present invention perform noise cancellation to improve the signal-to-noise ratio, the greatest difference is that the methods for canceling noise or noise cancellation are different, the method of addition and subtraction between analog signals with different phases is adopted in DE4135708A, and the present invention adopts a digital signal processing method, namely, an adaptive noise cancellation technique. That is, the method of combining, the order, the technical means for realizing the functions of the components, and the like are different from those of the present invention.
The application number is 200410005527.X, and the signal received by the device is a frequency modulation carrier wave electromagnetic signal sent underground. The signal demodulation processing adopts a traditional technical method of a hardware FSK demodulator and a hardware wave detector, and can only receive signals adopting an FSK modulation mode. In the solution of application No. 200410004275.9, the receivers are installed at the joints of drill collars located downhole and in the drill bits 1-2, and both the transmitters and receivers are located in a close proximity to each other in the downhole environment. The received signal is a frequency modulated carrier electromagnetic signal transmitted by a transmitter mounted downhole near the drill bit. The signal demodulation processing adopts a traditional technical method of a hardware FSK demodulator and a hardware wave detector, and can only receive signals adopting an FSK modulation mode.
Disclosure of Invention
According to the technical problems in the prior art, the ground signal receiving device in the electromagnetic measurement while drilling system is developed, and a signal receiving and detecting method is established. The invention adopts software radio technology, adaptive filtering technology and signal coupling technology, can meet the requirements of electromagnetic signal receiving and detection in severe noise environment, and can be compatible with electromagnetic measurement-while-drilling systems with different modulation modes.
The invention provides a ground signal receiving method and a ground signal receiving device of an electromagnetic measurement while drilling system, wherein the device is not influenced by a drilling fluid medium, data transmission can be carried out without circulating the drilling fluid under any working condition, and the problem of measurement while drilling in gas drilling and inflation drilling can be solved.
In order to achieve the object of the invention, a receiving apparatus is developed comprising:
the device comprises a signal receiving end, a signal processing unit and a signal output unit.
The signal receiving end is a ground receiving antenna group and comprises an electromagnetic signal receiving antenna and an interference noise receiving antenna which are respectively used for receiving electromagnetic signals transmitted underground, ground interference signals and well site interference noise signals;
the signal processing unit comprises a double-channel signal coupler, a double-channel program-controlled preamplifier, a double-channel signal conditioner, a double-channel A/D converter, a DSP circuit and a power supply;
the output unit is used for outputting the signal of the signal processing unit through a communication port;
the electromagnetic signal receiving antenna and the interference noise receiving antenna sequentially process received signals through a dual-channel signal coupler, a dual-channel program-controlled preamplifier, a dual-channel signal conditioner, a dual-channel A/D converter and a DSP circuit, and underground data signals are output through a communication port.
In order to provide an effective ground signal receiving mode, the invention respectively receives signals and noise by using two different antennas. The electromagnetic signal receiving antenna adopts a horizontal polarization receiving mode and is an asymmetric dipole antenna; for receiving electromagnetic signals including downhole transmissions and surface interference signals;
the interference noise receiving antenna adopts a monopole vertical polarization receiving mode and is a passive whip antenna; for receiving a wellsite disturbance noise signal.
In practical application, the two-channel signal coupler comprises a signal coupler of an electromagnetic signal channel and a signal coupler of an interference noise signal channel; the ground receiving antenna group is used for coupling the signals received by the ground receiving antenna group to a lower circuit and realizing signal amplification, superposition and impedance transformation;
the dual-channel program-controlled preamplifier comprises an electromagnetic signal channel preamplifier and an interference noise signal channel preamplifier, and voltage preamplifiers are arranged in the dual channels;
the dual-channel signal conditioner comprises a signal conditioner of an electromagnetic signal channel and a signal conditioner of an interference noise signal channel; the system is used for conditioning electromagnetic signals and interference noise signals, namely filtering power frequency interference and anti-aliasing filtering;
the dual-channel A/D converter comprises an A/D converter of an electromagnetic signal channel and an A/D converter of an interference noise signal channel; the dual-channel signal conditioner is used for quantizing the two channels of signals sent by the dual-channel signal conditioner and sending the bit stream information to a lower circuit.
To achieve linear amplification, the noise introduced by the amplification path is reduced. In the dual-channel program-controlled preamplifier, the preamplifier of any channel comprises an ultra-low noise amplifier, a program-controlled amplifier, a 50Hz stuffing wave filter, a high-pass filter, a low-pass filter, an output amplifier, an output stage, an input mode control circuit, an amplification factor control circuit, a stuffing wave control circuit, a high-pass and low-pass filter cut-to-frequency control circuit and a power supply circuit;
in order to condition signals, any channel in the dual-channel signal conditioner comprises an active low-pass filter, a zero setting circuit and an A/D protection circuit;
the DSP circuit comprises a digital signal processor and a peripheral circuit, wherein the digital signal processor comprises a FLASH, an SDRAM, a crystal oscillator, a communication interface and the like; the DSP circuit adopts a radio technology and is used for collecting, digitally filtering, adaptively denoising, demodulating, decoding and communicating two paths of signals.
In order to improve the anti-interference capability of the device, an integrated design is adopted. The device also comprises a signal coupler box and a receiver box; the signal coupler box is connected with the receiver box body;
the signal coupler box comprises a metal explosion-proof box body and the two-channel signal coupler; the metal explosion-proof box body is provided with two input and output ports. The two input ports are respectively connected with the electromagnetic signal receiving antenna and the interference noise receiving antenna through cables; the two output ports are connected to the signal input port of the receiver box body by a cable;
the receiver box body comprises a metal explosion-proof box body, and the dual-channel program-controlled preamplifier, the dual-channel signal conditioner, the dual-channel A/D converter, the DSP circuit, the power supply and the communication port are all arranged in the receiver box body.
The invention adopts a receiving method according to the device, wherein the receiving method comprises a signal receiving end, a signal processing unit and a signal output unit;
the receiving method comprises the following steps:
1) a signal acquisition step: receiving an electromagnetic signal and an interference signal containing underground measurement data transmitted from an electromagnetic channel formed by the earth and a drill string according to the electromagnetic signal receiving antenna and the interference noise receiving antenna;
2) signal superposition and coupling steps: superposing and coupling the two paths of received signals by using the dual-channel signal coupler;
3) a signal amplification step: amplifying, conditioning and quantizing the two paths of signals obtained by coupling by using the dual-channel program-controlled preamplifier;
4) a signal filtering step: filtering the quantized digital signal by using the dual-channel signal conditioner;
5) a signal self-adaptive noise cancellation step: applying a DSP circuit to perform adaptive noise cancellation on the filtered signal;
6) signal demodulation and decoding steps;
7) a signal output step: and outputting the processed signal through the communication port.
In the step 2, the superposition and the coupling are to input two paths of signals into a lower circuit through a coupler; amplifying, conditioning and quantizing the two paths of signals in the step 3 into two paths of coupled signals which are amplified to 0-5V, filtering the amplified signals by the 50Hz wave trap and the 8-order low-pass filter, inputting the signals into the two paths of A/D converters for quantization, and outputting two paths of quantized digital signals;
in step 4, the quantized digital signal is filtered, the signal is further filtered through the DSP circuit, and the filtered signal is subjected to adaptive noise cancellation processing;
the self-adaptive noise cancellation operation in the step 5 is to detect and extract a useful signal from an environment in which the signal is submerged by noise interference;
demodulating and decoding the signals in the step 6, demodulating the filtered signals by adopting a software radio technology, and decoding the data stream obtained after demodulation;
and 7, transmitting the measurement data obtained after decoding to a data processing computer through a communication interface.
According to the device and the method, two antennas are used on a well site to respectively receive electromagnetic signals and well site noise signals sent underground; the two paths of signals are coupled through an impedance converter; then the data enters a program-controlled low-noise preamplifier for amplification, then enters a signal conditioning module for processing, then enters a digital signal processing module after analog-to-digital conversion, is subjected to digital filtering, adaptive noise cancellation, differential coherent demodulation and software Viterbi decoding, and finally is transmitted to a computer terminal through an interface module. The invention is matched with an underground electromagnetic signal transmitting mechanism to form an electromagnetic measurement while drilling system so as to form underground and ground information communication. The electromagnetic measurement while drilling system is not influenced by a drilling fluid medium, can transmit data without circulating the drilling fluid under any working condition, and can solve the measurement while drilling problem in gas drilling and inflation drilling. The signal receiving capability and the detection capability in a strong noise environment are improved, and the measurement depth of the electromagnetic measurement while drilling system can be improved; the radio technology can be compatible with various modulation and coding modes of downhole signals, and the functions and the application range of the downhole signals can be expanded. The method can be applied to underground and ground data communication in industries such as petroleum, mines, geological exploration and the like.
Drawings
FIG. 1 is a schematic block diagram of a receiving apparatus of the present invention;
FIG. 2 is a schematic diagram of a receiving apparatus according to the present invention;
FIG. 3 is a schematic diagram of the arrangement of the ground receiving antenna group in the receiving apparatus of the present invention;
fig. 4 is a flow chart of a receiving method of the present invention;
FIG. 5 is a schematic diagram of the adaptive noise cancellation process of the present invention;
the drawings described above are to be considered in connection with the following detailed description.
Detailed Description
The receiving apparatus of the present invention comprises: the device comprises a signal receiving end, a signal processing unit and a signal output unit.
The signal receiving end is a ground receiving antenna group and comprises an electromagnetic signal receiving antenna and an interference noise receiving antenna which are respectively used for receiving electromagnetic signals transmitted underground, ground interference signals and well site interference noise signals;
the signal processing unit comprises a double-channel signal coupler, a double-channel program-controlled preamplifier, a double-channel signal conditioner, a double-channel A/D converter, a DSP circuit and a power supply;
the output unit is used for outputting the signal of the signal processing unit through a communication port;
the electromagnetic signal receiving antenna and the interference noise receiving antenna sequentially process received signals through a dual-channel signal coupler, a dual-channel program-controlled preamplifier, a dual-channel signal conditioner, a dual-channel A/D converter and a DSP circuit, and underground data signals are output through a communication port.
Wherein,
1. electromagnetic signal receiving antenna: the antenna is composed of two metal rods and a connecting cable, and is arranged on two buried electrodes which are arranged on the ground at a certain distance; the received signals comprise underground transmitted electromagnetic signals and ground interference signals, and are sent to a signal coupler of an electromagnetic signal channel through a connecting cable;
2. interference noise receiving antenna: the antenna is vertically placed on the ground and consists of a passive whip antenna; a signal coupler for receiving the interference noise signal of the well site and sending the received signal to the interference noise channel through a connecting cable;
3. two-channel signal coupler: the couplers contained in either channel are identical in performance and structure. And coupling the signals received by the two antennas to a lower circuit, and realizing signal amplification, superposition and impedance transformation.
4. Two-channel program-controlled preamplifier: the two channels are provided with programmable voltage preamplifiers with the same amplification factor. Any channel of the preamplifier consists of an ultra-low noise amplifier, a program-controlled amplifier, a 50Hz filling wave device, a high-pass filter, a low-pass filter, an output amplifier, an output stage, an input mode control circuit, an amplification factor control circuit, a filling wave control circuit, a high-pass and low-pass filter cut-to-frequency control circuit and a power supply circuit. The A channel amplifies the received electromagnetic signal voltage, and the B channel amplifies the received noise voltage. Linear amplification is achieved, reducing noise introduced by the amplification path.
5. Two-channel signal conditioner: any channel comprises an active low-pass filter, a zero setting circuit and an A/D protection circuit, and is divided into A, B two symmetrical channels, wherein the A channel conditions received electromagnetic signals: filtering power frequency interference and anti-aliasing filtering; the B channel conditions the received noise, further filters power frequency interference, and performs anti-aliasing filtering, so that the broadband noise is changed into narrow-band noise, and the requirement of post-stage self-adaptive noise elimination is met.
6. Two-channel A/D converter: and the quantization of the two paths of signals sent by the dual-channel signal conditioner is finished, and the obtained bit stream information is sent to a lower-level circuit.
7. A DSP circuit: the digital signal processor is composed of TMS320VC5509A, FLASH, SDRAM, crystal oscillator, communication interface and other peripheral circuits, and combines radio technology to mainly complete two-way signal acquisition, digital filtering, adaptive noise elimination, demodulation, decoding and communication.
8. Power and communication interface: the power supply supplies power to the receiver, and the communication interface transmits the received data to the data processing computer.
9. Signal coupler box: the explosion-proof metal box comprises a metal explosion-proof box body and two signal couplers arranged in the metal explosion-proof box body, wherein the two signal couplers are respectively provided with two input ports and two output ports. The input port is connected with the electromagnetic signal antenna and the interference antenna by a cable; the output port is connected to the signal input port of the receiver box by a cable.
10. A receiver box body: the explosion-proof metal box comprises a metal explosion-proof box body and a double-channel program-controlled preamplifier, a double-channel signal conditioner, a double-channel A/D converter, a DSP circuit, a power supply and a communication port which are arranged in the box body.
In the present invention, in the case of the present invention,
(1) on the premise of establishing an effective ground receiving method for underground transmitted electromagnetic signals, aiming at the conditions that underground transmitted extremely-weak (microvolt level signals) electromagnetic signals which are transmitted to the ground through a channel formed by a drill column and a stratum and are attenuated are transmitted to the ground, and various interference signals on the ground are abundant, the invention provides the effective ground signal receiving method. In practical application, a very low frequency carrier signal with downhole measurement data is transmitted to the ground through an electromagnetic channel formed by a drill string and a stratum, the attenuation of the channel is very weak in the transmission process and is submerged in various noise and interference signals, the signal-to-noise ratio is poor, the performance of a receiving device is reflected to increase the error rate, and in order to reduce the error rate of the receiving device, the signal needs to be properly processed and noise filtered, so that the signal-to-noise ratio is improved. The specific contents are as follows:
arrangement and signal coupling of receiving antennas
The ground receiving antenna comprises an electromagnetic signal receiving antenna 1 and an interference receiving antenna 2, the electromagnetic signal receiving antenna is an asymmetric dipole antenna and is used for horizontal polarization receiving, a receiving electrode is buried underground, and the two electrodes are separated by a certain distance. The interference receiving antenna is a monopole vertical polarization antenna and is vertically arranged relative to the ground. Signals received by the two antennas enter subsequent program-controlled preamplifiers 5 and 6 through couplers 3 and 4 to be amplified. Wherein the coupler has the effect of matching the antenna to the preamplifier impedance.
Filtering of signals
Since the effective signal is a very low frequency signal of 2-30 Hz, any high frequency part in the signal is interference. In order to filter out high-frequency interference as much as possible, two ways of hardware and software are used for low-pass filtering the signal. The hardware anti-aliasing low-pass filters are realized in the signal conditioners 7 and 8 by adopting 8-order Butterworth active low-pass filters, signals after being filtered by the hardware are quantized through the A/D converters 9 and 10 and then enter the DSP circuit 12 for software filtering, and the software filtering can flexibly select window functions and parameter design or change the filters and the like. In order to obtain good filtering effect, the method adopts 100-order FIR filtering.
Thirdly, software demodulation and decoding
And performing software demodulation and decoding on the useful signal extracted from the adaptive noise cancellation according to the modulation mode of the signal. Due to the adoption of the radio technology, the demodulation and decoding of the signals can be completed by only selecting different demodulation and decoding algorithms for the signals adopting different modulation and coding modes. If the modulation mode of the signal is 2DPSK, and the coding mode is convolutional coding, the signal can be processed by selecting a corresponding differential coherent demodulation algorithm and a Viterbi decoding algorithm, and the measured data obtained after processing can be transmitted to a data processing computer through a communication interface.
The receiving method of the present invention comprises,
1) a signal acquisition step: receiving an electromagnetic signal and an interference signal containing underground measurement data transmitted from an electromagnetic channel formed by the earth and a drill string according to the electromagnetic signal receiving antenna and the interference noise receiving antenna;
2) signal superposition and coupling steps: superposing and coupling the two paths of received signals by using the dual-channel signal coupler;
3) a signal amplification step: amplifying, conditioning and quantizing the two paths of signals obtained by coupling by using the dual-channel program-controlled preamplifier;
4) a signal filtering step: filtering the quantized digital signal by using the dual-channel signal conditioner;
5) a signal self-adaptive noise cancellation step: applying a DSP circuit to perform adaptive noise cancellation on the filtered signal;
6) signal demodulation and decoding steps;
7) a signal output step: and outputting the processed signal through the communication port.
Wherein,
1, using two different types of antennae on the surface to respectively receive well site interference noise containing no or little downhole transmitted signals and signals from downhole transmitted signals containing noise, wherein the two signals are connected to a lower circuit through a cable.
And 2, signal superposition and coupling, wherein two paths of signals from the antenna enter a lower-stage circuit through a coupler, and the coupler can counteract interference noise in partial signals and enables the antenna to be matched with the impedance of the lower-stage circuit.
3, a signal amplification step, namely amplifying the two paths of signals which are coupled into the signal amplification step to 0-5V, and automatically switching amplification multiplying power; the amplified signals enter a 50Hz wave trap formed by a hardware circuit and an 8-order low-pass filter for filtering, then enter a 2-path A/D converter for quantization, and two paths of quantized digital signals are output.
And 4, signal filtering, namely forming a digital low-pass filter by using a DSP (digital signal processor) to further filter the signals, adopting an FIR (finite Impulse response) filtering algorithm, wherein the cut-off frequency is 30Hz, and performing self-adaptive noise cancellation processing on the filtered signals.
And 5, a step of signal adaptive noise cancellation, wherein adaptive noise filtering refers to detecting and extracting a useful signal from an environment in which the signal is submerged by noise interference, and the adaptive noise cancellation takes the noise interference as a processing object and suppresses or greatly attenuates the noise interference so as to improve the signal-to-noise ratio quality of signal transmission and reception. The adaptive noise interference canceller is an extension of the principle of the adaptive filter, and in brief, the desired signal input d (n) of the adaptive filter is changed to the original input end of the signal plus noise interference, and its input end is changed to the noise interference end, and the output is adjusted by the parameters of the transversal filter to cancel the noise interference at the original input end, and then the error output is the useful signal.
6, signal demodulation and decoding step and signal output step, adopting radio technology to carry out software demodulation on the filtered signal, wherein the demodulation algorithm is optional, and the corresponding demodulation algorithm can be selected according to the modulation mode adopted by the signal; carrying out decoding processing on the demodulated data stream, wherein the decoding algorithm is also optional, and a corresponding decoding algorithm is selected according to the encoding mode of the received signal; and transmitting the measurement data obtained after decoding to a data processing computer through a communication interface.
Wherein, the radio technology refers to: in a digital wireless communication system, the digital modulation and demodulation technology realizes the modulation and demodulation of signals by using a digital method, so that the problems of signal phase and the like can be more accurately processed, the performances of system frequency bandwidth and the like are improved, a method of combining a digital circuit and software is convenient to use, and the possibility of realizing the software of system functions is provided. The device uses the DSP processing board to realize compatibility of various modulation modes and coding modes by adopting the technology, and can upgrade the software on line at any time to expand the function of the device.
The demodulation algorithm can be selected, the method of the device has the demodulation algorithm suitable for various signal modulation modes in the prior art, and different algorithms can be selected through method setting so as to receive signals transmitted by adopting different modulation modes, and the adaptability of the device is improved.
The decoding algorithm is optional, the method of the device has the decoding algorithm which is suitable for various signal coding modes in the prior art, and different algorithms can be selected through the method so as to receive signals transmitted by adopting different coding modes and improve the adaptability of the device.
Fig. 5 is a schematic diagram of adaptive noise cancellation. Since the useful signal is often drowned by noise or interference, the signal-to-noise ratio is poor, which reflects the increase of the bit error rate on the performance of the receiving device, in order to reduce the bit error rate of the receiving device, the signal needs to be subjected to noise filtering, the signal-to-noise ratio is improved, and adaptive noise cancellation is an effective noise filtering method, and can effectively improve the signal-to-noise ratio.
Where the noise comprises intentional or unintentional interference, the signal is transmitted to the sensor with the addition of uncorrelated noise n0Combined signal s + n0From the primary input to the canceller, the second sensor receives noise n1，n1Not related to signal s, but to n0There is some unknown correlation. n is1Through filteringRaw outputs y and n0Very similar. This y is input s + n from the original0Subtracting to obtain the system output s + n0-y。
In the adaptive cancellation system shown in fig. 5, the reference input is used to automatically adjust the filter of the system impulse response by the minimum mean square error algorithm, and the error signal is used to adjust its weight vector by the adaptive algorithm, so that the filter gives the desired output, which is then summed with n0The error minimization is obtained by subtracting the correlated components of (a).
Suppose s, n0，n1Y is statistically fixed and has a mean of 0, assuming again s and n0，n1Not related, only n0And n1Correlation, output error of
ε＝s+n0-y
Squaring the two sides to obtain
ε2＝s2+(n0-y)2+2s(n0-y)
Take both sides mathematically expected because s and n0Y is not related, therefore
E[ε2]＝E[s2]+E[(n0-y)2]+2E[s(n0-y)]
＝E[s2]+E[(n0-y)2]
When the filter parameters are adjusted to make E [ epsilon ]2]When minimized, the signal energy Es is not desired2]Will be affected so that the minimum output energy is:
Emin[ε2]＝E[s2]+Emin[(n0-y)2]
when the filter parameters change to make E [ epsilon ]2]When decreasing, E [ (n)0-y)2]Also reduced at the same time, the filter output y being the noise n in the original input0Is estimated. This means E [ (n)0-y)2]To minimize, E [ (epsilon-s)2]Also minimum, and thus, represented by the formula s + n0-y is obtained
(ε-s)＝(n0-y)
For a given adaptive filter structure and adjustability, and a given reference input, the filter parameters are adjusted to minimize their output energy, which is equivalent to having the output error s, which is mainly composed of the signal s and some noise, as estimated by the minimum variance of the signal s, given by the equation (s-s) ═ n0Y) knowing that the output noise is (n)0-y); since E [ epsilon ]2]And E [ (n)0-y)2]Having been minimized, the power of the output noise must be minimized; also the signal is constant in the output, so that a minimum output power corresponds to the case where the signal-to-noise ratio is maximum.
From the formula E [ epsilon ]2]＝E[s2]+E[(n0-y)2]+2E[s(n0-y)]It can be seen that the minimum possible output power is Emin[ε2]＝E[s2]When this is reached, E [ (n)0-y)2]0, so y is n0And s, in which case minimizing the output power leaves the output completely free of noise, which is an ideal case for adaptive filtering.
It can be seen that, by applying a proper receiving antenna form, one path of signals which mainly contains useful signals and simultaneously contains partial noise interference and the other path of signals which mainly contains a small amount of useful signals (ideally, the signals do not contain the useful signals) can be obtained, and the two paths of signals are respectively used as an original input end and a reference input end of the adaptive noise interference canceller for adaptive filtering, so that the signal-to-noise ratio of the output signals can be improved.
The above-described embodiments are intended to be illustrative only, and various modifications and alterations will readily occur to those skilled in the art based upon the teachings herein and the principles and applications of the present invention, which are to be considered in the foregoing detailed description of the invention.
Claims (6)
1. A ground signal receiving device of an electromagnetic measurement while drilling system comprises a signal receiving end, a signal processing unit and a signal output unit; it is characterized in that the preparation method is characterized in that,
the signal receiving end is a ground receiving antenna group and comprises an electromagnetic signal receiving antenna and an interference noise receiving antenna which are respectively used for receiving electromagnetic signals transmitted underground, ground interference signals and well site interference noise signals;
the signal processing unit comprises a double-channel signal coupler, a double-channel program-controlled preamplifier, a double-channel signal conditioner, a double-channel A/D converter, a DSP circuit and a power supply;
the signal output unit is used for outputting the signal of the signal processing unit through a communication port;
the electromagnetic signal receiving antenna and the interference noise receiving antenna sequentially process received signals through a dual-channel signal coupler, a dual-channel program-controlled preamplifier, a dual-channel signal conditioner, a dual-channel A/D converter and a DSP circuit, and underground data signals are output through a communication port;
the electromagnetic signal receiving antenna adopts a horizontal polarization receiving mode and is an asymmetric dipole antenna; for receiving electromagnetic signals including downhole transmissions and surface interference signals;
the interference noise receiving antenna adopts a monopole vertical polarization receiving mode and is a passive whip antenna; for receiving a wellsite disturbance noise signal.
2. The surface signal receiving device of the electromagnetic measurement while drilling system as recited in claim 1,
the dual-channel signal coupler comprises a signal coupler of an electromagnetic signal channel and a signal coupler of an interference noise signal channel; the ground receiving antenna group is used for coupling the signals received by the ground receiving antenna group to a lower circuit and realizing signal amplification, superposition and impedance transformation;
the dual-channel program-controlled preamplifier comprises an electromagnetic signal channel preamplifier and an interference noise signal channel preamplifier, and voltage preamplifiers are arranged in the dual channels;
the dual-channel signal conditioner comprises a signal conditioner of an electromagnetic signal channel and a signal conditioner of an interference noise signal channel; the system is used for conditioning electromagnetic signals and interference noise signals, namely filtering power frequency interference and anti-aliasing filtering;
the dual-channel A/D converter comprises an A/D converter of an electromagnetic signal channel and an A/D converter of an interference noise signal channel; the dual-channel signal conditioner is used for quantizing the two channels of signals sent by the dual-channel signal conditioner and sending the bit stream information to a lower circuit.
3. The surface signal receiving device of the electromagnetic measurement while drilling system according to claim 1 or 2,
in the dual-channel program-controlled preamplifier, the preamplifier of any channel comprises an ultra-low noise amplifier, a program-controlled amplifier, a 50Hz stuffing wave filter, a high-pass filter, a low-pass filter, an output amplifier, an output stage, an input mode control circuit, an amplification factor control circuit, a stuffing wave control circuit, a high-pass and low-pass filter cut-to-frequency control circuit and a power supply circuit;
in the dual-channel signal conditioner, any channel comprises an active low-pass filter, a zero setting circuit and an A/D protection circuit;
the DSP circuit comprises a digital signal processor and a peripheral circuit; the DSP circuit adopts a radio technology and is used for collecting, digitally filtering, adaptively denoising, demodulating, decoding and communicating two paths of signals.
4. The surface signal receiving device of the electromagnetic measurement while drilling system according to claim 1 or 2,
the device also comprises a signal coupler box and a receiver box; the signal coupler box is connected with the receiver box body;
the signal coupler box comprises a metal explosion-proof box body and the two-channel signal coupler; the metal explosion-proof box body is provided with two input and output ports. The two input ports are respectively connected with the electromagnetic signal receiving antenna and the interference noise receiving antenna through cables; the two output ports are connected to the signal input port of the receiver box body by a cable;
the receiver box body comprises a metal explosion-proof box body, and the dual-channel program-controlled preamplifier, the dual-channel signal conditioner, the dual-channel A/D converter, the DSP circuit, the power supply and the communication port are all arranged in the receiver box body.
5. The receiving method adopted by the ground signal receiving device of the electromagnetic measurement while drilling system according to any one of claims 1 to 4, wherein the receiving method comprises a signal receiving end, a signal processing unit and a signal output unit;
the receiving method is characterized by comprising the following steps:
1) a signal acquisition step: receiving an electromagnetic signal and an interference signal containing underground measurement data transmitted from an electromagnetic channel formed by the earth and a drill string according to the electromagnetic signal receiving antenna and the interference noise receiving antenna;
2) signal superposition and coupling steps: superposing and coupling the two paths of received signals by using the dual-channel signal coupler;
3) a signal amplification step: amplifying, conditioning and quantizing the two paths of signals obtained by coupling by using the dual-channel program-controlled preamplifier;
4) a signal filtering step: filtering the quantized digital signal by using the dual-channel signal conditioner;
5) a signal self-adaptive noise cancellation step: applying a DSP circuit to perform adaptive noise cancellation on the filtered signal;
6) signal demodulation and decoding steps;
7) a signal output step: and outputting the processed signal through the communication port.
6. The method for receiving the surface signal of the electromagnetic measurement while drilling system according to claim 5, wherein the method for receiving the surface signal comprises:
in the step 2, the superposition and the coupling are to input two paths of signals into a lower circuit through a coupler;
amplifying, conditioning and quantizing the two paths of signals in the step 3 into two paths of coupled signals which are amplified to 0-5V, filtering the amplified signals by a 50Hz wave trap and an 8-order low-pass filter, inputting the signals into two paths of A/D converters for quantization, and outputting two paths of quantized digital signals;
in step 4, the quantized digital signal is filtered, the signal is further filtered through the DSP circuit, and the filtered signal is subjected to adaptive noise cancellation processing;
the self-adaptive noise cancellation operation in the step 5 is to detect and extract a useful signal from an environment in which the signal is submerged by noise interference;
demodulating and decoding the signals in the step 6, demodulating the filtered signals by adopting a software radio technology, and decoding the data stream obtained after demodulation;
and 7, transmitting the measurement data obtained after decoding to a data processing computer through a communication interface.
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