CN102900430B - Pumping pressure interference elimination method for drilling fluid continuous pressure wave signals - Google Patents

Abstract

The invention provides a pumping pressure interference elimination method for drilling fluid continuous pressure wave signals. Two pressure sensors are installed on a straight pipe and are away from a distance, one end of the straight pipe is connected with a drilling fluid pump, the other end of the straight pipe is connected with a wellhead, the underground drilling fluid pressure signals for reflecting underground information of measurement while drilling are conveyed to the ground from the wellhead through the straight pipe and received by the pressure sensors installed on the straight pipe, and measurement signals of the two pressure sensors are subtracted to obtain delay differential detection signals. Due to the fact that pump pressure interference transmission direction is opposite to underground drilling fluid pressure signal transmission direction, pressure interference generated by the drilling fluid pump is eliminated in the process, no pump pressure interference contents exist in the delay differential detection signals, and the underground drilling fluid pressure signals contained in the delay differential detection signals are recovered through a signal reconstruction method based on a time domain differential equation or Fourier transformation so as to eliminate pump pressure interference influence in the signals and improve signal to noise ratio of the signals.

Description

The pump pressure interference elimination method of drilling fluid continuous pressure ripple signal

Technical field:

The present invention relates to the processing method of the measurement while drilling/well logging during up-delivering signal in a kind of oil/gas drilling process, particularly a kind of pump pressure interference elimination method carrying out the drilling fluid continuous pressure ripple signal of downhole data transmission based on drilling fluid.

Background technology:

DHM-MWD/well logging during (MWD/LWD) is a kind of modern drilling ancillary technique measured in real time in drilling process and transmit down-hole information.In drilling process, drilling fluid is pumped to down-hole by earth's surface by drill string, and be used for the lubrication and cooling of drill bit from bit port ejection and upwards return out well head by the toric space of the borehole wall and drill string, MWD/LWD instrument is arranged in the drill collar on drill bit top, sees accompanying drawing 1.In MWD/LWD instrument, be arranged on sensor in nearly drill bit drill string and obtain survey data and by drilling liquid pressure information telemetry system transfers to ground, information telemetry is by modulate the drilling liquid pressure in drill string and DHM-MWD/well logging during data are transmitted in the propagation of compression wave in drill string.Pressure information remote measurement adopts base band pressure pulse or continuous pressure ripple to transmit down-hole information usually, and wherein continuous pressure ripple has the down-hole information transfer rate more much higher than base band pressure pulse, is the developing direction of pressure information telemetry; Continuous pressure ripple signal mainly contains drilling liquid pressure differential phase keying (DPSK) (DPSK) signal and QPSK (QPSK) signal, and signal spectrum is concentrated, and has the feature of frequency band transmission.Transmit earthward at the bottom of drilling hydraulic force signal artesian well and very large noise and interference can be run in ground signal testing process, wherein to effect of signals maximum be drilling fluid pump produce pressure fluctuation interference.The pressure disturbances that drilling fluid pump produces is relevant with pump punch speed rate, comprise first-harmonic and higher hamonic wave, when each cylinder piston of drilling fluid pump exist sealing problem cause the imbalance of work or pump to be in abnormal operating state time, the amplitude of some higher hamonic wave can become very large, although drilling fluid pump pipeline is all provided with pressure buffer or damper, but the pressure fluctuation that drilling fluid pump produces still can meet or exceed the down-hole drilling fluids pressure signal intensity that ground standpipe detects, the frequency band that these higher hamonic waves can enter drilling fluid continuous pressure ripple signal produces interference greatly, the signal to noise ratio of signal is seriously reduced, thus affect the extraction of DHM-MWD signal.Current drilling liquid pressure signal detection mainly adopts a pressure sensor to be arranged on standpipe place, ground and measures drilling liquid pressure, the signal processing method adopted, if matched filter method, adaptive compensation, wavelet analysis method etc. are mainly for the lower pressure signal transmitted in base band mode of transfer rate; And for the relatively high drilling fluid continuous pressure ripple signal of transfer rate, because signal has frequency band transmission feature, the pressure disturbances very easily entering signal frequency band that drilling fluid pump produces, the detection and treatment method of above-mentioned down-hole drilling fluids pressure signal all effectively cannot eliminate the drilling fluid pump pressure disturbances impact of entering signal frequency band.

Summary of the invention:

Technical problem to be solved by this invention is exactly the defect existed for existing signal processing technology, provides the pump pressure interference elimination method in a kind of drilling fluid continuous pressure ripple signal.

Technical problem to be solved by this invention realizes by following technical scheme:

1. adopt and postpone the pump pressure interference effect that differential detection method eliminates drilling fluid pump

Setting pressure sensors A and pressure sensor B on one section of drilling fluid straight pipeline between well head and drilling fluid pump, wherein pressure sensor A is near well head, pressure sensor B is near drilling fluid pump, DHM-MWD data change drilling hydraulic force signal into by modulation drilling liquid pressure, after shaft bottom is transferred to well head by drill string, pressure sensor A is first arrived with undulating manner, then arrive pressure sensor B, the pressure signal that two sensors receives all comprises the pump pressure interference of down-hole drilling fluids pressure signal and drilling fluid pump generation; Flow to according to signal and analyze, the transmission direction of pump pressure interference is contrary with down-hole drilling fluids pressure signal, therefore the down-hole drilling fluids pressure signal that pressure sensor A receives will delay to reach pressure sensor B, the time that this section postpones is the transmission time of drilling hydraulic Reeb by the spacing of two pressure sensors, and the pump pressure interference that pressure sensor B receives will arrive pressure sensor A after the delay of this period; Therefore, the signal that A, B two pressure sensors receive can be expressed as following Mathematical Modeling

$\left\{\begin{array}{c}{p}_A\left(t\right)=s\left(t\right)+h\left(t\right)*n_p\left(t\right)\\ p_B\left(t\right)=h\left(t\right)*s\left(t\right)+n_p\left(t\right)\end{array}\right.---\left(1\right)$

In formula (1), p _at signal that () receives for pressure sensor A; p _bt signal that () receives for pressure sensor B; S (t) is down-hole drilling fluids pressure signal; n _pt pump pressure interference that () produces for drilling fluid pump; The unit impact response that h (t) is setting pressure sensors A and pressure sensor B segment pipe; Symbol " * " represents convolution algorithm.

By the p in formula (1) _bt () convolution h (t), has

p _B(t)*h(t)=[h(t)*s(t)]+n _p(t)*h(t) （2）

By the p in formula (1) _at () and formula (2) subtract each other the Mathematical Modeling obtaining postponing differential detection signal

Δp(t)=p _A(t)-p _B(t)*h(t)=s(t)-h(t)*h(t)*s(t) （3）

As can be seen from formula (3), pump distracter n _pt () passes through p _bthe convolution of (t) and h (t) and p _at the differential operational of () is eliminated, postpone in differential detection signal delta p (t) without pump pressure interference component.

Because the propagation path of pump interference is from pressure sensor B to pressure sensor A.Formula (2) means the detection signal p of pressure sensor B _bt () is the linear system of h (t) by a unit impact response again, because h (t) includes the delay τ that signal produced by setting pressure sensors A and pressure sensor B segment pipe ₀, its physical significance is by p _bt the pump pressure distracter in () postpones a τ again ₀after time, will with p _at the pump pressure distracter in () has identical time lag, due to signal p _a(t) and signal p _bt time that in () * h (t), pump pressure interference occurs is identical, by signal p _a(t) and signal p _bt () * h (t) subtracts each other the object that can reach and eliminate pump pressure interference.But due to formula (2) just a kind of mathematic(al) representation, in implementation process, can not p be made _bt () has by one the physical system that unit impact response is h (t) again, therefore the acquisition of delay differential detection signal is necessary can physics realization.And according to the same thinking of formula (3), if postpone τ ₀time is detected the signal of pressure sensor A again, then pressure sensor A detection signal p ' _at the pump pressure interference in () is namely propagate the pump pressure of coming by setting pressure sensors A and pressure sensor B segment pipe through pressure sensor B to disturb, by signal p ' _a(t) and signal p _bt () subtracts each other the impact can eliminating pump pressure interference equally, thus realize delay differential detection signal delta p (t) that formula (3) describes physically.Therefore, the acquisition postponing differential detection signal is by postponing τ ₀the signal p ' of time detected pressures sensors A again _a(t) and with the detection signal p of pressure sensor B _bt () subtracts each other to realize, namely

Δp(t)=p′ _A(t)-p _B(t) （4）

Down-hole drilling fluids pressure signal s (t) postponing to comprise in differential detection signal delta p (t) can be recovered by mathematical reconfiguration.

2. the mathematical reconfiguration of down-hole drilling fluids pressure signal

Reconstruct is referred to as from the process postponing to recover differential detection signal down-hole drilling fluids pressure signal, realize the reconstruct of underground signal, the structure of h (t) is a key issue, the present invention is achieved in that the restriction by transmission range and signal transmission rate, the highest frequency of drilling fluid continuous pressure ripple signal spectrum is generally tens hertz, and therefore the frequency of signal is limited; In limited frequency band, if regard the pipeline between setting pressure sensors A and pressure sensor B as none distortion linear system, then it forms ideal low-pass filter, and the frequency domain transfer function of system is

$H\left(\mathrm{j\ω}\right)=\mathrm{aG}\left(\mathrm{\ω}\right)e^{-\mathrm{j\ω}{\mathrm{\τ}}_0}---\left(5\right)$

In formula (5), a is the signal attenuation coefficient that signal is produced by setting pressure sensors A and pressure sensor B segment pipe; for unit gate function, ω _bfor the single-side belt width of unit gate function; represent the imaginary-part operator of plural number; ω=2 π f is signal angular frequency, and f is signal frequency; τ ₀=L ₀/ c ₀for the transmission time of compression wave between pressure sensor A and B, L ₀for the distance between pressure sensor A and B, c ₀for celerity of pressure wave.Then the unit impact response of setting pressure sensors A and pressure sensor B segment pipe is

$h\left(t\right)=\frac{a{\mathrm{\ω}}_b}{\mathrm{\π}}\·\frac{\sin \left[{\mathrm{\ω}}_b(t-{\mathrm{\τ}}_0)\right]}{{\mathrm{\ω}}_b(t-{\mathrm{\τ}}_0)}=\frac{{\mathrm{a\ω}}_b}{\mathrm{\π}}\mathrm{Sa}\left[{\mathrm{\ω}}_b(t-{\mathrm{\τ}}_0)\right]---\left(6\right)$

Get Fourier transformation to formula (3) to obtain

$\mathrm{\ΔP}\left(\mathrm{j\ω}\right)=S\left(\mathrm{j\ω}\right)\·[1-a^2{G}^2\left(\mathrm{\ω}\right)\·e^{-j2\mathrm{\ω}{\mathrm{\τ}}_0}]---\left(7\right)$

The spectral density function of down-hole drilling fluids pressure signal is

$S\left(\mathrm{j\ω}\right)=\frac{\mathrm{\ΔP}\left(\mathrm{j\ω}\right)}{1-a^2{G}^2\left(\mathrm{\ω}\right)\·e^{-j2\mathrm{\ω}{\mathrm{\τ}}_0}}=H\left(\mathrm{j\ω}\right)\mathrm{\ΔP}\left(\mathrm{j\ω}\right)---\left(8\right)$

Wherein, Δ P (j ω)=F [Δ p (t)]=F [p ' _a(t)-p _b(t)] for postponing the Fourier transformation of differential detection signal delta p (t); for the frequency domain transfer function of down-hole drilling fluids pressure signal recovery system, the reconstruct of down-hole drilling fluids pressure signal can be realized by H (j ω).

The reconstructing method of drilling hydraulic force signal can adopt the signal reconstruction based on time-domain difference equation and the signal based on Fourier transformation.

Theoretical according to digital filter, H (j ω) is a k(k=2 τ ₀/ T _s, T _sfor signal sampling period) rank IIR filter system.Therefore, under H (j ω) forms perfect low pass transmission conditions, signal reconstruction process based on time-domain difference equation makes delay differential detection signal delta p (t) have the closed loop Delay Feedback system of recursive structure by one, obtain the down-hole drilling fluids pressure signal postponing to comprise in differential detection signal with recursive algorithm, expression formula is

$s\left(t\right)=\mathrm{\Δp}\left(t\right)+{\left(\frac{{\mathrm{a\ω}}_b}{\mathrm{\π}}\right)}^2\mathrm{Sa}\left({\mathrm{\ω}}_{b}t\right)*\mathrm{Sa}\left({\mathrm{\ω}}_{b}t\right)*s(t-2{\mathrm{\τ}}_0)---\left(9\right)$

Signal reconstruction based on Fourier transformation obtains down-hole drilling fluids pressure signal by carrying out inverse Fourier transform to formula (8), and expression formula is

$s\left(t\right)=\frac{1}{2\mathrm{\π}}{\∫}_{-\∞}^{+\∞}\frac{\mathrm{\ΔP}\left(\mathrm{j\ω}\right)}{1-a^2{G}^2\left(\mathrm{\ω}\right)\·e^{-j2\mathrm{\ω}{\mathrm{\τ}}_0}}{e}^{\mathrm{j\ωt}}\mathrm{d\ω}---\left(10\right)$

3. the determination of pressure sensor reasonable distance

Two pressure sensors are when nearer, and drilling hydraulic Reeb is very little by transmission loss during two pressure sensors, and signal attenuation coefficient is in close proximity to 1(and a=1).Therefore, there is limit in the transfer function H (j ω) of down-hole drilling fluids pressure signal recovery system, pole frequency is

$f_0=\frac{1}{2{\mathrm{\τ}}_0}---\left(11\right)$

When pole frequency enters into signal band, can greatly interference be caused to the reconstruct of signal and cannot remove.For avoiding occurring this kind of situation, all pole frequency values should be greater than the band connection frequency of ideal low-pass filter, i.e. f ₀>f _b, obtain determining that the constraints of two pressure sensor spacing is thus

$L_0<\frac{c_0}{2f_b}---\left(12\right)$

The spacing of two pressure sensors can be determined on the basis meeting formula (12) constraints.

The invention has the beneficial effects as follows: adopt two pressure sensors to carry out postponing differential detection to eliminate the impact of drilling fluid pump pressure disturbances, and from delay differential detection signal, recover down-hole drilling fluids pressure signal by mathematical reconfiguration, reach raising Signal-to-Noise, ensure the correct extraction of the DHM-MWD information through drilling fluid transmission.

Accompanying drawing illustrates:

Fig. 1 is the drilling rig schematic diagram including measurement while drilling/well logging during instrument and drilling liquid pressure signal detection and process in prior art.

Fig. 2 is the detection and treatment flow chart of drilling fluid continuous pressure ripple signal in the present invention.

Fig. 3 a is the Computer Data Handling software block diagram carrying out signal reconstruction based on time-domain difference equation of the present invention.

Fig. 3 b is the Computer Data Handling software block diagram carrying out signal reconstruction based on Fourier transformation of the present invention.

Fig. 4 a is the wave simulation figure of the drilling liquid pressure DPSK original signal of 10 binary elements in the present invention.

Fig. 4 b is the wave simulation figure that in the present invention, drilling liquid pressure DPSK original signal is mixed into pump pressure interference.

Fig. 4 c is the wave simulation figure postponing differential detection signal in the present invention.

Fig. 4 d is the wave simulation figure of drilling liquid pressure dpsk signal reconstruct in the present invention.

In figure: 1-drilling fluid, 2-earth's surface, 3-drill string, 4-drilling fluid pump, 5-drill bit, 6-annular space, 7-stratum, 8-drilling parameter and formation parameter measurement mechanism, 9-drilling fluid continuous pressure wave generator, 10-pressure sensor, 11-signal processing apparatus, 12-drill collar, 13-drilling fluid tank, 14-pressure sensor A, 15-pressure sensor B, 16-data acquisition and signal processing system, 17-drilling hydraulic force signal, 18-well head, 19-drilling fluid pump press interfering signal, 20-straight pipeline.

Detailed description of the invention:

The present invention is further described below in conjunction with drawings and Examples.

It is the existing drilling rig including measurement while drilling/well logging during instrument and drilling liquid pressure signal detection and process shown in Fig. 1.Drilling fluid 1 in drilling fluid tank 13 injects the drill string 3 of formation drilling 7 by the drilling fluid pump 4 on earth's surface 2, arrive the drill bit 5 of drill string 3 bottom, after bit port flows out, be back to earth's surface 2 by the annular space 6 between drill string 3 and stratum 7, arrow represents the flow path of drilling fluid.

In the drill collar 12 of drill bit 5, place instrument in drill string 3, drill collar top jointed rod forms drill string, and whole drill string applies enough the pressure of the drill for formation drilling 7 to drill bit 5.Instrument in drill collar 12 comprises drilling parameter and formation parameter measurement mechanism 8 for monitoring the physical characteristic of drill-well operation and evaluation of earth formations.

In order to produce pressure oscillation and transmit downhole data by drilling fluid in drilling fluid, drilling fluid continuous pressure wave generator 9 is arranged on the top of drill collar 12, drilling hydraulic force signal is uploaded to ground by drill string, detects and sends into signal processing apparatus 11 carry out signal transacting through pressure sensor 10.

The pump pressure interference elimination method of drilling fluid continuous pressure ripple signal, realizes by following technical scheme:

1. adopt and postpone the impact of differential detection method elimination drilling fluid pump pressure disturbances

Setting pressure sensors A and pressure sensor B in one section of drilling fluid straight tube road between well head and drilling fluid pump, wherein pressure sensor A is near well head, pressure sensor B is near drilling fluid pump, first DHM-MWD signal runs into pressure sensor A after shaft bottom is transferred to well head, and the pressure signal that two pressure sensors receive all comprises the pump pressure interference of down-hole drilling fluids pressure signal and drilling fluid pump generation.Flow to according to signal and analyze, the transmission direction of pump pressure interference is contrary with the transmission direction of down-hole drilling fluids pressure signal, therefore the down-hole drilling fluids pressure signal that pressure sensor A receives will arrive pressure sensor B after delay after a while, this period is the transmission time of drilling hydraulic Reeb by the spacing of two pressure sensors, and the pump pressure interference that pressure sensor B receives will arrive pressure sensor A after the delay of this period.The a certain moment, pressure sensor B has a certain pressure measuring value, carry out detection after this period is postponed to the output signal of pressure sensor A again and obtain measured value, the measured value of pressure sensor A measured value and pressure sensor B subtracts each other and obtains postponing differential detection signal, pump pressure interference is eliminated in this course, postpone in differential detection signal without pump pressure interference component, and the down-hole drilling fluids pressure signal postponing to comprise in differential detection signal can be recovered by special mathematical reconfiguration, therefore the method is referred to as to postpone differential detection method, the Mathematical Modeling of the delay differential detection signal that the time domain Mathematical Modeling of the pressure sensor A that through type (1) represents and pressure sensor B signal and formula (3) represent can clearly describe.

2. the mathematical reconfiguration of down-hole drilling fluids pressure signal

Be referred to as reconstruct from the process postponing to recover differential detection signal down-hole drilling fluids pressure signal, reconstruct adopts the signal reconstruction based on time-domain difference equation and the signal reconfiguring method based on Fourier transformation.Signal reconstruction process based on time-domain difference equation makes delay differential detection signal have the closed loop Delay Feedback system of recursive structure by one, obtains the down-hole drilling fluids pressure signal postponing to comprise in differential detection signal with recursive algorithm.Signal reconstruction based on Fourier transformation obtains down-hole drilling fluids pressure signal by the inverse Fourier transform represented by formula (10).

3. the determination of pressure sensor reasonable distance

Two pressure sensors are when nearer, drilling hydraulic Reeb is very little by transmission loss during two pressure sensors, the mould of its transfer function is close to 1, therefore there is limit in the transfer function of down-hole drilling fluids pressure signal recovery system, when limit respective frequencies enters into signal band, can greatly interference be caused to the reconstruct of signal and cannot remove.For avoiding occurring this kind of situation, all pole frequency values should be greater than the band connection frequency of ideal low-pass filter, can obtain the transducer spacing constraints represented by formula (12) thus: pressure sensor spacing should be less than pressure velocity of wave divided by the ideal low-pass filter band connection frequency of 2 times.The spacing of two pressure sensors can be determined on the basis meeting above-mentioned constraints.

Detection and the process chart of drilling fluid continuous pressure ripple signal shown in Fig. 2, the present invention adopts the drilling liquid pressure measured respectively at a distance of two pressure sensors of a segment distance in specific straight pipeline, wherein pressure sensor A will postpone relative to pressure sensor B the measurement that a period of time carries out drilling liquid pressure again, this period is the transmission time of drilling hydraulic Reeb by the spacing of two pressure sensors, the signal of two pressure sensors is by the data acquisition and procession of computer, realize the elimination of drilling fluid pump pressure disturbances and the reconstruct of down-hole drilling fluids pressure signal.Its technical scheme is: straight pipeline 20 is connected between well head 18 and drilling fluid pump 4, drilling fluid 1 is injected into down-hole by this segment pipe by well head 18, pressure sensor A14 is near well head 18, pressure sensor B15 is near drilling fluid pump 4, the drilling hydraulic force signal 17 that down-hole is uploaded is propagated to drilling fluid pump 4 direction from well head 18, successively through pressure sensor A14 and pressure sensor B15, pump pressure interfering signal 19 is propagated to well head 18 direction from drilling fluid pump 4, successively through pressure sensor B15 and pressure sensor A14, pressure sensor A14 can be connected with signal processing system 16 with computer data acquiring by wired or wireless mode with the signal of telecommunication of pressure sensor B15, the signal of computer to pressure sensor A14 and pressure sensor B15 processes the reconstruct of elimination and the down-hole drilling fluids pressure signal realizing drilling fluid pump pressure disturbances, the core of Computer signal handling procedure is the delay differential detection algorithm of signal and the mathematical reconfiguration algorithm of down-hole drilling fluids pressure signal, wherein, postpone differential detection algorithm by calculating the transmission time of drilling hydraulic Reeb through the spacing of two pressure sensors, make pressure sensor A postpone this period relative to pressure sensor B and carry out drilling liquid pressure measurement again, then the measured value of pressure sensor A measured value and pressure sensor B is subtracted each other and obtain postponing differential detection signal, the mathematical reconfiguration algorithm of down-hole drilling fluids pressure signal adopts formula (9) based on the signal reconstruction of time-domain difference equation or formula (10) signal reconfiguring method based on Fourier transformation.

In Fig. 3 a, the delay differential detection of pressure signal and the reconstruct of down-hole drilling fluids pressure signal are all realized by the data Collection & Processing System of computer under time domain condition, and signal reconstruction adopts the recursive algorithm based on time-domain difference equation.

In Fig. 3 b, in computer data acquisition and treatment system, first the delay differential detection value of pressure signal is obtained in time domain, then Fourier transformation is carried out to it and be converted to frequency domain value, be multiplied with the frequency domain transfer function of down-hole drilling fluids pressure signal recovery system again and obtain the spectral density function of drilling hydraulic force signal, the reconstruct that inverse Fourier transform realizes down-hole drilling fluids pressure signal is got to the spectral density function of drilling hydraulic force signal.

In Fig. 4 a, the modulating data of drilling liquid pressure DPSK original signal is encoded to [1 11111111 1], carrier frequency 20Hz, amplitude 1Pa.

In Fig. 4 b, the fundamental frequency 3.2Hz of pump pressure interference, overtone order 2-9, first-harmonic and each harmonic amplitude are all 1Pa, after drilling liquid pressure DPSK original signal is mixed into pump pressure interference, pump pressure interference amplitude much larger than drilling liquid pressure DPSK original signal amplitude, signal to noise ratio is 0.11, signal completely by pump pressure disturb flood.

In Fig. 4 c, as can be seen from delay differential detection signal, pump pressure interference is completely eliminated.

In Fig. 4 d, drilling liquid pressure DPSK reconstruction signal is consistent with the Changing Pattern of Fig. 4 a original signal, and signal is well recovered.

Claims (1)

1. a pump pressure interference elimination method for drilling fluid continuous pressure ripple signal, is characterized in that carrying out according to the following steps:

(1) the pump pressure interference effect postponing differential detection method elimination drilling fluid pump is adopted

Setting pressure sensors A and pressure sensor B on one section of drilling fluid straight pipeline between well head and drilling fluid pump, wherein pressure sensor A is near well head, pressure sensor B is near drilling fluid pump, DHM-MWD data change drilling hydraulic force signal into by modulation drilling liquid pressure, after shaft bottom is transferred to well head by drill string, pressure sensor A is first arrived with undulating manner, then arrive pressure sensor B, the pressure signal that two sensors receive all comprises the pump pressure interference that down-hole drilling fluids pressure signal and drilling fluid pump produce; Flow to according to signal and analyze, the transmission direction of pump pressure interference is contrary with down-hole drilling fluids pressure signal, therefore the down-hole drilling fluids pressure signal that pressure sensor A receives will delay to reach pressure sensor B, the time postponed is the transmission time of drilling hydraulic Reeb by the spacing of two pressure sensors, and the pump pressure interference that pressure sensor B receives will arrive pressure sensor A after the delay of this period; In a certain moment, pressure sensor B measures pipeline pressure value, and pressure sensor A measures pipeline pressure value after postponing this period, and the measured value of pressure sensor A and the measured value of pressure sensor B subtract each other and obtain postponing differential detection signal; Pump pressure interference is eliminated in this course, postpone without pump pressure interference component in differential detection signal, and the down-hole drilling fluids pressure signal postponing to comprise in differential detection signal can be recovered by mathematical reconfiguration;

(2) mathematical reconfiguration of down-hole drilling fluids pressure signal

Adopt based on time-domain difference equation signal reconstruction or adopt based on the signal reconfiguring method of Fourier transformation, signal reconstruction process based on time-domain difference equation makes delay differential detection signal have the closed loop Delay Feedback system of recursive structure by one, the down-hole drilling fluids pressure signal postponing to comprise in differential detection signal is obtained with recursive algorithm, or, signal reconstruction based on Fourier transformation passes through the finite bandwidth ideal low-pass filter Mathematical Modeling building pipeline between setting pressure sensors A and pressure sensor B, set up the frequency domain transfer function of down-hole drilling fluids pressure signal recovery system, down-hole drilling fluids pressure signal is obtained by the inverse Fourier transform of output function during down-hole drilling fluids pressure signal recovery system to postpone differential detection signal,

(3) determination of pressure sensor spacing

The spacing of two pressure sensors should be less than the finite bandwidth ideal low-pass filter band connection frequency of pressure velocity of wave divided by pipeline between installation two pressure sensors of 2 times.