CN116181323A

CN116181323A - While-drilling acoustic wave remote detection method based on dipole single-shot dual-receive measurement mode

Info

Publication number: CN116181323A
Application number: CN202211642995.2A
Authority: CN
Inventors: 唐晓明; 李杨虎; 苏远大
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2022-12-20
Filing date: 2022-12-20
Publication date: 2023-05-30

Abstract

The invention discloses a method for remotely detecting acoustic waves while drilling based on a dipole single-shot dual-reception measurement mode, which mainly comprises the following steps: placing a dipole acoustic source and receiver pointing along the instrument x-axis in the well and connecting to the drilling system, exciting the acoustic source and collecting signal XX during drilling ₁ And XX ₂ The method comprises the steps of carrying out a first treatment on the surface of the Filtering, wave field separation and offset imaging processing are carried out on the acquired signals; composing dipole data XX with an off-well reflected signal and comparing the measurements to find the maximum amplitude signal XX (AZ) ₀ ) The method comprises the steps of carrying out a first treatment on the surface of the Selecting a speed model according to stratum types, determining the orientation of the geologic body and correcting the rotation effect of the instrument; according to signal XX ₁ And XX ₂ The difference in time is used for distinguishing the real azimuth of the geologic body; for maximum amplitude signal XX (AZ ₀ ) And (3) performing offset imaging, and determining the well-leaving distance of the geologic body to obtain a final well external reflection imaging result. The invention can realize accurate detection and imaging of the geological structure outside the well in the drilling process, provide real-time geosteering and wellbore track optimization for the well drilling, and improve the accuracy of the well drilling constructionDegree and drilling efficiency.

Description

While-drilling acoustic wave remote detection method based on dipole single-shot dual-receive measurement mode

Technical Field

The invention belongs to the field of geophysical acoustic logging, in particular to the method, which comprises the steps of radiating elastic waves outside a well for a plurality of times by utilizing a directional dipole sound source in the drilling process, measuring sound waves reflected by an underground geologic body by using two groups of receivers which are in the same direction as the sound source, and processing a plurality of measurement signals to realize detection and imaging of the underground geologic structure in the drilling process and provide real-time geosteering for drilling.

Background

With the continuous deep development of oil and gas resource exploration, the conventional vertical well technology is difficult to meet the requirements of field application, and the drilling and logging technology of complex wells such as high-inclination wells, horizontal wells and the like needs to be developed. The key point of the complex well drilling and exploitation is the accurate and effective geosteering while drilling function, so that the reservoir boundary can be effectively tracked in the real-time drilling process, the optimal drilling direction can be further guided, and the drilling meeting rate of the hydrocarbon reservoir can be improved.

At present, the geosteering function is mainly realized by a measurement technology of resistivity of azimuth electromagnetic waves while drilling, but the frequency of the azimuth electromagnetic waves is usually higher, and the signal attenuation is large, so that the method can only detect geological structures in the range of a few meters beside a well, and cannot obtain the optimal borehole drilling track (Liu Naizhen, wang Zhong, liu Ce, 2015, the geosteering key technology [ J ] of the azimuth resistivity instrument of propagation of the electromagnetic waves while drilling, namely geophysical school report, 58 (5), 1767-1775).

The acoustic wave remote detection technology is an important technology in the field of oil and gas exploration and development in recent years, and radiates elastic waves into an external stratum of a well through a dipole acoustic source in a liquid filled well, and performs well periphery imaging by utilizing acoustic waves received in the well and reflected back through the external geologic body. The method has the advantages of strong azimuth sensitivity, deep radial detection depth and the like, is well-established in cable logging and is applied to detection of geological structures such as cracks, faults, corrosion holes and the like beside a well (Tang Xiaoming, gu Xihao, li Yanghu, su, 2021, interaction of a well hole and elastic waves: theory, method and application [ J ]: geophysical school, 64 (12), 4227-4238). One potential application of dipole acoustic remote detection technology is to provide geosteering in logging while drilling, however, unlike the wireline logging case, where the drill collar rotates at high speed, the effect of instrument rotation on the measurement process must be considered. Zeng Yijin et al propose to perform acoustic measurement while drilling (Zeng Yijin, zhu Zuyang, li Fengbo, etc. 2022) prior to single joint gap or tripping, acoustic remote detection while drilling system and method [ P ]: chinese patent, CN 110805433B), but the method is only applicable when the instrument is in (or near) stationary state, cannot be applied when the instrument drills, has low measurement efficiency, and is difficult to meet the requirement of real-time geosteering.

Thus, based on the urgent need for geosteering while drilling, the present invention proposes a method for scanning detection and imaging of geologic formations outside of a well by high-speed rotation of a drill collar using multiple transmissions and receptions of one dipole source in a real-time drilling process.

Disclosure of Invention

The invention aims to provide a sound wave remote detection while drilling method based on a dipole single-shot double-receiving measurement mode, which utilizes a directional dipole source to excite P waves, SH and SV transverse waves to the outside of a well in a real-time drilling process, elastic waves act on geologic bodies in stratum and then return to the well to be recorded by two groups of receivers on instruments, and the detection and imaging of geologic structures beside the well are realized by processing measurement signals, so that an effective solution is provided for real-time geosteering and borehole track optimization in the drilling process of complex wells such as a highly-deviated well and a horizontal well.

In order to achieve the above object, the present invention adopts the following specific steps:

step one, placing a dipole acoustic logging while drilling instrument in a well and connecting the instrument with a drilling system, exciting a dipole acoustic source pointing along the x axis of the instrument in a real-time drilling process, and radiating elastic waves into an underground stratum.

And step two, recording azimuth AZ of the instrument coordinate axis (such as the x axis) relative to a fixed direction (such as the magnetic north pole of the earth).

Step three, acquiring signals XX by two receivers symmetrically distributed along the two sides of the x axis of the instrument ₁ And XX ₂ 。

And fourthly, filtering and wave field separation processing are carried out on the acquired signals, direct waves propagating along the well holes are suppressed and removed, reflected signals from an external interface of the well are extracted, and offset imaging is carried out on the reflected signals.

Step five, forming dipole data xx=xx by using the imaged off-well reflection signals ₁ -XX ₂ Selecting a plurality of measurement data XX adjacent to each other before and after, comparing waveform amplitude values, and finding out a maximum amplitude signal XX (AZ ₀ )。

Step six, performing transverse wave processing on dipole data in a hard stratum and a conventional soft stratum, and constructing a speed model by using transverse wave time difference, wherein the orientation of the underground geologic body is as follows

Or->

In the ultra-soft stratum, carrying out longitudinal wave processing on dipole data, and constructing a speed model by adopting longitudinal wave time difference, wherein the orientation of the underground geologic body is +.>

Or->

Correcting the azimuth of the geologic body in the step six according to the rotation angle delta of the instrument, wherein the corrected azimuth is

Or->

Step eight, according to signal XX ₁ And XX ₂ Is different from the correction result

And->

The true azimuth of the geologic body is judged: if signal XX ₁ Time of arrival leading to XX ₂ Then->

And->

Near X in the middle ₁ The angle of the receiver side is true, and the receiver side is close to X ₂ The angle of the receiver side is the true bearing.

Step nine, for maximum amplitude signal XX (AZ ₀ ) And D, performing offset imaging, performing deep conversion on imaging according to the speed model in the step six, and further determining the well-leaving distance of the geologic body to obtain a final well external reflection imaging result.

In the first step, the dipole sound source points to the x-axis direction of the instrument coordinate system and consists of two polar plates symmetrically distributed on the outer rings at two sides of the instrument x-axis, and the two polar plates have the same energy and opposite polarities of excitation signals. In operation of the instrument, the dipole source is excited to radiate an elastic wave into the formation outside the well.

In the second step, for a vertical well, the earth magnetic north pole is selected as the fixed direction; for inclined and horizontal wells, the fixed azimuth references the high end of the wellbore.

In the third step, the receiver consists of two receiving polar plates symmetrically distributed on two sides of the x axis of the instrument, the elastic wave excited by the dipole source is reflected by the geologic body in the stratum and returns to the well, and the receiver records the signal XX ₁ And XX ₂ Wherein the first letter represents the sound source direction and the second letter and number represent the receiver. In the drilling process, the dipole sources are excited and data are acquired repeatedly from step one to step three as the drill collar rotates at high speed. It should be noted that the time interval between two adjacent excitations of the sound source should be long enough to ensure that the signal received for the first time is not affected by the excitation for the second time.

The fourth step is specifically as follows: first for the acquisition signal XX ₁ And XX ₂ Filtering and direct wave pressure vibration treatment are carried out to reduce noise interference and direct wave period, then wave field separation is carried out by selecting methods such as median filtering or F-K filtering, direct wave interference is removed, and reflected waves of an external interface are extracted from the full wave. To the outside of the wellAnd the reflected wave is subjected to signal enhancement processing according to the common-center point superposition, inclination angle superposition and radial compensation methods, and finally is imaged by using deep-conversion offset imaging.

In the fifth step, since the instrument rotates continuously during measurement, for a certain depth point, multiple measurement data of the depth point adjacent to each other up and down can be regarded as measurement results of the instrument in different directions of the depth point, and then the amplitudes of the multiple measurement XX data are compared to find the azimuth AZ of the instrument corresponding to the maximum amplitude ₀ . In the invention, for the common drilling speed, about 20 times of measurement data are generally selected for comparison to obtain an accurate result.

In the sixth step, under the conditions of hard stratum and conventional soft stratum, the dipole transverse wave is used for conducting far detection, transverse wave processing is conducted on dipole data, a velocity model is built by adopting transverse wave time difference, and the orientation of the underground geologic body is that

Or->

Under the condition of ultra-soft stratum, the measured external signals are elastic longitudinal waves, the dipole data are subjected to longitudinal wave processing, a speed model is built by adopting longitudinal wave time difference, and the external geologic body azimuth is +.>

Or (b)

In the seventh step, the tool rotation angle δ during actual logging may be determined according to the tool rotation speed RPM and the reflected signal arrival time T ₀ Calculation is performed, i.e. δ=rpm·t ₀ 。

In the step eight, according to the signal XX ₁ And XX ₂ Is different (lead or lag), from the corrected result

And->

Judging the true azimuth of the geologic body, and eliminating the azimuth 180-degree uncertainty of the results of the step six and the step seven: if signal XX ₁ Time of arrival leading to XX ₂ Then->

And->

Near X in the middle ₁ The angle of one side of the receiver is the true azimuth of the geologic body, and the angle is close to X ₂ The angle of one side of the receiver is the true azimuth of the geologic body. It should be noted that the instrument records the azimuth AZ in which the acoustic source is transmitting, but as the instrument rotates, the reflected wave returns to the borehole by delta degrees, so the instrument records the corresponding received waveform at virtually (AZ + delta) for azimuth AZ. Comparison signal XX ₁ And XX ₂ By directly observing the waveforms, or by using fast fourier transforms (Fast Fourier Transform, FFT) or dynamic time warping (Dynamic Time Warping, DWT), etc.

The step nine specifically comprises the following steps: for the maximum amplitude signal XX (AZ) ₀ ) Firstly, carrying out signal enhancement processing according to a common center point superposition, inclination angle superposition and radial compensation method; then, performing deep conversion on imaging according to the speed model determined in the step six, and determining the well-leaving distance of the reflector; and finally, performing further noise reduction treatment on the imaging result by utilizing direct filtering or F-K filtering to finally obtain a reflection imaging result of the underground geologic body.

In addition, the present invention is described in three points:

firstly, in the fifth and eighth steps, reflection data or imaging data after time depth conversion can be used, depending on whether the signal to noise ratio of the two data in the actual well logging is good or bad. This is because offset imaging is a linear transformation that does not change signal XX ₁ And XX ₂ From reflected data, relative amplitude magnitude and time-of-arrival relationshipAnd the results obtained in the imaging data are consistent.

Secondly, the rotation effect of the instrument is strictly considered and the position recognition result is corrected in the invention, but in actual measurement, when the geological structure outside the well is close to the well hole (within 50 m), the rotation effect of the instrument can be ignored (namely, the step seven is omitted), and the accurate position result can be obtained at the moment.

Thirdly, in actual drilling, the drill collar often deviates from the well axis due to complex movements of the drilling tool, the dead weight of the drill collar and the like. The method is mainly used for positioning the underground geologic body by utilizing the azimuth amplitude characteristic and the arrival time delay relation of the received waveform, and the relative magnitude of the waveform amplitude and the arrival time are not affected by the smaller drill collar eccentricity, so that the method can be well applied to the condition of the drill collar eccentricity.

The invention has the advantages and positive effects that: the method for detecting the dipole acoustic wave along with drilling can realize accurate detection and imaging of the geological structure outside the well, provide real-time geosteering and borehole track optimization for drilling, and improve the accuracy and drilling efficiency of drilling construction.

Drawings

FIG. 1 is a working flow chart of a method for detecting acoustic wave far while drilling based on a dipole single-shot double-shot measurement mode;

FIG. 2 is a schematic diagram of a model of the detection of an outdoor geologic body in accordance with the present invention;

FIG. 3 (a) is a schematic cross-sectional view of a borehole pointing along the x-axis toward a dipole acoustic source in accordance with the present invention;

FIG. 3 (b) is a schematic cross-sectional view of a well bore of the receiver of the present invention symmetrically disposed along the x-axis;

FIG. 4 is a schematic illustration of a four-component reflected acoustic imaging logging while drilling dipole according to the present invention;

FIG. 5 (a) is a dipole transverse wave waveform XX for azimuth measurement in the present invention;

FIG. 5 (b) is a normalized amplitude of the dipole transverse wave waveform XX for azimuth measurement in the present invention;

FIG. 6 (a) is a dipole longitudinal wave waveform XX of the azimuth measurement of the present invention;

FIG. 6 (b) is a normalized amplitude of the dipole longitudinal wave waveform XX for azimuth measurement in the present invention;

FIG. 7 (a) shows a dipole transverse XX wave received at an azimuth angle of 30℃for the instrument of the present invention ₁ And XX ₂ Is a waveform comparison of (1);

FIG. 7 (b) shows a dipole longitudinal wave XX received when the azimuth of the instrument is 30 DEG in the present invention ₁ And XX ₂ Is a waveform comparison of (1);

FIG. 8 is a graph of the results of a synthetic example of the detection of an extra-well geologic volume using a dipole shear while drilling method in accordance with the present invention;

FIG. 9 is a graph of the results of an example of the synthesis of a method for detecting an extrawell geologic volume using a dipole longitudinal wave while drilling method in accordance with the present invention.

Numbering in the figures: 1. a fluid-filled wellbore; 2. a drill collar; 3. a receiver; 4. a dipole sound source; 5. a reflective interface; 6. virtual sources.

Detailed description of the preferred embodiments

The method of the present invention will be further described with reference to the specific principles of downhole geologic formation detection in combination with a single-shot, dual-shot measurement mode of while-drilling, using theoretical synthesis examples, which are not intended to limit the scope of the invention, so that those skilled in the art may better understand the invention and practice it.

As shown in fig. 1, the invention provides a method for detecting acoustic wave along with drilling based on a dipole single-shot dual-receive measurement mode, which comprises the following specific working procedures:

step one, placing the while-drilling dipole acoustic logging instrument shown in fig. 2 in a well and connecting the while-drilling dipole acoustic logging instrument with a drilling system, and exciting a dipole acoustic source to radiate elastic waves into an external stratum of the well in a real-time drilling process. Wherein, the dipole sound source points to the X-axis direction of the instrument coordinate system, and two polar plates X symmetrically distributed on two sides of the instrument X-axis are used ₁ And X ₂ The energy of the excitation signals of the two plates are identical and of opposite polarity, as shown in fig. 3 (a).

And step two, recording azimuth AZ of the instrument coordinate axis (such as the x axis) relative to the fixed direction when the sound source is excited. For a vertical well, the fixed direction is the magnetic north pole of the earth; for inclined and horizontal wells, the fixed azimuth references the high end of the wellbore.

Step three, collecting signal XX by a receiver ₁ And XX ₂ Wherein the first letter represents the sound source direction and the second letter and number represent the receiver. The receiver consists of two receiving plates symmetrically distributed on both sides of the x-axis of the instrument, as shown in fig. 3 (b). In the drilling process, the dipole sources are excited and data are acquired repeatedly from step one to step three as the drill collar rotates at high speed. It is noted that the time interval between two adjacent excitations of the sound source should be long enough to ensure that the first received signal is not affected by the second excitation.

In order to better explain the method by utilizing the theoretical example, firstly, according to the interaction theory of the well hole and the elastic wave, an analytic solution of the acoustic field received by the far detection of the azimuth of the dipole acoustic wave while drilling in the liquid-filled well is established. FIG. 2 shows a schematic diagram of the detection of a near-well geologic volume using an acoustic logging while drilling instrument, with a dipole acoustic source on the instrument radiating elastic waves out of the well, reflected by the geologic volume and incident back into the well for receipt by a receiver on the instrument. For far field reception, the polar plate transmit/receive effect in fig. 3 can be described using the point transmit/receive effect when solving for the theoretical sound field.

Describing by adopting the coordinate system shown in fig. 2 and 3 (a) and (b), the medium space of the logging while drilling model is divided into four parts of fluid in a drill collar, the drill collar, a fluid ring outside the drill collar and a stratum outside the well in the radial direction, wherein the outer radius of each part is r respectively ₁ 、r ₂ A and infinity. Assuming that the drill collar is completely centered in the borehole, an annular dipole sound source is placed on the surface of the drill collar and points in the positive x-axis direction, and the radius r of the annular sound source ₀ Equal to the outer radius r of the drill collar ₂ . All three interfaces contained in the model are fluid-solid interfaces, and the boundary conditions require that radial displacement and radial stress are continuous, and the shearing stress in the circumferential direction and the axial direction is zero. By linking the boundary conditions at the three interfaces, a matrix equation containing twelve unknown coefficients can be obtained

H×[A ^fin ,A ^dc ,B ^dc ,C ^dc ,D ^dc ,E ^dc ,F ^dc ,A ^fout ,B ^fout ,B ^fm ,D ^fm ,F ^fm ] ^T In the formula (1), H is a 12×12 matrix, b is a 12×1 vector, and the vector b represents the direct contribution of the annular dipole sound source at the drill collar surface, and the specific expression is shown in (Tang, x.m., and C.H.Cheng,2004,Quantitative borehole acoustic methods[M]Elsevier Science publishing level); letters marked as fin, dc and fout in the coefficient vector respectively represent amplitude coefficients of elastic waves in the fluid in the drill collar, the drill collar and the fluid ring, and represent the intensity of a guided wave sound field in the well; letters marked fm correspond to the amplitude coefficients of the radiation waves in the formation, which are the basis for imaging the geologic formations downhole by dipole remote detection. In the case of far field radiation, the far field asymptotic solution of the displacement potential function of the P-wave, SH, and SV transverse waves radiated by the dipole acoustic source into the formation in FIG. 2 is

Wherein omega is the circular frequency, S is the sound source function spectrum, alpha _fm And beta _fm The formation longitudinal wave velocity and the formation transverse wave velocity,

and->

The wave numbers of the longitudinal wave and the transverse wave are respectively degraded at the fastest speed, theta _t Is the angle between the wave radiation direction and the positive direction of the z-axis, < >>

For the angle between the projection of wave radiation direction on horizontal plane and the direction of sound source, R is the distance between sound source and radiation field point, and the amplitude coefficient B ^fm 、D ^fm And F ^fm The result is obtained by the matrix equation (1).

From (2), it is known that the dipole radiation acoustic field while drilling is set to e ^iωR/v The spherical wave form of R propagates deep into the formation, and when a reflector is present in the formation, the radiated wave will interact with the reflector, where the reflector is larger in sizeThe incident wave field reflected back into the borehole at wavelength can be represented by formula (3) (Tang, X.M., J.J.Cao, and Z.T.Wei,2014, shear-wave radiation, recovery, and reciprocity of a borehole dipole source: with application to modeling of shear-wave reflection survey [ J)]Geophysics,79, no.2, T43-T50.). It is noted that during this time the orientation of the reflector changes. For the model shown in FIG. 2, when the acoustic source is excited, the reflector is oriented with respect to the x-axis of the instrument coordinate system as

As the instrument rotates (assuming the instrument rotates clockwise), the orientation of the reflector with respect to the x-axis of the instrument becomes when the radiation wave is reflected back into the well by the reflector

Where δ is the angle through which the instrument is rotated during propagation of the acoustic wave in the formation.

Where v is the formation longitudinal or transverse velocity (i.e., alpha _fm Or beta _fm ) The method comprises the steps of carrying out a first treatment on the surface of the RD is the far-field radiation function of the sound source, which is formed by the part inside the square brackets of (2), and will be calculated

Is taken as->

RF is the reflection coefficient of an acoustic wave at the reflector, which can be calculated from the zopriz equation; the specific form of RD and RF depends on the type of incident wave considered (i.e., P, SH or SV wave); and D is the total propagation distance of the sound wave in the stratum, and the propagation path is a fold line from the sound source to the reflection point and then from the reflection point to the receiving point. By regarding the far detected sound field as the radiation sound field of the virtual source, the position of the virtual source is +.>

Coincident with the mirror image of the acoustic source in the well on the outward side of the reflector as shown in fig. 2. The propagation path D of the acoustic wave is converted into a straight line, so that the spherical wave propagation factor in the formula (3) can be expanded into a form of superposition of multipole cylindrical waves (Li, Y.H., X.M.Tang, H.R.Li, and S.Q.Lee,2021,Characterizing the borehole response for single-well wave-wave reflection imaging [ J)]:Geophysics,86,no.1,D15-D26)

Wherein k and k _v The axial wave number and the radial wave number k of the incident wave are respectively _v ＝(k ² -ω ² /v ² ) ^1/2 ；I _n And K _n N-order modified Bessel functions of the first class and the second class are respectively represented, and sound waves transmitted from outside to inside and from inside to outside are described; n is the order of the multipole; epsilon _n Epsilon for n=0 for Neumann factor _n Epsilon when =1, n > 0 _n ＝2；

When the incident wave interacts with the borehole, elastic wave is induced in the medium inside and outside the borehole, the general solution of the longitudinal and transverse wave displacement potential function in the frequency-wave number domain has the same form as that in the formula (4), as follows

Wherein phi is _f Representing a displacement potential function of longitudinal waves in a fluid (or fluid ring) in the drill collar; phi, x and Γ represent displacement potential functions of P-wave, SH and SV transverse waves in the drill collar (or formation), respectively;

is the radial wave number of longitudinal wave of fluid, alpha _f Is the longitudinal wave velocity of the fluid; p= (k) ² -ω ² /α ² ) ^1/2 Sum s= (k) ² -ω ² /β ² ) ^1/2 Longitudinal wave and transverse wave radial wave numbers of the drill collar (or stratum) respectively, and alpha and beta are longitudinal wave and transverse wave speeds of the drill collar (or stratum) respectively; />

And->

For the amplitude coefficient of the sound field, for the fluid in the drill collar, only the sound wave propagates from outside to inside, thus +.>

Whereas for an out-of-well infinite formation, the radiation conditions require +.>

(4) The application of equation (3) converts the interface reflected wave into a spherical incident wave from a virtual source, and the response of the borehole to the incident spherical wave can be solved by combining the wave field solution of equation (5). Similar to when analyzing the radiation of acoustic sources in a well, two matrix equations and the following can be obtained by linking three boundary conditions under the logging while drilling model

Wherein the upper label in the coefficient vector on the left of the equation has the same meaning as in the formula (1), the matrix H is also the same as in the formula (1), and the vectors c and c' on the right of the equation represent the contributions of the P wave, SH and SV transverse wave from the virtual source and also contain the rotation effect of the instrument. For different orders n, the amplitude coefficient +.>

And A' _n ^fin ～F′ _n ^fm By substituting equation (6) corresponding to n into equation (5) to superimpose each polar acoustic field and integrate wave number k, the bullet caused by incident wave inside and outside the well hole can be determinedA sexual wave field. Radial distance r 'of virtual source considered for acoustic wave remote detection' ₀ Is generally far larger than the wavelength and meets the far-field condition of |k _v r′ ₀ ? 1, whereby the wave number integral in the expression (5) can be calculated by using the steepest descent method. During measurement while drilling, the receiver is positioned on the outer ring of the drill collar and receives a radial value equal to the radial value r of the annular sound source ₀ So that the far detection wavefield received by the instrument can be represented by a solution in the fluid loop that tends to the drill collar boundary, i.e.>

For pressure field (p=ρ _f ω ² φ _fout )

For radial displacement fields

In the formulas (7) and (8),

radial wave number for longitudinal wave of fluid, +.>

For the most rapid degradation of the wave number of the incident wave, θ _i Is the included angle between the incident direction of the wave and the negative direction of the z axis; d= [ r ]' ₀ ² +(z-z′ ₀ ) ² ] ^1/2 . And finally, performing fast Fourier transform on the equation (7) and the equation (8) in a frequency domain to obtain a sound field waveform received in a time-space domain.

In connection with the far detection model shown in FIG. 2, in equations (2) to (8), for a given reflector position

Exciting x-direction dipole sound source, andthe +.A in the formulas (7) and (8) is used>

Taking 0 degree and 180 degree respectively, the well receiving signal XX under the condition of remote detection can be simulated ₁ And XX ₂ . In the present invention, the receiver records the fluid sound pressure as an example, and the radial displacement result is similar to the sound pressure result, which is not described herein.

Extracting an off-well reflection signal from the full-wave signal and performing offset imaging on the off-well reflection signal, wherein the off-well reflection signal comprises the following specific steps of: first for the acquisition signal XX ₁ And XX ₂ Filtering and direct wave pressure vibration treatment are carried out to reduce noise interference and direct wave period, then wave field separation is carried out by selecting methods such as median filtering or F-K filtering, direct wave interference is removed, and reflected waves of an external interface are extracted from the full wave. And (3) carrying out signal enhancement processing on the reflected wave outside the well according to the common-center point superposition, inclination angle superposition and radial compensation methods, and finally carrying out imaging by using deep-conversion offset imaging.

Step five, forming dipole data by using the imaged reflection signals outside the well, wherein the dipole data comprises the following steps of

XX＝XX ₁ -XX ₂ . (9)

Under the condition of instrument centering, the measurement signals after the combination of the formula (9) mainly comprise dipole components, and the sound source emission and the data reception can be subjected to vector projection in the orthogonal direction. FIG. 4 is a schematic illustration of four-component reflected acoustic imaging logging while drilling, where the vibrations of the acoustic source can be resolved into two orthogonal directions perpendicular and parallel to the reflective interface and excite SV (and P) and SH waves polarized in these two planes, reflected by reflectors in the formation, back into the well for reception by receivers in the instrument x-direction. The dipole transverse wave and longitudinal wave data acquired by the instrument after the excitation of the sound source and the two projections are respectively given by the (10) expression and the (11) expression in consideration of the influence of the rotation of the instrument, and are as follows

AZ is the included angle between the x axis of the instrument and the fixed direction (magnetic north pole is selected) during sound source emission;

is the angle of the reflector relative to the north pole. From the formulae (10) and (11) by +.>

Replacement->

It can be demonstrated that during each transmission and reception, the azimuth information of the transverse and longitudinal waveforms XX are both shifted by δ/2 degrees in opposite directions of rotation of the instrument, with respect to the stationary state of the instrument (i.e. δ=0), when the instrument is rotated (i.e. δ+.0), as detailed by the calculation legend below.

The XX data of the position measurement can be accurately simulated and analyzed by using the formulas (2) to (9), taking the example that the reflector is located in the north direction (namely

) An explanation is given. Wherein the radial distance from the sound source to the virtual source on the outward side of the reflector is 20m, the source distance is 3m, and the sound source adopts Rake wavelets with the center frequency of 2500 Hz. During simulation, the azimuth AZ of the instrument is changed from 0 degree to 360 degrees, and the waveform XX measured in different azimuth is calculated ₁ And XX ₂ And constitutes a dipole waveform XX. In order not to lose generality, it is first assumed that the instrument does not rotate during each sound source emission to signal acquisition, i.e. δ=0. The dipole transverse wave azimuth waveform obtained by simulation is shown in fig. 5 (a), the dipole longitudinal wave azimuth waveform is shown in fig. 6 (a), the circular scale in the figure represents the instrument azimuth AZ, and the radial scale represents the arrival time of the waveform. Comparing the waveforms of different orientations yields a plot of normalized amplitude |xx| versus instrument orientation AZ, as shown by the solid lines in fig. 5 (b) and 6 (b). The graph shows that the maxima of curve |XX| correspond exactly to the maxima for transverse wavesOrientation of the reflector, in this case the instrument orientation AZ ₀ 90 ° or 270 °; for longitudinal waves, the maxima of the curve |XX| correspond exactly to the tendency of the reflector, in which case the instrument orientation AZ ₀ 0 ° or 180 °. The relationship between the maximum value of the curve |XX| and the trend (or tendency) of the reflector is just a theoretical basis for solving the azimuth of the reflector by using the dipole while drilling data. However, because of the high rotation of the instrument, the instrument orientation has changed during each sound source emission to signal acquisition, assuming delta = 20 °, the plot of the borehole azimuth measurement waveform amplitude |xx| with instrument orientation AZ in this case is given in dotted lines in fig. 5 (b) and 6 (b). The figure shows that the orientation of the maxima of curve |xx| at δ=20° is shifted by exactly 10 ° in the opposite direction of instrument rotation, as compared with δ=0, consistent with the theoretical conclusion from equations (10) and (11). The above analysis shows that when the reflector orientation is determined using the amplitude information of dipole data |xx| measured at different orientations, it is necessary to shift the result by δ/2 degrees in the instrument rotation direction to eliminate the instrument rotation effect.

In practical drilling, since the drilling speed of the drill is generally slow, for a certain depth point, multiple measurement data of the depth point adjacent to each other can be regarded as measurement results of the instrument at different orientations of the depth point, and then the multiple measurement data are compared to find the azimuth AZ of the instrument corresponding to the maximum amplitude ₀ . In the invention, for the common drilling speed, about 20 times of measurement data are generally selected for comparison to obtain an accurate result.

Step six, utilizing the instrument azimuth AZ corresponding to the maximum amplitude determined in the step five ₀ Calculating the azimuth of the underground geologic body: under the conditions of hard stratum and conventional soft stratum, the method has the advantages that the dipole transverse wave is used for conducting far detection, the dipole data is processed by the transverse wave, a velocity model is built by adopting transverse wave time difference, and the orientation of the underground geologic body is that

Or->

In the case of ultra-soft formationsUnder the condition that the measured external signals are elastic longitudinal waves, longitudinal wave processing is carried out on dipole data, a velocity model is built by adopting longitudinal wave time difference, and the orientation of the external geologic body is ∈>

Or->

In the case of δ=0 in fig. 5 (b) and 6 (b), the geologic body azimuth determined by the transverse wave and the longitudinal wave is 0 ° or 180 °; and when δ=20°, the reflector orientations determined by the transverse wave and the longitudinal wave are 170 ° or 350 °.

The results of step seven, formulas (10) and (11) and fig. 5 (b) and fig. 6 (b) show that the rotation of the instrument causes errors in the azimuth result in step six, and therefore correction is required, and the corrected azimuth is

Or (b)

In both cases of δ=0 and δ=20° in fig. 5 (b) and 6 (b), the corrected geologic body orientation is either 0 ° or 180 °. In an actual well logging, the instrument rotation angle delta can be based on the instrument rotation speed RPM and the reflected signal arrival time T ₀ Calculation is performed, i.e. δ=rpm·t ₀ 。

Step eight, the geologic body azimuth obtained from the steps five to seven has multiple resolvable property (the two values differ by 180 degrees), so that the authenticity of the two results needs to be further distinguished. Specifically, since the receiver on one side of the instrument, which is closer to the incident wave (i.e., the azimuth of the geologic volume), will record the waveform earlier than the receiver on the other side, the signal XX can be used ₁ And XX ₂ Is different from the correction result

And->

Middle judgmentBreaking out the true azimuth of the geologic body: if signal XX ₁ Time of arrival leading to XX ₂ Then->

And->

Near X in the middle ₁ The angle of the receiver side is true, and the receiver side is close to X ₂ The angle of the receiver side is the true bearing. Comparison signal XX ₁ And XX ₂ By directly observing the waveforms, or by using fast fourier transforms (Fast Fourier Transform, FFT) or dynamic time warping (Dynamic Time Warping, DWT), etc. />

For the case of δ=0 in fig. 5 (b) and 6 (b), the received transverse and longitudinal waveforms XX at 30 ° of azimuth angle of the instrument are given in fig. 7 (a) and 7 (b), respectively ₁ And XX ₂ . As can be seen from FIGS. 7 (a), (b), waveform XX, whether transverse or longitudinal ₁ Time to average ratio XX ₂ Earlier, explain at this time X ₁ The receiver is positioned at one side close to the geologic body, and X ₂ The receiver is located on a side remote from the body. And D, combining the azimuth result of 0 degree or 180 degrees obtained in the step seven, and judging that 0 degree is the true azimuth of the geologic body, wherein the result is consistent with the theoretical model. Here, XX is shown in FIG. 7 (a) for more visual comparison ₂ But this does not affect the arrival time of the waveform. It should be noted that the instrument records the azimuth AZ in which the acoustic source is transmitting, but as the instrument rotates, the reflected wave returns to the borehole by delta degrees, so the instrument records the corresponding received waveform at virtually (AZ + delta) for azimuth AZ.

It should be noted that the reflection data or the imaging data after time depth conversion in the fifth step and the eighth step are determined according to whether the signal to noise ratio of the two data in the actual well logging is good or bad. This is because offset imaging is a linear transformation that does not change signal XX ₁ And XX ₂ The relative amplitude magnitude and time-of-arrival relationship are consistent from the reflection data and the imaging data. For a pair ofIn the theoretical data without noise interference, the invention directly aims at the signal XX ₁ And XX ₂ Is processed.

Step nine, after determining the orientation of the geologic body, determining the maximum amplitude signal XX (AZ ₀ ) Firstly, carrying out signal enhancement processing according to a common center point superposition, inclination angle superposition and radial compensation method; then, performing deep conversion on imaging according to the speed model selected in the step six, and determining the well-leaving distance of the reflector; and finally, performing further noise reduction treatment on the imaging result by utilizing direct filtering or F-K filtering to finally obtain a reflection imaging result of the underground geologic body.

The application effect of the acoustic remote detection while drilling method based on the dipole single-shot dual-receive measurement mode is further described below with reference to a specific synthetic well section logging example. The well section with depth interval of 140m has a reflection interface with inclination angle of 60 deg. and lower and upper sections of the interface are respectively positioned at 60 deg. and 240 deg., and the periphery of the well hole is a hard stratum (longitudinal wave speed is 4000m/s, transverse wave speed is 2300m/s, and density is 2500 kg/m) ³ ). FIG. 8 is a graph of the results of the orientation of an external reflector of a well obtained by using a dipole shear method for this model, assuming a rotational speed of the instrument of 100 revolutions per minute, a drilling speed of 10 meters per hour, a sound source excitation time interval of 5 seconds, and a time sampling interval and sampling points of the logging sound field of 36 μs and 1024 points, respectively. FIG. 8, lane 1, shows the azimuth curve of the instrument relative to the north pole, showing the instrument rotated at high speed during measurement; the measured waveform XX is shown in variable density figures in

lanes

2 and 3, respectively ₁ And XX ₂ It can be seen from the figure that the reflected wave from the interface of the formation outside the well follows a strong amplitude borehole direct wave. The method of the invention is used for processing the well section data, and firstly, the waveform XX is processed ₁ And XX ₂ Filtering, wave field separation and offset imaging are performed, and then dipole data XX is synthesized by using the imaged off-well reflection signals. At each depth point, the measurement data XX of 15 depth points adjacent to each other above and below the depth point are selected and compared in waveform amplitude to obtain amplitude energy diagrams in different directions, which are given in lane 4. Tracking the strong energy region to obtain different depthsInstrument azimuth AZ corresponding to maximum waveform amplitude at point ₀ As shown by the black line in lane 4, the curve corresponds to the reflector trend of about 140-150 or 320-330, so that the reflector orientation can be calculated to be about 50-60 or 230-240. When the reflected wave is extracted from the waveform, the angle at which the sound source at different depth points is transmitted to the reflected wave is rotated by the instrument during the time when the reflected wave is received by the instrument is calculated according to the rotation speed of the instrument, and is given in lane 5. The reflector orientation is corrected according to the rotation angle of the instrument, and the 6 th track is the corrected orientation result, and it can be seen that the reflector orientation result has 180 degrees of uncertainty, namely about 60 degrees or 240 degrees. From signals XX at different depth points ₁ And XX ₂ The difference in time to the direction results, the true direction is given in lane 7. The figure shows that the orientation of the reflector is about 60 degrees in the lower part of the well section, and about 240 degrees in the upper part of the well section, which is consistent with the theoretical model, and the correctness of the result of the method is verified. After determining the true orientation of the reflector, the maximum amplitude signal XX (AZ) ₀ ) And performing offset imaging, performing deep conversion on imaging according to the transverse wave speed, and further determining the well-leaving distance of the reflector to obtain a final well external reflection imaging result.

To further examine the effect of the dipole longitudinal wave detection method of the present invention, the circumference of the borehole was changed to a soft formation (longitudinal wave velocity 2074m/s, transverse wave velocity 869m/s, density 2250kg/m ³ ) Referring to the process flow of fig. 8, the result of the orientation of the reflector outside the well using longitudinal wave detection is shown in fig. 9. Unlike transverse wave detection, in longitudinal wave detection, the strong energy area in the 4 th azimuth amplitude energy diagram corresponds to the azimuth of the reflector, rather than the trend. In the 7 th channel, the accurate reflector orientation can be obtained by adopting a longitudinal wave method to detect in the whole well section interval, and the accuracy of the method is verified.

It should be noted that, as can be seen from fig. 8 and fig. 9 in lane 4, even under the conditions of an instrument rotation speed of 100 rpm and an off-well detection distance of about 40 meters, a more accurate azimuth result can be obtained without considering the influence of the instrument rotation on the measurement result, and further illustrates that the method of the invention has a stronger practicability.

The above examples are only some of the preferred examples given for the purpose of fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and changes are intended by those skilled in the art on the basis of the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.

Claims

1. A method for acoustic remote detection while drilling based on a dipole single-shot dual-receive measurement mode adopts the following processing steps:

step one, placing a dipole acoustic logging while drilling instrument in a well and connecting the instrument with a drilling system, exciting a dipole acoustic source pointing along the x axis of the instrument in a real-time drilling process, and radiating elastic waves into an underground stratum;

recording an azimuth AZ of the coordinate axis of the instrument relative to the fixed direction;

step three, acquiring signals XX by two receivers symmetrically distributed along the two sides of the x axis of the instrument ₁ And XX ₂ ；

Step four, filtering and wave field separation processing are carried out on the acquired signals, direct waves transmitted along a well hole are suppressed and removed, reflected signals from an external interface of the well are extracted, and offset imaging is carried out on the reflected signals;

step five, forming dipole data xx=xx by using the imaged off-well reflection signals ₁ -XX ₂ Selecting a plurality of measurement data XX adjacent to each other before and after, comparing waveform amplitude values, and finding out a maximum amplitude signal XX (AZ ₀ )；

Or->

Or->

Or->

When the geological structure outside the well is within 50m from the well hole, the rotation effect of the instrument can be ignored, namely the step seven is omitted, and the step eight is directly omitted;

And->

And->

Near X in the middle ₁ The angle of the receiver side is true, and the receiver side is close to X ₂ The angle of one side of the receiver is the true azimuth;

step nine, for maximum amplitude signal XX (AZ ₀ ) Offset imaging is performed, andand D, performing deep conversion on imaging according to the speed model in the step six, and further determining the well-leaving distance of the geologic body to obtain a final well external reflection imaging result.

2. The method for remote detection of acoustic waves while drilling based on a dipole single-shot and double-shot measurement mode according to claim 1, wherein in the first step, a dipole sound source points to the x-axis direction of an instrument coordinate system and consists of two polar plates symmetrically distributed on outer rings on two sides of the x-axis of the instrument, and the two polar plates have the same energy and opposite polarities of excitation signals. In operation of the instrument, the dipole source is excited to radiate an elastic wave into the formation outside the well.

3. The method for acoustic remote detection while drilling based on dipole single-shot dual-receive measurement mode according to claim 1, wherein in the second step, for a vertical well, the earth magnetic north pole is selected as the fixed direction; for inclined and horizontal wells, the fixed azimuth references the high end of the wellbore.

4. The method for remote detection of acoustic waves while drilling based on dipole single-shot and double-shot measurement mode as claimed in claim 1, wherein in the third step, the receiver is composed of two receiving polar plates symmetrically distributed on two sides of the x-axis of the instrument, the elastic wave excited by the dipole source is reflected by the geologic body in the stratum and returns to the well, and the receiver records signal XX ₁ And XX ₂ Wherein the first letter represents the sound source direction and the second letter and number represent the receiver; in the drilling process, the dipole sources are excited and data are acquired repeatedly along with the high-speed rotation of the drill collar; the time interval between two adjacent excitations of the sound source should be long enough to ensure that the signal received for the first time is not affected by the excitation for the second time.

5. The method for acoustic remote detection while drilling based on the dipole single-shot dual-receive measurement mode according to claim 1, wherein the fourth step is specifically as follows: first for the acquisition signal XX ₁ And XX ₂ Filtering and direct wave pressure vibration treatment are carried out to reduce noise interference and direct wave period, and then median filtering or F-K filtering method is selected for proceedingThe traveling wave field is separated, direct wave interference is removed, and reflected waves from an external interface of the well are extracted from the full wave; and (3) carrying out signal enhancement processing on the reflected wave outside the well according to the common-center point superposition, inclination angle superposition and radial compensation methods, and finally carrying out imaging by using deep-conversion offset imaging.

6. The method for remote detection of acoustic while drilling based on dipole single-shot dual-receive measurement mode as claimed in claim 1, wherein in the fifth step, since the instrument rotates continuously during measurement, for a certain depth point, multiple measurement data adjacent to the depth point are regarded as measurement results of the instrument in different directions of the depth point, and then the amplitudes of the multiple measurement XX data are compared to find the azimuth AZ of the instrument corresponding to the maximum amplitude ₀ The method comprises the steps of carrying out a first treatment on the surface of the For the common drilling speed, 20 times of measurement data are selected for comparison to obtain an accurate result.

7. The method for remote detection of acoustic waves while drilling based on a dipole single-shot dual-receive measurement mode according to claim 1, wherein in the sixth step, under the conditions of hard stratum and conventional soft stratum, the remote detection by utilizing dipole transverse waves is more advantageous, the transverse wave processing is performed on dipole data, a velocity model is built by adopting transverse wave time difference, and the orientation of the underground geologic body is that

Or (b)

Or->

8. The method for acoustic remote detection while drilling based on dipole single-shot dual-receive measurement mode according to claim 1, wherein in the seventh step, the instrument rotation angle δ during actual logging can be determined according to the instrument rotation speed RPM and the reflected signal arrival time T ₀ Calculation is performed, i.e. δ=rpm·t ₀ 。

9. The method for acoustic remote detection while drilling based on dipole single-shot dual-receive measurement mode according to claim 1, wherein in the eighth step, the signal XX is used for ₁ And XX ₂ Is different from the arrival time difference, i.e. lead or lag, from the correction result

And->

And->

Near X in the middle ₁ The angle of one side of the receiver is the true azimuth of the geologic body, and the angle is close to X ₂ The angle of one side of the receiver is the real azimuth of the geologic body; the instrument records the azimuth AZ of the sound source when transmitting, but as the instrument rotates, the reflected wave returns to the well hole and the instrument rotates by delta degrees, so the instrument records the corresponding received wave at the position (AZ+delta) when the azimuth AZ is the azimuth; comparison signal XX ₁ And XX ₂ The time difference of (a) can be obtained by directly observing the waveform or by utilizing a fast fourier transform or dynamic time warping method.

10. A dipole-based single-shot dual-shot survey according to claim 1The method for detecting the acoustic wave distance while drilling in the measuring mode comprises the following steps: for the maximum amplitude signal XX (AZ) ₀ ) Firstly, carrying out signal enhancement processing according to a common center point superposition, inclination angle superposition and radial compensation method; then, performing deep conversion on imaging according to the speed model determined in the step six, and determining the well-leaving distance of the reflector; and finally, performing further noise reduction treatment on the imaging result by utilizing direct filtering or F-K filtering to finally obtain a reflection imaging result of the underground geologic body.