A method for remote detection of acoustic waves while drilling based on dipole single-transmitter dual-receiver measurement mode

Abstract

The present invention discloses a method for remote detection of acoustic waves while drilling based on a dipole single-transmitter dual-receiver measurement mode. The method mainly comprises: placing a dipole sound source and a receiver pointing along the instrument x-axis in a well and connecting them to a drilling system; exciting the sound source and collecting signals XX1 and XX2 during drilling; filtering, wave field separation, and offset imaging processing the collected signals; forming dipole data XX with off-hole reflected signals and comparing multiple measurement results to find the maximum amplitude signal XX (AZ0); selecting a velocity model according to the formation type, determining the azimuth of the geological body, and correcting for the instrument rotation effect; identifying the true azimuth of the geological body based on the arrival time difference between signals XX1 and XX2; performing offset imaging on the maximum amplitude signal XX (AZ0), determining the distance of the geological body from the well, and obtaining a final off-hole reflection imaging result. The present invention can achieve accurate detection and imaging of off-hole geological structures during drilling, provide real-time geological guidance and wellbore trajectory optimization for drilling, and improve the accuracy and drilling efficiency of drilling operations.

Description

Technical Field

[0001] The present invention belongs to the field of applied geophysical acoustic logging. Specifically, the present invention utilizes a directional dipole sound source to radiate elastic waves multiple times out of the well during the drilling process, and uses two groups of receivers in the well pointing in the same direction as the sound source to measure the sound waves reflected by the geological body outside the well. By processing the multiple measurement signals, the present invention realizes the detection and imaging of the geological structure outside the well during the drilling process, thereby providing real-time geological guidance for drilling. Background Art

[0002] With the continuous advancement of oil and gas exploration and development, conventional vertical well technology is no longer able to meet the needs of field applications. It is necessary to develop drilling and logging technologies for complex wells such as highly deviated and horizontal wells. The key to the development of these complex wells is accurate and effective geosteering while drilling. This allows for effective tracking of reservoir boundaries during real-time drilling, further guiding the optimal drilling direction and improving the penetration rate of oil and gas reservoirs.

[0003] At present, the geological steering function is mainly realized by the azimuthal electromagnetic wave resistivity measurement technology while drilling. However, the frequency of azimuthal electromagnetic waves is usually high and the signal attenuation is large. Therefore, this method can only detect geological structures within a few meters around the well and cannot obtain the optimal wellbore drilling trajectory (Liu Naizhen, Wang Zhong, Liu Ce, 2015, Key technologies for geological steering using azimuthal resistivity instrument while drilling electromagnetic waves [J]: Chinese Journal of Geophysics, 58(5), 1767-1775).

[0004] Acoustic remote detection technology has become an important technology in the field of oil and gas exploration and development in recent years. This technology uses a dipole acoustic source in a fluid-filled well to radiate elastic waves into the formation outside the well, and uses the acoustic waves received in the well and reflected back by the geological body outside the well to perform well circumference imaging. This method has the advantages of strong azimuth sensitivity and deep radial detection depth. It has been maturely applied to the detection of geological structures such as fractures, faults, and dissolution holes near the well in wireline logging (Tang Xiaoming, Gu Xihao, Li Yanghu, Su Yuanda, 2021, Interaction between wellbore and elastic waves: theory, methods and applications [J]: Chinese Journal of Geophysics, 64(12), 4227-4238). A potential application of dipole acoustic remote detection technology is to provide geological guidance in while-drilling logging. However, unlike wireline logging, the drill collar rotates at high speed during while-drilling logging, and the influence of instrument rotation on the measurement process must be considered. Zeng Yijin et al. proposed performing acoustic measurement while drilling during the gap between single roots or before starting the drill (Zeng Yijin, Zhu Zuyang, Li Fengbo et al., 2022, Acoustic Remote Detection System and Method While Drilling [P]: Chinese Patent, CN110805433B). However, this method is only applicable when the instrument is in (or near) a stationary state and cannot be applied while the instrument is drilling. The measurement efficiency is low and it is difficult to meet the needs of real-time geosteering.

[0005] Therefore, based on the urgent need for geological guidance while drilling, the present invention proposes a method for scanning, detecting and imaging off-hole geological structures by using a dipole source to transmit multiple times and receive in the same direction during real-time drilling, with the help of high-speed rotation of the drill collar. Summary of the Invention

[0006] The purpose of the present invention is to provide a long-range acoustic detection method while drilling based on a dipole single-transmitter dual-receiver measurement mode. During the real-time drilling process, a directional dipole source is used to excite P waves, SH waves and SV shear waves out of the well. After the elastic waves interact with the geological bodies in the formation, they return to the well and are recorded by two sets of receivers on the instrument. By processing the measurement signals, the geological structure near the well is detected and imaged. This provides an effective solution for real-time geological guidance and wellbore trajectory optimization during the drilling of complex wells such as highly deviated wells and horizontal wells.

[0007] In order to achieve the above-mentioned object of the invention, the specific steps adopted by the present invention are as follows:

[0008] Step 1: Place the dipole acoustic logging tool while drilling in the well and connect it to the drilling system. During the real-time drilling process, a dipole acoustic source pointing along the instrument's x-axis is excited to radiate elastic waves into the formation outside the well.

[0009] Step 2: Record the azimuth angle AZ of the instrument's coordinate axis (such as the x-axis) relative to a fixed direction (such as the Earth's magnetic north pole).

[0010] Step 3: Use two receivers symmetrically distributed on both sides of the instrument's x-axis to collect signals XX1 and XX2.

[0011] Step 4: Filter and perform wave field separation on the collected signals to suppress and eliminate the direct waves propagating along the wellbore, extract the reflected signals from the interface outside the well, and perform offset imaging on the reflected signals.

[0012] Step 5: Use the imaged out-of-hole reflection signal to form dipole data XX=XX1-XX2, select multiple adjacent measurement data XX and compare the waveform amplitudes to find the maximum amplitude signal XX(AZ0).

[0013] Step 6: In hard formations and conventional soft formations, the dipole data is processed by shear wave and the velocity model is constructed using the shear wave time difference. The orientation of the geological body outside the well is or In ultra-soft formations, the dipole data is processed with longitudinal waves, and the velocity model is constructed using the longitudinal wave time difference. The orientation of the geological body outside the well is or

[0014] Step 7: Correct the orientation of the geological body in step 6 according to the instrument rotation angle δ. The corrected orientation is or

[0015] Step 8: Based on the arrival time difference of signals XX1 and XX2, the correction result and The true position of the geological body can be determined by: If the signal XX1 arrives ahead of XX2, then and The angle closer to the X1 receiver is the true direction, and conversely, the angle closer to the X2 receiver is the true direction.

[0016] Step nine: perform migration imaging on the maximum amplitude signal XX(AZ0), and perform time-depth conversion on the imaging according to the velocity model in step six to further determine the distance of the geological body from the well and obtain the final out-of-well reflection imaging result.

[0017] In step 1, the dipole acoustic source is oriented in the x-axis direction of the instrument coordinate system. It consists of two plates symmetrically located on the outer ring of the instrument's x-axis. The excitation signals from the two plates have equal energy and opposite polarity. When the instrument is operating, the excited dipole source radiates elastic waves into the formation outside the wellbore.

[0018] In step 2, for vertical wells, the fixed direction is the Earth's magnetic north pole; for inclined wells and horizontal wells, the fixed orientation is referenced to the top end of the wellbore.

[0019] In step three, the receiver consists of two receiving plates symmetrically distributed on both sides of the instrument's x-axis. The elastic wave excited by the dipole source is reflected by the geological body in the formation and then returns to the well. The receiver records signals XX1 and XX2, where the first letter represents the direction of the sound source and the second letter and number represent the receiver. During the drilling process, as the drill collar rotates at high speed, steps one to three are repeated multiple times to excite the dipole source and collect data. 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 second excitation.

[0020] Step 4 specifically involves filtering and performing direct wave pressure-vibration processing on the acquired signals XX1 and XX2 to reduce noise interference and direct wave period. Then, wavefield separation is performed using methods such as median filtering or FK filtering to remove direct wave interference and extract the reflected wave from the external well interface from the full wave. Signal enhancement processing is performed on the external well reflection wave using common center point stacking, dip stacking, and radial compensation methods. Finally, imaging is performed using time-depth conversion migration imaging.

[0021] In step 5, because the instrument rotates continuously during measurement, multiple measurements above and below a particular depth point can be considered as measurements taken at different azimuths at that depth point. The amplitudes of these multiple measurements (XX) are then compared to find the instrument azimuth angle AZ0 corresponding to the maximum amplitude. In the present invention, for commonly used drilling rates, approximately 20 measurements are typically selected for comparison to obtain an accurate result.

[0022] In step 6, in the case of hard formation and conventional soft formation, it is more advantageous to use dipole shear wave for long-range detection. The dipole data is processed by shear wave, and the velocity model is constructed using the shear wave time difference. The orientation of the geological body outside the well is or In the case of ultra-soft formations, the measured out-hole signal is elastic longitudinal wave. The dipole data is processed with longitudinal wave and the velocity model is constructed using the longitudinal wave time difference. The orientation of the geological body outside the well is or

[0023] In step seven, the tool rotation angle δ during actual logging can be calculated based on the tool rotation speed RPM and the arrival time T0 of the reflection signal, that is, δ=RPM·T0.

[0024] In step eight, according to the arrival time difference (advance or lag) of signals XX1 and XX2, the correction result and Determine the true orientation of the geological body and eliminate the 180° uncertainty of the orientation of the results of steps 6 and 7: If the signal XX1 arrives ahead of XX2, then and The angle closer to the X1 receiver is the true azimuth of the geological body, while the angle closer to the X2 receiver is the true azimuth. It's important to note that the instrument records the azimuth AZ at the time of emission. However, as the instrument rotates, the reflected wave rotates δ degrees before returning to the wellbore. Therefore, the recorded azimuth AZ actually corresponds to the received waveform at (AZ + δ). The arrival time differences between signals XX1 and XX2 can be compared by directly observing the waveforms or using methods such as Fast Fourier Transform (FFT) or Dynamic Time Warping (DWT).

[0025] The step nine is specifically as follows: the maximum amplitude signal XX(AZ0) determined in step five is first subjected to signal enhancement processing according to the common center point stacking, dip stacking and radial compensation methods; then, the imaging is subjected to time-depth conversion according to the velocity model determined in step six to determine the distance of the reflector from the wellbore; finally, the imaging result is further subjected to noise reduction processing using direct filtering or FK filtering to ultimately obtain the reflection imaging result of the geological body outside the wellbore.

[0026] In addition, the present invention has the following three points:

[0027] First, in steps 5 and 8, either reflection data or imaging data after time-depth conversion can be used, depending on the signal-to-noise ratio of the two data types in the actual logging process. This is because migration imaging is a linear transformation that does not change the relative amplitude and arrival time relationship of signals XX1 and XX2. The results obtained from reflection data and imaging data are consistent.

[0028] Secondly, the present invention strictly considers the rotation effect of the instrument and corrects the orientation recognition result. However, in actual measurement, when the geological structure outside the well is close to the wellbore (within 50m), the rotation effect of the instrument can be ignored (that is, step seven is omitted), and a more accurate orientation result can be obtained at this time.

[0029] Third, in actual drilling, the drill collar often deviates from the wellbore axis due to the complex movement of the drill tool and the weight of the drill collar. The present invention primarily utilizes the azimuth amplitude characteristics of the received waveform and the relationship between arrival delays to locate the geological body outside the wellbore. Small drill collar eccentricity does not significantly affect the relative size of the waveform amplitude or the relative order of arrival times, so the present method is also well suited for situations with drill collar eccentricity.

[0030] Advantages and positive effects of the present invention: The long-range detection method of dipole acoustic waves while drilling described in the present invention can realize accurate detection and imaging of geological structures outside the well, provide real-time geological guidance and wellbore trajectory optimization for drilling, and improve the accuracy and drilling efficiency of drilling construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flowchart of a method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode provided by the present invention;

[0032] Figure 2 A schematic diagram of a model for detecting a geological body outside a well in the present invention;

[0033] FIG3( a ) is a schematic diagram of a cross section of a wellbore pointing toward a dipole sound source along the x-axis according to the present invention;

[0034] FIG3( b ) is a schematic diagram of a cross-section of a wellbore with receivers symmetrically distributed along the x-axis according to the present invention;

[0035] Figure 4 Schematic diagram of dipole four-component reflection acoustic imaging logging while drilling in the present invention;

[0036] FIG5( a ) is a dipole shear wave waveform XX measured in the present invention;

[0037] FIG5( b ) is the normalized amplitude of the dipole shear wave waveform XX measured in the present invention;

[0038] FIG6( a ) is a dipole longitudinal wave waveform XX measured in azimuth in the present invention;

[0039] FIG6( b ) is the normalized amplitude of the dipole longitudinal wave waveform XX measured in the present invention;

[0040] FIG7( a ) is a waveform comparison of dipole shear waves XX1 and XX2 received when the instrument azimuth angle is 30° in the present invention;

[0041] FIG7( b ) is a waveform comparison of dipole longitudinal waves XX1 and XX2 received when the instrument azimuth angle is 30° in the present invention;

[0042] Figure 8 This is a synthetic example result diagram of the use of the dipole shear wave method while drilling to detect geological bodies outside the well in the present invention;

[0043] Figure 9 This is a synthetic example result diagram of the use of the while-drilling dipole longitudinal wave method to detect geological bodies outside the well in the present invention.

[0044] Numbers in the figure: 1, fluid-filled wellbore; 2, drill collar; 3, receiver; 4, dipole sound source; 5, reflection interface; 6, virtual source. Specific implementation plan

[0045] The specific principles of off-hole geological structure detection using a dipole single-transmitter dual-receiver measurement mode while drilling are combined below, and the method of the present invention is further illustrated using theoretical synthesis examples so that those skilled in the art can better understand the content of the present invention and implement it. However, the examples given are not intended to limit the present invention.

[0046] like Figure 1 As shown, the present invention provides a method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode. The specific working process is as follows:

[0047] Step 1: Figure 2 The dipole acoustic logging tool shown is placed in a well and connected to the drilling system. During real-time drilling, it excites a dipole acoustic source to radiate elastic waves into the formation outside the wellbore. The dipole acoustic source is oriented along the x-axis of the tool coordinate system and consists of two plates, X1 and X2, symmetrically located on either side of the tool's x-axis. The excitation signals from the two plates have equal energy and opposite polarity, as shown in Figure 3(a).

[0048] Step 2: Record the azimuth angle AZ of the instrument's coordinate axis (e.g., the x-axis) relative to a fixed direction when the sound source is excited. For vertical wells, the fixed direction is the Earth's magnetic north pole; for inclined and horizontal wells, the fixed direction is referenced to the top of the wellbore.

[0049] Step 3: Use the receiver to collect signals XX1 and XX2, where the first letter represents the direction of the sound source, and the second letter and number represent the receiver. The receiver consists of two receiving plates symmetrically located on either side of the instrument's x-axis, as shown in Figure 3(b). During drilling, as the drill collar rotates at high speed, steps 1 through 3 are repeated multiple times to excite the dipole source and collect data. It is important to ensure that the interval between two consecutive excitations of the sound source is long enough to ensure that the signal received from the first excitation is not affected by the second.

[0050] In order to better illustrate the method of the present invention using theoretical examples, firstly, an analytical solution for the receiving acoustic field of the dipole acoustic wave azimuth remote detection while drilling in a fluid-filled well is established based on the interaction theory between the wellbore and elastic waves. Figure 2 This diagram shows how a while-drilling acoustic logging tool can be used to detect geological structures near a wellbore. A dipole acoustic source on the tool radiates elastic waves outward from the wellbore. After reflection from the geological structure, these waves are incident back into the wellbore and received by the tool's receiver. For far-field reception, the theoretical acoustic field solution can be used to describe the plate emission / reception effect shown in Figure 3 using the point emission / reception effect.

[0051] use Figure 2 Described in the coordinate system shown in Figures 3(a) and (b), the medium space of the LWD model is radially divided into four parts: the fluid inside the drill collar, the drill collar, the fluid ring outside the drill collar, and the formation outside the well. The outer radius of each part is r1, r2, a, and infinity, respectively. Assuming that the drill collar is completely centered in the wellbore, an annular dipole sound source is placed on the surface of the drill collar and points in the positive direction of the x-axis. The radius r0 of the annular sound source is equal to the outer radius r2 of the drill collar. The three interfaces included in the above model are all fluid-solid interfaces, and their boundary conditions require that the radial displacement and radial stress are continuous, and the annular and axial shear stresses are zero. By connecting the boundary conditions at the three interfaces, a matrix equation with twelve unknown coefficients can be obtained:

[0052] 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 =b, (1)

[0053] In the formula, H is a 12×12 matrix, b is a 12×1 vector, and vector b represents the direct contribution of the annular dipole sound source at the drill collar surface. For detailed expressions, see (Tang, XM, and CHCheng, 2004, Quantitative borehole acoustic methods [M]: Elsevier Science Publishing.); the letters superscripted with fin, dc, and fout in the coefficient vector represent the amplitude coefficients of the elastic waves in the fluid in the drill collar, the drill collar, and the fluid annulus, respectively, and characterize the strength of the guided wave acoustic field in the well; the letters superscripted with fm correspond to the amplitude coefficients of the radiation waves in the formation. These radiation waves are the basis for dipole far detection to perform wellside geological structure imaging. In the case of far-field radiation, Figure 2 The far-field asymptotic solution of the displacement potential function of the P wave, SH wave and SV wave radiated into the formation by the medium dipole sound source is:

[0054]

[0055] Among them, ω is the circular frequency, S is the sound source function spectrum, α fm and β fm are the formation compressional and shear wave velocities, and are the fastest descent solutions of the radiated longitudinal and shear wave numbers, θ t is the angle between the wave radiation direction and the positive direction of the z axis, is the angle between the projection of the wave radiation direction on the horizontal plane and the direction of the sound source, R is the distance between the sound source and the radiation field point, and the amplitude coefficient B is fm 、D fm and F fm It is obtained from the matrix equation (1).

[0056] From formula (2), we can know that the dipole radiation acoustic field while drilling is e iωR / v The spherical wave form of / R propagates deep into the formation. When there is a reflector in the formation, the radiation wave will interact with the reflector. Under the condition that the size of the reflector is larger than the wavelength, the wave field of the incident wave reflected back to the borehole can be expressed by formula (3) (Tang, XM, JJCao, and ZTWei, 2014, Shear-wave radiation, reception, and reciprocity of a boreholedipole source: With application to modeling of shear-wave reflection survey [J]: Geophysics, 79, no. 2, T43-T50.). It should be noted that during this period, the orientation of the reflector has changed. For Figure 2In the model shown in , when the sound source is excited, the orientation of the reflector relative to the x-axis of the instrument coordinate system is As the tool rotates (assuming the tool rotates clockwise), when the radiation wave is reflected back into the well by the reflector, the orientation of the reflector relative to the tool x-axis becomes Where δ is the angle through which the instrument rotates during the propagation of the sound wave in the formation.

[0057]

[0058] Where v is the velocity of the formation P-wave or S-wave (i.e. α fm or β fm );RD is the far-field radiation function of the sound source, which is composed of the part inside the square brackets of formula (2). Take RF is the reflection coefficient of the sound wave at the reflector, which can be calculated by the Zoplitz equation; the specific forms of RD and RF depend on the type of incident wave considered (i.e., P, SH, or SV wave); D is the total propagation distance of the sound wave in the formation, and its propagation path is a broken line from the sound source to the reflection point and then from the reflection point to the receiving point. By considering the far-detection sound field as the radiation sound field of a virtual source, the position of the virtual source is It coincides with the mirror image of the sound source in the well on the outward side of the reflector, such as Figure 2 As shown in . At this time, the propagation path D of the sound wave is transformed into a straight line, so the spherical wave propagation factor in formula (3) can be expanded into the form of superposition of multipole cylindrical waves (Li, YH, XMTang, HRLi, and S.Q.Lee, 2021, Characterizing the borehole response for single-well shear-wave reflection imaging[J]: Geophysics, 86, no. 1, D15-D26)

[0059]

[0060] Where k and k v are the axial and radial wave numbers of the incident wave, respectively, k v =(k 2 -ω 2 / v 2 ) 12 ;I n and K n denote the first and second n-order modified Bessel functions, respectively, describing the sound waves propagating from outside to inside and from inside to outside; n is the order of the multipole; ε n is the Neumann factor, when n=0, ε n =1, n>0 n=2;

[0061]

[0062] When the incident wave interacts with the wellbore, it will cause elastic fluctuations in the medium inside and outside the wellbore. The general solution of its longitudinal and transverse wave displacement potential functions in the frequency-wavenumber domain has the same form as that in equation (4), as follows:

[0063]

[0064] Among them, φ f represents the displacement potential function of the longitudinal wave in the fluid (or fluid annulus) in the drill collar; φ, χ, and Γ represent the displacement potential functions of the P wave, SH, and SV shear wave in the drill collar (or formation), respectively; is the radial wave number of the fluid longitudinal wave, α f is the longitudinal wave velocity of the fluid; p=(k 2 -ω 2 / α 2 ) 12 and s=(k 2 -ω 2 / β 2 ) 12 are the radial wave numbers of the longitudinal and shear waves of the drill collar (or formation), α and β are the longitudinal and shear wave velocities of the drill collar (or formation), respectively; and A n ' f ~F n ' is the amplitude coefficient of the sound field. For the fluid in the drill collar, there is only sound wave propagating from the outside to the inside, so For the infinite stratum outside the well, since the wave field generated by the sound source in the well is zero at infinity, the radiation condition requires =0.

[0065] The application of Equation (4) to Equation (3) converts the interface reflection wave into a spherical incident wave from a virtual source. Combined with the general solution of the wave field of Equation (5), the response of the wellbore to the incident spherical wave can be solved. Similar to the analysis of the radiation of the sound source in the well, by connecting the three boundary conditions under the LWD model, two matrix equations and The meaning of the superscripts in the coefficient vectors on the left side of the equation is the same as in equation (1), and the matrix H is also the same as in equation (1). The vectors c and c′ on the right side of the equation represent the contributions of P waves, SH and SV shear waves from the virtual source, and also include the rotation effect of the instrument. For different orders n, the amplitude coefficients and The equation (6) corresponding to the value of n is substituted into equation (5) to superimpose the acoustic fields of each pole and integrate the wave number k, so that the elastic wave field caused by the incident wave inside and outside the wellbore can be determined. The radial distance r0′ of the virtual source considered in acoustic wave remote detection is generally much larger than the wavelength, so the wave number integral in equation (5) can be calculated using the steepest descent method. During downhole measurement, the receiver is located on the outer ring of the drill collar, and its receiving radius is equal to the radius r0 of the annular sound source. Therefore, the remote detection wave field received by the instrument can be expressed by the solution in the fluid annulus that tends to the drill collar boundary, that is, for the pressure field (p = ρ f ω 2 φ fout )

[0066]

[0067] For the radial displacement field

[0068]

[0069] In formula (7) and formula (8), is the radial wave number of the fluid longitudinal wave, is the steepest descent solution of the incident wave number, θ i is the angle between the incident direction of the wave and the negative z-axis; Finally, by performing fast Fourier transform on equations (7) and (8) in the frequency domain, the received sound field waveform in the time and space domain is obtained.

[0070] Combine Figure 2 The far detection model shown in (2) to (8) is given by Excite x to point to the dipole sound source, and change the values ​​in (7) and (8) to Taking 0° and 180° respectively, we can simulate the receiving signals XX1 and XX2 in the well under the condition of long-range detection. In this invention, the receiver records the fluid sound pressure as an example. The radial displacement results are similar to the sound pressure results, which will not be repeated here.

[0071] Step 4: Extract the out-of-hole reflection signal from the full-wave signal and perform migration imaging on it. Specifically, the acquired signals XX1 and XX2 are first filtered and subjected to direct wave pressure-oscillation processing to reduce noise interference and the direct wave period. Then, wavefield separation is performed using methods such as median filtering or FK filtering to remove direct wave interference and extract the reflection wave from the out-of-hole interface from the full wave. The out-of-hole reflection wave is enhanced using common center point stacking, dip stacking, and radial compensation methods. Finally, imaging is performed using time-depth conversion migration imaging.

[0072] Step 5: Use the imaged out-of-hole reflection signal to form dipole data, as follows

[0073] XX = XX1 - XX2. (9)

[0074] When the instrument is centered, the measurement signal after the combination of formula (9) mainly contains dipole components. At this time, the sound source emission and data reception can be vector-projected in orthogonal directions. Figure 4 The diagram of the dipole four-component reflection acoustic imaging logging while drilling is shown in Figure 1. The vibration of the sound source can be decomposed into two orthogonal directions perpendicular to and parallel to the reflection interface, and excites SV (and P) and SH waves polarized in these two planes. After being reflected by the reflectors in the formation, they return to the well and are received by the receiver in the x direction of the instrument. Considering the influence of the instrument rotation, the dipole shear wave and longitudinal wave data collected by the instrument after two projections of the sound source are given by equations (10) and (11), respectively, as follows:

[0075]

[0076] Where AZ is the angle between the instrument's x-axis and the fixed direction (the magnetic north pole) when the sound source is emitted; is the angle between the reflector and the North Pole. From equations (10) and (11), Replacement It can be proved that during each transmission and reception, relative to the instrument's stationary state (i.e., δ = 0), when the instrument rotates (i.e., δ ≠ 0), the azimuth information of the shear wave and longitudinal wave waveforms XX are offset by δ / 2 degrees in the opposite direction of the instrument's rotation, as detailed in the following calculation diagram.

[0077] Formulas (2) to (9) can be used to accurately simulate and analyze the XX data of the orientation measurement. For example, the reflector is located in the north direction (i.e. ) is explained. 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 uses a Ricker wavelet with a center frequency of 2500Hz. During the simulation, the instrument azimuth AZ is changed from 0° to 360°, and the waveforms XX1 and XX2 measured at different azimuths are calculated to form a dipole waveform XX. In order to maintain generality, it is first assumed that the instrument does not rotate from each sound source emission to signal acquisition, that is, δ = 0. The simulated dipole shear wave azimuth waveform is shown in Figure 5(a), and the dipole longitudinal wave azimuth waveform is shown in Figure 6(a). The circumferential scale in the figure represents the instrument azimuth AZ, and the radial scale represents the waveform arrival time. Comparing the waveforms in different azimuths, the curve of the normalized amplitude |XX| changing with the instrument azimuth AZ is obtained, as shown Figure 5(b) and 6(b)As shown by the solid line in the middle. The figure shows that for shear waves, the maximum value of the curve |XX| corresponds exactly to the direction of the reflector, and the instrument azimuth AZ0 is 90° or 270° at this time; for longitudinal waves, the maximum value of the curve |XX| corresponds exactly to the inclination of the reflector, and the instrument azimuth AZ0 is 0° or 180° at this time. This relationship between the maximum value of the curve |XX| and the direction (or inclination) of the reflector is the theoretical basis for obtaining the azimuth of the reflector from the dipole data while drilling. However, due to the high-speed rotation of the instrument, the instrument azimuth has changed from each time the sound source is emitted to the signal acquisition. Assuming δ = 20°, in this case, the curve of the change of the waveform amplitude |XX| of the well azimuth measurement with the instrument azimuth AZ is Figure 5(b) and 6(b) The figure shows that, compared to the case of δ = 0, the position of the maximum value of the curve |XX| at δ = 20° is exactly offset by 10° in the direction opposite to the instrument rotation, which is consistent with the theoretical conclusions obtained from equations (10) and (11). The above analysis shows that when using the amplitude information of dipole data |XX| measured at different orientations to determine the orientation of the reflector, it is necessary to offset the result by δ / 2 degrees in the direction of instrument rotation to eliminate the instrument rotation effect.

[0078] In actual drilling, because the drill bit's penetration speed is typically slow, multiple measurements taken above and below a particular depth point can be considered as the instrument's measurement results at different azimuths at that depth point. These measurements are then compared to find the instrument azimuth angle AZ0 corresponding to the maximum amplitude. In this invention, for commonly used drilling speeds, approximately 20 measurements are typically selected for comparison to obtain an accurate result.

[0079] Step 6: Calculate the orientation of the geological body outside the well using the instrument orientation AZ0 corresponding to the maximum amplitude determined in step 5: In the case of hard formations and conventional soft formations, it is more advantageous to use dipole shear waves for long-range detection. The dipole data is processed by shear waves, and the velocity model is constructed using the shear wave time difference. The orientation of the geological body outside the well is or In the case of ultra-soft formations, the measured out-hole signal is elastic longitudinal wave. The dipole data is processed with longitudinal wave and the velocity model is constructed using longitudinal wave time difference. The orientation of the geological body out-hole is or For the case of δ = 0 in Figure 5(b) and Figure 6(b), the orientation of the geological body determined by the shear wave and the longitudinal wave is 0° or 180°; while when δ = 20°, the orientation of the reflector determined by the shear wave and the longitudinal wave is 170° or 350°.

[0080] The results of step 7, equations (10) and (11), and Figures 5(b) and 6(b) show that the rotation of the instrument will cause errors in the orientation results in step 6, so they need to be corrected. The corrected orientation is or In Figures 5(b) and 6(b), for δ = 0 and δ = 20°, the corrected geological body orientation is 0° or 180°. In actual logging, the tool rotation angle δ can be calculated based on the tool rotation speed (RPM) and the arrival time (T0) of the reflected signal: δ = RPM·T0.

[0081] Step 8: The geological body orientation obtained from steps 5 to 7 has multiple solutions (the two values ​​differ by 180 degrees), so it is necessary to further distinguish the authenticity of the two results. Specifically, since the receiver on the instrument close to the direction of the incident wave (i.e. the geological body orientation) will record the waveform earlier than the receiver on the other side, the difference in the arrival time of signals XX1 and XX2 can be used to correct the error. and The true position of the geological body can be determined by: If the signal XX1 arrives ahead of XX2, then and The angle closer to the X1 receiver is the true bearing, while the angle closer to the X2 receiver is the true bearing. The arrival time differences between signals XX1 and XX2 can be compared by directly observing the waveforms or using methods such as Fast Fourier Transform (FFT) or Dynamic Time Warping (DWT).

[0082] For the case of δ = 0 in Figures 5(b) and 6(b), Figures 7(a) and 7(b) show the shear and longitudinal wave waveforms XX1 and XX2, respectively, received at an instrument azimuth of 30°. As can be seen in Figures 7(a) and 7(b), waveform XX1 arrives earlier than waveform XX2 for both the shear and longitudinal waves, indicating that receiver X1 is located closer to the geological body, while receiver X2 is located farther away. Combined with the azimuth results of 0° or 180° obtained in Step 7, 0° can be determined to be the true azimuth of the geological body, consistent with the theoretical model. For a more intuitive comparison, the inverted waveform of XX2 is shown in Figure 7(a), but this does not affect the waveform arrival time. It should be noted that the instrument records the azimuth AZ at the time of emission. However, as the instrument rotates, the reflected wave rotates δ degrees by the time it returns to the wellbore. Therefore, the waveform recorded at AZ actually corresponds to the received waveform at (AZ + δ).

[0083] It should be noted that steps 5 and 8 can use either reflection data or imaging data after time-depth conversion, depending on the signal-to-noise ratio of the two data types in actual logging. This is because migration imaging is a linear transformation that does not change the relative amplitude and arrival time relationship between signals XX1 and XX2. The results obtained from reflection and imaging data are consistent. For theoretical data without noise interference, the present invention directly processes the reflection waveforms of signals XX1 and XX2.

[0084] Step 9. After determining the orientation of the geological body, the maximum amplitude signal XX(AZ0) is first enhanced using the common center point stacking, dip stacking, and radial compensation methods. Then, the imaging is time-depth converted based on the velocity model selected in step 6 to determine the distance of the reflector from the wellbore. Finally, the imaging result is further denoised using direct filtering or FK filtering to ultimately obtain the reflection imaging result of the geological body outside the wellbore.

[0085] The following is a specific synthetic well logging example to further illustrate the application effect of the downhole acoustic wave remote detection method based on the dipole single-transmitter dual-receiver measurement mode described in the present invention. In a well section with a depth interval of 140m, there is a through-well reflection interface with an inclination of 60°. The lower and upper sections of the interface are located at 60° and 240° respectively. The wellbore is surrounded by hard formations (with a longitudinal wave velocity of 4000m / s, a shear wave velocity of 2300m / s, and a density of 2500kg / m 3 ). Figure 8 This is the result map of the out-of-hole reflector orientation obtained using the dipole shear wave detection method for this model. During the measurement, it was assumed that the instrument rotation speed was 100 rpm, the drilling speed was 10 m / h, the sound source excitation time interval was 5 seconds, and the time sampling interval and number of sampling points of the logging acoustic field were 36 μs and 1024 points, respectively. Figure 8Track 1 shows the instrument's azimuth relative to the North Pole, demonstrating the instrument's high-speed rotation during measurement. Tracks 2 and 3, respectively, display measured waveforms XX1 and XX2 as variable density plots. These plots reveal that the reflected wave from the out-of-hole formation interface trails the high-amplitude direct wave from the borehole. This well data section was processed using the method described in this invention. Waveforms XX1 and XX2 were first filtered, subjected to wavefield separation, and subjected to migration imaging. The imaged out-of-hole reflection signal was then used to synthesize dipole data XX. At each depth point, measured data XX from 15 depth points immediately above and below that depth point were selected and their waveform amplitudes compared, yielding a wave amplitude energy plot at different azimuths, shown in Track 4. By tracking the high-energy region, the instrument azimuth angle AZ0 corresponding to the maximum waveform amplitude at different depths is obtained, as shown by the black line in Track 4. This curve corresponds to a reflector strike of approximately 140°–150° or 320°–330°, allowing the reflector's azimuth to be calculated to be approximately 50°–60° or 230°–240°. The arrival time of the reflected wave is extracted from the waveform, and the instrument rotation angle between the source emission and the reflection wave reception at different depths is calculated based on the instrument rotation speed. This is shown in Track 5. The reflector's azimuth is corrected based on the instrument rotation angle. Track 6 shows the corrected azimuth result, which shows an uncertainty of 180°, approximately 60° or 240°. The azimuth result is discriminated based on the arrival time differences of signals XX1 and XX2 at different depths, with the true azimuth shown in Track 7. The figure shows that the reflector's azimuth is approximately 60° in the lower section and approximately 240° in the upper section, consistent with the theoretical model and validating the accuracy of the results of the proposed method. After determining the reflector's true azimuth, the maximum amplitude signal XX(AZ0) corresponding to that azimuth is migrated and imaged. Time-depth conversion of the image is performed based on the shear wave velocity to further determine the reflector's distance from the wellbore, resulting in the final out-of-well reflection imaging result.

[0086] In order to further investigate the application effect of the dipole longitudinal wave detection method in the present invention, the area around the wellbore is transformed into a soft formation (with a longitudinal wave velocity of 2074 m / s, a shear wave velocity of 869 m / s, and a density of 2250 kg / m 3 ), refer to Figure 8 The processing flow is as follows: the azimuth of the reflector outside the well is obtained by longitudinal wave detection. Figure 9 Unlike shear wave detection, when using P-wave detection, the high-energy region in the azimuth amplitude energy map in Track 4 corresponds to the reflector's azimuth, not its strike. Track 7 shows that P-wave detection can accurately determine the reflector's azimuth throughout the entire wellbore, validating the accuracy of this method.

[0087] It is worth noting that from Figure 8 and Figure 9 It can be observed in the fourth track that even when the instrument rotation speed is 100 rpm and the detection distance outside the well is about 40 meters, a relatively accurate azimuth result can be obtained without considering the influence of the instrument rotation on the measurement result, which further illustrates that the method of the present invention has strong practicality.

[0088] The above examples are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode, employing the following processing steps: Step 1: Place a dipole acoustic logging tool while drilling in the well and connect it to the drilling system. During the real-time drilling process, a dipole acoustic source pointing along the instrument's x-axis is excited to radiate elastic waves into the formation outside the well. Step 2: Record the azimuth angle AZ of the instrument coordinate axis relative to the fixed direction; Step 3: Use two receivers symmetrically distributed on both sides of the instrument's x-axis to collect signals XX1 and XX2; Step 4: Filter and perform wave field separation on the collected signals to suppress and eliminate the direct waves propagating along the wellbore, extract the reflected signals from the interface outside the well, and perform offset imaging on the reflected signals; Step 5: Use the imaged out-of-hole reflection signal to form dipole data XX=XX1-XX2, select multiple adjacent measurement data XX and compare the waveform amplitudes to find the maximum amplitude signal AZ0; Step 6: In hard formations and conventional soft formations, the dipole data is processed by shear wave and the velocity model is constructed using the shear wave time difference. The orientation of the geological body outside the well is or In ultra-soft formations, the dipole data is processed with longitudinal waves, and the velocity model is constructed using the longitudinal wave time difference. The orientation of the geological body outside the well is or Step 7: Correct the orientation of the geological body in step 6 according to the instrument rotation angle δ. The corrected orientation is or When the geological structure outside the well is within 50m from the wellbore, ignore the rotation effect of the instrument, that is, skip step 7 and go directly to step 8; Step 8: Based on the arrival time difference of signals XX1 and XX2, the correction result and The true position of the geological body can be determined by: If the signal XX1 arrives ahead of XX2, then and The angle closer to the X1 receiver is the true direction, and the angle closer to the X2 receiver is the true direction. Step nine: perform migration imaging on the maximum amplitude signal AZ0, and perform time-depth conversion on the imaging according to the velocity model in step six, further determine the distance of the geological body from the well, and obtain the final out-of-well reflection imaging result.

2. A method for long-range acoustic detection while drilling based on a dipole single-transmitter, dual-receiver measurement mode according to claim 1, wherein in step 1, the dipole sound source points to the x-axis direction of the instrument coordinate system and is composed of two plates symmetrically distributed on the outer rings on both sides of the instrument x-axis, and the energy of the excitation signals of the two plates is the same but the polarity is opposite; when the instrument is working, the dipole source is excited to radiate elastic waves into the formation outside the well.

3. A method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein in step 2, for vertical wells, the fixed direction is selected from the Earth's magnetic North Pole; for inclined wells and horizontal wells, the fixed orientation is referenced to the high end of the wellbore.

4. A method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein in the step 3, a receiver is composed of two receiving plates symmetrically distributed on both sides of the instrument x-axis, and the elastic wave excited by the dipole source is reflected back into the well by the geological body in the stratum, and the receiver records signals XX1 and XX2, wherein the first letter represents the direction of the sound source, and the second letter and number represent the receiver; during the drilling process, as the drill collar rotates at high speed, steps 1 to 3 are repeated to repeatedly excite the dipole source and collect data; 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 second excitation.

5. According to the method of long-range acoustic detection while drilling based on the dipole single-transmitter and dual-receiver measurement mode described in claim 1, the step four is specifically as follows: first, the collected signals XX1 and XX2 are filtered and subjected to direct wave pressure-vibration processing to reduce noise interference and direct wave period, and then the median filter or FK filter method is used to perform wave field separation to remove direct wave interference and extract the reflected wave from the outer well interface from the full wave; the outer well reflected wave is subjected to signal enhancement processing according to the common center point superposition, dip angle superposition and radial compensation methods, and finally imaging is performed using time-depth conversion offset imaging.

6. a kind of sonic detection while drilling method based on dipole single-transmit dual-receive measurement mode according to claim 1, in described step 5, because the instrument constantly rotates during measurement, therefore for a certain depth point, the multiple measurement data adjacent up and down the depth point are regarded as the measurement result on the different orientations carried out by the instrument at the depth point, then the amplitude of multiple measurement XX data is compared, and the instrument azimuth AZ0 corresponding to the maximum amplitude is found.

7. A method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein in step 6, in the case of hard formations and conventional soft formations, it is more advantageous to use dipole shear waves for long-range detection, the dipole data is subjected to shear wave processing, and the velocity model is constructed using shear wave time difference. The azimuth of the geological body outside the well is or In the case of ultra-soft formations, the measured out-hole signal is elastic longitudinal wave. The dipole data is processed with longitudinal wave and the velocity model is constructed using the longitudinal wave time difference. The orientation of the geological body outside the well is or 8. The method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein in step 7, the tool rotation angle δ during actual logging is calculated based on the tool rotation speed RPM and the arrival time T0 of the reflected signal, that is, δ = RPM·T0.

9. The method for long-range acoustic wave detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein in step eight, according to the difference in arrival time of signals XX1 and XX2, i.e., the advance or lag, the correction result is obtained. and Determine the true orientation of the geological body and eliminate the 180° uncertainty of the orientation of the results of steps 6 and 7: If the signal XX1 arrives ahead of XX2, then and The angle close to the X1 receiver is the true azimuth of the geological body, and conversely, the angle close to the X2 receiver is the true azimuth of the geological body. The instrument records the azimuth AZ at the time of emission of the sound source, but as the instrument rotates, the instrument rotates δ degrees when the reflected wave returns to the wellbore. Therefore, when the instrument records the azimuth AZ, it actually corresponds to the received waveform at (AZ+δ). Compare the arrival time differences of signals XX1 and XX2.

10. A method for long-range acoustic detection while drilling based on a dipole single-transmitter dual-receiver measurement mode according to claim 1, wherein the step nine is specifically: the maximum amplitude signal AZ0 determined in step five is first subjected to signal enhancement processing according to the common center point superposition, inclination superposition and radial compensation methods; then, the imaging is subjected to time-depth conversion according to the velocity model determined in step six to determine the distance of the reflector from the wellbore; finally, the imaging result is further subjected to noise reduction processing using direct filtering or FK filtering to ultimately obtain the reflection imaging result of the geological body outside the wellbore.

Images