Wellbore fracture shear stiffness evaluation method based on dipole shear wave far detection logging

Abstract

The application provides a well-side fracture shear stiffness evaluation method based on dipole shear wave far detection logging, and belongs to the technical field of oil and gas exploration and development. The method comprises the following steps: step 1, extracting the shear wave velocity and shear wave attenuation of a target formation from the direct wave information of the dipole shear wave far detection logging data; step 2, performing migration imaging on the reflection wave information in the dipole shear wave far detection logging data, and picking up the dip angle and distance from the well of the fracture from the imaging result; step 3, calculating the shear wave reflection coefficient at the reflection point on the fracture surface; step 4, inverting the shear stiffness of the fracture through the obtained shear wave reflection coefficient; and step 5, circulating step 3 and step 4, obtaining the shear wave reflection coefficient on the fracture surface corresponding to each depth point and inverting the shear stiffness of the fracture at each depth point. The method has important significance for the quantitative characterization of the well-side fracture parameters of the dipole shear wave far detection logging, and fills the blank of the quantitative evaluation of the well-side large-scale fracture.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development technology, and in particular to a method for evaluating well-side fracture shear stiffness based on dipole shear wave remote logging. Background Technology

[0002] Fracture systems are a crucial component of the exploration and development of complex oil and gas reservoirs. Large peri-well fractures (wide and far-reaching) are particularly critical, directly controlling the extent of oil and gas accumulation and forming the main seepage channels. Therefore, accurately characterizing the spatial structure of large peri-well fractures and evaluating their effectiveness is of great guiding significance for exploration evaluation and optimization of development plans. Conventional imaging logging can identify the occurrence and aperture of fractures in the wellbore, but it is difficult to accurately quantify the scale of fracture extension. Seismic anisotropy analysis can predict the orientation of fractures in the region, but insufficient vertical resolution limits the detailed characterization of near-wellbore fractures.

[0003] Dipole shear wave remote detection logging is a rapidly developing large-scale fracture detection technology near wells in recent years. This technology utilizes the direct wave measurement capabilities of existing array acoustic logging instruments to transmit elastic waves outside the wellbore and receive and record reflected shear wave information from nearby fractures. The reflected shear waves are then processed and migrated for imaging to obtain fracture information near the wellbore. Domestic and international research on dipole shear wave remote detection for fracture evaluation mainly focuses on accurate imaging and determining fracture geometry, specifically determining the distance of fractures from the wellbore through accurate migration imaging and obtaining fracture orientation, dip angle, and other occurrence information through circumferential scanning imaging. However, research on the effectiveness evaluation of fractures near wells is currently limited.

[0004] In recent years, domestic scholars have proposed to evaluate the effectiveness of fractures based on the principle of rock fracture mechanics analysis by the relative relationship between the occurrence of fractures near the well and formation stress. However, this method is qualitative and cannot quantitatively characterize the effectiveness of fractures near the well. Furthermore, this method is a prediction rather than a direct evaluation of fracture effectiveness. Summary of the Invention

[0005] In view of this, this invention aims to propose a method for evaluating the shear stiffness of wellbore fractures based on dipole shear wave long-range logging. By using dipole shear wave long-range logging technology to image the fractures near the wellbore, the method obtains the fracture orientation and distance from the wellbore, thereby reconstructing the incident and reflected shear wave paths. Combined with formation shear wave velocity and attenuation, the maximum amplitude of the incident and reflected shear waves at the reflection point on the fracture surface is determined, and used to calculate the shear wave reflection coefficient. The magnitude of the shear wave reflection coefficient is related to the fluid content inside the fracture. The ratio of the fracture filling shear modulus to the fracture aperture, i.e., the fracture shear stiffness, is quantitatively characterized to reflect the effectiveness of the fracture. Finally, the fracture shear stiffness is inverted using the shear wave reflection coefficient to achieve a quantitative evaluation of fracture effectiveness.

[0006] To achieve the above objectives, the technical solution of this invention is as follows: a method for evaluating the shear stiffness of fractures near the wellbore based on dipole shear wave remote detection logging, comprising the following steps: Step 1: Extract the shear wave velocity and shear wave attenuation of the target formation from the direct wave information of the dipole shear wave remote logging data; Step 2: Perform migration imaging on the reflected wave information in the dipole shear wave remote detection logging data, and extract the dip angle and distance from the well from the imaging results; Step 3: Use the shear wave velocity and shear wave attenuation obtained in Step 1 and the fracture dip angle and distance from the well obtained in Step 2 to jointly establish the incident path and reflection path of the shear wave on the fracture surface, and calculate the shear wave reflection coefficient at the reflection point on the fracture surface. Step 4: Invert the shear stiffness of the crack using the transverse wave reflection coefficient obtained in Step 3; Step 5: Repeat steps 3 and 4 to obtain the transverse wave reflection coefficient on the crack surface at each depth point and invert the crack shear stiffness at each depth point.

[0007] Furthermore, in step 1, the cross-dipole shear wave data is rotated by an angle α to obtain a shear wave with a polarization direction parallel to the crack direction, denoted as SH wave, and its shear wave velocity v is extracted. s and transverse wave attenuation Q -1 ; Wherein, the transverse wave velocity v s Obtained via the time-slow method; shear wave attenuation Q. -1 Calculated using the spectral ratio method.

[0008] Furthermore, in step 2, the vertical distance r of the fracture from the well is picked up from the dipole shear wave far-field detection reflected wave imaging results, where the fracture endpoint (z) s r s ) and (z e r e ), used to calculate the crack inclination angle θ: (3) In the formula, θ: crack inclination angle, °; z s : Depth of the crack initiation point, in meters; z e : Depth of the crack termination point, in meters; r s : Vertical distance from the fracture initiation point to the well, in meters; r e : Vertical distance from the fracture initiation point to the well, in meters.

[0009] Furthermore, step 3 includes: Step 31: Calculate the maximum amplitude of the incident shear wave at the crack surface; First, the transverse wave waveform SH from the nth receiver. n Source distance d, center frequency f of transverse wave waveform m Shear wave attenuation Q -1 transverse wave velocity v s These parameters restore the maximum amplitude A of the shear wave waveform on the well wall at the depth of the sound source. src : (4) In the formula, SH n : The transverse wave waveform of the nth receiver, Pa; A src : Maximum amplitude of the transverse wave waveform on the well wall at the sound source, Pa; d: The distance from the sound source to the nth receiver, i.e., the source distance; hilbert(·): Performs a Hilbert transformation on the variable within the parentheses; max(·): Retrieves the maximum value of the variable within the parentheses; Where d, f m Q -1 v s These four variables are used only as correction values ​​for geometric diffusion in equation (4), and are dimensionless; Then, the incident path of the transverse wave at the current depth point from the sound source to the slit surface and the reflection path from the slit surface to the receiver are established, where the incident transverse wave propagates over a distance p. inc for: (5) In the formula, r: the vertical distance from a point on the fracture surface at the current depth to the wellbore, in meters; p inc : The propagation path length of the transverse wave from the sound source to the incident point on the crack surface, in meters; Finally, the maximum amplitude A of the incident transverse wave at the crack surface is calculated using the following formula. inc : (6) In the formula, A inc : Maximum amplitude of the incident shear wave at the incident point on the crack surface, Pa; Where, p inc f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (6), and are dimensionless; Step 32: Calculate the maximum amplitude of the reflected shear wave at the crack surface; The propagation distance p of the reflected transverse wave refl for: (7) In the formula, p refl : The propagation path length of the transverse wave from the reflection point on the crack surface to the receiver, in meters; By analyzing the original waveform SH n Wave field separation yields the reflected transverse wave RSH, and the reflected transverse wave is represented by the waveform SH. n The time t' is: (8) In the formula, t': the reflected transverse wave at waveform SH n When it arrives, s; Set the portion of the reflected wave in RSH before time t' to 0 to form a new waveform, and denote the new waveform as RSH'; The maximum amplitude A of the reflected transverse wave at the reflection point of the slit surface refl for: (9) In the formula, A refl : Maximum amplitude of the reflected transverse wave at the reflection point of the crack surface, Pa; RSH': A new waveform in the reflected transverse wave where the amplitude is set to 0 before the reflected wave arrives at time t', Pa; Where, p refl f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (9), and are dimensionless; Step 33: Calculate the transverse wave reflection coefficient at the reflection point on the crack surface; The transverse wave reflection coefficient RCS at the reflection point on the crack surface is the maximum amplitude A of the transverse wave reflection. refl And the maximum amplitude A of the incident transverse wave inc The ratio is calculated using the following formula: (10) In the formula, RCS is the transverse wave reflection coefficient, which is dimensionless.

[0010] Furthermore, step 4 includes: First, calculate the incident / reflection angle γ at the incident / reflection point on the crack surface. The calculation formula is as follows: (11) In the formula, γ: the incident / reflection angle of the transverse wave on the crack surface, °; Then, the theoretical transverse wave reflection coefficient at the incident / reflection point at the crack surface, and the theoretical transverse wave reflection coefficient RSC at the incident / reflection point at the crack surface are calculated. m From the formation density ρ and the shear wave velocity v s The center frequency f of the transverse wave waveform mThe incident / reflection angle γ of the transverse wave on the crack surface and the crack stiffness η T The calculation is as follows: (12) In the formula, RCS m Theoretical transverse wave reflection coefficient, dimensionless; ρ: Formation density, kg·m -3 ; η T Crack shear stiffness, kg·m -2 ·s -2 ; i: Imaginary unit; Finally, the objective function E is constructed, and the formula for calculating the objective function E is as follows: (13) Shear stiffness η of traversing cracks T The actual crack shear stiffness is obtained when the objective function E is minimized.

[0011] Compared to existing technologies, the wellbore fracture shear stiffness evaluation method based on dipole shear wave remote sounding logging described in this invention has the following advantages: The method obtains fracture orientation and distance from the wellbore based on shear wave remote sounding logging imaging, reconstructs the incident and reflection paths of the shear waves, and determines the maximum amplitude of the incident and reflected shear waves at the reflection point by combining formation shear wave velocity and attenuation, thus calculating the shear wave reflection coefficient. This coefficient is related to the proportion of fluid inside the fracture. By quantitatively characterizing the fracture shear stiffness, the effectiveness of the fracture is reflected, and the fracture shear stiffness is inverted. This invention achieves, for the first time, a quantitative evaluation of large-scale fractures near the wellbore observed through dipole shear wave remote sounding logging. This invention fills the gap in the quantitative evaluation of large-scale fractures near the wellbore and has important guiding significance for reservoir evaluation, horizontal well trajectory design, and development well pattern optimization. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A flowchart of a well-side fracture shear stiffness evaluation method based on dipole shear wave remote detection logging provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of fracture inclination angle and distance pickup in dipole shear wave remote detection logging provided in an embodiment of the present invention; Figure 3 A schematic diagram of the incident and reflection paths of a dipole shear wave in remote detection logging provided in an embodiment of the present invention; Figure 4The image shows the comprehensive results of wellside fracture stiffness evaluation based on dipole shear wave remote detection logging for well X, provided in an embodiment of the present invention. Detailed Implementation

[0013] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0014] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0015] This invention provides a method for evaluating the shear stiffness of fractures near the wellbore based on dipole shear wave remote sensing logging. By imaging fractures near the wellbore using dipole shear wave remote sensing technology, the method obtains the fracture orientation and distance from the wellbore, reconstructs the paths of incident and reflected shear waves, and determines the maximum amplitude of the incident and reflected shear waves on the fracture surface by combining formation shear wave velocity and attenuation. The shear wave reflection coefficient is then calculated. The magnitude of the shear wave reflection coefficient is related to the fluid content within the fracture. This quantitative characterization of fracture shear stiffness reflects the effectiveness of the fracture, and the quantitative evaluation of fracture effectiveness is achieved by inverting the fracture shear stiffness using the shear wave reflection coefficient. Figure 1 As shown, this invention is a method for evaluating the shear stiffness of fractures near the wellbore based on dipole shear wave remote detection logging, comprising the following steps: Step 1: Extract the shear wave velocity and shear wave attenuation of the target formation from the direct wave information of the dipole shear wave remote logging data; Crossed dipole sound sources are directional; transverse waves from any direction can be obtained by rotating the four components. Specifically, when the polarization direction of the transverse wave is parallel to the crack's orientation, the reflection from the crack surface is strongest, denoted as a horizontally polarized transverse wave (SH wave). A transverse wave perpendicular to its polarization direction is denoted as a vertically polarized transverse wave (SV wave). In actual measurements, X and Y represent the dipole system in a fixed coordinate system. The four components of the crossed dipole are XX, XY, YY, and YX, where XX represents the waveform received in the X direction after the sound source excites the wave. The angle between the fixed coordinate system and the measurement coordinate system is AZ, and the angle between the measurement coordinate system and the reflector's orientation is α. Therefore, the measured waveform is the projection of SH (horizontally polarized transverse wave) and SV (vertically polarized transverse wave) onto the measurement coordinate system. By combining the four received components, the SH and SV waves can be deduced.

[0016] (1) In the formula, XX, XY, YY, YX: cross-dipole four-component waveform data, Pa; t: Waveform time series, seconds; α: Angle between the measurement coordinate system and the crack orientation, °; SH: Horizontally polarized (relative to crack orientation) shear wave waveform data, Pa; SV: Vertically polarized (relative to crack orientation) shear wave waveform data, Pa; The transverse wave has the fastest velocity when its polarization direction is parallel to the principal stress, and is denoted as a fast transverse wave. Under formation conditions, the effective fracture orientation is usually approximately parallel to the principal stress direction. Therefore, the azimuth of the fast transverse wave is approximately equal to the angle α between the measurement coordinate system and the fracture orientation, which can be obtained by equation (2). (2) The wave velocity and attenuation of the SH wave (horizontally polarized shear wave) are calculated separately (hereinafter referred to as shear wave velocity and attenuation). The shear wave velocity can be obtained by the STC (time-slowness method) and denoted as v. s The transverse wave attenuation is calculated using the spectral ratio method and denoted as Q. -1 (The detailed steps are existing technology and will not be repeated here).

[0017] Step 2: Perform migration imaging on the reflected wave information in the dipole shear wave remote detection logging data, and extract the dip angle and distance from the well from the imaging results; Cross-dipole shear wave data includes direct wave information and reflected wave information from formation fractures, using the depth-varying shear wave velocity v extracted in step 1. s As a velocity model at different depths (assuming that the shear wave velocity near the well at the same depth does not change radially), the direct wave data DSH and reflected wave data RSH are extracted through wavefield separation. The reflected wave data RSH is then offset to obtain the reflected wave imaging results. This step can be fully implemented using existing commercial software. The reflected wave image obtained by commercial software is presented in image form, reflecting the reflection information near the well as varying radial distance r, i.e., fracture characteristics. The distance r from the well to each point on the fracture surface can be directly read from the reflected wave image. The trajectory of the fracture is picked up on the reflected wave image. The trajectory of any fracture can be represented by the coordinates of its starting and ending points, i.e., (z... s r s ) and (z e r e Then the crack inclination angle θ is: (3) In the formula, θ: crack inclination angle, °; z s : Depth of the crack initiation point, in meters; z e : Depth of the crack termination point, in meters; r s : Vertical distance from the fracture initiation point to the well, in meters; r e : Vertical distance from the fracture initiation point to the well, in meters.

[0018] Step 3: Use the shear wave velocity and shear wave attenuation obtained in Step 1 and the fracture dip angle and distance from the well obtained in Step 2 to jointly establish the incident path and reflection path of the shear wave on the fracture surface, and calculate the shear wave reflection coefficient at the reflection point on the fracture surface. (1) Calculate the maximum amplitude of the incident shear wave at the crack surface; First, the transverse wave waveform SH from the nth receiver. n Source distance d, center frequency f of transverse wave waveform m Shear wave attenuation Q -1 transverse wave velocity v s These parameters restore the maximum amplitude A of the shear wave waveform on the well wall at the depth of the sound source. src : (4) In the formula, SH n : The transverse wave waveform of the nth receiver, Pa; A src : Maximum amplitude of the transverse wave waveform on the well wall at the sound source, Pa; d: The distance from the sound source to the nth receiver, i.e., the source distance; hilbert(·): Performs a Hilbert transformation on the variable within the parentheses; max(·): Retrieves the maximum value of the variable within the parentheses; Where d, f m Q -1 v s These four variables are used only as correction values ​​for geometric diffusion in equation (4), and are dimensionless; Then, the incident path of the transverse wave at the current depth from the sound source to the slit surface and the reflection path from the slit surface to the receiver are established, with the incident transverse wave propagation distance p. inc for: (5) In the formula, r: the vertical distance from a point on the fracture surface at the current depth to the wellbore, in meters; p inc : The propagation path length of the transverse wave from the sound source to the incident point on the crack surface, in meters; Finally, the maximum amplitude A of the incident transverse wave at the crack surface is calculated using the following formula. inc : (6) In the formula, A inc : Maximum amplitude of the incident shear wave at the incident point on the crack surface, Pa; Where, p inc f m Q -1 v sThese variables are used only as correction values ​​for geometric diffusion in equation (6), and are dimensionless; (2) Calculate the maximum amplitude of the reflected shear wave at the crack surface; The propagation distance p of the reflected transverse wave refl for: (7) In the formula, p refl : The propagation path length of the transverse wave from the reflection point on the crack surface to the receiver, in meters; By analyzing the original waveform SH n Wave field separation yields the reflected transverse wave RSH, and the reflected transverse wave is represented by the waveform SH. n The time t' is: (8) In the formula, t': the reflected transverse wave at waveform SH n When it arrives, s; Set the portion of the reflected wave in RSH before time t' to 0 to form a new waveform, and denote the new waveform as RSH'; The maximum amplitude A of the reflected transverse wave at the reflection point of the slit surface refl for: (9) In the formula, A refl : Maximum amplitude of the reflected transverse wave at the reflection point of the crack surface, Pa; RSH': A new waveform in the reflected transverse wave where the amplitude is set to 0 before the reflected wave arrives at time t', Pa; Where, p refl f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (9), and are dimensionless; (3) Calculate the transverse wave reflection coefficient at the reflection point on the crack surface; The transverse wave reflection coefficient RCS at the reflection point on the crack surface is the maximum amplitude A of the transverse wave reflection. refl And the maximum amplitude A of the incident transverse wave inc The ratio is calculated using the following formula: (10) In the formula, RCS is the transverse wave reflection coefficient, which is dimensionless.

[0019] Step 4: Invert the shear stiffness of the crack using the transverse wave reflection coefficient obtained in Step 3; First, calculate the incident / reflection angle γ at the incident / reflection point on the crack surface. The calculation formula is as follows: (11) In the formula, γ: the incident / reflection angle of the transverse wave on the crack surface, °; Then, the theoretical transverse wave reflection coefficient at the incident / reflection point at the crack surface, and the theoretical transverse wave reflection coefficient RSC at the incident / reflection point at the crack surface are calculated. m From the formation density ρ and the shear wave velocity v s The center frequency f of the transverse wave waveform m The incident / reflection angle γ of the transverse wave on the crack surface and the crack stiffness η T The calculation is as follows: (12) In the formula, RCS m Theoretical transverse wave reflection coefficient, dimensionless; ρ: Formation density, kg·m -3 ; η T Crack shear stiffness, kg·m -2 ·s -2 ; i: Imaginary unit; Finally, the objective function E is constructed, and the formula for calculating the objective function E is as follows: (13) Shear stiffness η of traversing cracks T The actual crack shear stiffness is obtained when the objective function E is minimized.

[0020] Step 5: Repeat steps 3 and 4 to obtain the transverse wave reflection coefficient on the crack surface at each depth point and invert the crack shear stiffness at each depth point.

[0021] Example 1 Taking Well X in a certain area as an example The wellbore fracture stiffness evaluation method based on dipole shear wave remote detection logging is performed according to the following steps: Step 1: Extract the shear wave velocity and shear wave attenuation of the target formation from the direct wave information of the dipole shear wave remote logging data; Crossed dipole sound sources are directional; transverse waves from any direction can be obtained by rotating the four components. Specifically, when the polarization direction of the transverse wave is parallel to the crack's orientation, the reflection from the crack surface is strongest, denoted as a horizontally polarized transverse wave (SH wave). A transverse wave perpendicular to its polarization direction is denoted as a vertically polarized transverse wave (SV wave). In actual measurements, X and Y represent the dipole system in a fixed coordinate system. The four components of the crossed dipole are XX, XY, YY, and YX, where XX represents the waveform received in the X direction after the sound source excites the wave. The angle between the fixed coordinate system and the measurement coordinate system is AZ, and the angle between the measurement coordinate system and the reflector's orientation is α. Therefore, the measured waveform is the projection of SH (horizontally polarized transverse wave) and SV (vertically polarized transverse wave) onto the measurement coordinate system. By combining the four received components, the SH and SV waves can be deduced.

[0022] (1) In the formula, XX, XY, YY, YX: cross-dipole four-component waveform data, Pa; t: Waveform time series, seconds; α: Angle between the measurement coordinate system and the crack orientation, °; SH: Horizontally polarized (relative to crack orientation) shear wave waveform data, Pa; SV: Vertically polarized (relative to crack orientation) shear wave waveform data, Pa; The transverse wave has the fastest velocity when its polarization direction is parallel to the principal stress, and is denoted as a fast transverse wave. Under formation conditions, the effective fracture orientation is usually approximately parallel to the principal stress direction. Therefore, the azimuth of the fast transverse wave is approximately equal to the angle α between the measurement coordinate system and the fracture orientation, which can be obtained by equation (2). (2) Next, the wave velocity and attenuation of the SH wave (horizontally polarized shear wave) are calculated (hereinafter referred to as shear wave velocity and attenuation). The shear wave velocity can be obtained through the STC (time-slowness method) and denoted as v. s The transverse wave attenuation is calculated using the spectral ratio method and denoted as Q. -1 (The detailed steps are existing technology and will not be repeated here.) The calculated shear wave velocity v s and transverse wave attenuation Q -1 Each as Figure 4 The blue and red lines in the third lane are shown.

[0023] Step 2: Perform migration imaging on the reflected wave information in the dipole shear wave remote detection logging data, and extract the dip angle and distance from the well from the imaging results; Crossed dipole shear wave data ( Figure 4 The fourth channel contains direct wave information and reflected wave information from formation fractures, using the depth-varying shear wave velocity v extracted in step 1. sAs a velocity model at different depths (assuming that the shear wave velocity at the same depth does not change radially), the direct wave data DSH and reflected wave data RSH are then extracted through wavefield separation. Figure 4 Tracks 5 and 6 show the waveform data from the first receiver in DSH and RSH, respectively. By shifting the reflected wave data (RSH), the reflected wave imaging results can be obtained. Figure 4 (Step 7 in the middle) This step can be fully implemented using existing commercial software. The reflected wave image obtained by commercial software is presented in image form, reflecting the reflection information around the well as varying radial distance r, i.e., fracture characteristics. The distance r from the well to each point on the fracture surface can be directly read from the reflected wave image. The trajectory of the fracture is picked up on the reflected wave image. The trajectory of any fracture can be represented by the coordinates of its starting and ending points, i.e., (z... s r s ) and (z e r e Then the crack inclination angle θ is: (3) In the formula, θ: crack inclination angle, °; z s : Depth of the crack initiation point, in meters; z e : Depth of the crack termination point, in meters; r s : Vertical distance from the fracture initiation point to the well, in meters; r e : Vertical distance from the fracture initiation point to the well, in meters.

[0024] In this embodiment, the fracture trajectory picking result of well X is as follows: Figure 2 As shown, the fractal dip angle and distance from the well are obtained as follows: Figure 4 As shown in questions 8 and 9.

[0025] Step 3: Use the shear wave velocity and shear wave attenuation obtained in Step 1 and the fracture dip angle and distance from the well obtained in Step 2 to jointly establish the incident path and reflection path of the shear wave on the fracture surface, and calculate the shear wave reflection coefficient at the reflection point on the fracture surface. Figure 3 The diagram illustrates the incident and reflection paths of the transverse wave excited by the instrument's sound source on the crack surface. Based on the paths shown in the diagram, the maximum amplitude of the incident transverse wave and the maximum amplitude of the reflected transverse wave at the incident and reflection points on the crack surface are calculated respectively. (1) Calculate the maximum amplitude of the incident shear wave at the crack surface; The transverse wave waveform SH through the nth receiver n Source distance d, center frequency f of transverse wave waveform m Shear wave attenuation Q -1 transverse wave velocity vs These parameters restore the maximum amplitude A of the shear wave waveform on the well wall at the depth of the sound source. src : (4) In the formula, SH n : The transverse wave waveform of the nth receiver, Pa; A src : Maximum amplitude of the transverse wave waveform on the well wall at the sound source, Pa; d: The distance from the sound source to the nth receiver, i.e., the source distance; hilbert(·): Performs a Hilbert transformation on the variable within the parentheses; max(·): Retrieves the maximum value of the variable within the parentheses; Where d, f m Q -1 v s These four variables are used only as correction values ​​for geometric diffusion in equation (4), and are dimensionless; Incident transverse wave propagation distance p inc for: (5) In the formula, r: the vertical distance from a point on the fracture surface at the current depth to the wellbore, in meters; p inc : The propagation path length of the transverse wave from the sound source to the incident point on the crack surface, in meters; The maximum amplitude A of the incident transverse wave at the crack surface is calculated using the following formula. inc : (6) In the formula, A inc : Maximum amplitude of the incident shear wave at the incident point on the crack surface, Pa; Where, p inc f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (6), and are dimensionless; (2) Calculate the maximum amplitude of the reflected shear wave at the crack surface; The propagation distance p of the reflected transverse wave refl for: (7) In the formula, p refl : The propagation path length of the transverse wave from the reflection point on the crack surface to the receiver, in meters; The reflected transverse wave in waveform SH n The time t' is: (8) In the formula, t': the reflected transverse wave at waveform SH n When it arrives, s; Set the portion of the reflected wave in RSH before time t' to 0 to form a new waveform, and denote the new waveform as RSH'; The maximum amplitude A of the reflected transverse wave at the reflection point of the slit surface refl for: (9) In the formula, A refl : Maximum amplitude of the reflected transverse wave at the reflection point of the crack surface, Pa; RSH': A new waveform in the reflected transverse wave where the amplitude is set to 0 before the reflected wave arrives at time t', Pa; Where, p refl f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (9), and are dimensionless; (3) Calculate the transverse wave reflection coefficient at the reflection point on the crack surface; The transverse wave reflection coefficient RCS at the reflection point on the crack surface is the maximum amplitude A of the transverse wave reflection. refl And the maximum amplitude A of the incident transverse wave inc The ratio is calculated using the following formula: (10) In the formula, RCS is the transverse wave reflection coefficient, which is dimensionless.

[0026] In this embodiment, taking the waveform of the first receiver as an example, the propagation distance of the incident transverse wave, the propagation distance of the reflected wave, and the incident (reflected) angle of the transverse wave on the slit surface, calculated based on the incident and reflected transverse wave paths, are as follows: Figure 4 As shown in channels 10, 11, and 12, the transverse wave reflection coefficient (RCS) is calculated by reconstructing the maximum amplitude of the incident transverse wave and the maximum amplitude of the reflected transverse wave on the crack surface based on the transverse wave propagation path. Figure 4 As shown in the 13th question.

[0027] Step 4: Invert the shear stiffness of the crack using the transverse wave reflection coefficient obtained in Step 3; First, calculate the incident / reflection angle γ at the incident / reflection point on the crack surface. The calculation formula is as follows: (11) In the formula, γ: the incident / reflection angle of the transverse wave on the crack surface, °; it should be noted that, as is well known to those skilled in the art, the incident angle of reflection is equal, so the calculation formula for the incident / reflection angle of the transverse wave on the crack surface is the same, and the same symbol γ is used to represent it.

[0028] Then, the theoretical transverse wave reflection coefficient at the incident / reflection point at the crack surface, and the theoretical transverse wave reflection coefficient RSC at the incident / reflection point at the crack surface are calculated. m From the formation density ρ and the shear wave velocity v s The center frequency f of the transverse wave waveform m The incident / reflection angle γ of the transverse wave on the crack surface and the crack stiffness η T The calculation is as follows: (12) In the formula, RCS m Theoretical transverse wave reflection coefficient, dimensionless; ρ: Formation density, kg·m -3 ; η T Crack shear stiffness, kg·m -2 ·s -2 ; i: Imaginary unit; Finally, the objective function E is constructed, and the formula for calculating the objective function E is as follows: (13) Shear stiffness η of traversing cracks T The actual crack shear stiffness is obtained when the objective function E is minimized.

[0029] Step 5: Repeat steps 3 and 4 to obtain the transverse wave reflection coefficient at each depth point on the crack surface and invert the crack shear stiffness at each depth point.

[0030] In this embodiment, the calculated shear stiffness of the fracture in well X is as follows: Figure 4 As shown in question 14.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the shear stiffness of fractures near the wellbore based on dipole shear wave remote detection logging, characterized in that, Includes the following steps: Step 1: Extract the shear wave velocity and shear wave attenuation of the target formation from the direct wave information of the dipole shear wave remote logging data; Step 2: Perform migration imaging on the reflected wave information in the dipole shear wave remote detection logging data, and extract the dip angle and distance from the well from the imaging results; Step 3: Use the shear wave velocity and shear wave attenuation obtained in Step 1 and the fracture dip angle and distance from the well obtained in Step 2 to jointly establish the incident path and reflection path of the shear wave on the fracture surface, and calculate the shear wave reflection coefficient at the reflection point on the fracture surface. Step 4: Invert the shear stiffness of the crack using the transverse wave reflection coefficient obtained in Step 3; Step 5: Repeat steps 3 and 4 to obtain the transverse wave reflection coefficient on the crack surface at each depth point and invert the crack shear stiffness at each depth point.

2. The well-side fracture shear stiffness evaluation method based on dipole shear wave remote detection logging according to claim 1, characterized in that: In step 1, the cross-dipole shear wave data is rotated by an angle α to obtain a shear wave with a polarization direction parallel to the crack direction, denoted as SH wave, and its shear wave velocity v is extracted. s and transverse wave attenuation Q -1 ; Wherein, the transverse wave velocity v s Obtained via the time-slow method; shear wave attenuation Q. -1 Calculated using the spectral ratio method.

3. The wellbore fracture shear stiffness evaluation method based on dipole shear wave remote detection logging according to claim 1, characterized in that: In step 2, the vertical distance r of the fracture from the well is picked up from the dipole shear wave far-field detection reflected wave imaging results, where the fracture endpoint (z) s r s ) and (z e r e ), used to calculate the crack inclination angle θ: （3） In the formula, θ: crack inclination angle, °; z s : Depth of the crack initiation point, in meters; z e : Depth of the crack termination point, in meters; r s : Vertical distance from the fracture initiation point to the well, in meters; r e : Vertical distance from the fracture initiation point to the well, in meters.

4. The method for evaluating well-side fracture shear stiffness based on dipole shear wave remote detection logging according to claim 2, characterized in that, Step 3 includes: Step 31: Calculate the maximum amplitude of the incident shear wave at the crack surface; First, the transverse wave waveform SH from the nth receiver. n Source distance d, center frequency f of transverse wave waveform m Shear wave attenuation Q -1 transverse wave velocity v s These parameters restore the maximum amplitude A of the shear wave waveform on the well wall at the depth of the sound source. src : （4） In the formula, SH n : The transverse wave waveform of the nth receiver, Pa; A src : Maximum amplitude of the transverse wave waveform on the well wall at the sound source, Pa; d: The distance from the sound source to the nth receiver, i.e., the source distance; hilbert(·): Performs a Hilbert transformation on the variable within the parentheses; max(·): Retrieves the maximum value of the variable within the parentheses; Where d, f m Q -1 v s These four variables are used only as correction values ​​for geometric diffusion in equation (4), and are dimensionless; Then, the incident path of the transverse wave at the current depth from the sound source to the slit surface and the reflection path from the slit surface to the receiver are established, where the incident transverse wave propagates a distance p. inc for: （5） In the formula, r: the vertical distance from a point on the fracture surface at the current depth to the wellbore, in meters; p inc : The propagation path length of the transverse wave from the sound source to the incident point on the crack surface, in meters; Finally, the maximum amplitude A of the incident transverse wave at the crack surface is calculated using the following formula. inc : （6） In the formula, A inc : Maximum amplitude of the incident shear wave at the incident point on the crack surface, Pa; Where, p inc f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (6), and are dimensionless; Step 32: Calculate the maximum amplitude of the reflected shear wave at the crack surface; The propagation distance p of the reflected transverse wave refl for: （7） In the formula, p refl : The propagation path length of the transverse wave from the reflection point on the crack surface to the receiver, in meters; By analyzing the original waveform SH n Wave field separation yields the reflected transverse wave RSH, and the reflected transverse wave is represented by the waveform SH. n The time t' is: （8） In the formula, t': the reflected transverse wave at waveform SH n When it arrives, s; Set the portion of the reflected wave in RSH before time t' to 0 to form a new waveform, and denote the new waveform as RSH'; The maximum amplitude A of the reflected transverse wave at the reflection point of the slit surface refl for: （9） In the formula, A refl : Maximum amplitude of the reflected transverse wave at the reflection point of the crack surface, Pa; RSH': A new waveform in the reflected transverse wave where the amplitude is set to 0 before the reflected wave arrives at time t', Pa; Where, p refl f m Q -1 v s These variables are used only as correction values ​​for geometric diffusion in equation (9), and are dimensionless; Step 33: Calculate the transverse wave reflection coefficient at the reflection point on the crack surface; The transverse wave reflection coefficient RCS at the reflection point on the crack surface is the maximum amplitude A of the transverse wave reflection. refl And the maximum amplitude A of the incident transverse wave inc The ratio is calculated using the following formula: （10） In the formula, RCS is the transverse wave reflection coefficient, which is dimensionless.

5. The method for evaluating well-side fracture shear stiffness based on dipole shear wave remote detection logging according to claim 1, characterized in that, Step 4 includes: First, calculate the incident / reflection angle γ at the incident / reflection point on the crack surface. The calculation formula is as follows: （11） In the formula, γ: the incident / reflection angle of the transverse wave on the crack surface, °; Then, the theoretical transverse wave reflection coefficient at the incident / reflection point at the crack surface, and the theoretical transverse wave reflection coefficient RSC at the incident / reflection point at the crack surface are calculated. m From the formation density ρ and the shear wave velocity v s The center frequency f of the transverse wave waveform m The incident / reflection angle γ of the transverse wave on the crack surface and the crack stiffness η T The calculation is as follows: （12） In the formula, RCS m Theoretical transverse wave reflection coefficient, dimensionless; ρ: Formation density, kg·m -3 ; η T Crack shear stiffness, kg·m -2 ·s -2 ; i: Imaginary unit; Finally, the objective function E is constructed, and the formula for calculating the objective function E is as follows: （13） Shear stiffness η of traversing cracks T The actual crack shear stiffness is obtained when the objective function E is minimized.

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