Identification analogue simulation method for identifying well wall crack by ultrasonic transducer

Abstract

The invention discloses a recognition simulation method for recognizing well wall cracks by an ultrasonic transducer, which belongs to the technical field of ultrasonic transducer design and comprises the following steps: step 1, determining initial values of model parameters; step 2, constructing an ultrasonic identification logging simulation model; step 3, adding a crack in the ultrasonic identification logging simulation model; 4, performing simulation calculation to obtain waveform data formed by echo signals; 5, determining the identification position of the crack boundary and the identification width of the crack; 6, changing the value of the width l or / and the curvature radius or / and the distance h to the well wall to obtain the identification results of the different ultrasonic identification logging simulation models on the cracks of different sizes; and 7, judging the identification effect of the ultrasonic transducer on the crack. According to the method, the echo data are processed to obtain identification simulation of the crack, and data support is provided for optimizing the curvature radius of the transducer and the distance between the signal transmitting end of the ultrasonic transducer and the well wall in the actual logging process.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic transducer design methods, and particularly relates to a method for identifying and simulating wellbore fractures using an ultrasonic transducer. Background Art

[0002] As one of the important methods of imaging logging, the basic principle of ultrasonic imaging logging is to continuously emit ultrasonic signals to the surrounding of the wellbore through a continuously rotating ultrasonic transducer, and continuously collect and analyze the ultrasonic echo signals to detect the size, shape, distribution, etc. of the fractures with high resolution and reflect the wellbore state information in the form of an image, effectively improving the oil well development efficiency and ensuring the drilling safety.

[0003] Among them, as Figure 1 shown, the ultrasonic transducer includes a body 01, and the signal emitting end of the body 01 is a concave spherical structure. When the fracture widths are different and the distances between the signal emitting end of the ultrasonic transducer and the wellbore are different, and when the concave spherical surface of the body 01 has different curvature radii, there are differences in the recognition accuracy of the fracture positions.

[0004] In order to ensure the fracture position recognition accuracy, it is urgent to determine the recognition law of the ultrasonic transducer for fractures when the fracture widths are different, the distances between the signal emitting end of the ultrasonic transducer and the wellbore are different, or the curvature radii of the concave spherical surface of the body 01 are different.

[0005] Based on this, the present application proposes a method for identifying and simulating wellbore fractures using an ultrasonic transducer. Based on the COMSOL software, the ultrasonic transducer is used to identify the fracture positions on the wellbore. By processing the echo data, the recognition simulation of the fractures is obtained. By changing the numerical values of the model parameters and the fracture sizes, the recognition law of the ultrasonic transducer for fractures can be obtained, the minimum fracture width that can be recognized by transducers with different curvature radii based on the corresponding recognition accuracy can be determined, and the recognition effect can be judged, providing data support for optimizing the curvature radius of the transducer and the distance between the signal emitting end of the ultrasonic transducer and the wellbore in the actual logging process. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for identifying and simulating wellbore fractures using an ultrasonic transducer.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A method for identifying and simulating wellbore fractures using an ultrasonic transducer includes the following steps:

[0009] Step 1, determine the initial values of the model parameters;

[0010] The model parameters include the borehole radius, the ultrasonic transducer radius, the radius of curvature of the spherical structure in the ultrasonic transducer body, and the distance h from the center point of the ultrasonic transducer signal transmitting end to the wellbore wall;

[0011] Step 2, in the COMSOL software, construct an ultrasonic identification logging simulation model, which includes a borehole model and an ultrasonic transducer model located inside the borehole model;

[0012] Step 3, add a crack to the ultrasonic identification logging simulation model constructed in Step 2. The crack extends from the borehole to the formation, and determine the width l of the crack along the circumferential direction of the borehole and the depth of the crack along the radial direction of the borehole;

[0013] Step 4, perform simulation calculations in the COMSOL software. During the circumferential movement of the ultrasonic transducer model around the central axis of the borehole model, perform simulation transmission and reception of ultrasonic waves to obtain waveform data composed of echo signals, where the crack is within the range of the central angle of the circumferential movement of the ultrasonic transducer model;

[0014] Step 5, according to the waveform data, determine the identification position of the crack boundary and the identification width m of the crack;

[0015] Step 6, change the value of the width l or / and the radius of curvature or / and the distance h from the wellbore wall, while keeping the numerical values of other model parameters unchanged, to obtain different ultrasonic identification logging simulation models and cracks of different sizes;

[0016] For each corresponding ultrasonic identification logging simulation model and crack, perform Steps 3 to 4 to obtain the identification results of different ultrasonic identification logging simulation models for cracks of different sizes;

[0017] Step 7, perform data processing on the identification results obtained in Step 6 to judge the identification effect of the ultrasonic transducer on the crack.

[0018] Preferably, in Step 2, constructing the ultrasonic identification logging simulation model includes the following sub-steps:

[0019] Step 21, in the COMSOL software, click "Model Wizard", set the three-dimensional spatial dimension, and select "Acoustic-Piezoelectric Interaction, Transient and Circuit" for the physical field;

[0020] Step 22, construct an ultrasonic transducer model based on the ultrasonic transducer radius and the radius of curvature of the spherical structure in the ultrasonic transducer model body;

[0021] Step 23, the borehole model includes a borehole and a formation, and construct the borehole model based on the borehole radius;

[0022] Step 24, add material parameters. The borehole is filled with water, the wellbore wall is granite, and the ultrasonic transducer model is PZT-5H;

[0023] Step 25: Make the central axis of the ultrasonic transducer model perpendicular to and intersect with the central axis of the wellbore model. Based on the distance h from the center point of the signal transmitting end of the ultrasonic transducer to the wellbore and the initial relative position relationship between the ultrasonic transducer model and the crack, construct an ultrasonic identification logging simulation model.

[0024] Preferably, in step 5, the echo amplitude method is used to determine the curve of the echo amplitude A versus the circumferential displacement x of the ultrasonic transducer model and the second derivative of the echo amplitude versus the circumferential displacement x of the ultrasonic transducer model, and then determine the identification position of the crack boundary and the identification width m of the crack;

[0025] Or the echo arrival time method is used to determine the curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model, and then determine the identification position of the crack boundary and the identification width m of the crack.

[0026] Preferably, the echo amplitude method is specifically as follows:

[0027] Import the waveform data obtained in step 4 into Matlab software, extract the peak value in the ultrasonic echo curve as the echo amplitude A, and plot the curve of the echo amplitude A versus the circumferential displacement x of the ultrasonic transducer model;

[0028] Based on the curve of the echo amplitude versus the circumferential displacement of the ultrasonic transducer model, plot the second derivative of the echo amplitude versus the circumferential displacement x of the ultrasonic transducer model;

[0029] In the curve of the second derivative of the echo amplitude versus the circumferential displacement x of the ultrasonic transducer model, find the point with the largest absolute value of the ordinate and the second largest point. The abscissas x1 and x2 corresponding to these two points are the identification positions of the two boundaries of the crack, where (x1 < x2);

[0030] The identification width m of the crack = x2 - x1.

[0031] Preferably, the echo arrival time method is specifically as follows:

[0032] Import the waveform data obtained in step 4 into Matlab software. For each circumferential position of the ultrasonic transducer model, extract the ultrasonic echo arrival time. The echo arrival time refers to the time required from transmission to reception, and plot the curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model;

[0033] In the curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model, the section where the ordinate starts to suddenly increase and ends with the sudden increase corresponds to the position of the crack. The abscissas x1 and x2 corresponding to the two endpoints from the start of the sudden increase to the end of the sudden increase are the characterization positions of the two boundaries of the crack, where (x1 < x2);

[0034] The recognized width of the crack m = x2 - x1.

[0035] Preferably, in the said step 7, the judgment of the recognition effect of the ultrasonic transducer on the crack is carried out through the minimum width of the crack that can be recognized and the change of the ratio of the echo amplitudes at the crack and at the wellbore.

[0036] Preferably, for the same ultrasonic recognition logging simulation model, the method for determining the minimum width of the crack that can be recognized by its ultrasonic transducer is as follows:

[0037] Step 711, extract the simulation recognition result data of cracks with different widths by the same ultrasonic recognition logging simulation model;

[0038] Step 712, let i = 1, l i is the maximum value of the crack width;

[0039] Step 713, calculate the error η i between the recognized width m i of the crack with the simulation recognized width of l i and the characterized width n i of the crack;

[0040] When the error η i is less than the set value, enter step 714;

[0041] Otherwise, take the width l i as the minimum width of the crack that can be recognized by the corresponding ultrasonic transducer of this ultrasonic recognition logging simulation model;

[0042] Step 714, let i = i + 1, l i = l i-1 - δ, where δ is the difference between adjacent crack widths;

[0043] Then enter step 713.

[0044] Preferably, in the said step 713, the determination method of the error η i between the recognized width m i and the characterized width n i of the crack is as follows:

[0045]

[0046] In the formula, the recognized width m i is determined by step 5; R is the wellbore radius, and h is the distance from the center point of the signal transmitting end of the ultrasonic transducer to the wellbore.

[0047] Preferably, in the said step 7, the determination method of the change of the ratio of the echo amplitudes at the crack and at the wellbore is as follows:

[0048] Step 721: Extract all simulation identification data for the minimum-width cracks.

[0049] Step 722: According to the different distances h from the wellbore, divide the simulation identification data extracted in Step 721 into several sub-data. Each sub-data contains the simulation data of several ultrasonic identification logging simulation models for the minimum-width cracks, and the curvature radii of the ultrasonic identification logging simulation models in the sub-data are different.

[0050] Step 723: For each sub-data, calculate the ratio of the echo amplitudes at the crack and the wellbore when the curvature radius is different.

[0051] Step 724: Establish a coordinate system with the ratio of the echo amplitudes at the crack and the wellbore as the ordinate and the curvature radius as the abscissa. Mark each point in the coordinate system, and connect the points for the same sub-data to obtain several curves showing the variation of the ratio of the echo amplitudes at the crack and the wellbore with the curvature radius at different distances h from the wellbore.

[0052] The beneficial effects of the present invention are as follows:

[0053] Based on the COMSOL software, the present invention identifies the position of cracks on the wellbore by ultrasonic transducers, obtains the identification simulation of cracks by processing the echo data, can obtain the identification law of cracks by ultrasonic transducers by changing the numerical values of model parameters and crack sizes, determine the minimum width of cracks that can be identified by transducers with different curvature radii based on the corresponding identification accuracy, and can judge the identification effect, providing data support for optimizing the curvature radius of the transducer and the distance between the signal transmitting end of the ultrasonic transducer and the wellbore during the actual logging process. Description of the Drawings

[0054] The specification drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application.

[0055] Figure 1 is a schematic structural diagram of an ultrasonic transducer;

[0056] Figure 2 is a schematic three-dimensional structural diagram of the method for identifying and simulating wellbore cracks by the ultrasonic transducer of the present invention;

[0057] Figure 3 is a schematic structural diagram of the ultrasonic identification logging simulation model in the present invention;

[0058] Figure 4 is a curve graph of the echo amplitude A determined by the echo amplitude method with respect to the circumferential displacement x of the ultrasonic transducer model in the embodiment of the present invention;

[0059] Figure 5 is the second derivative of the echo amplitude determined by the echo amplitude method in the embodiment of the present invention which is a curve graph of the second derivative of the echo amplitude varying with the circumferential displacement x of the ultrasonic transducer model;

[0060] Figure 6 is a curve graph of the echo arrival time varying with the circumferential displacement x of the ultrasonic transducer model determined by the echo arrival time method in the embodiment of the present invention;

[0061] Figure 7 is a comparison graph of the crack widths that can be recognized by transducers with different curvature radii when the distance h from the center point of the signal transmitting end of the ultrasonic transducer to the wellbore wall surface is 30 mm in the embodiment of the present invention;

[0062] Figure 8 is a curve graph of the change of the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore wall with the curvature radius when the crack width is 1 mm in the embodiment of the present invention;

[0063] Wherein:

[0064] 01 - body;

[0065] 1 - wellbore model, 11 - wellbore, 12 - formation, 13 - crack, 2 - ultrasonic transducer model, 21 - central axis of the ultrasonic transducer model, 22 - center point. Detailed implementation manners

[0066] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0067] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0068] In the present invention, terms such as "upper", "lower", "bottom", "top", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only relationship terms determined for facilitating the description of the structural relationship of each component or element of the present invention and do not specifically refer to any component or element of the present invention and should not be construed as a limitation to the present invention.

[0069] In the present invention, terms such as "connected" and "coupled" should be understood in a broad sense, which may mean a fixed connection, an integral connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances, and it should not be construed as a limitation to the present invention.

[0070] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0071] As Figure 2 shown, a method for identifying and simulating wellbore fractures by an ultrasonic transducer includes the following steps:

[0072] Step 1: Determine the initial values of the model parameters;

[0073] The model parameters include the wellbore radius, the ultrasonic transducer radius, the radius of curvature of the spherical structure in the ultrasonic transducer body 01, and the distance h from the center point of the ultrasonic transducer signal transmitting end to the wellbore wall surface;

[0074] Step 2: In the COMSOL software, construct an ultrasonic logging simulation model. As Figure 3 shown, the ultrasonic logging simulation model includes a wellbore model 1 and an ultrasonic transducer model 2 located inside the wellbore model 1;

[0075] Step 3: Add a fracture 13 to the ultrasonic logging simulation model constructed in Step 2. The fracture 13 extends from the wellbore 11 into the formation 12, and determine the width l of the fracture 13 along the circumferential direction of the wellbore 11 and the depth of the fracture 13 along the radial direction of the wellbore 11;

[0076] Step 4: Perform simulation calculations in the COMSOL software. During the circumferential movement of the ultrasonic transducer model 2 around the central axis of the wellbore model 1, perform simulation transmission and reception of ultrasonic waves to obtain waveform data composed of echo signals, where the fracture 13 is located within the central angle range of the circumferential movement of the ultrasonic transducer model 2;

[0077] Step 5: According to the waveform data, determine the identification position of the boundary of the fracture 13 and the identification width m of the fracture 13;

[0078] Step 6: Change the value of the width l or / and the radius of curvature or / and the distance h from the wellbore, while keeping the values of other model parameters unchanged, to obtain different ultrasonic logging simulation models and fractures 13 of different sizes;

[0079] For each corresponding ultrasonic logging simulation model and fracture 13, perform Steps 3 to 4 to obtain the identification results of different ultrasonic logging simulation models for fractures of different sizes;

[0080] Step 7: Process the recognition results obtained in Step 6 to determine the recognition effect of the ultrasonic transducer on the crack.

[0081] Specifically, in Step 2, constructing the ultrasonic recognition logging simulation model includes the following sub-steps:

[0082] Step 21: In the COMSOL software, click "Model Wizard", set the three-dimensional spatial dimension, and select "Acoustic-Piezoelectric Interaction, Transient and Circuit" for the physical field;

[0083] Step 22: Based on the radius of the ultrasonic transducer and the radius of curvature of the spherical structure in the ultrasonic transducer model body 01, construct the ultrasonic transducer model 2;

[0084] Step 23: The wellbore model 1 includes the wellbore 11 and the formation 12. Based on the wellbore radius, construct the wellbore model 1;

[0085] Step 24: Add material parameters. The wellbore 11 is filled with water, the wellbore wall of the wellbore 11 is granite, and the ultrasonic transducer model 2 is PZT-5H;

[0086] Step 25: Make the central axis 21 of the ultrasonic transducer model perpendicular to the central axis of the wellbore model. Based on the distance h from the center point of the signal emission end of the ultrasonic transducer to the wellbore and the initial relative position relationship between the ultrasonic transducer model 2 and the crack 13, construct the ultrasonic recognition logging simulation model.

[0087] Specifically, in Step 5, the echo amplitude method is used to determine the curve of the echo amplitude A with respect to the circumferential displacement x of the ultrasonic transducer model 2 and the second derivative of the echo amplitude with respect to the circumferential displacement x of the ultrasonic transducer model 2, and then determine the recognition position of the crack 13 boundary and the recognition width m of the crack 13;

[0088] Or the echo arrival time method is used to determine the curve of the echo arrival time with respect to the circumferential displacement x of the ultrasonic transducer model 2, and then determine the recognition position of the crack 13 boundary and the recognition width m of the crack 13.

[0089] Specifically, the echo amplitude method is as follows:

[0090] Import the waveform data obtained in Step 4 into the Matlab software, extract the peak value in the ultrasonic echo curve as the echo amplitude A, and plot the curve of the echo amplitude A with respect to the circumferential displacement x of the ultrasonic transducer model 2;

[0091] Based on the curve of the echo amplitude with respect to the circumferential displacement of the ultrasonic transducer model 2, plot the curve of the second derivative of the echo amplitude with respect to the circumferential displacement x of the ultrasonic transducer model 2;

[0092] In the second derivative of the echo amplitude In the curve of the circumferential displacement x of the ultrasonic transducer model 2 for 2 weeks, find the point with the largest absolute value of the ordinate and the second largest point. The abscissas x1 and x2 corresponding to these two points are the recognition positions of the two boundaries of the crack 13, where (x1 < x2);

[0093] The recognized width m of the crack 13 = x2 - x1.

[0094] At the position of the crack 13, the amplitude of the echo curve will decrease. The position of the crack 13 can be visually judged. In this application, the peak value of the absolute value of the second derivative of the echo amplitude at the crack is used as the standard for identifying the boundary position of the crack. This method can effectively identify the boundary position of the crack.

[0095] Specifically, the echo arrival time method is as follows:

[0096] Import the waveform data obtained in step 4 into the Matlab software. For each circumferential position of the ultrasonic transducer model 2, extract the ultrasonic echo arrival time. The echo arrival time refers to the time required from transmission to reception, and draw a curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model 2;

[0097] In the curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model 2, the section where the ordinate starts to increase suddenly to the end of the sudden increase corresponds to the position of the crack 13. The abscissas x1 and x2 corresponding to the two endpoints from the start of the sudden increase to the end of the sudden increase are the characterization positions of the two boundaries of the crack 13, where (x1 < x2);

[0098] The recognized width m of the crack 13 = x2 - x1.

[0099] In this application, the time window energy ratio method is used to extract the echo arrival time. The use of the time window energy ratio method to extract the arrival time is a prior art, and its specific implementation method will not be elaborated here. During the circumferential movement of the ultrasonic transducer model 2, when there is no encounter with the crack 13, the distance between the center point 22 and the wall surface of the wellbore 11 remains unchanged. Therefore, the transmission path and reflection path of the ultrasonic wave remain unchanged, making the echo arrival time consistent; when encountering the crack 13, the distance between the center point 22 and the wall surface of the crack 13 increases. Therefore, the transmission path and reflection path of the ultrasonic wave increase, making the echo arrival time increase. Therefore, the position corresponding to the sudden increase in the echo arrival time is the position corresponding to the crack 13.

[0100] Specifically, in this application, the circumferential displacement x of the ultrasonic transducer model 2 refers to the axial displacement of the center point 22 around the central axis of the wellbore 11.

[0101] Specifically, in step 7, the judgment of the recognition effect of the ultrasonic transducer on the crack is carried out by the minimum width of the crack that can be recognized and the change in the ratio of the echo amplitude at the crack to the echo amplitude at the well wall.

[0102] Specifically, for the same ultrasonic identification logging simulation model, the method for determining the minimum width of the fracture that can be identified by its ultrasonic transducer is as follows:

[0103] Step 711: Extract the simulation identification result data of fractures with different widths by the same ultrasonic identification logging simulation model;

[0104] Step 712: Let i = 1, and l i is the maximum value of the fracture width;

[0105] Step 713: Calculate the error η i between the identified width m i and the fracture characterization width n i when simulating and identifying a fracture with width l i ;

[0106] When the error η i is less than the set value, go to Step 714;

[0107] Otherwise, take the width l i as the minimum width of the fracture that can be identified by the ultrasonic transducer corresponding to this ultrasonic identification logging simulation model;

[0108] Step 714: Let i = i + 1, and l i = l i-1 -δ, where δ is the difference between adjacent fracture widths; in this application, the fracture width values are arranged at equal intervals;

[0109] Then go to Step 713.

[0110] Specifically, in the said Step 713, the determination method of the error η i between the identified width m i and the fracture characterization width n i is as follows:

[0111]

[0112] In the formula, the identified width m i is determined by Step 5; R is the wellbore radius, and h is the distance from the center point of the signal transmitting end of the ultrasonic transducer to the wellbore.

[0113] Specifically, in the said Step 7, the determination method of the change in the ratio of the echo amplitude at the fracture to that at the wellbore is as follows:

[0114] Step 721: Extract all the simulation identification data of the fracture with the minimum width;

[0115] Step 722: Divide the simulation recognition data extracted in Step 721 into several sub-data according to different distances h from the wellbore. Each sub-data contains the simulation data of the minimum-width cracks by several ultrasonic recognition logging simulation models, and the curvature radii of the ultrasonic recognition logging simulation models in the sub-data are different.

[0116] Step 723: For each sub-data, calculate the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore when the curvature radius is different.

[0117] Step 724: Establish a coordinate system with the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore as the ordinate and the curvature radius as the abscissa. Mark each point in the coordinate system, and connect the points for the same sub-data to obtain several curves of the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore varying with the curvature radius at different distances h from the wellbore.

[0118] For each curve of the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore varying with the curvature radius, the curvature radius corresponding to the point with the minimum ordinate value is taken as the optimal value for the ultrasonic transducer to identify cracks.

[0119] In this application, the method for obtaining the ratio of the echo amplitude at the crack to the echo amplitude at the wellbore is as follows:

[0120] In the curve graph of the echo amplitude A varying with the circumferential displacement x of the ultrasonic transducer model 2, take the average value of the echo amplitudes corresponding to the two end points of the abscissa as the echo amplitude at the wellbore, take the echo amplitude at the middle position point in the section where the ordinate suddenly decreases as the echo amplitude at the crack, and then take the ratio of the two echo amplitudes.

[0121] Example:

[0122] Perform simulation based on the simulation method for identifying wellbore cracks by the ultrasonic transducer in Example 1.

[0123] The initial values of the model parameters are:

[0124] The wellbore radius is 100 mm, the ultrasonic transducer radius is 15 mm, the curvature radius of the spherical structure in the ultrasonic transducer model body 01 is 20 mm, and the distance h from the center point of the ultrasonic transducer signal transmitting end to the wellbore wall surface is 20 mm.

[0125] The initial size of crack 13:

[0126] The width l of crack 13 along the circumferential direction of wellbore 11 is 5 mm, and the depth of crack 13 along the radial direction of wellbore 11 is 10 mm.

[0127] For the above model parameter values and a crack with a width of 5 mm, the curve of the echo amplitude A varying with the circumferential displacement x of the ultrasonic transducer model 2 determined by the echo amplitude method is as Figure 4As shown, the second derivative of the determined echo amplitude The curve of the second derivative of the echo amplitude with respect to the circumferential displacement x of the ultrasonic transducer model for 2 cycles is as Figure 5 shown. From Figure 5 it can be obtained that x1 is 15 mm, x2 is 20 mm, and the recognition width m is 5 mm. For the above model parameter values, a 5-mm-wide crack, and the recognition width value determined by the echo amplitude method, calculate the error between the recognition width and the crack characterization width. Here, R is 100 mm and h is 20 mm. Therefore, the crack characterization width is 4 mm, and the error between the recognition width and the crack characterization width is 25%.

[0128] For the above model parameter values and a 5-mm-wide crack, the curve of the echo arrival time with respect to the circumferential displacement x of the ultrasonic transducer model for 2 cycles determined by the echo arrival time method is as Figure 6 shown. From Figure 6 it can be obtained that x1 is 15 mm, x2 is 20 mm, and the recognition width m is 5 mm. For the above model parameter values, a 5-mm-wide crack, and the recognition width value determined by the echo arrival time method, calculate the error between the recognition width and the crack characterization width. Here, R is 100 mm and h is 20 mm. Therefore, the crack characterization width is 4 mm, and the error between the recognition width and the crack characterization width is 25%.

[0129] From the above analysis, it can be seen that both the echo amplitude method and the echo arrival time method in this application can identify the crack boundary, and the recognition results are consistent.

[0130] The model parameter values and the crack size are changed as follows:

[0131] The initial radius of curvature is 20 mm, and the radius of curvature is gradually increased to 60 mm at intervals of 10 mm; the initial distance from the center point of the signal transmitting end of the ultrasonic transducer to the borehole wall surface is 20 mm, and it is increased to 60 mm at intervals of 10 mm; the initial crack width is 5 mm, and the crack width is gradually decreased to 1 mm at intervals of 1 mm.

[0132] For each corresponding ultrasonic identification logging simulation model and crack, simulation is carried out to obtain the recognition results of different ultrasonic identification logging simulation models for cracks of different sizes.

[0133] For the above simulation, determine the minimum crack width that can be recognized. Among them, the comparison of the crack widths that can be recognized by transducers with different radii of curvature when the distance h from the center point of the signal transmitting end of the ultrasonic transducer to the borehole wall surface is 30 mm is as Figure 7 shown. In this application, the minimum crack width that can be recognized is determined based on the error between the recognition width and the crack characterization width being less than 40%. From Figure 7It can be known that when the distance h between the center point of the signal transmitting end of the ultrasonic transducer and the wellbore wall surface is 30 mm, based on the recognition accuracy with an error less than 40%, the minimum crack width that can be recognized by transducers with a curvature radius of 20 mm or 30 mm is 1 mm, the minimum crack width that can be recognized by transducers with a curvature radius of 40 mm or 50 mm is 2 mm, and the minimum crack width that can be recognized by a transducer with a curvature radius of 60 mm is 4 mm.

[0134] For the above simulation, the change in the ratio of the echo amplitudes at the crack and the wellbore is determined. Among them, the curve of the ratio of the echo amplitudes at the crack and the wellbore with a crack width of 1 mm changing with the curvature radius is as Figure 8 shown. Since the greater the difference in the echo amplitudes between the crack and the wellbore, that is, the lower the ratio, the better the corresponding recognition effect. That is, the curvature radius value corresponding to the point with the smallest ordinate value is the optimal value for the ultrasonic transducer to recognize the crack. Therefore, from Figure 8 it can be known that when the distance h between the center point of the signal transmitting end of the ultrasonic transducer and the wellbore wall surface is 20 mm, the optimal curvature radius value for the ultrasonic transducer to recognize the crack is 20 mm; when the distance h between the center point of the signal transmitting end of the ultrasonic transducer and the wellbore wall surface is 30 mm or 40 mm or 50 mm, the optimal curvature radius value for the ultrasonic transducer to recognize the crack is 30 mm; when the distance h between the center point of the signal transmitting end of the ultrasonic transducer and the wellbore wall surface is 60 mm, the optimal curvature radius value for the ultrasonic transducer to recognize the crack is 40 mm.

[0135] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation to the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A method for simulating the identification of wellbore cracks by using an ultrasonic transducer, characterized in that: The following steps are involved: Step 1, determine the initial values ​​of model parameters; The model parameters include the wellbore radius, the ultrasonic transducer radius, the curvature radius of the spherical structure in the ultrasonic transducer body, and the distance h between the center point of the ultrasonic transducer signal transmitting end and the wellbore wall; Step 2: In COMSOL software, an ultrasonic identification logging simulation model is constructed, where the ultrasonic identification logging simulation model includes a wellbore model and an ultrasonic transducer model located inside the wellbore model; Step 3, adding a fracture to the ultrasonic identification logging simulation model constructed in step 2, wherein the fracture extends from the wellbore to the formation, and determining the width l of the fracture along the circumferential direction of the wellbore and the depth of the fracture along the radial direction of the wellbore; Step 4, performing simulation calculation in COMSOL software, simulating the transmission and reception of ultrasonic waves while the ultrasonic transducer model moves circumferentially around the central axis of the wellbore model, and obtaining waveform data composed of echo signals, wherein the crack is located within the central angle range of the circumferential movement of the ultrasonic transducer model; Step 5, determining the identification position of the crack boundary and the identification width m of the crack according to the waveform data; Step 6, changing the value of the width l and / or the radius of curvature and / or the distance h from the wellbore wall, while keeping other model parameter values ​​unchanged, to obtain different ultrasonic identification logging simulation models and fractures of different sizes; For each corresponding ultrasonic identification logging simulation model and fracture, steps 3 and 4 are performed to obtain the identification results of fractures of different sizes using different ultrasonic identification logging simulation models; Step 7, performing data processing on the recognition result obtained in step 6 to determine the recognition effect of the ultrasonic transducer on the crack.

2. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 1, characterized in that: In step 2, constructing an ultrasonic identification logging simulation model includes the following sub-steps: Step 21. In COMSOL software, click "Model Wizard", set the three-dimensional space dimension, and select "Acoustic-Piezoelectric Interaction, Transient and Circuit" for the physical field. Step 22, constructing an ultrasonic transducer model based on the ultrasonic transducer radius and the curvature radius of the spherical structure in the ultrasonic transducer model body; Step 23, the wellbore model includes the wellbore and the formation, and the wellbore model is constructed based on the wellbore radius; Step 24, adding material parameters, the wellbore is filled with water, the wellbore wall is granite, and the ultrasonic transducer model is PZT-5H; Step 25, making the central axis of the ultrasonic transducer model intersect the central axis of the wellbore model vertically, and constructing an ultrasonic identification logging simulation model based on the distance h between the center point of the ultrasonic transducer signal transmitting end and the wellbore and the initial relative position relationship between the ultrasonic transducer model and the fracture.

3. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 1, characterized in that: In step 5, the echo amplitude method is used to determine the curve of the echo amplitude A versus the circumferential displacement x of the ultrasonic transducer model, the echo amplitude second-order derivative The curve of the circumferential displacement x of the ultrasonic transducer model is used to determine the identification position of the crack boundary and the identification width m of the crack; Alternatively, the echo arrival time method is used to determine the curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model, and then the identification position of the crack boundary and the identification width m of the crack are determined.

4. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 3, characterized in that: The echo amplitude method is as follows: The waveform data obtained in step 4 is imported into Matlab software, the peak value in the ultrasonic echo curve is extracted as the echo amplitude A, and a curve graph of the echo amplitude A versus the circumferential displacement x of the ultrasonic transducer model is drawn; Based on the curve of echo amplitude versus circumferential displacement of the ultrasonic transducer model, the second-order derivative of the echo amplitude is plotted. Graph with circumferential displacement x of ultrasonic transducer model; The second derivative of the echo amplitude Find the point with the largest absolute value of the ordinate and the second largest absolute value of the ordinate in the curve of the circumferential displacement x of the ultrasonic transducer model. The abscissas x1 and x2 corresponding to these two points are the identification positions of the two boundaries of the crack, where (x1<x2); The identified width of the crack is m=x2-x1.

5. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 3, characterized in that: The echo arrival time method is as follows: Import the waveform data obtained in step 4 into Matlab software, extract the ultrasonic echo arrival time for each circumferential position of the ultrasonic transducer model, where the echo arrival time refers to the time required from emission to reception, and draw a curve of the echo arrival time versus the circumferential displacement x of the ultrasonic transducer model; The section where the vertical coordinate of the curve of the circumferential displacement x of the ultrasonic transducer model at the time of echo arrival begins to suddenly increase and ends to correspond to the location of the crack, and the horizontal coordinates x1 and x2 corresponding to the two endpoints where the vertical coordinate begins to suddenly increase and ends to suddenly increase are the characterization positions of the two boundaries of the crack, where (x1<x2); The identified width of the crack is m=x2-x1.

6. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 3, characterized in that: In step 7, the recognition effect of the ultrasonic transducer on the crack is judged by the change in the minimum width of the crack that can be recognized and the ratio of the echo amplitude at the crack to the well wall.

7. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 6, characterized in that: For the same ultrasonic identification logging simulation model, the method for determining the minimum width of the fracture that can be identified by the ultrasonic transducer is as follows: Step 711, extracting simulation recognition result data of the same ultrasonic recognition logging simulation model for fractures of different widths; Step 712, let i=1, l i is the maximum value of the crack width; Step 713, calculate the simulation recognition width as l i The crack width is m i and crack characterization width n i The error between i ; When the error η i When it is less than the set value, go to step 714; Otherwise, the width l i The minimum width of the fracture that can be identified by the ultrasonic transducer corresponding to the ultrasonic identification logging simulation model; Step 714, let i=i+1, l i = l i-1 -δ, δ is the difference between adjacent crack widths; Then proceed to step 713.

8. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 7, characterized in that: In step 713, the width m is identified. i and crack characterization width n i The error between i The method of determining is: In the formula, the recognition width m i and is determined by step 5; R is the wellbore radius, and h is the distance from the center point of the ultrasonic transducer signal transmitting end to the wellbore.

9. The method for simulating the identification of well wall cracks by using an ultrasonic transducer according to claim 6, characterized in that: In step 7, the method for determining the change in the echo amplitude ratio at the crack and at the well wall is: Step 721, extracting all simulation identification data of the minimum width crack; Step 722, dividing the simulation recognition data extracted in step 721 into a plurality of sub-data according to different distances h from the wellbore, each sub-data containing simulation data of a plurality of ultrasonic recognition logging simulation models for minimum width fractures, and the curvature radii of the ultrasonic recognition logging simulation models in the sub-data are different; Step 723, for each sub-data, calculating the echo amplitude ratio between the crack and the wellbore wall when the curvature radius is different; Step 724, establish a coordinate system with the echo amplitude ratio at the fracture and the wellbore wall as the vertical coordinate and the curvature radius as the horizontal coordinate, mark each point in the coordinate system, connect each point for the same sub-data, and obtain several curves of the echo amplitude ratio at the fracture and the wellbore wall with different distances h from the wellbore as a inverse of the curvature radius.

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