Ultrasonic Imaging Logging Device Based on Fiber Optic Acoustic Sensing and Its Measuring Method

Abstract

The present invention discloses an ultrasonic imaging logging device based on fiber optic acoustic sensing and its measurement method. Different frequency ultrasonic transmitters and fiber optic ultrasonic receiving sensors installed in the downhole ultrasonic imaging logging device are used to replace the piezoelectric crystal ultrasonic receiving transducers widely used at present, and the reflected ultrasonic signals around the 360-degree wellbore are received, so as to realize fiber optic ultrasonic imaging logging with different frequencies and different resolutions downhole. The fiber optic ultrasonic receiving sensor replaces the piezoelectric crystal ultrasonic transducer and its supporting electronic amplifier, analog-to-digital conversion and data storage devices, as well as the downhole electronic data transmission module, solves the problem that the ultrasonic imaging logging device cannot work for a long time in a high-temperature environment, simplifies the design of the imaging instrument, and reduces the manufacturing cost. In addition, due to the use of armored optical and electrical composite cables, the bottleneck problem of high-speed real-time transmission of a large amount of high-resolution imaging data downhole to the control computer in the logging truck is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of geophysical logging, and in particular to an ultrasonic imaging logging device based on fiber optic acoustic sensing and a measurement method thereof. Background Art

[0002] Ultrasonic imaging logging uses the reflection characteristics of ultrasonic waves by the wellbore wall or the inner wall of the casing to study the wellbore profile. In an open hole well, by measuring the acoustic image, the fracture density, dip azimuth, and fracture-cavity distribution of the fractured formation can be understood, providing reliable geological basic data for the exploration and development of fractured reservoirs. In the casing, through the acoustic image, the perforation position or the damage condition of the casing caused by construction or production can be understood, providing data for well repair. Ultrasonic imaging logging gives logging data in the form of an acoustic image. Compared with the previous logging curve data, it has the advantages of more information, high resolution, and being intuitive and convenient for analysis and judgment.

[0003] Ultrasonic imaging logging consists of four parts: an acoustic system, signal acquisition, signal transmission, and ground processing. The acoustic system part is composed of a rotatable ultrasonic probe (or sensor), and this probe serves as both a transmitting and a receiving probe. By displaying the measured reflection wave amplitude and propagation time as an image in 360 degrees azimuth in the wellbore, the lithology and surface characteristics of the wellbore wall (including fractures, holes, and erosion zones) can be analyzed, and it can also be used to observe the changes in the inner wall of the casing.

[0004] The ultrasonic transducer emits ultrasonic pulses 1500 - 3000 times per second with a frequency of 0.1 MHz - 2 MHz. During logging, it is driven by a motor and drives the transducer and the magnetometer to rotate around the instrument axis at a fixed rate (about 3 - 6 revolutions per second) to scan and measure the entire wellbore wall of the wellbore. Each time it rotates to the magnetic north direction and generates a magnetic north signal, the azimuth information of the transducer is sent to the ground in the form of an electrical pulse. When the instrument rotates, the ultrasonic pulses emitted by the probe propagate through the mud to reach the wellbore wall. A part of the ultrasonic energy is reflected back to the transducer and received. After signal processing, an amplitude image and a travel time image of the wellbore wall echo are obtained.

[0005] Currently, piezoelectric crystal ultrasonic transducers are used in current downhole ultrasonic imaging logging tools to receive ultrasonic signals reflected from the wellbore wall. The piezoelectric crystal ultrasonic transducers, their supporting electronic amplifiers, analog-to-digital conversion and data storage devices, as well as downhole electronic data transmission modules, etc. cannot work for a long time in a high-temperature environment (deep well). In addition, since current downhole ultrasonic imaging logging tools are all electronic instruments, their downhole data transmission modules currently cannot solve the bottleneck problem of high-speed real-time transmission of a large amount of high-resolution imaging data in the downhole to the control computer in the logging truck at the wellhead. Due to the bottleneck problem of downhole data transmission, it is impossible to deploy multiple ultrasonic transducers with different frequencies in the downhole ultrasonic imaging logging tool to realize the acquisition of ultrasonic imaging logging data with different resolutions in one trip downhole. Summary of the Invention

[0006] The object of the present invention is to provide an ultrasonic imaging logging device based on fiber optic acoustic sensing, mainly using ultrasonic receiving sensors between different-frequency ultrasonic transmitter pairs installed in the downhole ultrasonic imaging logging device to replace the currently widely used piezoelectric crystal ultrasonic receiving transducers, and receiving reflected ultrasonic signals around the 360-degree wellbore wall, so as to achieve the purpose of downhole fiber optic ultrasonic imaging logging.

[0007] The technical solution of the present invention:

[0008] The ultrasonic imaging logging device based on fiber optic acoustic sensing includes an open-hole borehole, an ultrasonic imaging logging device, a high-temperature-resistant optoelectronic composite logging cable, a surface wellhead logging truck, and a surface distributed fiber optic ultrasonic sensing modulation and demodulation instrument;

[0009] The ultrasonic imaging logging device includes three high-temperature-resistant fiber optic ultrasonic receiving sensors as the ultrasonic signal receiving unit in the well; three different-frequency ultrasonic transmitter pairs; a fiber optic gyroscope; an ultrasonic transmitter electronic short circuit; and an electric motor for driving the three pairs of ultrasonic transmitters to rotate uniformly;

[0010] The surface wellhead logging truck is connected to the downhole ultrasonic imaging logging device through an armored optoelectronic composite cable;

[0011] The three ultrasonic transmitter pairs are respectively a low-frequency ultrasonic transmitter pair, a medium-frequency ultrasonic transmitter pair, and a high-frequency ultrasonic transmitter pair.

[0012] The surface wellhead logging truck controls the lowering and raising of the downhole ultrasonic imaging logging device through the optoelectronic composite cable and provides power to the downhole ultrasonic imaging logging device. The ultrasonic transmitter electronic short circuit drives the low-frequency ultrasonic transmitter pair, the medium-frequency ultrasonic transmitter pair, and the high-frequency ultrasonic transmitter pair to continuously and repeatedly emit ultrasonic signals with different frequencies during operation;

[0013] The ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument installed at the wellhead is connected to the downhole ultrasonic imaging logging tool through an armored fiber optic composite cable, emits laser pulses into three fiber optic ultrasonic receiving sensors, and synchronously collects the backscattered Rayleigh waves in the fiber optic ultrasonic receiving sensors.

[0014] Further, the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument has three distributed fiber optic ultrasonic sensor signal input ports and one fiber optic gyroscope signal input port.

[0015] Further, the frequency of the low-frequency ultrasonic transmitter pair is 100 kHz to 250 kHz, the frequency of the medium-frequency ultrasonic transmitter pair is 250 kHz to 500 kHz, and the frequency of the high-frequency ultrasonic transmitter pair is 500 kHz to 1 MHz.

[0016] Further, the fiber optic ultrasonic receiving sensor is a spiral high-temperature and high-reflection coefficient single-mode fiber optic ultrasonic receiving sensor wound around a cylindrical elastic body. The frequency of the low-frequency fiber optic ultrasonic receiving sensor is 100 kHz to 250 kHz, the frequency of the medium-frequency fiber optic ultrasonic receiving sensor is 250 kHz to 500 kHz, and the frequency of the high-frequency fiber optic ultrasonic receiving sensor is 500 kHz to 1 MHz. Each fiber optic ultrasonic receiving sensor is placed between two ultrasonic transmitters and does not rotate together with the ultrasonic transmitter pair.

[0017] Further, the fiber optic gyroscope is installed at the top of the downhole ultrasonic imaging logging tool and measures the azimuth, inclination, and dip of the ultrasonic imaging logging tool in real time through the fiber optic composite cable.

[0018] Further, the ultrasonic transmitter electronic short circuit is placed behind the fiber optic gyroscope and is used to drive the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair, and high-frequency ultrasonic transmitter pair in the ultrasonic imaging logging tool to emit ultrasonic waves of different frequencies.

[0019] Further, the electric motor is installed behind the ultrasonic transmitter electronic short circuit and is used to drive the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair, and high-frequency ultrasonic transmitter pair in the ultrasonic imaging logging tool to rotate synchronously and uniformly at a rotation speed of three to six revolutions per minute.

[0020] Further, the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair, and high-frequency ultrasonic transmitter pair continuously emit low-frequency, medium-frequency, and high-frequency ultrasonic signals to the borehole wall during uniform rotation.

[0021] Further, the low-frequency fiber optic ultrasonic receiving sensor, the medium-frequency fiber optic ultrasonic receiving sensor, and the high-frequency fiber optic ultrasonic receiving sensor respectively and continuously, simultaneously, and synchronously collect the low-frequency, medium-frequency, and high-frequency ultrasonic signals reflected from the borehole wall after being emitted by the low-frequency ultrasonic transmitter pair, the medium-frequency ultrasonic transmitter pair, and the high-frequency ultrasonic transmitter pair.

[0022] A measurement method for ultrasonic imaging based on fiber optic acoustic sensing, and a measurement method for a logging device for ultrasonic imaging based on fiber optic acoustic sensing, characterized by comprising the following steps:

[0023] S1: Connect the armored high-temperature-resistant optoelectronic composite cable on the winch of the surface wellhead logging vehicle to the downhole ultrasonic imaging logging device;

[0024] S2: Use the armored high-temperature-resistant optoelectronic composite cable on the winch of the surface wellhead logging vehicle to lower the downhole ultrasonic imaging logging device to the bottom of the well;

[0025] S3: Slowly lift the downhole ultrasonic imaging logging device upward through the armored high-temperature-resistant optoelectronic composite cable on the winch of the surface wellhead logging vehicle and send commands to the electronic short circuit of the ultrasonic transmitter in the downhole ultrasonic imaging logging device, drive the electric motor connected to the ultrasonic transmitter to rotate uniformly, and synchronously drive three ultrasonic transmitter pairs with different frequencies to continuously emit ultrasonic signals to the well wall during uniform rotation;

[0026] S4: Simultaneously start the fiber optic gyroscope, and real-time measure and record the azimuth, dip angle, and inclination of the uphole ultrasonic imaging logging device along the well trajectory, which is used for correcting and projecting the instrument's own rotation of the reflected ultrasonic data recorded by the instrument during subsequent data processing. The fiber optic gyroscope can overcome the defect that the downhole magnetometer cannot work properly in the metal casing well;

[0027] S5: Simultaneously start the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument, and continuously emit high-power multi-frequency narrow pulse laser signals to different frequency fiber optic ultrasonic receiving sensors in the downhole fiber optic ultrasonic imaging logging device through the optoelectronic composite cable. The three fiber optic ultrasonic receiving sensors simultaneously and continuously receive the ultrasonic backscattered Rayleigh light signals reflected from the well wall in a 360-degree azimuth in the wellbore back to their respective fiber optic ultrasonic receiving sensors;

[0028] S6: The ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument performs modulation and demodulation processing on the backscattered Rayleigh light signals on each fiber optic ultrasonic receiving sensor, and demodulates the fiber strain or strain rate data measured by each fiber optic ultrasonic receiving sensor into the ultrasonic data reflected from the well wall in a 360-degree azimuth in the wellbore (reflected ultrasonic amplitude and reflected ultrasonic propagation time);

[0029] S7: Convert the amplitude of the reflected ultrasonic wave into the reflection wave impedance data around the wellbore, and use a color plan view to display the measured reflection wave impedance data in an image according to the 360-degree azimuth in the wellbore to show the difference in the reflection wave impedance data of the wellbore wall. The wellbore wall with a small wave impedance is displayed in a dark color, and the wellbore wall with a large wave impedance is displayed in a bright color;

[0030] S8: Perform borehole radius imaging on the propagation time of the reflected ultrasonic wave, and use a color plan view to display the difference in the borehole radius in an image according to the 360-degree azimuth in the wellbore. The borehole radius with a long time (large radius) is displayed in a dark color, and the borehole radius with a short time (small radius) is displayed in a bright color;

[0031] S9: Conduct comprehensive interpretation on the borehole wall ultrasonic imaging data (wave impedance and propagation time), identify geological structures such as fractures, unconformities, faults, etc. on the 360-degree borehole wall, determine the occurrence and development direction of the fractures, and determine the direction of the maximum horizontal principal stress;

[0032] S10: Describe sedimentary characteristics: laminated bedding, cross-bedding, erosion, nodules, sedimentary rhythm;

[0033] S11: Divide the thin interbeds of sandstone and mudstone and the effective thickness;

[0034] S12: Determine the borehole geometry;

[0035] S13: Check the deformation of the casing and determine the position of the casing deformation;

[0036] S14: Check the perforated interval and determine the position of the perforation holes;

[0037] S15: Check the shape of the casing after explosive shaping of the casing;

[0038] S16: Determine the position of casing damage or casing fracture.

[0039] Advantages of the present invention:

[0040] The present invention provides an ultrasonic imaging logging device based on fiber optic acoustic sensing. Different frequency ultrasonic transmitters and fiber optic ultrasonic receiving sensors installed in the downhole ultrasonic imaging logging device are used to replace the piezoelectric crystal ultrasonic receiving transducers widely used at present, and the reflected ultrasonic signals around the 360-degree wellbore are received, so as to realize synchronous acquisition of fiber optic ultrasonic imaging logging data with different frequencies and different resolutions during a single trip downhole. The fiber optic ultrasonic receiving sensor replaces the piezoelectric crystal ultrasonic transducer and its supporting electronic amplifier, analog-to-digital conversion and data storage devices, as well as the downhole electronic data transmission module, solves the problem that the ultrasonic imaging logging device cannot work for a long time in a high-temperature environment, simplifies the design of the imaging instrument, and reduces the manufacturing cost. In addition, since an armored optical cable is used to connect the downhole ultrasonic imaging logging device, the bottleneck problem of high-speed real-time transmission of a large amount of high-resolution imaging data in the downhole to the control computer in the logging truck at the wellhead is solved at one stroke. Brief Description of the Drawings

[0041] Figure 1 is a schematic diagram of the downhole operation of the wellbore ultrasonic imaging logging device based on fiber optic ultrasonic sensors of the present invention.

[0042] Figure 2 is a schematic diagram of the structure of the wellbore ultrasonic imaging logging device based on fiber optic ultrasonic sensors of the present invention.

[0043] Figure 3 is a schematic diagram of the structure of the ultrasonic transmitter in the wellbore ultrasonic imaging logging device of the present invention.

[0044] Description of the Reference Numerals:

[0045] 1 - open hole, 2 - ultrasonic imaging logging device, 3 - optoelectronic composite logging cable, 4 - surface wellhead logging truck, 5 - surface distributed fiber optic ultrasonic sensing modulation and demodulation instrument, 6 - fiber optic gyroscope, 7 - ultrasonic transmitter electronic short circuit, 8 - electric motor, 9 - low-frequency ultrasonic transmitter pair, 12 - medium-frequency ultrasonic transmitter pair, 15 - high-frequency ultrasonic transmitter pair, 10 - low-frequency ultrasonic transmitter, 13 - medium-frequency ultrasonic transmitter, 16 - high-frequency ultrasonic transmitter, 11 - low-frequency ultrasonic receiving sensor, 14 - medium-frequency ultrasonic receiving sensor, 17 - high-frequency ultrasonic receiving sensor. Detailed Description of the Invention

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0047] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0048] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn in accordance with the actual proportional relationship.

[0049] In addition, for the sake of clarity and conciseness, the descriptions of well-known structures, functions, and configurations may be omitted. Those of ordinary skill in the art will recognize that various changes and modifications can be made to the examples described herein without departing from the spirit and scope of the present disclosure.

[0050] The techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said techniques, methods, and devices should be regarded as part of the authorization specification.

[0051] In all the examples shown and discussed here, any specific value should be construed as merely exemplary, rather than as a limitation. Therefore, other examples of the exemplary embodiments may have different values. Embodiment

[0052] The present invention will be described in detail below by referring to the accompanying drawings and in conjunction with the embodiments:

[0053] As Figure 1 shown, the downhole ultrasonic imaging logging device based on a fiber optic ultrasonic sensor includes an open hole 1, a downhole ultrasonic imaging logging device 2 based on fiber optic acoustic sensing, a high-temperature resistant optoelectronic composite logging cable 3, a surface wellhead logging vehicle 4, and a surface distributed fiber optic ultrasonic sensing modulation and demodulation instrument 5;

[0054] As Figure 2As shown in the figure, the ultrasonic imaging logging tool 2 based on fiber optic acoustic sensing includes three high-temperature resistant fiber optic ultrasonic receiving sensors, serving as the ultrasonic signal receiving unit in the well; three pairs of ultrasonic transmitters with different frequencies: the low-frequency ultrasonic transmitter pair 9, the medium-frequency ultrasonic transmitter pair 12, and the high-frequency ultrasonic transmitter pair 15; a fiber optic gyroscope 6; an ultrasonic transmitter electronic short circuit 7, and an electric motor 8 that drives the two ultrasonic transmitters of each pair to rotate at a constant speed. The surface wellhead logging vehicle 4 is connected to the ultrasonic imaging logging tool 2 based on fiber optic acoustic sensing in the well through an electro-optical composite logging cable 3;

[0055] Among them, the low-frequency ultrasonic transmitter pair 9 includes two low-frequency ultrasonic transmitters 10; the medium-frequency ultrasonic transmitter pair 12 includes two medium-frequency ultrasonic transmitters 13, and the high-frequency ultrasonic transmitter pair 15 includes two high-frequency ultrasonic transmitters 16.

[0056] As Figure 2 and Figure 3 shown in the figure, the three pairs of ultrasonic transmitters respectively include: two low-frequency ultrasonic transmitters 10, two medium-frequency ultrasonic transmitters 13, and two high-frequency ultrasonic transmitters 16. A fiber optic ultrasonic receiving sensor is arranged between each pair of ultrasonic transmitters. Each pair of ultrasonic transmitters continuously emits low-frequency, medium-frequency, and high-frequency ultrasonic signals at the same position corresponding to each pair of ultrasonic transmitters on the wellbore wall. The ultrasonic signals of the same frequency simultaneously emitted by each pair of ultrasonic transmitters, when reflected back from the corresponding wellbore wall, are exactly projected onto the fiber optic ultrasonic receiving sensor between each pair of ultrasonic transmitters, that is, the intensity of the reflected ultrasonic signals is enhanced (double-source superposition effect), and the reflected ultrasonic signals also contain the two-directional irradiation characteristics of the ultrasonic signals emitted in both directions, realizing precise ultrasonic imaging of the wellbore wall.

[0057] The surface wellhead logging vehicle 4 controls the lowering and raising of the ultrasonic imaging logging tool 2 based on fiber optic acoustic sensing in the well through the electro-optical composite logging cable 3, and provides power to the ultrasonic imaging logging tool 2 based on fiber optic acoustic sensing in the well. The ultrasonic transmitter electronic short circuit 7 drives the two low-frequency ultrasonic transmitters 10, the two medium-frequency ultrasonic transmitters 13, and the two high-frequency ultrasonic transmitters 16 to continuously and repeatedly emit ultrasonic signals of different frequencies during operation;

[0058] The ground distributed fiber optic ultrasonic sensor modulation and demodulation instrument 5 installed at the wellhead is connected to the downhole ultrasonic imaging logging tool 2 through the electro-optical composite logging cable 3, emits laser pulses into the three fiber optic ultrasonic receiving sensors 11, 14, and 17, and synchronously collects the backscattered Rayleigh waves in the distributed fiber optic ultrasonic receiving sensors 11, 14, and 17.

[0059] The ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument 5 has three distributed fiber optic ultrasonic sensor signal input ports and one fiber optic gyroscope 6 signal input port.

[0060] The frequency of the low-frequency ultrasonic transmitter 10 is 100 kHz to 250 kHz, the frequency of the medium-frequency ultrasonic transmitter 13 is 250 kHz to 500 kHz, and the frequency of the high-frequency ultrasonic transmitter 16 is 500 kHz to 1 MHz.

[0061] The distributed fiber optic ultrasonic receiving sensor is a spiral high-temperature resistant and high-reflection coefficient single-mode fiber optic ultrasonic receiving sensor wound around a cylindrical elastic body, including: the frequency of the low-frequency fiber optic ultrasonic receiving sensor 11 is 100 kHz to 250 kHz, the frequency of the medium-frequency fiber optic ultrasonic receiving sensor 14 is 250 kHz to 500 kHz, and the frequency of the high-frequency fiber optic ultrasonic receiving sensor 17 is 500 kHz to 1 MHz. Each fiber optic ultrasonic receiving sensor is arranged between two ultrasonic transmitters and does not rotate together with the ultrasonic transmitter pair.

[0062] The fiber optic gyroscope 6 is installed at the top of the downhole ultrasonic imaging logging tool 2 and measures the azimuth, dip angle, and trend of the ultrasonic imaging logging tool 2 in real time through an electro-optical composite logging cable 3.

[0063] The ultrasonic transmitter electronic short circuit 7 is placed behind the fiber optic gyroscope 6 and is used to drive the low-frequency ultrasonic transmitter 10, medium-frequency ultrasonic transmitter 13, and high-frequency ultrasonic transmitter 16 in the ultrasonic imaging logging tool 2 to emit ultrasonic waves of different frequencies.

[0064] The electric motor 8 is installed behind the ultrasonic transmitter electronic short circuit 7 and is used to drive the low-frequency ultrasonic transmitter 10, medium-frequency ultrasonic transmitter 13, and high-frequency ultrasonic transmitter 16 in the ultrasonic imaging logging tool 2 to rotate synchronously and uniformly at a rotation speed of three to six revolutions per minute.

[0065] The low-frequency ultrasonic transmitter 10, medium-frequency ultrasonic transmitter 13, and high-frequency ultrasonic transmitter 16 continuously emit low-frequency, medium-frequency, and high-frequency ultrasonic signals to the borehole wall of the borehole 1 during uniform rotation.

[0066] The low-frequency fiber optic ultrasonic receiving sensor 11, medium-frequency fiber optic ultrasonic receiving sensor 14, and high-frequency fiber optic ultrasonic receiving sensor 17 respectively continuously and simultaneously synchronously collect the low-frequency, medium-frequency, and high-frequency ultrasonic signals reflected from the borehole wall of the borehole 1 after being emitted by the two low-frequency ultrasonic transmitters 10, two medium-frequency ultrasonic transmitters 13, and two high-frequency ultrasonic transmitters 16.

[0067] The measurement method of the ultrasonic imaging logging device 2 based on fiber optic acoustic sensing includes the following steps:

[0068] S1: Connect the armored high-temperature-resistant optoelectronic composite logging cable 3 on the winch of the surface wellhead logging truck 4 to the downhole fiber optic ultrasonic imaging logging device 2;

[0069] S2: Use the armored high-temperature-resistant optoelectronic composite logging cable 3 on the winch of the surface wellhead logging truck 4 to lower the downhole ultrasonic imaging logging device 2 to the bottom of the well;

[0070] S3: Slowly lift the downhole fiber optic ultrasonic imaging logging device 2 upward through the armored high-temperature-resistant optoelectronic composite logging cable 3 on the winch of the surface wellhead logging truck 4 and send commands to the short circuit 7 of the ultrasonic transmitter circuit in the downhole fiber optic ultrasonic imaging logging device 2, drive the electric motor 8 connected to the ultrasonic transmitter to rotate at a constant speed, and simultaneously synchronously drive the excitation of three ultrasonic transmitters with different frequencies to continuously emit ultrasonic signals to the well wall during the constant-speed rotation;

[0071] S4: At the same time, start the fiber optic gyroscope 6, and measure and record the azimuth, inclination, and dip of the upward-lifted downhole ultrasonic imaging logging device 2 along the well trajectory in real time, which is used for the correction and projection processing of the instrument's own rotation for the reflected ultrasonic data recorded by the instrument in subsequent data processing. The fiber optic gyroscope can overcome the defect that the downhole magnetometer cannot work properly in the metal casing well;

[0072] S5: At the same time, start the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument 5, and continuously emit high-power multi-frequency narrow pulse laser signals to the fiber optic ultrasonic receiving sensors 11, 14, and 17 with different frequencies in the downhole fiber optic ultrasonic imaging logging device 2 through the optoelectronic composite logging cable 3. The three fiber optic ultrasonic receiving sensors 11, 14, and 17 simultaneously continuously receive the ultrasonic backscattered Rayleigh light signals reflected from the well wall in a 360-degree azimuth in the wellbore;

[0073] S6: The ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument 5 performs modulation and demodulation processing on the backscattered Rayleigh light signals on each fiber optic ultrasonic receiving sensor, and demodulates the fiber strain or strain rate data measured on each fiber optic ultrasonic receiving sensor into the ultrasonic data reflected from the well wall in a 360-degree azimuth in the wellbore (reflected ultrasonic amplitude and reflected ultrasonic propagation time);

[0074] S7: Convert the reflected ultrasonic amplitude into the reflected wave impedance data around the well wall, and use a color plan view to display the measured reflected wave impedance in an image according to the 360-degree azimuth in the wellbore to show the numerical difference of the wave impedance of the well wall. The well wall with a small wave impedance is displayed in a dark color, and the well wall with a large wave impedance is displayed in a bright color;

[0075] S8: Perform borehole radius imaging on the propagation time of reflected ultrasonic waves, and display the differences in borehole radius using a color plan view presented as an image in a 360-degree azimuth within the borehole. A longer propagation time (larger radius) of the borehole is displayed in a dark color, while a shorter propagation time (smaller radius) is displayed in a bright color.

[0076] S9: Conduct comprehensive interpretation of borehole wall ultrasonic imaging data (reflected wave impedance and propagation time), identify geological structures such as fractures, unconformities, and faults on the 360-degree borehole wall, determine the occurrence and development direction of fractures, and determine the direction of the maximum horizontal principal stress.

[0077] S10: Describe sedimentary characteristics: laminated bedding, cross-bedding, erosion, nodules, sedimentary rhythm.

[0078] S11: Divide thin interbeds of sandstone and mudstone and effective thickness.

[0079] S12: Determine the borehole geometry.

[0080] S13: Inspect the deformation of the casing and determine the location of casing deformation.

[0081] S14: Inspect the perforated interval and determine the location of perforation holes.

[0082] S15: Inspect the shape of the casing after explosive casing shaping.

[0083] S16: Determine the location of casing damage or casing fracture.

[0084] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Based on the technical essence of the present invention, any simple modifications, equivalent replacements, and improvements made to the above embodiments within the spirit and principles of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. An ultrasonic imaging logging device based on fiber optic acoustic sensing, characterized in that, it includes an open-hole borehole, an ultrasonic imaging logging device, a high-temperature-resistant optoelectronic composite logging cable, a surface wellhead logging vehicle, and a ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument; the ultrasonic imaging logging device includes three high-temperature-resistant fiber optic ultrasonic receiving sensors, serving as the in-well ultrasonic signal receiving unit; three pairs of ultrasonic transmitters with different frequencies; a fiber optic gyroscope; an ultrasonic transmitter electronic short circuit; an electric motor for driving the three pairs of ultrasonic transmitters to rotate uniformly; the surface wellhead logging vehicle is connected to the in-well ultrasonic imaging logging device through an armored optoelectronic composite cable; the three pairs of ultrasonic transmitters with different frequencies are respectively a low-frequency ultrasonic transmitter pair, a medium-frequency ultrasonic transmitter pair, and a high-frequency ultrasonic transmitter pair; a fiber optic ultrasonic receiving sensor is arranged between each pair of ultrasonic transmitters and does not rotate together with the ultrasonic transmitter pair; each pair of ultrasonic transmitters continuously emits low-frequency, medium-frequency, and high-frequency ultrasonic signals towards the same position corresponding to each pair of ultrasonic transmitters on the wellbore wall, and the ultrasonic signals reflected from the wellbore wall of the same-frequency ultrasonic signals simultaneously emitted by each pair of ultrasonic transmitters are exactly projected onto the fiber optic ultrasonic receiving sensor between each pair of ultrasonic transmitters; the surface wellhead logging vehicle controls the lowering and raising of the in-well ultrasonic imaging logging device through the optoelectronic composite cable and provides power to the in-well ultrasonic imaging logging device, and the ultrasonic transmitter electronic short circuit drives the low-frequency ultrasonic transmitter pair, the medium-frequency ultrasonic transmitter pair, and the high-frequency ultrasonic transmitter pair to continuously and repeatedly emit ultrasonic signals with different frequencies during operation; the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument arranged at the wellhead is connected to the downhole ultrasonic imaging logging device through an armored optoelectronic composite cable, emits laser pulses into the three fiber optic ultrasonic receiving sensors, and synchronously collects the backscattered Rayleigh waves in the fiber optic ultrasonic receiving sensors.

2. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument has three distributed fiber optic ultrasonic sensor signal input ports and one fiber optic gyroscope signal input port.

3. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the frequency of the low-frequency ultrasonic transmitter pair is 100 kHz to 250 kHz, the frequency of the medium-frequency ultrasonic transmitter pair is 250 kHz to 500 kHz, and the frequency of the high-frequency ultrasonic transmitter pair is 500 kHz to 1 MHz.

4. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, The fiber optic ultrasonic receiving sensor is a helical high-temperature resistant and high-reflection coefficient single-mode fiber optic ultrasonic receiving sensor wound around a cylindrical elastic body. The frequency of the low-frequency fiber optic ultrasonic receiving sensor is 100 kHz to 250 kHz, the frequency of the medium-frequency fiber optic ultrasonic receiving sensor is 250 kHz to 500 kHz, and the frequency of the high-frequency fiber optic ultrasonic receiving sensor is 500 kHz to 1 MHz.

5. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the fiber optic gyroscope is installed at the top of the downhole ultrasonic imaging logging device, and the azimuth, inclination and dip of the ultrasonic imaging logging device are measured in real time through an electro-optical composite cable.

6. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the ultrasonic transmitter electronic short circuit is placed behind the fiber optic gyroscope, and is used to drive the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair and high-frequency ultrasonic transmitter pair in the ultrasonic imaging logging device to emit ultrasonic waves of different frequencies.

7. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the electric motor is installed behind the ultrasonic transmitter electronic short circuit, and is used to drive the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair and high-frequency ultrasonic transmitter pair in the ultrasonic imaging logging device to rotate synchronously and uniformly, and its rotation speed is three to six revolutions per minute.

8. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 1, characterized in that, the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair and high-frequency ultrasonic transmitter pair continuously emit low-frequency, medium-frequency and high-frequency ultrasonic signals to the borehole wall during uniform rotation.

9. The ultrasonic imaging logging device based on fiber optic acoustic sensing according to claim 4, characterized in that, the low-frequency fiber optic ultrasonic receiving sensor, medium-frequency fiber optic ultrasonic receiving sensor and high-frequency fiber optic ultrasonic receiving sensor respectively continuously, simultaneously and synchronously collect the low-frequency, medium-frequency and high-frequency ultrasonic signals reflected back from the borehole wall after being emitted by the low-frequency ultrasonic transmitter pair, medium-frequency ultrasonic transmitter pair and high-frequency ultrasonic transmitter pair.

10. The measurement method for ultrasonic imaging based on fiber optic acoustic sensing, characterized in that, applying the ultrasonic imaging logging device based on fiber optic acoustic sensing as described in claim 1, including the following steps: S1: Connect the armored high-temperature resistant electro-optical composite cable on the winch of the surface wellhead logging truck to the downhole ultrasonic imaging logging device; S2: Lower the downhole ultrasonic imaging logging device to the bottom of the well by using the armored high-temperature resistant electro-optical composite cable on the winch of the surface wellhead logging truck; S3: Slowly lift the downhole ultrasonic imaging logging device upward through the armored high-temperature resistant electro-optical composite cable on the winch of the surface wellhead logging truck and send an instruction to the ultrasonic transmitter electronic short circuit in the downhole ultrasonic imaging logging device to drive the electric motor connected to the ultrasonic transmitter to rotate uniformly, and synchronously drive the three ultrasonic transmitter pairs with different frequencies to continuously emit ultrasonic signals to the well wall during uniform rotation; S4: Simultaneously start the fiber optic gyroscope to measure and record in real time the azimuth, inclination, and dip of the downhole ultrasonic imaging logging tool being lifted upward along the well trajectory, which is used for correcting the instrument's own rotation and projection processing of the reflected ultrasonic data recorded by the instrument during subsequent data processing; S5: Simultaneously start the ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument, and continuously transmit high-power multi-frequency narrow pulse laser signals to different frequency fiber optic ultrasonic receiving sensors in the downhole ultrasonic imaging logging tool through the electro-optical composite cable. The three fiber optic ultrasonic receiving sensors simultaneously and continuously receive the ultrasonic backscattered Rayleigh light signals reflected from the wellbore wall in a 360-degree azimuth in the wellbore back to their respective fiber optic ultrasonic receiving sensors; S6: The ground distributed fiber optic ultrasonic sensing modulation and demodulation instrument performs modulation and demodulation processing on the backscattered Rayleigh light signals on each fiber optic ultrasonic receiving sensor, and demodulates the fiber strain or strain rate data measured by each fiber optic ultrasonic receiving sensor into the ultrasonic data reflected from the wellbore wall in a 360-degree azimuth in the wellbore, including: the amplitude of the reflected ultrasonic wave and the propagation time of the reflected ultrasonic wave; S7: Convert the amplitude of the reflected ultrasonic wave into the reflected wave impedance data around the wellbore wall, and use a color plan view to display the measured reflected wave impedance data in an image according to the 360-degree azimuth in the wellbore to show the difference in the reflected wave impedance data of the wellbore wall. The wellbore wall with a small wave impedance is displayed as a dark color, and the wellbore wall with a large wave impedance is displayed as a bright color; S8: Perform wellbore radius imaging on the propagation time of the reflected ultrasonic wave, and use a color plan view to display the difference in the wellbore radius in an image according to the 360-degree azimuth in the wellbore. The wellbore with a long propagation time has a large radius and is displayed as a dark color, and the wellbore with a short propagation time has a small radius and is displayed as a bright color; S9: Conduct comprehensive interpretation of the wellbore wall ultrasonic imaging data, including the reflected wave impedance data and the propagation time of the reflected ultrasonic wave, identify the geological structures on the 360-degree wellbore wall, determine the occurrence and development direction of fractures, and determine the direction of the maximum horizontal principal stress; S10: Describe the sedimentary characteristics: laminated bedding, cross-bedding, erosion, nodules, sedimentary rhythm; S11: Divide the thin interbeds of sandstone and mudstone and the effective thickness; S12: Determine the wellbore geometry; S13: Check the deformation of the casing and determine the location of the casing deformation; S14: Check the perforated interval and determine the location of the perforation holes; S15: Check the shape of the casing after explosive shaping of the casing; S16: Determine the location of casing damage or casing fracture.

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