Wellbore annulus fluid level position safety monitoring device and method

Abstract

The present application belongs to the technical field of oil and gas development, and relates to a wellbore safety monitoring device and method in the process of drilling and completion of oil and gas field development. A wellbore annulus liquid level position safety monitoring device comprises: a sound wave measuring unit, a control unit and a sound wave oscilloscope; wherein the sound wave measuring unit is connected with the control unit and the sound wave oscilloscope; the sound wave oscilloscope is connected with a host computer; the sound wave measuring unit is installed at a plurality of monitoring points and a calibration point; the plurality of monitoring points are arranged on the outer wall of the technical casing from top to bottom, and the distance between the monitoring points at the upper and lower ends is greater than the wellbore liquid level safety depth; and the calibration point is arranged at the wellhead position. The present application overcomes the limitation of the wellbore environment (sealing property) on the wellbore liquid level monitoring, and can work under different operation modes in the drilling process, and has perfect functions. The monitoring probe can work continuously, and the ground can feed back in real time, so that the accurate real-time monitoring of the wellbore liquid level is realized.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology, and relates to a wellbore safety detection device and method during the drilling and completion process of oil and gas field development. Background Technology

[0002] Currently, oil and gas development is increasingly focused on complex fractured formations. Taking fractured gas reservoirs as an example, wellbore leakage is a prominent issue. When leakage occurs, the wellbore fluid level drops. Due to a lack of monitoring and delayed grouting, bottomhole pressure imbalances can easily occur, leading to gas-liquid displacement and potentially resulting in well kicks or even blowouts. Furthermore, during tripping out of the well, a significant drop in the wellbore fluid level, if not addressed promptly with grouting, can also cause bottomhole pressure imbalances, leading to overflows, well kicks, or even blowouts. Effective monitoring of the wellbore fluid level and timely injection of drilling fluid to maintain bottomhole pressure balance are crucial for the safe development of fractured gas reservoirs.

[0003] Currently, the main tools used for fluid level monitoring at drilling and completion sites are bottom-of-well pressure gauges and ultrasonic echo ranging. The former involves lowering an electronic pressure gauge into the well using a test vehicle to detect the fluid level depth and accumulation, providing data for subsequent operations. However, this method is time-consuming, expensive, and cannot be used for annular fluid level monitoring. The latter is the mainstream monitoring method, suitable for measuring fluid levels inside the tubing and at close range in the annulus. However, domestically produced ultrasonic echo ranging instruments can only monitor under no-pressure or very low-pressure conditions at the wellhead, and their installation location is limited. Ultrasonic fluid level monitoring requires a sealed monitoring channel from the launching gun to the fluid level. This makes it impossible to achieve real-time, rapid, and economical monitoring of wellbore fluid levels under various complex conditions (incomplete sealing) during drilling, thus hindering wellbore operation safety.

[0004] Furthermore, in the field of hydraulic rock anchor grouting, multi-node electrodes are inserted into the borehole to measure fluid level by measuring changes in fluid resistance within the borehole, which to some extent solves the dependence on wellbore sealing. However, this monitoring device can only be installed inside the tubing string and can only work when in direct contact with the fluid. When there are downhole tools inside the wellbore, the electrodes of the device are easily worn, so it still cannot be applied in the drilling and completion field. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a device and method for monitoring the position of fluid level in the wellbore annulus. The present invention monitors the fluid level height in the wellbore during the drilling process, provides timely warning of mud loss in the wellbore, and adjusts the wellbore pressure. At the same time, it solves the problems of high cost or high requirements for the effective working environment of existing monitoring systems.

[0006] The technical solution adopted by this invention to solve its technical problem is: a wellbore annular fluid level position safety monitoring device, comprising: an acoustic wave measurement unit, a control unit, and an acoustic wave oscilloscope; wherein the acoustic wave measurement unit is connected to the control unit and the acoustic wave oscilloscope; the oscilloscope is connected to a host computer; the acoustic wave measurement unit is installed at several monitoring points and one calibration point; the several monitoring points are arranged from top to bottom on the outer wall of the casing, and the distance between the monitoring points at the upper and lower ends is greater than the safe depth of the wellbore fluid level; the calibration point is located at the wellhead.

[0007] Furthermore, the acoustic wave measurement unit consists of a transmitting probe and a receiving probe, which are arranged symmetrically and parallel to each other along the wellbore.

[0008] Furthermore, the control unit includes an acoustic power transmission control box; the acoustic power transmission control box is connected to the acoustic transmission probe and the acoustic oscilloscope via signal lines, and is used to control the acoustic power signal.

[0009] Furthermore, the wellbore annular fluid level position safety monitoring device also includes an alarm device, which is connected to a host computer.

[0010] Furthermore, the host computer is equipped with an acoustic data processing module, a safety assessment module, and an early warning module. The acoustic data processing module is used to determine the annular fluid type at each monitoring point and the depth range of the annular interface based on the acoustic propagation time interval between different monitoring points and calibration points measured by the acoustic measurement unit. The safety assessment module is used to compare the depth range of the annular interface with the safe depth of the annular fluid surface in the wellbore to assess the wellbore safety status. The early warning module is used to trigger an alarm device to issue a signal based on the wellbore safety status.

[0011] This invention also provides a method for safe monitoring of the annular fluid level in a wellbore, the method comprising:

[0012] (1) Simultaneously send data to each monitoring point T n The calibration point T0 and the acoustic oscilloscope send electrical signals to acquire the acoustic wave curves of each monitoring point and calibration point. Using the oscilloscope waveform curves as a reference, the acoustic wave propagation time interval Δt at each monitoring point and calibration point is calculated by comparing the first peak position of the acoustic wave curves at each monitoring point and calibration point. n , Δt0;

[0013] (2) Calculate the difference in sound wave propagation time interval between each monitoring point and the calibration point:

[0014] ΔD h =ΔD-2Δd C -D O ;

[0015] In the formula: Δtn Δt0 is the time interval for sound wave propagation at each monitoring point; ΔD is the time interval for sound wave propagation at the calibration point; h ΔD is the length of the annular fluid cross-section, in meters; ΔD is the outer diameter of the wellbore string, in meters; Δd C D is the wall thickness of the wellbore string, in meters. O V is the outer diameter of the drill pipe, in meters (m); n V represents the acoustic velocity of the annular fluid at the nth monitoring point, in m / s; g V is the speed of sound waves through air, in m / s; w The velocity of sound waves through fresh water is m / s; n is the nth monitoring point from top to bottom.

[0016] (3) Calculate the velocity v of the annular fluid as the sound wave passes through the nth monitoring point. n :

[0017]

[0018] (4) The annular fluid velocity v at the monitoring point n By comparing the sound wave velocity in air and the sound wave velocity in fresh water, the type of annular fluid at this monitoring point can be identified:

[0019] If v n ≤v g If so, the fluid type is gas;

[0020] If v g <v n <v w If so, the fluid is a mixture of gas and liquid;

[0021] If v n ≥v w If so, then the fluid is a liquid.

[0022] (5) Determine the depth range of the annular interface based on the depth of each monitoring point and the annular fluid type at each monitoring point;

[0023] (6) Compare the safe depth of the annular fluid level in the wellbore with the depth range of the measured annular interface to obtain the safety status of the wellbore.

[0024] Furthermore, if the safe depth of the annular fluid level is greater than the lower limit of the annular interface depth range, the wellbore is safe and controllable; if the safe depth of the annular fluid level is within the annular interface depth range, an early warning is issued; if the safe depth of the annular fluid level is less than the upper limit of the annular interface depth, the wellbore is uncontrollable, an alarm is issued, and grouting is automatically injected into the wellbore.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Overcomes the limitations of wellbore environment (sealing) on ​​wellbore fluid level monitoring, and can operate in different working modes during drilling, with complete functions. 2. Employs cable transmission, offering high flexibility, small size, and easy installation. Mounted on the outer wall of the tubing string, it avoids wear and offers high reliability. 3. Simple structure, requiring minimal modification to wellhead equipment, and low cost. 4. The probe can operate continuously and provides real-time feedback at the surface, achieving accurate real-time monitoring of the wellbore fluid level. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure and installation of the wellbore annulus fluid level safety monitoring device in an embodiment of the present invention;

[0028] In the diagram, 1: Acoustic receiving probe at the monitoring point; 2: Acoustic transmitting probe at the monitoring point; 3: Cluster signal line; 4: Acoustic transmitting probe at the calibration point; 5: Acoustic receiving probe at the calibration point; 6: Buckle; 7: Sealed interface; 8: Acoustic power transmission control box; 9: Acoustic switch; 10: Acoustic oscilloscope; 11: Alarm device; 12: Computer; 13: Grouting pipeline; 14: Grouting pump; 15: Wellhead device; 16: Hanger sealing device; 17: Surface casing; 18: Arrow check valve; 19: External cement sheath; 20: Technical casing; 21: Pipe shoe; 22: Drill string;

[0029] Figure 2 This is a schematic diagram illustrating the principle of wellbore annular fluid level measurement according to the present invention: In the diagram, T0: the acoustic wave emitting probe at the calibration point; T1, T... (n-1) T n : Monitoring point acoustic wave transmitting probe, the subscript represents the location number of the transmitting probe; R0: Calibration point acoustic wave receiving probe; R1, R (n-1) R n : Monitoring point acoustic wave receiving probe, the subscript represents the location number of the receiving probe; L (n-1) L n : Monitoring point probe T (n-1) T n Distance from wellhead; UT: Acoustic power source; M: Oscilloscope; P: Acoustic waveform; D: Drill pipe or downhole tool; C: Casing string; B: Annular fluid interface; F1: Annular drilling fluid or completion fluid; F2: Gas;

[0030] Figure 3 The figure shows the acoustic waveforms for monitoring different annular fluids; in the figure, t: acoustic time; P n P0: Acoustic waveform of the monitoring point channel; P1: Acoustic waveform of the calibration point T0-F2-R0 channel; P m The acoustic waveform of oscilloscope M; Δt n :P n The transit time of the sound wave; Δt0: the transit time of the sound wave P0; e n :Pn The peak energy of a sound wave; e0: P0 is the peak energy of the sound wave;

[0031] Figure 4 This is a flowchart illustrating the safety monitoring of the annular fluid level position in a wellbore according to an embodiment of the present invention. Detailed Implementation

[0032] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0033] Example 1 This example provides a wellbore annulus fluid level position safety monitoring device. The structure and installation position of the device are as follows: Figure 1 As shown, the structure mainly includes: a monitoring point acoustic wave receiving probe 1, a monitoring point acoustic wave transmitting probe 2, a clustered signal line 3, a calibration point acoustic wave transmitting probe 4, a calibration point acoustic wave receiving probe 5, a buckle 6, a sealed interface 7, an acoustic wave power transmission control box 8, a power switch 9, an acoustic wave oscilloscope 10, an alarm device 11, a computer 12, etc.

[0034] First, based on the wellbore fluid level safety depth L required for drilling and well control safety, s Determine the location and number of monitoring points on the outer wall of the wellbore tubing, ensuring that the monitoring points cover the wellbore fluid level at a safe depth L. s The more monitoring points there are, the higher the accuracy; in addition, a calibration point is set at the wellhead (the annulus is air). During the field drilling process, the wellbore includes the wellhead device 15 (four-way valve, blowout preventer, etc.), the hanger sealing device 16, the surface casing 17 and the casing shoe and the external cement sheath (first opening), the technical casing 20 and the casing shoe 21 and the external cement sheath (second opening) 19, the drill string 22 and the arrow check valve 18.

[0035] like Figure 1 As shown, a calibration point acoustic wave transmitting probe 4 and a calibration point acoustic wave receiving probe 5 are fixed on the outer wall of the technical casing near the wellhead. Below the wellhead, multiple monitoring points are set at different positions along the outer wall of the technical casing 20, with a monitoring point acoustic wave receiving probe 1 and a monitoring point acoustic wave transmitting probe 2 fixed at each monitoring point. The transmitting and receiving probes are fixed parallel and symmetrically on the outer wall of the technical casing.

[0036] To secure the probe and signal line, a clip 6 is installed on the casing head. Simultaneously, two sealed interfaces 7 are installed on the blowout connection line of the four-way connector at the wellhead. The bundled signal line 3 of the transmitting and receiving probes is connected to the pre-installed sealed interfaces 7 at the wellhead four-way connector, achieving lossless transmission of the bundled signal line 3 and ensuring wellbore sealing. The bundled signal line 3 is led out of the well and connected to the acoustic power transmission control box 8 and the acoustic oscilloscope 10, respectively. The acoustic power transmission control box 8 is connected to a power switch 9. Furthermore, the acoustic power transmission control box 8 and the acoustic oscilloscope 10 are connected via signal lines to form a complete acoustic monitoring system. Simultaneously, the acoustic oscilloscope 10 is connected to a computer 12 to transmit waveform results and process data. The computer 12 is connected to the alarm device 11 and the grouting pump 14 to input alarm and automatic grouting signals. The grouting pipeline 13 connects the grouting pump 14 to the wellhead to perform grouting operations.

[0037] The computer 12 incorporates an acoustic data processing module, a safety assessment module, and an early warning module. The acoustic data processing module compares the received acoustic waveforms from different monitoring and calibration points with the waveforms on an acoustic oscilloscope. Based on the position of the first peak, it determines the propagation time interval between the acoustic waves at different monitoring and calibration points and the acoustic waves on the oscilloscope, thereby calculating the velocity of the annular fluid at each monitoring point. Comparing this velocity with the velocity of gas and liquid acoustic waves identifies the type of annular fluid at each monitoring point. Based on the location of the monitoring points, it determines the depth range of the annular interface. The safety assessment module, based on the determined depth range of the annular interface, compares the upper and lower limits of this range with the safe depth of the annular fluid surface in the wellbore to assess the wellbore's safety status. For example: if the safe depth of the annular fluid level is greater than the lower limit of the measured annular interface depth range, the wellbore is safe and controllable; conversely, if the safe depth of the annular fluid level is less than the upper limit of the measured annular interface depth, the wellbore is uncontrollable, an alarm is issued, and grouting is automatically injected into the annulus; and if the safe depth of the annular fluid level is within the measured annular interface depth range, a warning is issued.

[0038] The alarm device 11 uses light and sound alarms, for example: green light for safety, orange light for warning, and red light for alarm.

[0039] In this embodiment, the working principle of the wellbore annulus fluid level position safety monitoring device is as follows: during drilling and completion operations, if... Figure 2As shown, the casing C near the wellhead contains drill pipe D or downhole tools, and there is annular fluid between the inner wall of casing C and drill pipe D. When drilling fluid or completion fluid is insufficient, the annular fluid surface B is divided into upper fluid F2 and lower fluid F1. Mechanical wave theory indicates that the medium determines the mechanical wave velocity, and there are significant differences in the sound wave velocity of gases and liquids (approximately 340 m / s for air and 1430 m / s for fresh water) and their ability to transmit sound wave energy. Drilling fluid is composed of water and solid particles, and its sound wave velocity is faster, resulting in a stronger ability to transmit sound wave energy. Therefore, sound wave testing can clearly distinguish whether the annular fluid is F1 (drilling fluid or completion fluid), F2 (air), or a mixture of the two fluids (F1 and F2). Based on the known depth position at the probe, the location of the annular fluid surface B can be determined, and the safety of the annular fluid surface B for well control operations can be judged according to the wellbore fluid surface safety depth requirements for drilling and completion.

[0040] Example 2 This example provides a method for safe monitoring of the annular fluid level in a wellbore. The method flow is as follows: Figure 4 As shown, it includes the following steps:

[0041] (1) First, based on the wellbore fluid level safety depth L required for drilling and well control safety, s Determine the location and number of monitoring points on the outer wall of the wellbore tubing, ensuring that the monitoring points cover the wellbore fluid level at a safe depth L. s The more monitoring points there are, the higher the accuracy; in addition, a calibration point is set at the wellhead (the annulus is filled with air).

[0042] (2) The acoustic velocity of the annular fluid is measured using the accurate time-difference method, such as... Figure 3 As shown, with T n -F1-R n Taking channel monitoring as an example, the UT acoustic power supply transmits sound waves through the acoustic wave emitting probe T. n An acoustic pulse wave is emitted, and the sound wave propagates in the medium (two layers of casing wall, annular fluid F1, two layers of drill pipe wall, and fluid inside the pipe). After a certain period of time, it reaches the acoustic wave receiving probe R1, where the sound wave is converted from an acoustic signal into an electrical signal, and finally the waveform is displayed on the acoustic oscilloscope M, as shown below. Figure 3 China P n curve.

[0043] Similarly, the channel waveform of the wellhead position calibration point monitoring T0-F2-R0 is as follows: Figure 3 The P0 curve is shown in the middle. The UT acoustic power supply is directed towards T. n -F1-R n While the monitoring channel and the T0-F2-R0 monitoring channel send signals, they also send the same signal to the acoustic oscilloscope M, as shown in the waveform curve. Figure 3 China P m As shown.

[0044] Compare with P respectivelyn P0 and P m The position of each of the first peaks can be used to obtain T. n -F1-R n The acoustic wave propagation time interval Δt of the monitoring channel and the T0-F2-R0 monitoring channel n Δt0. Sound waves pass through T n -F1-R n The time intervals of both the monitoring channel and the T0-F2-R0 monitoring channel include the time for the sound wave to pass through the two layers of casing wall, the two layers of drill pipe wall, and the fluid inside the pipe. Therefore, the difference in their time intervals is equal to the difference in the time intervals for the sound wave to pass through the annular fluid F1 and F2. This can be expressed as a formula:

[0045]

[0046] ΔD h =ΔD-2Δd C -D O (2)

[0047] In the formula, Δt n For T n -F1-R n The time interval of sound wave propagation at each monitoring point in the monitoring channel; Δt0 is the time interval of sound wave propagation at the calibration point of the T0-F2-R0 channel; ΔD h ΔD is the length of the annular fluid cross-section, in meters; ΔD is the outer diameter of the wellbore string, in meters; Δd C D is the wall thickness of the wellbore string, in meters. O V is the outer diameter of the drill pipe, in meters (m); n V represents the acoustic velocity of the annular fluid at the nth monitoring point, in m / s; g The speed of sound waves through air is approximately 340 m / s; v w The velocity of sound waves through fresh water is approximately 1430 m / s; n is the nth monitoring point from top to bottom.

[0048] (3) By combining equations (1) and (2), the sound wave passing through the measuring point T can be obtained. n The velocity v of the annular fluid n :

[0049]

[0050] (4) v n By comparing the acoustic wave velocity with that of gas and liquid, the type of annular fluid at the monitoring point can be identified.

[0051] If v n ≤v g If so, the fluid type is gas;

[0052] If v g<v n <v w If so, the fluid is a mixture of gas and liquid;

[0053] If v n ≥v w If so, the fluid is a liquid (drilling fluid or completion fluid).

[0054] Similarly, the type of annular fluid at other monitoring points can be identified through acoustic measurement.

[0055] (5) The depth location of each monitoring point is known, such as Figure 2 As shown, after determining the annular fluid type at each monitoring point, the depth range L of the gas-liquid interface (annular interface) can be determined. (n-1) ~L n .

[0056] (6) If the safe depth of the annulus fluid level in the wellbore is L s If the depth of the annular interface is greater than the lower limit of the measured range, the wellbore is safe and controllable (green); otherwise, the safe depth L of the annular fluid level in the wellbore is [not specified]. s If the depth is less than the upper limit of the measured annular interface depth, the wellbore safety is uncontrollable, an alarm (red) is issued, and grouting is automatically injected into the wellbore annulus; while the safe depth of the wellbore annular fluid level L... s If the location is within the depth range of the measured annular interface, an early warning (orange) will be issued.

[0057] For example: Assuming the safe depth L of the annulus fluid level in the wellbore. s The depth is 105 meters. If the measured depth range of the annulus interface is 90-100 meters, then the safe depth L of the annulus fluid level in the wellbore is... s A depth greater than the lower limit of the measured annular interface depth range (100 meters) indicates sufficient drilling fluid, meaning the wellbore is safe and controllable. If the measured annular interface depth range is 100-110 meters, the safe depth L of the wellbore annular fluid level is... s If the depth falls within this range, it indicates a potential drilling fluid deficiency, and a warning is issued. If the measured depth range of the annulus interface is 110-120 meters, the safe depth L of the wellbore annulus fluid level... s If the depth is less than the upper limit of the measured annular interface depth (110 meters), it indicates that the drilling fluid is too low and the fluid level is below the safe position of the annular fluid level in the wellbore. In this case, the wellbore safety is out of control, an alarm (red) is issued, and grouting is automatically injected into the annulus.

[0058] Example 3: This example uses the drilling process of a well in the western Sichuan gas reservoir block of the Sichuan-Chongqing Basin as an example to illustrate the specific implementation of the method of the present invention. In this fractured gas reservoir block, well leakage and well kick are prominent issues. Especially during the tripping process, the drop in the annular fluid level and untimely grouting lead to pressure imbalance at the bottom of the well, threatening well control safety. Therefore, the device and method of the present invention are applied to a well to monitor changes in the fluid level in the wellbore, provide timely warnings, and ensure well control safety. The specific implementation steps are as follows:

[0059] (1) According to the well control safety requirements of the gas reservoir in this area, the safe annular fluid level depth should not exceed 30m, meaning the actual annular fluid level should be located at a depth of 30m or less. For ease of explanation, three annular monitoring points, T1, T2, and T3, were set along the outer wall of the technical casing from the wellhead downwards, at distances of 25m, 30m, and 35m from the wellhead, respectively. A calibration point was also set at the wellhead. The acoustic monitoring at each monitoring point and calibration point consisted of a transmitting probe and a receiving probe, which were parallel and symmetrical.

[0060] (2) In order to facilitate the installation and removal of the device of the present invention and to ensure the sealing of the well shaft, two sealed line interfaces are modified at the four-way pipeline at the wellhead.

[0061] (3) Before inserting the casing (conduit), fix the acoustic wave transmitting probe and acoustic wave receiving probe at the pre-set positions on both sides of the outer wall of the technical casing, and correctly connect the signal lines. Cover the probe and signal lines with an insulating, wear-resistant, and corrosion-resistant integrated jacket to form a bundled signal line.

[0062] (4) Install a buckle at the end of the bundled signal line, and fix it in place at the casing head position, ensuring that the bundled signal line can be led out of the wellhead.

[0063] (5) Lower the casing (conduit) and connect the bundled signal line to the pre-installed sealing interface at the wellhead four-way.

[0064] (6) According to the following Figure 1 As shown, install and connect the acoustic power supply transmitter control box, acoustic switch and acoustic oscilloscope, and connect them to the computer and alarm device (light and sound).

[0065] (7) Following the standard drilling operation procedures, the drill string is tripped up and down. The power switch is turned on, and the annular fluid level monitoring system begins normal operation. For its specific working principle and procedures, please refer to [link to relevant documentation]. Figure 2 , Figure 3 and Figure 4 .

[0066] (8) The calculated velocities of the sound waves through the annular fluid at the three monitoring points at a certain moment were 980 m / s, 2130 m / s, and 2320 m / s (from top to bottom). That is, the positions of the wellbore annular monitoring points T1, T2, and T3 from top to bottom are: gas-liquid mixture, liquid, and liquid, respectively. It can be determined that the depth of the annular interface is about 25 meters from the wellhead.

[0067] (9) Based on the integrated display and automatic judgment of the measurement and calculation results by the computer, if the required safe position of the annulus fluid level in the wellbore (30m depth) is within the warning range, a signal is sent to the alarm device. The alarm device's yellow light illuminates, reminding the operators to adjust the grouting in a timely manner.

[0068] (10) The device of the present invention monitors the changes in the depth of the annulus fluid level in the wellbore in real time, issues multiple timely alarms, and automatically grouts.

[0069] (11) When it is necessary to stop working, disconnect the power switch and disconnect the connection between the external circuit of the wellhead and the sealing interface. Considering the cost and size advantages of this device, the wiring and probes in the well can be unhooked, pulled up and retrieved, or directly discarded according to actual needs.

Claims

1. A safety monitoring device for the position of fluid level in the annulus of a well, characterized in that, include: Acoustic wave measurement unit, control unit, acoustic wave oscilloscope; The acoustic wave measurement unit is connected to the control unit and the acoustic wave oscilloscope; the acoustic wave oscilloscope is connected to the host computer; the acoustic wave measurement unit is installed at several monitoring points and one calibration point; the several monitoring points are arranged from top to bottom on the outer wall of the casing, and the distance between the monitoring points at the upper and lower ends is greater than the safe depth of the wellbore fluid surface; the calibration point is located at the wellhead; the acoustic wave measurement unit consists of a transmitting probe and a receiving probe, which are arranged symmetrically parallel to the wellbore; the host computer is equipped with an acoustic wave data processing module, a safety assessment module, and an early warning module; the acoustic wave data processing module is used to determine the annular fluid type at each monitoring point and determine the depth range of the annular interface based on the acoustic wave propagation time interval between different monitoring points and the calibration point measured by the acoustic wave measurement unit; the safety assessment module is used to compare the depth range of the annular interface with the safe depth of the wellbore annular fluid surface to assess the wellbore safety status; the early warning module is used to trigger an alarm device to issue a signal based on the wellbore safety status.

2. The wellbore annulus fluid level safety monitoring device according to claim 1, characterized in that: The control unit includes an acoustic power transmission control box; the acoustic power transmission control box is connected to an acoustic transmission probe and an acoustic oscilloscope via signal lines, and is used to control the acoustic power signal.

3. The wellbore annulus fluid level position safety monitoring device according to claim 1, characterized in that: It also includes an alarm device, which is connected to a host computer.

4. A method for safe monitoring of the fluid level position in the annulus of a wellbore, characterized in that: The method utilizes the apparatus as described in any one of claims 1-3 and includes the following steps: (1) Simultaneously send electrical signals to each monitoring point, calibration point, and acoustic oscilloscope to obtain the acoustic wave curves of each monitoring point and calibration point; using the waveform curves of the oscilloscope as a reference, calculate the acoustic wave propagation time interval of each monitoring point and calibration point by comparing the first peak position of the acoustic wave curves of each monitoring point and calibration point: , ; (2) Calculate the difference in sound wave propagation time interval between each monitoring point and the calibration point: ； ； In the formula: The time interval for sound wave propagation at each monitoring point; The time interval for sound wave propagation at the calibration point; The length of the annular fluid cross-section is in meters (m). The outer diameter of the wellbore string is in meters (m). The wall thickness of the well casing string is in meters (m). Let the outer diameter of the drill pipe be in meters (m). Let be the acoustic velocity of the annular fluid at the nth monitoring point, in m / s; The speed of sound waves through air, in m / s; The velocity of sound waves through fresh water is m / s; n is the nth monitoring point from top to bottom. (3) Calculate the velocity of the annular fluid as the sound wave passes through the nth monitoring point. : ； (4) Measure the annular fluid velocity at the monitoring point. By comparing the sound wave velocity in air and the sound wave velocity in fresh water, determine the type of annular fluid at this monitoring point: like If so, the fluid type is gas; like If so, the fluid is a mixture of gas and liquid; like If so, then the fluid is a liquid; (5) Determine the depth range of the annular interface based on the depth of each monitoring point and the type of annular fluid at each monitoring point; (6) Compare the safe depth of the annulus fluid level in the wellbore with the depth range of the measured annulus interface to obtain the safety status of the wellbore.

5. The method for safe monitoring of the annular fluid level in a wellbore according to claim 4, characterized in that: If the safe depth of the annular fluid level is greater than the lower limit of the annular interface depth range, the wellbore is safe and controllable; if the safe depth of the annular fluid level is within the annular interface depth range, an early warning is issued; if the safe depth of the annular fluid level is less than the upper limit of the annular interface depth, the wellbore is uncontrollable, an alarm is issued, and grouting is automatically injected into the wellbore.

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