A shallow casing precise leak detection string and precise leak detection method

Abstract

A shallow casing precise leak detection string and a precise leak detection method belong to the field of leak detection and water blocking in oil well operations. The shallow casing precise leak detection string of the present invention includes a No. 1 string and a No. 2 string, wherein the No. 1 string is provided with an oil pipe, a guide wire plug is provided at the bottom of the oil pipe, and a packer, a pressure-controlled switch, and a pressure relief device are provided above the guide wire plug. The present invention first lowers the No. 1 string K344 hydraulic packer to a depth of 400 meters in a shallow well section, determines whether there is a leak in the shallow well section casing, determines the position and upper limit of the leak point in the casing above 400 meters, adjusts the position of the pressure-controlled switch in the No. 1 string, and then lowers the No. 2 string; then uses the No. 2 string to clearly define the lower limit of the leak point and determine the specific positions of multiple leak points. The present invention ensures the safety of leak detection construction; shortens the leak detection construction time, and improves the leak detection time rate, accuracy, and one-time success rate.

Description

Technical Field

[0001] The invention belongs to the field of leak detection and water blocking in oil well operations, and particularly relates to a shallow casing and a precise leak detection method thereof. Background Art

[0002] During shallow leak detection in oilfields, the conventional method is to use a single Y521 packer to seal the tubing string. However, setting the Y521 packer requires a certain tubing load to establish a seal. In shallow oil and water wells, due to the limited tubing in the well, the tubing weight alone cannot meet the packer's setting load. (The packer rubber requires 5-6 tons of wellhead pressure to expand and seal the oil and casing annular space. However, applying wellhead pressure at depths between 0 and 400 meters is challenging. Because shallow wells lack the pressure of suspended drill string weight, wellhead pressure is essential for achieving a packer seal.) Consequently, the packer cannot be set or effectively sealed. Traditionally, two wire ropes are used to thread two elevators through the gates on either side of a large four-way connection. The elevators are then reversed to apply pressure, increasing downward pressure on the tubing string. When the rig pulls up the wire ropes by 4-5 tons, the reverse elevators apply downward force on the tubing string, further setting the packer. However, this method has the problems of cumbersome operation, complicated construction and long time. Because the load of the wire rope pulled by the large hook of the workover rig is large, it is easy to cause the rope to be stuck and broken, the wire rope to slip and fall out and injure people, the wire rope to break, and there are great safety hazards. The sealing method uses a short section of the well pipe string, a tubing elevator, and a wire rope around the wellhead big four-way. The workover rig is used as the power to reversely pull the seal to pressurize and seal. During operation, the wellhead oil tree is easily damaged, and the wire rope is often broken due to the large friction resistance. There are great safety hazards. This sealing technology is not conducive to repeated sealing and leakage detection operations. There is also a situation where the pressure cannot be increased, and the pressure drop caused by the sealing device is easily misjudged as a leak point. In addition, the failure to find multiple leak points is easy to miss the leak point, which misleads subsequent measures.

[0003] In order to solve the safety risk of wire rope back-pressurization, ZL200920018970.9 provides an oil and water well wellhead pressurization device, but the wellhead needs to add a pressure mechanism and a straightening support mechanism, and it is also relatively cumbersome to use. ZL201922012594.9 also provides a shallow well leak detection and sealing device, but the device requires additional equipment at the wellhead and requires a lifting ring. If it is in a stress-free state, it means that the seal is successfully suspended. It is also necessary to adjust the pressure adjustment arms on both sides. The pressure adjustment arms on both sides are adjusted to the maximum adjustment length and the fixing bolts are tightened into place. At this time, the pressure adjustment arms have reached the stress adjustment state; then, by adjusting the margin of the positive and negative buckle adjustment rod, the sealing operation is completed to implement the casing leakage detection operation. After the detection is completed, the positive and negative buckle adjustment rod is adjusted to a powerless state to perform the next designed well end replacement and leakage detection operation; the device requires adjustment of the positive and negative buckle adjustment rod, and also has limitations such as complicated construction, high labor intensity, and inability to accurately determine the number and lower limit of leakage points. In view of the on-site needs of conventional shallow casing string leakage detection and the increasingly severe current safety situation, the research and development of this project was carried out. Summary of the Invention

[0004] In view of the above shortcomings, the present invention provides a shallow casing precise leak detection string and a precise leak detection method. The precise leak detection string and method shorten the leak detection construction time, improve the leak detection time rate, reduce the labor intensity of workers, and improve the accuracy and one-time success rate of shallow casing leak detection.

[0005] The casing used to solve the technical problem of the present invention includes a No. 1 shallow casing leak detection string and a No. 2 shallow casing leak detection string, wherein the No. 1 shallow casing precise leak detection string is provided with an oil pipe, a guide wire plug is provided at the bottom of the oil pipe, a pressure-controlled switch is provided above the guide wire plug, and a pressure relief device is provided between the pressure-controlled switch and the guide wire plug; a hydraulic packer is provided between the oil pipe above the pressure relief device and the oil pipe below the pressure-controlled switch, and a mechanical packer is provided between the oil pipe below the pressure relief device and the oil pipe above the guide wire plug.

[0006] Furthermore, the hydraulic packer and the mechanical packer are arranged in sequence from top to bottom.

[0007] Furthermore, the vertical position of the hydraulic packer is lower than the pressure-controlled switch and higher than the pressure relief device.

[0008] Furthermore, the vertical position of the mechanical packer is lower than the pressure relief device and higher than the guide wire plug.

[0009] Furthermore, several oil pipes are arranged between the mechanical packer and the pressure-controlled switch.

[0010] Furthermore, the number of oil pipes is 2 to 10.

[0011] Furthermore, the No. 2 shallow casing precise leak detection string is provided with an oil pipe, and mechanical packers and hydraulic packers are arranged in sequence from top to bottom between the oil pipe and the casing; among them, the vertical position of the mechanical packer is higher than the pressure-controlled switch, and the hydraulic packer is lower than the pressure relief device and higher than the guide wire plug.

[0012] Furthermore, the compression point between the rubber sleeve and the iron ring of the hydraulic packer is reinforced, the wiring is denser, and a sealing ring and an end compression sealing ring are added inside the upper and lower pressure rings of the rubber sleeve.

[0013] Furthermore, three circumferential sealing rings are added inside the upper and lower pressure rings of the rubber sleeve.

[0014] Furthermore, the hydraulic packer may be a K344 hydraulic packer.

[0015] Furthermore, the mechanical packer may be a Y521 mechanical packer.

[0016] The present invention also provides a method for accurately detecting shallow casing leaks, the method comprising the following steps:

[0017] (1) First, run the No. 1 shallow casing string to the predetermined depth to accurately locate the leak. Use the cement truck oil pipe to positively pressurize the casing to determine whether there is a leak in the shallow well section above 400 meters. If there is a leak, lift the string to a certain depth and continue to pressurize the casing to determine whether there is a leak in the casing above the K344 packer until the specific location and upper limit of the leak are determined.

[0018] (2) After determining the specific location and upper limit of the shallow casing leak point above 400 meters, adjust the position of the pressure control switch in the No. 1 shallow casing precise leak detection string and then lower the No. 2 shallow casing precise leak detection string;

[0019] (3) Use No. 2 shallow casing to accurately find the leak string. After both double packers are set, determine the lower limit of the leak point and determine whether there are other leak points above the leak point. If there are leak points, find out the specific location of the leak point.

[0020] Furthermore, the hydraulic packer in step S1 may be a K344 hydraulic packer.

[0021] Furthermore, the positive pressing pressure in step 1 may be 15 MPa.

[0022] Furthermore, after determining the specific location and upper limit of the shallow casing leak point above 400 meters in step S2, a No. 2 shallow casing precise leak detection string is lowered.

[0023] Principle: 1. The matching hydraulic setting packer replaces the conventional rotary and lowering compression packer, and solves the weighting and setting problems of shallow well sections through the No. 1 shallow casing precise leak detection string.

[0024] (1) The supporting shallow casing precise leak detection construction string is sealed by oil pipe pressure. The sealing does not require a sealing load, thus avoiding back pressurization.

[0025] (2) The hydraulically set packer does not require a set distance, and the set seal does not need to be lifted up or lowered, so the leak point can be accurately narrowed to a smaller range.

[0026] (3) The matching hydraulically set packer achieves multiple resetting and effective sealing by improving reliability. Based on the original K344 type packer rubber cartridge, the rubber cartridge quality is further improved, with improved toughness and wear resistance. The effective sealing frequency of the setting is guaranteed to be at least 4-5 times.

[0027] The K344 hydraulic packer's setting is unaffected by the weight of the tubing string and can be set repeatedly. However, due to weaknesses in its structural design, it sometimes loses its stability. Analysis revealed two main weaknesses: the tightness between the upper rubber sleeve and the iron ring, and the tightness between the lower rubber sleeve and the iron ring. To ensure reliable sealing throughout the entire leak detection process in shallow wells, the following innovative improvements were implemented, resulting in an average increase of more than eight effective seals compared to the original packer.

[0028] ① To address the weak point where the upper rubber sleeve and the iron ring are pressed together: the rubber sleeve and the iron ring are pressed together to strengthen the area, increase the wiring density, and lengthen the effective length. This will improve the sealing performance of the packer after it is seated.

[0029] ② In order to solve the weak point where the lower rubber sleeve and the iron ring are pressed together, three circumferential sealing rings and one end compression sealing ring are added to the upper and lower pressure rings of the rubber sleeve to prevent the phenomenon of unstable pressure.

[0030] 2. A Y521 mechanical packer is innovatively installed in series at the lower end of the conventional K344 hydraulic packer string. The hydraulic anchor on the Y521 mechanical packer is used to solve the problem of upward movement of the conventional hydraulic packer string in shallow well sections.

[0031] When leak detection in shallow wells, due to the limited number of tubing strings in the well, the tubing needs to be positively pressurized to 15 MPa. The downward pressure differential generated by the tubing string's own weight is far less than the upward pressure differential during the pressurization. Conventional hydraulic packers, lacking anchoring devices, can cause tubing string to rise, leading to leak detection failure. To address this issue, we adopted innovative thinking and utilized a hydraulic anchor on the Y521 mechanical packer to solve the tubing string upward movement problem, ensuring the hydraulic packer's effective pressure stabilization and avoiding misidentification of pressure drops caused by tubing string upward movement as leak points, thus expanding the hydraulic packer's applicability.

[0032] Working principle: During construction, the Y521 mechanical packer is not set first, and the oil pipe is pressurizing the packer to seal it. When the lower pressure difference of the packer is higher than the upper pressure difference, the anchor claws on the hydraulic anchor will be pushed out by the lower pressure and anchor the packer to the casing, so that the packer remains fixed under the action of the higher lower pressure difference, solving the problem of upward movement of the pipe string.

[0033] When the hydraulically set packer fails to generate pressure or maintains pressure steadily during operation and a leak occurs, the leak can be located at the next position by lifting the tubing string, and the upper limit of the leak can be accurately determined, which reduces the time for removing and hanging the wire rope, makes the setting position selection more flexible, and makes the leak location more accurate.

[0034] When the hydraulically set packer is pressurized to 15 MPa and the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped, it proves that there is no leakage point in the upper casing of the packer. It is only necessary to lower a certain length of tubing to conduct leak detection at the next position. When there is a leakage point, the leak detection rate is high.

[0035] 3. It can clearly identify the number of shallow casing leakage points and the lower limit of the leakage points, and realize the accurate regular leakage points of shallow casing.

[0036] The conventional method of using a single Y521 mechanical packer string can only identify one leak point (the top leak point) in a shallow well section, as well as the upper limit of the leak point, which poses a risk of missing a leak point.

[0037] After a leak point and the upper limit of the leak point are clearly identified using the No. 1 shallow casing precision leak detection string, the pressure-controlled switch position is changed and the No. 2 shallow casing precision leak detection string is used to determine the lower limit of the leak point. Double seals are then set to determine if there are other leaks above the leak point. The number of tubings clamped by the two packers must ensure that the packer depth is below 400 meters.

[0038] 4. Double insurance of the tool is achieved: The shallow casing precise leak detection construction string realizes multiple leak detection functions in one trip through the innovation of the string structure assembly, which improves the leak detection efficiency and saves the number of trips to run the leak detection string.

[0039] If there is no leakage in the casing of the shallow well section, when the hydraulically set packer has been set too many times and the sealing of the rubber sleeve is poor, and the weight of the deepening string is greater than the setting load of the Y521 mechanical packer, the Y521 mechanical packer casing can be used to reversely pressurize the casing instead of the hydraulically set packer to continue leak detection in the deep well section, thus achieving double insurance of the leak detection packer tool and saving the number of leak detection string trips; and it can also realize the verification of the leakage point in the shallow well section to avoid misjudging the non-leakage point as the leakage point.

[0040] 5. The matching split-type rod-throwing pressure relief device avoids the risk of no drainage device on the pipe string, residual liquid in the pipe string, pollution of the environment by pipe top spraying, and incomplete well jamming caused by incomplete packer release.

[0041] This drainage device is designed for use on shallow casing precise leak detection strings. When the string needs to be drained, a striker rod is deployed from the tubing to knock open the copper pin, connecting the oil and casing, completely draining the oil and water into the well and completely releasing the packer. This effectively solves the problems of conventional hydraulic packers, such as top blowout when the pipe is pulled without pressure relief and incomplete well blocking when the packer is released. It also improves the field adaptability and safety of the shallow casing precise leak detection string. When the leak detection is completed and there is no water in the leak detection pipe and no need for drainage, the striker rod does not need to be deployed from the tubing, and the drainage device can be used again for the next leak detection.

[0042] Beneficial effects: The present invention changes the conventional shallow casing leak detection method of relying on reverse pressurization of forward and reverse elevators, solves a series of problems such as counterweight, setting seal, hydraulic packer pressure on pipe string, eliminates the safety hazards of conventional reverse buckle elevator wire rope pressurization, avoids the use of wellhead equipment, cumbersome pressurization methods, and ensures the safety of leak detection construction; shortens the leak detection construction time, improves the leak detection time rate, reduces the labor intensity of workers, and improves the accuracy of shallow casing leak detection and the one-time success rate.

[0043] (1) The innovative hydraulically set packer replaces the conventional rotary and lowered compression packer to solve the problems of counterweight and setting in shallow well sections: the innovative shallow casing precise leak detection construction string is set by pressure pumping through the tubing, and no setting load is required for setting, thus avoiding back-pressurization; the matching hydraulically set packer does not require a setting distance, and the setting does not require lifting and lowering, so the leak point location can be accurately narrowed to a smaller range.

[0044] (2) An innovative Y521 mechanical packer was connected in series at the lower end of the conventional K344 packer string. By using the hydraulic anchor on the Y521 packer, the problem of upward movement of the conventional hydraulic packer string in shallow well sections was solved.

[0045] (3) The problem of limited sealing times of conventional hydraulic packers has been solved. Compared with the original packers, the effective sealing times have increased by an average of more than 8 times.

[0046] (4) It can clearly identify the number of shallow casing leaks and the lower limit of the leaks, thus realizing the accurate conventional leaks of shallow casings: the conventional Y521 mechanical packer single sealing string can only determine one leak (the top leak) in the shallow well section, as well as the upper limit of the leak, which poses a risk of missing leaks.

[0047] (5) The tool has achieved double insurance: one leak detection string has multiple leak detection functions, which improves the leak detection efficiency and saves the number of leak detection string runs.

[0048] If there is no leakage in the casing of the shallow well section, when a hydraulic packer seals abnormally when it is set, and the weight of the deepening string is greater than the setting load of the Y521 mechanical packer, the Y521 mechanical packer casing can be used to reversely pressurize the casing to continue leak detection in the deep well section, thus realizing double insurance of the tool and saving the number of leak detection string trips; and it can also realize the verification of the leakage point in the shallow well section to avoid misjudging the non-leakage point as the leakage point.

[0049] (6) The leak detection efficiency is higher: the leak detection position can be changed by lifting and lowering the pipe string, which reduces the time of removing and hanging the wire rope and adjusting the adjustment rod. The setting position selection is more flexible and the leak point location is more accurate.

[0050] (7) It is equipped with a split-type plunger pressure relief device to avoid the risk of no discharge device on the pipe string, residual liquid in the pipe string, pollution of the environment by pipe top spraying, and incomplete release of the packer, which may cause the well to get stuck. It also avoids the problems of incomplete release of the hydraulic packer and residual liquid in the leak detection pipe, reduces labor intensity, improves the efficiency of pipe lifting operations, and avoids oil and water falling to the ground, scalding workers and polluting the environment.

[0051] This drainage device is designed for use on shallow casing precise leak detection work strings. When the string needs to be drained, a striker rod is inserted from the tubing to knock open the copper pin, connecting the oil and casing, allowing the complete release of oil and water into the well and the complete release of the packer. This effectively solves the problems of conventional hydraulic packers, such as top blowout caused by incomplete pressure relief and incomplete packer release, and avoids problems such as incomplete hydraulic packer release and residual liquid in the leak detection pipe. It reduces labor intensity, improves pipe lifting efficiency, and prevents oil and water from falling to the ground, scalding workers and polluting the environment. This improves the on-site adaptability and safety of shallow casing precise leak detection work strings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of the structure of the No. 1 shallow casing precise leak detection string in the present invention.

[0053] Figure 2 This is a top view of the No. 2 shallow casing precise leak detection string structure of the present invention.

[0054] Figure 3 It is a structural schematic diagram of the K344 hydraulic packer in the present invention.

[0055] As shown in the figure, 1. Oil well casing, 2. Pressure-controlled switch, 3. Oil pipe, 4. Hydraulic packer, 5. Pressure relief device, 6. Mechanical packer, 7. Guide wire plug, 41. End compression sealing ring, 42. Circumferential sealing ring. DETAILED DESCRIPTION

[0056] The present invention will be further described below with reference to the embodiments.

[0057] Conventional shallow casing leak detection methods utilize a single Y521 mechanical packer string, requiring wireline backpressure. This is cumbersome, labor-intensive, and time-consuming, often damaging the wellhead. Wireline breakage due to high friction is a common safety hazard. This setting technology is also not suitable for repeated leak detection operations. Furthermore, there are issues with pressure buildup, which can lead to misinterpretation of pressure drops caused by a packer leak as leaks. Furthermore, multiple leaks cannot be identified, leading to missed leaks and misleading subsequent measures. Therefore, an innovative leak detection string using tubing pressure to set a hydraulic packer string is being adopted, replacing the rotary lowering mechanical packer. Setting the packer requires no setting load, eliminating backpressure. Hydraulic packers require no setting distance or lifting or lowering, allowing the precise location of leaks to be narrowed down to a smaller area.

[0058] The Y521 mechanical packer requires a certain string load to set the packer. For shallow oil and water wells, the small amount of string running through the well during construction means the string's own weight cannot meet the packer's setting load. The packer rubber can only expand at a wellhead pressure of 5-6 tons to seal the oil and casing annular space. However, applying pressure at the wellhead at 0-400m to expand and seal the rubber is difficult because shallow wells lack the pressure of suspended drill string weight, necessitating wellhead pressure to achieve the necessary seal. If the packer cannot be set or effectively sealed, the conventional method is to use two wire ropes to thread two elevators together through the gates on both sides of a large four-way system. The reversed elevators are then used to apply pressure, increasing downward pressure on the string. When the rig pulls up the wire rope by 4-5 tons, the reversed elevators apply downward force on the string, further setting the packer. However, this method is cumbersome to operate, complex, and time-consuming. The heavy load on the wire rope pulled by the workover rig hook can easily cause the rope to jam, break, slip, and injure personnel, or even break, posing significant safety risks. Using the workover rig as the power source to reversely pull the seal and pressurize it can damage the wellhead Christmas tree during operation, and wire rope breakage due to high friction is a common occurrence, posing significant safety risks. Furthermore, this seal setting technology is not conducive to repeated seal setting and leak detection operations. Furthermore, there is a risk that pressure cannot be applied, making it easy to mistakenly identify a leak as a pressure drop caused by a leaky packer. Furthermore, the inability to identify multiple leaks can lead to missed leaks, misleading subsequent measures.

[0059] Conventional tubing pressure-set hydraulic packers can cause upward movement of the tubing when used for leak detection in shallow well sections. This leads to poor pressure stability, easily damaging the rubber sleeve, and easily misinterpreting pressure fluctuations caused by upward movement as casing leaks. This conflict has been addressed by innovatively leveraging the hydraulic anchor on the Y521 mechanical packer, leveraging its anchoring function to resolve the issue. This method also empowers the tubing with additional functionality, clearly identifying the number and lower bound of shallow casing leaks, enabling accurate and regular identification of shallow casing leaks and providing a safety feature for leak detection tools.

[0060] In order to solve the problem that the oil and water in the lifting string cannot be leaked into the well after the shallow casing leak detection string is pressurized, and there is a contradiction such as water leakage during lifting and polluting the environment, the oil pump string oil leakage principle is innovatively borrowed, and a split-type plunger pressure relief device is also designed on the string. This avoids the risk of no leakage device on the lifting string, liquid residue in the string, top spraying during lifting and polluting the environment, and incomplete release of the packer and well jamming. It reduces labor intensity, improves the efficiency of the lifting operation, and avoids oil and water falling to the ground and scalding workers and polluting the environment.

[0061] Example 1

[0062] This embodiment includes a No. 1 shallow casing precise leak detection string and a No. 2 shallow casing precise leak detection string, wherein the No. 1 shallow casing precise leak detection string is provided with an oil pipe 3, a guide wire plug 7 is provided at the bottom of the oil pipe 3, a pressure-controlled switch 2 is provided above the guide wire plug 7, and a pressure relief device 5 is provided between the pressure-controlled switch 2 and the guide wire plug 7. A K344 hydraulic packer 4 is provided between the oil pipe above the pressure relief device 5 and the oil pipe below the pressure-controlled switch 2. A Y521 mechanical packer is provided between the oil pipe below the pressure relief device 5 and the oil pipe above the guide wire plug 7. A Y521 mechanical packer is provided between the oil pipe below the pressure relief device 5 and the oil pipe above the guide wire plug 7. A Y521 mechanical packer 6 is provided between the oil pipe below the pressure relief device 5 and the oil pipe above the guide wire plug 7. The K344 hydraulic packer 4 and the Y521 mechanical packer 6 are installed sequentially from top to bottom. The K344 hydraulic packer 4 is vertically positioned below the pressure-controlled switch 2 and above the pressure relief device 5. The Y521 mechanical packer 6 is vertically positioned below the pressure relief device 5 and above the guide wire plug 7. The difference between the No. 2 shallow casing precise leak detection string, the No. 2 shallow casing precise leak detection string, and the No. 1 shallow casing precise leak detection string is that the Y521 mechanical packer 6 and the K344 hydraulic packer 4 are installed sequentially from top to bottom between the tubing 3 and the casing 1. The Y521 mechanical packer 6 is vertically positioned above the pressure-controlled switch 2, and the K344 hydraulic packer 4 is vertically positioned below the pressure relief device 5 and above the guide wire plug 7. The K344 hydraulic packer 4 is reinforced at the compression point between the rubber sleeve and the iron ring, with denser wiring. At the same time, three circumferential sealing rings 42 and one end compression sealing ring 41 are added inside the upper and lower pressure rings of the rubber sleeve.

[0063] Example 2

[0064] When the oil well needs to be leak-checked in shallow casing and the casing leakage situation (whether there are leakage points, the number of leakage points and the specific location) needs to be determined, the No. 1 shallow casing is first run into the precise leak-checking string, the surface pump truck positively pressurizes the oil pipe 3, the K344 hydraulic packer 4 is set, and the hydraulic anchor on the Y521 mechanical packer 6 works to anchor the leak-checking string to prevent the string from moving up and affecting the sealing of the K344 hydraulic packer 4 or damaging the rubber sleeve. The surface pump truck continues to positively pressurize the oil pipe 3. If the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped after the pressure is pressed to 15 MPa, it proves that there are no leaks in the casing above the K344 hydraulic packer 4. A certain length of string is lowered and the confirmation is continued until the K344 hydraulic packer 4 is lowered to above the well section and there are still no leaks.

[0065] If the surface pump truck fails to pressurize the oil pipe 3 at a certain position or fails to maintain the pressure after pumping to 15 MPa and stopping the pump, and there is a leak, it proves that there is a leak in the casing above the K344 hydraulic packer 4. The leak detection position is changed by lifting the leak detection string, and the leak detection position is carried out at the next position until the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped at 15 MPa (the position closest to the leak point is the lower limit of the leak point). After accurately finding the upper limit of the leak point, part of the leak detection string is pulled out, and the position of the pressure control switch 2 is changed. The pressure control switch 2 is replaced between the K344 hydraulic packer 4 and the Y521 mechanical packer 6. Several oil pipes (2-10, specifically according to the distance between the shallow leak point and the upper limit of the oil layer) are set between the Y521 mechanical packer 6 and the pressure control switch 2. 1. Determine the lower limit of the leak point: lower the Y521 mechanical packer to 2-5 meters below the upper limit of the leak point, rotate and lower it to set the seal, and the ground pump truck positively pressurizes from the oil pipe 3, and sets the K344 hydraulic packer 4. Continue positive pressure. If the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped when the pressure reaches 15 MPa, it proves that there is no leak in the casing between the two packers. Lift a certain string and continue positive pressure until the positive pressure cannot be pumped out or the pressure cannot be maintained after the pump is pumped to 15 MPa and the pump is stopped. The position closest to this position (the pressure drop is less than 0.4 MPa 30 minutes after the pressure is pumped to 15 MPa and the pump is stopped) is the lower limit of the leak point.

[0066] ② Determine whether there are multiple leaks: Lower the Y521 mechanical packer 6 to below the lower limit of the leak, rotate it, and set it (the setting depth is 2-10 tubings from the lower limit of the leak). Then, use a surface pump truck to apply positive pressure from tubing 3. Set the K344 hydraulic packer 4. The hydraulic anchor on the Y521 mechanical packer 6 activates, anchoring the leak-finding string to prevent it from moving upward, affecting the seal of the packer or damaging the rubber sleeve. Continue applying positive pressure to tubing 3. If pressure fails to build up, or if the pressure remains stable after stopping at 15 MPa, this indicates a leak in the casing between the two packers. The precise location of the leak can be determined by raising or lowering the string. This allows the precise location of multiple leaks. If the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped after the positive pressure is reached at 15 MPa, it proves that there is no leakage in the casing between the two packers. Lower the string for a certain length and continue to confirm until the K344 hydraulic packer 4 is lowered above the well section. The leakage situation of all casing positions above the completion section is determined.

[0067] Because the bottom is blocked by the guide wire, the water in the leak detection string cannot be quickly discharged into the wellbore. If oil and water are found in the pipe when the pipe is pulled out, a striker rod is inserted from the oil pipe to knock open the copper pin, exposing the drain hole, connecting the oil casing, and the oil and water will be able to completely leak into the well, and the packer will be completely unsealed, solving the problems of incomplete unsealing of the hydraulic packer and liquid residue in the leak detection pipe, reducing labor intensity, improving the efficiency of the pipe pulling operation, and avoiding oil and water falling to the ground to scald workers and pollute the environment.

[0068] The above embodiments are merely examples and illustrations of the present invention and are not intended to limit the present invention to the scope of the described embodiments. Furthermore, it will be understood by those skilled in the art that the present invention is not limited to the above embodiments and that various variations and modifications may be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention.

Claims

1. A method for accurately finding leaks in shallow casing, characterized in that: The following structure of the tubing string is used: No. 1 shallow casing precise leak detection tubing string is provided with an oil pipe (3), a guide wire plug (7) is provided at the bottom of the oil pipe (3), a pressure-controlled switch (2) is provided above the guide wire plug (7), and a pressure relief device (5) is provided between the pressure-controlled switch (2) and the guide wire plug (7); a hydraulic packer (4) is provided between the oil pipe above the pressure relief device (5) and the oil pipe below the pressure-controlled switch (2), and a mechanical packer (6) is provided between the oil pipe below the pressure relief device (5) and the oil pipe above the guide wire plug (7); the hydraulic packer (4) and the mechanical packer (6) are provided in sequence from top to bottom; the vertical position of the hydraulic packer (4) is lower than the pressure-controlled switch (2) and higher than the pressure relief device (5); the vertical position of the mechanical packer (6) is lower than the pressure relief device (5) and higher than the guide wire plug (7); and several oil pipes are provided between the mechanical packer (6) and the pressure-controlled switch (2); The hydraulic packer (4) is a K344 hydraulic packer, and the mechanical packer (6) is a Y521 mechanical packer; The No. 2 shallow casing precise leak detection string is provided with an oil pipe (3), and a mechanical packer (6) and a hydraulic packer (4) are arranged in sequence from top to bottom between the oil pipe (3) and the casing (1); wherein the mechanical packer (6) is vertically positioned higher than the pressure-controlled switch (2), and the hydraulic packer (4) is positioned lower than the pressure relief device (5) and higher than the guide wire plug (7); the hydraulic packer (4) is reinforced at the compression point between the rubber sleeve and the iron ring, and the wiring is encrypted, and a sealing ring (42) and an end compression sealing ring (41) are added in the upper and lower pressure rings of the rubber sleeve; Three circumferential sealing rings (42) are additionally provided in the upper and lower pressure rings of the rubber sleeve; The method comprises the following steps: Step 1: When the oil well needs to be shallow casing leak detection and the casing leakage situation needs to be determined, first lower the No. 1 shallow casing to accurately detect the leak. The ground pump truck positively pressurizes the oil pipe (3). The K344 hydraulic packer (4) is set. The hydraulic anchor on the Y521 mechanical packer (6) works to anchor the leak detection pipe to prevent the pipe from moving up and affecting the sealing of the K344 hydraulic packer (4) or damaging the rubber tube. The ground pump truck continues to positively pressurize the oil pipe (3). If the pressure drop is less than 0.4 MPa 30 minutes after the pump is stopped after the pressure is pressed to 15 MPa, it proves that there is no leak in the casing above the K344 hydraulic packer (4). Lower a certain length of pipe and continue to determine until there is still no leak after the K344 hydraulic packer (4) is lowered to the well section. The specific location and upper limit of the leak point are determined. Step 2: After determining the specific location and upper limit of the shallow casing leak, run the No. 2 shallow casing string to accurately locate the leak; Step 3: Use No. 2 shallow casing to accurately find leaks. After both the double packers of the tubing string are set, determine the lower limit of the leak point and whether there are other leak points above the leak point. If there are leaks, determine the specific locations of multiple leak points.

2. A shallow casing precise leak detection method according to claim 1, characterized in that: There are 2 to 10 oil pipes.

3. A shallow casing precise leak detection method according to claim 1, characterized in that: After determining the specific location and upper limit of the shallow casing leak above 400 meters in step 2, run the No. 2 shallow casing string to accurately locate the leak.

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