A method for loosening drill pipe using the superposition effect of explosions

Abstract

This invention discloses a method for loosening drill pipe threads using the superposition effect of explosions, relating to the field of oil and gas well drilling equipment technology. The invention establishes a finite element model of the drill pipe threaded connection joint to simulate the explosion-induced loosening mechanism of drill pipe under deep and ultra-deep well conditions, thereby determining the structural design of the explosive cartridge, the amount of explosive, the number of explosive charges, the charging position, and the explosion interval. The method for loosening drill pipe threads using the superposition effect of explosions provided by this invention has conducted research on the explosion-induced loosening mechanism under different working conditions in deep and ultra-deep wells, providing theoretical guidance for the selection of explosive charge amount, the determination of explosion position, and operational methods. Through the research of this invention's method, a small amount of explosive is used to generate vibration force in the downhole structure, breaking the inherent frictional torque between the threads, thereby achieving the loosening effect and improving the success rate of drill pipe thread loosening packaging in deep and ultra-deep wells.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well drilling equipment technology, and more particularly to the field of a design for loosening stuck drill pipe in oil and gas wells, and more specifically to a method for loosening drill pipe using the superposition effect of explosion. Background Technology

[0002] As exploration and development deepen, the structure of deep and ultra-deep wells becomes increasingly complex, making some sections prone to leakage and collapse, resulting in a high risk of stuck drill pipe. Types of stuck drill pipe accidents include sticking, collapse, sand bridging, necking, keyway, mud-covered, dry drilling, falling object, and cement-bonded stuck drill pipe. Treatment of stuck drill pipe generally involves circulating and rotating the drill string, moving it up and down, soaking it in brine, or acid baths. Explosive loosening is a technique used when other methods fail to release the stuck drill string, employing explosive vibration to loosen the threads of a drill string coupling above the stuck point.

[0003] Explosive loosening involves lowering a tool equipped with explosives via cable to a position above the jamming point, at the first coupling thread of the drill bit. The drill bit is then pulled up and sufficient counter-torque is applied to the drill bit, making the jamming point a neutral point with sufficient counter-torque. The explosive is then ignited, and the high-speed impact force generated by the explosion violently shakes the threads, instantly eliminating or greatly reducing friction and self-locking properties. This causes the joint threads to loosen under the pre-applied counter-torque, achieving the purpose of loosening and reversing the threads.

[0004] The explosive loosening operation mainly involves the following steps:

[0005] 1) Drill string is tightly fastened;

[0006] 2) Detonate the detonating cord, blast rod, or blast tube;

[0007] 3) Increase tonnage;

[0008] 4) Apply counter-torque and ensure that the counter-torque is delivered to the jamming point;

[0009] 5) Align the center of the explosive rod or explosive tube with the loose coupling and ignite the loose coupling.

[0010] Due to the complexity of deep and ultra-deep wells, existing explosive untangling techniques often suffer from problems such as excessive explosive dosage damaging the drill string or insufficient dosage failing to achieve the desired untangling effect. The study of the mechanism of explosive untangling essentially involves investigating the microscopic response characteristics of threaded connections under explosive impact loads. Under explosive impact loads, most threaded connections are subjected not only to circumferential tensile forces but also to the combined effects of forces and moments in all directions, as well as non-periodic transient forces and the combined effects of plastic deformation failure of the material.

[0011] Due to the special working environment of explosive loosening operations, the mechanism of explosive loosening cannot be reproduced through experiments. At present, most of the exploration of explosive loosening technology is based on operational experience. Summary of the Invention

[0012] To overcome the defects and shortcomings of the existing technology, this invention provides a method for loosening drill pipe threads using the superposition effect of explosions. The purpose of this invention is to address the problem that current exploration of explosive loosening techniques largely relies on operational experience, which can easily lead to problems such as excessive explosive dosage damaging the drill string or insufficient explosive dosage failing to loosen the threads. This invention provides a method for loosening drill pipe threads using the superposition effect of explosions, and has conducted research on the explosive loosening mechanism under different working conditions in deep and ultra-deep wells, providing theoretical guidance for selecting explosive dosage, determining the explosion location, and developing operational methods. Through the research of this invention, a small amount of explosive is used to generate vibration force in the downhole structure, breaking the inherent frictional torque between the threads, thereby achieving the loosening effect and improving the success rate of drill pipe thread loosening in deep and ultra-deep wells.

[0013] To address the problems existing in the prior art, the present invention is achieved through the following technical solution.

[0014] This invention provides a method for loosening drill pipe using the superposition effect of explosions, the method comprising the following steps:

[0015] S1. Establish a finite element model of the drill pipe threaded connection joint, and set the material, elastic modulus, Poisson's ratio, yield strength and ultimate strength parameters of the finite element model;

[0016] S2. Simplify the thread stress of the drill pipe threaded connection joint. One end of the drill pipe is set as a fixed constraint. The preload is applied to the drill pipe threaded connection joint by applying paired tensile forces. It is in a neutral state in the axial direction. Set the friction mode and friction coefficient of the drill pipe threaded connection joint.

[0017] S3. Perform calculations on the established finite element model according to the design conditions. The detonation point of the charge is set at the end of the explosive near the wellhead, which is simplified to instantaneous top detonation.

[0018] S4. Simulate and calculate the thread response state under well depth conditions of 5000m-7000m. Set different preset charge amount, charge number, charge position and explosion interval respectively, calculate and record the thread response state under different charge amount, charge number, charge position and explosion interval.

[0019] S5. Based on the thread response state obtained in step S4, determine the required charge quantity, number of charges, charge position, and explosion interval, and design the explosion tube structure according to the determined charge quantity, number of charges, charge position, and explosion interval.

[0020] In a further preferred embodiment, in step S4, the preset charge amount is 230g-300g, the number of charges is 2-5, the charge position is either unilateral or centered, and the explosion interval is 5μs-60μs.

[0021] More preferably, the charge position is unilateral charge, the number of charges is 3, the explosion interval is 50μs, the total charge amount is 230g after the well depth exceeds 6000m, and the total charge amount is ≤250g after the well depth exceeds 6500m.

[0022] More preferably, the thread response state refers to the displacement oscillation of the thread node in the X direction of the drill pipe threaded connection joint under simulated explosive impact.

[0023] In a further preferred embodiment, in step S5, after the designed explosive cylinder is lowered to the bottom of the well, it is positioned at the upper end of the drill pipe thread using depth calibration. It is then ignited using electric ignition, relying on multiple explosive cakes to provide the explosive power source, and using a 50μs gunpowder delay device to achieve the timing interval of the explosion.

[0024] More preferably, the explosive tube structure includes an explosive tube body, and three explosive cakes are arranged inside the explosive tube at intervals from top to bottom, with adjacent explosive cakes connected by a gunpowder delay device.

[0025] More preferably, in step S1, the finite element model of the drill pipe threaded connector is the finite element model of the NC40 threaded connector.

[0026] Furthermore, in the finite element model of the NC40 threaded connector, the model is made of special steel with an elastic modulus of 206 GPa and a Poisson's ratio of [missing value]. Yield limit of materials MPa, ultimate tensile strength MPa.

[0027] Furthermore, in the finite element model of the NC40 threaded connector, the material model adopts an ideal elastic-plastic model.

[0028] In a further preferred embodiment, in step S2, the friction mode of the drill pipe threaded connection joint is set to sliding friction, with a friction coefficient of 0.17.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0030] 1. This invention has carried out research on the explosive loosening mechanism under different working conditions of ultra-deep wells, and provided theoretical guidance for the selection of explosive loosening charge, the determination of explosion location and operation method.

[0031] 2. By using small-yield explosives to generate vibration in the downhole structure, the inherent frictional torque between the threads is broken, thereby achieving the loosening effect and improving the success rate of explosive loosening of drill pipes in deep and ultra-deep wells. Attached Figure Description

[0032] Figure 1 This invention provides an explosion cylinder structure suitable for NC40 threaded connectors.

[0033] Figure 2 The X-direction displacement and oscillation of the threaded node of the drill pipe threaded connection joint under the impact of a centrally loaded explosive charge.

[0034] Figure 3 The X-direction displacement oscillation of the thread node of the drill pipe threaded connection joint under the impact of a single-sided explosion of 3 charges with a time interval of 10μs;

[0035] Figure 4 The X-direction displacement oscillation of the thread node of the drill pipe threaded connection joint under the impact of a single-sided explosion with a 50μs time interval between three explosive charges;

[0036] Reference numerals: 1. Explosion tube; 2. Explosive cake; 3. Gunpowder delay device. Detailed Implementation

[0037] The following are exemplary embodiments of the invention as defined by the claims and their equivalents, taken in conjunction with the accompanying drawings, to aid in a comprehensive understanding. The specific details described herein are to be considered exemplary only and not to limit the scope of the invention. Therefore, those skilled in the art can make various changes and modifications to the embodiments without departing from the scope and spirit of the invention.

[0038] Example 1

[0039] As a preferred embodiment of the present invention, this embodiment discloses a method for loosening drill pipe using the superposition effect of explosions, the method comprising the following steps:

[0040] S1. Establish a finite element model of the drill pipe threaded connection joint, and set the material, elastic modulus, Poisson's ratio, yield strength and ultimate strength parameters of the finite element model;

[0041] S2. Simplify the thread stress of the drill pipe threaded connection joint. One end of the drill pipe is set as a fixed constraint. The preload is applied to the drill pipe threaded connection joint by applying paired tensile forces. It is in a neutral state in the axial direction. Set the friction mode and friction coefficient of the drill pipe threaded connection joint.

[0042] S3. Perform calculations on the established finite element model according to the design conditions. The detonation point of the charge is set at the end of the explosive near the wellhead, which is simplified to instantaneous top detonation.

[0043] S4. Simulate and calculate the thread response state under well depth conditions of 5000m-7000m. Set different preset charge amount, charge number, charge position and explosion interval respectively, calculate and record the thread response state under different charge amount, charge number, charge position and explosion interval.

[0044] S5. Based on the thread response state obtained in step S4, determine the required charge quantity, number of charges, charge position, and explosion interval, and design the explosion tube structure according to the determined charge quantity, number of charges, charge position, and explosion interval.

[0045] Example 2

[0046] As another preferred embodiment of the present invention, this embodiment is a further detailed supplement and explanation of the technical solution of the present invention based on the above embodiment 1. In this embodiment, in step S4, the preset loading amount of explosive is 230g-300g, the number of explosive charges is 2-5, the loading position is unilateral loading or central loading, and the detonation interval is 5μs-60μs.

[0047] In this embodiment, the finite element model of the drill pipe threaded connector is the finite element model of an NC40 threaded connector. In the finite element model of the NC40 threaded connector, a special steel material is used, with an elastic modulus of 206 GPa and a Poisson's ratio of... Yield limit of materials MPa, ultimate tensile strength MPa. In the finite element model of the NC40 threaded connector, the material model adopts an ideal elastic-plastic model. The friction mode of the drill pipe threaded connection is set as sliding friction, and the friction coefficient is 0.17.

[0048] After simulation, it was finally determined that for the NC40 threaded connector, the preferred charging position is single-sided charging, the number of charges is 3, the explosion interval is 50μs, the total charge is 230g when the well depth exceeds 6000m, and the total charge is ≤250g when the well depth exceeds 6500m.

[0049] The thread response state refers to the displacement oscillation of the thread node in the X direction of the drill pipe threaded connection joint under simulated explosive impact. In the simulation, after the designed explosive cylinder is lowered to the bottom of the well, it is positioned at the upper end of the drill pipe thread for depth calibration. It is then ignited using electric ignition, relying on multiple explosive cakes to provide the explosive power source, and using a 50μs gunpowder delay device to achieve the timing interval of the explosion.

[0050] Example 3

[0051] As another preferred embodiment of the present invention, this embodiment takes an NC40 threaded connector as an example, establishes a finite element model for the NC40 threaded connector, and simulates the drill pipe loosening due to the explosion superposition effect. The simulation process of this embodiment is as follows:

[0052] S1. Establish a finite element model of the NC40 threaded connection, assigning a special steel material to the NC40 joint. The elastic modulus of the joint material is 206 GPa, and the Poisson's ratio is... 0.29, the yield strength of the material MPa, ultimate tensile strength MPa, the material model adopts an ideal elastic-plastic model;

[0053] S2. Simplify thread stress: One end of the drill pipe is set as a fixed constraint, and a preload is applied to the threaded joint by applying paired tensile forces. Axially, it is in a neutral state, neither subjected to compressive nor tensile loads. For the joint contact, sliding friction contact is set, with a friction coefficient of 0.17.

[0054] S3. Perform calculations on the model according to the design conditions. The detonation point of the explosive is set at the end of the explosive near the wellhead, which is simplified to instantaneous top detonation.

[0055] S4. Simulate and calculate the thread response state under well depth conditions of 5000m to 7000m, with a preset charge of 230g to 300g. The maximum displacement of the transverse and longitudinal thread nodes on one side (explosion interval 50 microseconds) is 0.06mm. The entire cycle basically shows an oscillating trend, with a cycle of 50 microseconds between peaks and troughs. Figure 2 The displacement in the X direction of the transverse and longitudinal thread nodes of a single-sided 3-charge explosive charge (explosion interval 10 microseconds) is a maximum displacement of 0.05mm. The entire cycle exhibits a generally oscillating trend, with cycles between peaks and troughs that appear to have a period significantly longer than the 50-microsecond explosion interval. Figure 3 The maximum displacement in the Y direction of the centrally located charge thread nodes (both transverse and longitudinal) is 0.03 mm. The entire cycle exhibits a generally stable oscillation. Figure 4 .

[0056] S5. Under the calculated operating conditions, with a 290g-300g charge, due to the large charge volume and short operating distance, the thread strain is close to the failure value, and there is a risk of plastic deformation of the thread caused by the explosion. This situation may actually make loosening the thread more difficult. This situation occurs under the calculated conditions for 290g-300g charges, and the greater the well depth, the higher the residual strain of the thread and the higher the failure risk. This phenomenon is primarily considered to be caused by the superposition of static pressure response at deeper wells.

[0057] S6. After the calculation, although the oscillation of the strain response is consistent with that under loosening conditions, it can be observed that the strain oscillation curve does not dissipate over time, and the oscillation midline still revolves around the initial strain, with only a slight decrease; this situation occurs when the well depth exceeds 6000m and the loosening charge is 230g; and when the well depth exceeds 6500m and the charge is less than or equal to 250g.

[0058] S7. From the simulation results of the explosive loosening mechanism, the explosive loosening mechanism is based on the application of a small amount of explosive to generate vibration force in the downhole structure, thereby breaking the inherent friction torque between the threads and achieving the loosening effect.

[0059] S8. Calculations show that while the energy released by a loosening explosion may not always be sufficient to loosen the thread, it is enough to cause relative vibration at the threaded connection surface. Based on the mass-spring theory, if the explosion is applied at multiple points, with a reduced explosive charge, increased distance between explosives, and a longer detonation time interval, the stress wave generated by the explosion can be transmitted along the drill pipe structure to the joint interface. This results in multiple superimposed explosion vibration excitations on the strain curve of the threaded contact surface. This excitation accelerates the dissipation of the strain curve, increasing the irregularity of vibration at the contact surface and thus improving the success rate of explosive loosening.

[0060] S9. The simulation results show that reducing the amount of explosive and lengthening the explosion time and distance interval can effectively utilize the explosion superposition effect and achieve a better explosion loosening effect in deep and ultra-deep well operations.

[0061] S10. Design of explosive loose-charge structure, such as... Figure 1 As shown in the diagram, 1 is the explosive cartridge, 2 is the high-explosive cake, and 3 is the 50μs gunpowder delay device. After the explosive uncoupling device is lowered to the bottom of the well, it is positioned at the upper end of the drill pipe thread using depth calibration. It is then ignited electrically, relying on multiple high-explosive cakes to provide the explosive power source, and the 50μs gunpowder delay device to achieve the timing interval of the explosions. The resulting impact vibration acts on the drill pipe thread to be uncoupled, achieving the uncoupling effect.

[0062] Although the inventive concept has been specifically shown and described with reference to exemplary embodiments thereof, those skilled in the art should understand that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A method for loosening drill pipe threads using the superposition effect of explosions, characterized in that: The method includes the following steps: S1. Establish a finite element model of the drill pipe threaded connection joint, and set the material, elastic modulus, Poisson's ratio, yield strength and ultimate strength parameters of the finite element model; S2. Simplify the thread stress of the drill pipe threaded connection joint. One end of the drill pipe is set as a fixed constraint. The preload is applied to the drill pipe threaded connection joint by applying paired tensile forces. It is in a neutral state in the axial direction. Set the friction mode and friction coefficient of the drill pipe threaded connection joint. S3. Perform calculations on the established finite element model according to the design conditions. The detonation point of the charge is set at the end of the explosive near the wellhead, which is simplified to instantaneous top detonation. S4. Simulate and calculate the thread response state under well depth conditions of 5000m-7000m. Set different preset charge amount, charge number, charge position and explosion interval respectively, calculate and record the thread response state under different charge amount, charge number, charge position and explosion interval. S5. Based on the thread response state obtained in step S4, determine the required charge quantity, number of charges, charge position, and explosion interval, and design the explosion tube structure according to the determined charge quantity, number of charges, charge position, and explosion interval.

2. The method for loosening drill pipe using the superposition effect of explosion as described in claim 1, characterized in that: In step S4, the preset charge amount is 230g-300g, the number of charges is 2-5, the charge position is either unilateral or centered, and the detonation interval is 5μs-60μs.

3. A method for loosening drill pipe using the superposition effect of explosions as described in claim 1 or 2, characterized in that: The explosive charge is applied from one side only, with 3 charges and an explosion interval of 50 μs. The total explosive charge is 230 g for wells deeper than 6000 m and ≤250 g for wells deeper than 6500 m.

4. The method for loosening drill pipe using the superposition effect of explosion as described in claim 1, characterized in that: The thread response state refers to the displacement oscillation of the thread node in the X direction of the drill pipe threaded connection joint under simulated explosive impact.

5. A method for loosening drill pipe using the superposition effect of explosions as described in claim 1, 2, or 4, characterized in that: In step S5, after the designed explosive cylinder is lowered to the bottom of the well, it is positioned at the upper end of the drill pipe thread and activated by electric ignition. The explosion power source is provided by multiple explosive cakes, and the timing interval of the explosion is achieved by a 50μs gunpowder delay device.

6. A method for loosening drill pipe using the superposition effect of explosions as described in claim 1, 2, or 4, characterized in that: The explosive tube structure includes an explosive tube body, inside which three explosive cakes are arranged at intervals from top to bottom, and adjacent explosive cakes are connected by a gunpowder delay device.

7. A method for loosening drill pipe using the superposition effect of explosions as described in claim 1, 2, or 4, characterized in that: In step S1, the finite element model of the drill pipe threaded connector is established as the finite element model of the NC40 threaded connector.

8. The method for loosening drill pipe using the superposition effect of explosion as described in claim 7, characterized in that: In the finite element model of the NC40 threaded connector, the model is assigned a special steel material with an elastic modulus of 206 GPa and a Poisson's ratio of... Yield limit of materials MPa, ultimate tensile strength MPa.

9. A method for loosening drill pipe using the superposition effect of explosion as described in claim 8, characterized in that: In the finite element model of the NC40 threaded connector, the material model adopts an ideal elastic-plastic model.

10. A method for loosening drill pipe using the superposition effect of explosions as described in claim 9, characterized in that: In step S2, the friction mode of the drill pipe threaded connection joint is set to sliding friction, and the friction coefficient is 0.17.

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