Safety evaluation method for detonation loosening of oil and gas well

Abstract

The invention discloses a safety evaluation method for detonation loosening of an oil and gas well. The method comprises the steps that firstly, the working conditions of a stuck drill rod and a to-be-loosened joint thread are obtained; secondly, respectively establishing geometric models of a clamped drill rod and a to-be-loosened joint thread and a plurality of clamped drill rod-to-be-loosened joint thread-fluid domain geometric models of different gunpowder amounts; then, the loaded state of the clamped drill rod and the to-be-loosened joint thread before loosening is determined through simulation analysis; then, by taking the simulation result as an input condition, detonation loads are applied to different gunpowder amount models for simulation; evaluating the connection performance and the mechanical performance of the joint thread after gunpowder explosion based on a simulation analysis result; and finally, judging whether the thread of the joint is safely loosened under different gunpowder amounts, and determining the gunpowder amount required for loosening. The method is used for solving the problem that in the prior art, the deep well detonation loosening gunpowder amount is difficult to accurately select, and the purposes of improving the deep well loosening success rate, reducing the jam releasing cost and guaranteeing the structural integrity of a tubular column are achieved.

Description

Technical Field

[0001] The present invention relates to the field of stuck pipe release technology for oil and gas wells, and particularly to a safety evaluation method for detonation and back-off in oil and gas wells. Background Art

[0002] With the advancement of oil and gas exploration and development towards deep formations, the wellbore structures of deep wells and ultra-deep wells are becoming increasingly complex. Problems such as drilling fluid loss and wellbore collapse are likely to occur in some well sections, resulting in a significant increase in the risk of stuck pipe. Stuck pipe accidents can not only trigger major safety accidents but also cause serious economic losses. Currently, the explosion back-off technology is a commonly used method for dealing with stuck pipe accidents. Its principle is to lower special explosives to the first drill tool joint thread above the stuck point, and utilize the high-speed impact generated instantaneously by the explosion of the explosives to instantaneously weaken or eliminate the frictional force and self-locking effect between the threads. Then, under the action of a pre-applied reverse torque, the threads are loosened, and finally the purpose of back-off and stuck pipe release is achieved.

[0003] However, due to the complex and variable stress states of downhole drill tools, under stuck pipe conditions, specific positions of the drill tools are subject to the combined action of various factors such as formation adhesion and wellbore collapse. Coupled with the particularity of the explosion back-off operation environment, its action mechanism is difficult to reproduce through laboratory simulation. Currently, in on-site operations, the amount of explosives used is mainly estimated based on parameters such as the stuck point depth, drilling fluid density, and drill pipe specifications, combined with the experience of construction personnel. This approach often has the following problems: If the torque transmission is insufficient or the amount of explosives is too low, the first back-off may fail and multiple operations may be required; conversely, if the amount of explosives is too high, the pipe string may burst, not only significantly weakening the strength of the pipe string but also causing difficulties for subsequent fishing operations. Therefore, to achieve the safe and effective implementation of the explosion back-off process, it is necessary to accurately determine the amount of gunpowder and establish a safety assessment system for thread back-off, while ensuring the reliable separation of the joints and maximizing the maintenance of the integrity of the pipe string structure, which has a crucial guiding role in process optimization. Summary of the Invention

[0004] The present invention provides a safety evaluation method for detonation and back-off in oil and gas wells to solve the problems in the prior art that the determination of the amount of gunpowder is inaccurate due to relying on work experience and the success rate of operations in deep wells over 5000m drops sharply. By combining mechanical analysis, simulation, and safety assessment of thread back-off, the downhole back-off environment is reproduced to the greatest extent. While accurately calculating the amount of gunpowder, a safety evaluation criterion for thread back-off is established, so as to achieve the purpose of improving the success rate of back-off in deep wells, reducing the cost of stuck pipe release, and ensuring the integrity of the pipe string structure.

[0005] The present invention is realized through the following technical solutions:

[0006] A safety evaluation method for detonation and back-off in oil and gas wells includes:

[0007] Step S1: Obtain the working conditions of the stuck drill pipe and the thread of the joint to be released, where the thread of the joint to be released is the thread of the first joint above the stuck point; the working conditions include the depth of the stuck point, the density of the drilling fluid, the dimensions and steel grades of the drill pipe and the joint thread.

[0008] Step S2: Respectively establish the geometric models of the stuck drill pipe and the thread of the joint to be released, and the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder.

[0009] Step S3: Determine the loaded state of the stuck drill pipe and the thread of the joint to be released before releasing, and conduct a simulation analysis on the geometric models of the stuck drill pipe and the thread of the joint to be released.

[0010] Step S4: Using the simulation analysis results of the stuck drill pipe and the thread of the joint to be released as input conditions, conduct a simulation analysis on the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder under the detonation release load.

[0011] Step S5: Based on the simulation analysis results under the detonation release load, evaluate the connection performance and mechanical properties of the joint thread after the gunpowder explosion.

[0012] Step S6: Judge whether the joint thread can be safely released with different amounts of gunpowder, and determine the amount of gunpowder required for release.

[0013] Aiming at the problem that the amount of gunpowder required for detonation un-sticking of oil and gas wells in the prior art is inaccurate, the present invention first proposes a safety evaluation method for detonation release of oil and gas wells. This method first obtains the working conditions of the stuck drill pipe and the thread of the joint to be released, including the depth of the stuck point, the density of the drilling fluid, the dimensions and steel grades of the drill pipe and the joint thread; then respectively establish the geometric models of the stuck drill pipe and the thread of the joint to be released, and the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder; then determine the loaded state of the stuck drill pipe and the thread of the joint to be released before releasing, and conduct a simulation analysis on the geometric models of the stuck drill pipe and the thread of the joint to be released; then using the simulation analysis results of the stuck drill pipe and the thread of the joint to be released as input conditions, conduct a simulation analysis on the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder under the detonation release load; then based on the simulation analysis results under the detonation release load, evaluate the connection performance and mechanical properties of the joint thread after the gunpowder explosion; finally judge whether the joint thread can be safely released with different amounts of gunpowder, and determine the amount of gunpowder required for release.

[0014] During the research process, the inventors of this case found that the amount of explosive required for explosive back-off depends on work experience, such as the relationship table between drill pipe size and the amount of gunpowder. Moreover, when the well depth exceeds 5000m, the selection of the amount of gunpowder for back-off operation based on experience significantly decreases. Therefore, this application adopts a form that combines experience and simulation, considering the influence of the drill pipe and its joints during stuck pipe in the complex downhole environment, and restores the mechanism of explosive back-off from a mechanical perspective, overcoming the deficiencies of existing deep well back-off technologies, in order to accurately determine the safe back-off gunpowder amount and reduce the cost of fishing operations.

[0015] In addition, the safe back-off gunpowder amount obtained by this method is the result of joint analysis and optimization based on actual work experience, combined with explosive dynamics and fluid-structure interaction simulation, and is also applicable to the fishing operations of other oil and gas well strings, such as casing and tubing.

[0016] Furthermore, the method for obtaining the working conditions of the stuck drill pipe and the threads of the joint to be back-off includes:

[0017] The depth of the stuck point of the drill pipe is preliminarily determined by the following formula:

[0018]

[0019] Where: L is the preliminarily determined depth of the stuck point of the drill pipe; W is the unit mass of the drill pipe and its joints; E is the average elongation when lifting the drill string; P2 - P1 is the average pressure difference when lifting the drill string.

[0020] Based on the preliminarily determined depth of the stuck point, use a pipe caliper to measure the exact position of the stuck point.

[0021] Determine the density of the drilling fluid at the stuck point according to the wellsite drilling log.

[0022] Determine the thread size and steel grade of the drill pipe and the joint to be back-off according to the wellbore structure data during drilling.

[0023] In this solution, accurately obtaining working condition information such as the depth of the stuck point of the drill pipe, the density of the drilling fluid, the thread size and steel grade of the drill pipe and the joint is the basic guarantee for fishing; the depth of the stuck point directly affects the explosive layout position and energy requirement. After roughly calculating the stuck point position, and then obtaining the exact stuck point through the pipe caliper process, the initiation point position and the shock wave action range of explosive back-off can be designed specifically, avoiding damage to the drill string in non-stuck sections caused by ineffective energy release; the density of the drilling fluid is used to set the fluid boundary conditions and will affect the shock wave propagation characteristics; while the thread size and steel grade parameters are used to define the mechanical properties of the material and the contact surface and the initial amount of explosive.

[0024] Furthermore, the method for establishing the geometric model of the stuck drill pipe and the threads of the joint to be back-off includes:

[0025] Take the actual size of the drill pipe with the wall thickness and radial dimension of the drill pipe at the stuck point. The male and female thread models of the joint to be released should be consistent with the wellbore structure.

[0026] Axially divide the model into upper and lower parts:

[0027] The first part is the fixed end, including the stuck drill pipe at the lower end to the thread joint to be released, and its length is the actual length measured by the pipe caliper.

[0028] The second part is the free end, including the thread joint to be released to the upper drill pipe connected to the stuck drill pipe, and its length is twice the total length of the joint.

[0029] The inventor of this case found during the research that when modeling, using the actual length measured by the pipe caliper for the fixed end can accurately reproduce the distance from the stuck point to the thread area of the joint, ensuring the accurate calculation of the explosion load attenuation stage, and the actual thread parameters can characterize the contact characteristics and force behavior of the thread surface and shoulder surface; the length of the free end part should not be too long. The overall length greater than twice the joint can simulate the propagation process of the explosion load at the joint, while avoiding calculation deviations caused by boundary effects. If the length is set too long, it will increase the calculation time cost; a free section of drill pipe with sufficient length can effectively calculate the dynamic impact of the explosion load on thread loosening.

[0030] Furthermore, the method for establishing geometric models of stuck drill pipes - thread joints to be released - fluid domains with several different powder amounts includes:

[0031] Based on the geometric models of the stuck drill pipe and the thread joint to be released, add gunpowder and the drilling fluid domain to obtain the geometric model of the stuck drill pipe - thread joint to be released - fluid domain;

[0032] The gunpowder is equivalent to an explosion cylinder during modeling, and the middle of the explosion cylinder needs to be aligned with the thread to be released;

[0033] The length l of the gunpowder is obtained according to the following formula:

[0034]

[0035] In the formula: m is the gunpowder amount; ρ1 is the gunpowder charge density; R is the outer diameter of the explosion cylinder; r is the inner diameter of the explosion cylinder;

[0036] Calculate the gunpowder size according to different gunpowder amounts to determine geometric models of stuck drill pipes - thread joints to be released - fluid domains with several different gunpowder amounts;

[0037] The fluid domain of the drilling fluid is a cylindrical fluid domain, and the diameter of the cylindrical fluid domain is greater than the maximum outer diameter of the drill pipe.

[0038] In this scheme, considering that the charge form commonly used in explosive loosening operations is detonating cord explosive rods or explosive tubes, the gunpowder is equivalent to a cylindrical structure and aligned with the axial direction of the thread to be loosened, which can ensure the radial propagation symmetry of the explosion shock wave and reduce the stress distribution deviation caused by geometric eccentricity. Aligning the center axis of the cylinder with the threaded joint can maximize the efficiency of transferring the impact energy to the thread pair;

[0039] During the design, the explosive amount m is first roughly selected according to operating experience based on information such as well depth, drilling fluid density, and drill tool size. Then, the gunpowder gradient is set based on the m value. The length of the explosive tube is calculated according to different gunpowder amounts, and a comparison model group of multiple drill pipes and their joints thread-fluid domains is established to facilitate the selection of the best gunpowder amount for loosening the thread. The diameter of the fluid domain is larger than the outer diameter of the drill pipe, which can simulate the damping effect of the drilling fluid on the shock wave and avoid the superposition distortion of the pressure wave caused by wall reflection.

[0040] Further, the method for determining the load state of the stuck drill pipe and the thread of the joint to be loosened before loosening includes:

[0041] When stuck, the end face of the lower drill pipe is completely constrained in radial and axial directions; the end face of the upper connecting drill pipe is free;

[0042] The hydrostatic pressure P generated by the drilling fluid and other downhole fluids inside and outside the drill pipe is calculated by the following formula:

[0043] P=ρ2gh

[0044] Where: ρ2 is the density of downhole fluid such as drilling fluid; g is the acceleration of gravity; h is the depth of the well where the drill pipe is located;

[0045] The thread of the joint to be loosened is subjected to a tightening torque load in the radial direction and is at a neutral point in the axial direction. The neutral point is not subjected to either an upward lifting force or a suspension force.

[0046] In this scheme, it is necessary to conduct load analysis on the stuck drill pipe and the joint to be loosened. The drill pipe is completely "stuck" at the stuck point and cannot move radially and axially, while the upper connected drill pipe is free. The drill pipe is subjected to loads such as hydrostatic pressure generated by downhole fluids such as drilling fluid, which acts on the inner and outer surfaces of the drill pipe, and the size is calculated according to the hydrostatic pressure formula.

[0047] In addition, during on-site operations, the drill tool will be lifted to keep the loose joint threads in a neutral state, that is, neither tensile nor compressive in the axial direction, to facilitate the application of tightening torque; the purpose of tightening is to make the various threaded connection parts of the drill tool evenly stressed and achieve a sufficient degree of tightening, thereby preventing the drill tool from loosening due to the action of counter-torque when counter-torque is applied.

[0048] Furthermore, the method for simulating and analyzing the thread geometry model of the stuck drill pipe and the joint to be loosened includes:

[0049] Determine the drill pipe material properties according to the steel grade;

[0050] Perform geometric cleaning and divide the two-dimensional quadrilateral mesh of the thread surface;

[0051] Map from the thread surface to the non-thread drill pipe body to divide the three-dimensional hexahedron mesh, ensuring that the male and female thread meshes share nodes; and the mesh of the thread part is encrypted;

[0052] Create contact pairs for the joint shoulder surface and the thread meshing surface, set the contact type as surface-to-surface contact, use the penalty function method for tangential contact, and set the normal contact as hard contact;

[0053] Set coupling points on the non-thread end face of the upper drill pipe and apply the make-up torque at the coupling points;

[0054] Set coupling points on the non-thread end face of the stuck drill pipe in the lower part and apply fixed constraints at the coupling points;

[0055] Apply the hydrostatic pressure generated by the drilling fluid both inside and outside the drill pipe;

[0056] According to the simulation analysis results, analyze the connection performance and mechanical properties of the joint thread before unscrewing.

[0057] In this solution, the drill pipe material is an elastoplastic material. By simulating and quantifying the non-linear contact behavior and stress distribution law of the thread meshing surface during sticking, using the refined surface-to-surface contact algorithm for contact, and setting the coupling point loading mechanism to achieve the engineering equivalence of the make-up torque and the contact pressure of the sealing surface, the magnitude of the make-up torque is the optimal make-up torque value provided by the drill pipe manufacturer.

[0058] Furthermore, the methods for analyzing the connection performance and mechanical properties of the joint thread before unscrewing include:

[0059] Extract the stress characteristics and contact characteristics of the stuck drill pipe and the joint thread to be unscrewed under the make-up torque and hydrostatic pressure;

[0060] Including stress extremes, distribution laws, and the interference amount of the shoulder surface, and the interference amount is the axial displacement value of the shoulder surface.

[0061] Those skilled in the art should understand that the drill pipe joint is not only the most vulnerable part to failure in the drill pipe but also the unscrewing point. The design structure of the joint includes a male joint and a female joint. The joint includes thread teeth, a main shoulder, and a pipe body. The male joint and the female joint form an integral drill pipe joint through spiral meshing; during the make-up process of the drill pipe joint, the shoulder surface comes into contact under the action of the make-up torque, generating a certain displacement and initial contact pressure on the shoulder surface to ensure the sealing performance and connection strength of the drill pipe joint during downhole operations; when the drill pipe joint is stressed, the shoulder surface can share the load on the thread teeth, change the deformation coordination relationship of the thread teeth, and reduce the peak stress on the thread teeth.

[0062] Furthermore, the method for performing simulation analysis under the detonation loosening load includes:

[0063] Performing explicit dynamics simulation analysis using the fluid-structure interaction method;

[0064] Based on the simulation analysis results of the stuck drill pipe and the threads of the joint to be loosened, use them as the input conditions for the explicit dynamics finite element analysis of detonation loosening. The mesh type of the drill pipe is Lagrangian element;

[0065] Meshing the fluid domain with gunpowder. The mesh type of the fluid domain is Eulerian element;

[0066] The ignition time of the gunpowder is 0 s, and the ignition point is set at the top of the gunpowder;

[0067] Performing finite element simulation on models with several different amounts of gunpowder.

[0068] This solution uses Lagrangian elements to describe structural deformation, and Eulerian elements are used for gunpowder and the fluid domain to simulate the explosion product flow field. The movement of the two types of meshes is coordinated through the fluid-structure interaction method combined with the Lagrangian-Eulerian hybrid algorithm, which can not only reflect the details of drill pipe vibration but also avoid the mesh distortion problem caused by large explosion deformations. Setting the ignition point at the top of the gunpowder can characterize the evolution law of the detonation wave propagating along the axis and reveal the impact of the impact load on the connection interface;

[0069] The inventor of this case found during the research process that the first simulation is the state of the stuck drill pipe and the threads of the joint to be loosened when stuck, analyzing the connection performance and mechanical properties before the joint threads are loosened; the second simulation is the simulation of the explosive load, analyzing the state of the joint threads during detonation loosening; through two modeling-simulation analyses instead of one modeling-multiple step analyses, the problem that the fluid domain does not participate in the simulation during the first simulation is avoided, thus greatly improving the calculation efficiency, improving the convergence and accuracy of the model, and saving the computing power cost.

[0070] Furthermore, the method for evaluating the connection performance and mechanical properties of the joint threads after gunpowder explosion includes:

[0071] Based on the simulation analysis results under the detonation loosening load, extract the displacement-time curve of the shoulder surface of the joint threads, the circumferential path contact stress of the shoulder surface, and the maximum value of the drill pipe stress for several different amounts of gunpowder;

[0072] Analyze the changes in the mechanical properties and connection performance of the joint threads after gunpowder explosion.

[0073] In this solution, the unscrewing behavior is revealed by the dynamic displacement of the shoulder surface, and the amount of explosive for unscrewing is verified by combining the contact stress distribution. Finally, the structural safety is determined by the stress extreme value, forming an evaluation system from vibration response, separation verification, and strength check. Its value lies in establishing a quantitative relationship among the amount of gunpowder - unscrewing effect - damage risk, providing a basis for controlling the detonation energy and determining the safe unscrewing amount of gunpowder.

[0074] Furthermore, the method for judging whether the joint thread is safely unscrewed under different amounts of gunpowder includes:

[0075] S601. If, after the gunpowder explodes, the displacement of the shoulder surface of the joint thread oscillates gradually with time, and the contact stress along the circumferential path of the shoulder surface decreases, it is determined that the explosion causes the joint thread to vibrate and the shoulder surface of the threaded joint begins to separate, and the joint thread is loose under this amount of gunpowder.

[0076] S602. If, after the gunpowder explodes, the joint thread becomes loose, the displacement of the shoulder surface of the joint thread oscillates and decays gradually with time, lower than the displacement value at 0 s, and the contact stress along the circumferential path of the shoulder surface drops to zero, it is determined that the shoulder surface of the threaded joint is completely separated and the joint thread is fully unscrewed under this amount of gunpowder.

[0077] S603. If, after the gunpowder explodes, the joint thread is fully unscrewed and the maximum stress is lower than the material yield limit, it is determined that the joint thread is safely unscrewed under this amount of gunpowder.

[0078] S604. If multiple amounts of gunpowder all meet the requirements for the safe unscrewing of the joint thread, the minimum amount of gunpowder is taken as the final safe unscrewing amount of gunpowder.

[0079] In this solution, by comparing the simulation results of different amounts of gunpowder, the nonlinear problem related to thread unscrewing can be quantitatively evaluated, avoiding the risk of thread damage or pipe body rupture caused by overload shock while ensuring effective unscrewing. This method breaks through the limitations of traditional experience in transient shock problems through multi-scale dynamic response analysis, and establishes a safe unscrewing criterion and the selection of the amount of gunpowder based on the displacement-stress coupling response:

[0080] Vibration response, confirming that the vibration generated by the explosion shock wave destroys the self-locking mechanism of the thread;

[0081] Separation verification, proving that the contact stress and contact displacement being cleared to zero indicate that the pre-tightening force disappears and the contact surface separates;

[0082] Strength check, ensuring the structural integrity and avoiding overload damage;

[0083] Determine the amount of gunpowder: The selection of the amount of gunpowder can reach the minimum value that meets the requirements for safe unscrewing;

[0084] Thus, the dynamic balance between the unlocking effect and structural safety is achieved, providing a scientific quantitative index for the precise regulation of the powder amount and strong support for the design of detonation pipe sticking release process parameters and structural safety assessment under downhole complex working conditions.

[0085] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0086] 1. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, through explicit dynamic finite element simulation, combining the fluid-structure interaction algorithm and the Lagrangian-Eulerian hybrid grid technology, the whole process analysis of the thread from the static loading state to the transient detonation impact is realized, breaking through the limitation that the on-site pipe sticking release operation only relies on traditional working experience.

[0087] 2. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, based on different powder amounts, the non-linear response relationship between the explosion shock load and thread loosening is established, and the critical unlocking powder amount interval can be quantitatively evaluated. While ensuring the safe separation of the thread, the risk of pipe body damage is avoided, the success rate of one-time pipe sticking release is improved, and the operation cost is significantly saved.

[0088] 3. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, through the pipe sticking measurement process, the pipe sticking point depth and drilling fluid pressure parameters are accurately obtained. Combining the measures of geometric symmetry modeling of the explosion cylinder and quantification of the explosion load, it is ensured that the fluid domain boundary conditions are highly consistent with the downhole working conditions, and the engineering credibility is improved.

[0089] 4. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, the surface-to-surface contact algorithm and friction coefficient are adopted, fully considering the non-linear contact characteristics of the thread meshing surface. Combining the coupling point loading mechanism, the equivalent transfer of the make-up torque and sealing pressure is realized, ensuring the simulation accuracy of the thread unlocking under the impact load.

[0090] 5. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, based on the non-linear mechanics of thread connection and explosion dynamics, combining the thread displacement-stress response to establish an unlocking criterion, the dynamic balance between the unlocking effect and structural safety is achieved, providing strong support for the design of detonation pipe sticking release process parameters and structural safety assessment under downhole complex working conditions.

[0091] 6. For a safety evaluation method for detonation unlocking of oil and gas wells in the present invention, it can be migrated to different pipe sticking release scenarios such as casing and tubing, providing scientific support for efficient and safe pipe sticking release under complex well conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0093] Figure 1Schematic diagram of the specific embodiment of the present invention;

[0094] Figure 2 Displacement-time curve of the drill pipe thread shoulder surface under different powder amounts in the specific embodiment of the present invention.

[0095] Figure 3 Circumferential path contact stress curve of the drill pipe thread shoulder surface under different powder amounts in the specific embodiment of the present invention;

[0096] Figure 4 Maximum stress change of the drill pipe under different powder amounts in the specific embodiment of the present invention; Specific implementation mode

[0097] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments and drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0098] Embodiment 1

[0099] As Figure 1 shown, a safety evaluation method for detonation and releasing stuck in oil and gas wells includes the following steps:

[0100] Step S1, obtaining the working conditions of the stuck drill pipe and the thread of the joint to be released, where the thread of the joint to be released is the thread of the first joint above the stuck point; the working conditions include the depth of the stuck point, the density of the drilling fluid, the size and steel grade of the drill pipe and the joint thread;

[0101] Step S2, respectively establishing a geometric model of the stuck drill pipe and the thread of the joint to be released, and geometric models of the stuck drill pipe - the thread of the joint to be released - the fluid domain with several different powder amounts;

[0102] Step S3, determining the loaded state of the stuck drill pipe and the thread of the joint to be released before releasing, and performing simulation analysis on the geometric models of the stuck drill pipe and the thread of the joint to be released;

[0103] Step S4, taking the simulation analysis results of the stuck drill pipe and the thread of the joint to be released as input conditions, and performing simulation analysis on the geometric models of the stuck drill pipe - the thread of the joint to be released - the fluid domain with several different powder amounts under the detonation and releasing load;

[0104] Step S5, based on the simulation analysis results under the detonation and releasing load, evaluating the connection performance and mechanical properties of the joint thread after the powder explosion;

[0105] Step S6, judging whether the joint thread can be safely released under different powder amounts, and determining the powder amount required for releasing.

[0106] Among them, the method for obtaining the working conditions of the stuck drill pipe and the thread of the joint to be released includes:

[0107] The depth of the stuck point of the drill pipe is preliminarily determined by the following formula:

[0108]

[0109] In the formula: L is the depth of the stuck point of the drill pipe preliminarily determined; W is the unit mass of the drill pipe and its joints; E is the average elongation when lifting the drill string; P2 - P1 is the average pressure difference when lifting the drill string;

[0110] Based on the preliminarily determined depth of the stuck point, the precise position of the stuck point is measured using a pipe caliper instrument;

[0111] Determine the density of the drilling fluid at the stuck point according to the drilling log of the well site;

[0112] Determine the thread size and steel grade of the drill pipe and the joint to be released according to the wellbore structure data during drilling.

[0113] In this embodiment, the method for establishing the geometric model of the stuck drill pipe and the joint thread to be released includes:

[0114] Take the wall thickness and radial dimension of the drill pipe as the true size of the drill pipe at the stuck point, and the male and female thread models of the joint to be released are consistent with the wellbore structure;

[0115] Axially divide the model into upper and lower parts:

[0116] The first part is the fixed end, including the lower stuck drill pipe to the joint thread to be released, and its length is the true length measured by the pipe caliper;

[0117] The second part is the free end, including the joint thread to be released to the upper drill pipe connected to the stuck drill pipe, and its length is 2 times the total length of the joint.

[0118] In this embodiment, the method for establishing the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different powder amounts includes:

[0119] On the basis of the geometric model of the stuck drill pipe and the joint thread to be released, add gunpowder and the drilling fluid domain to obtain the geometric model of the stuck drill pipe - joint thread to be released - fluid domain;

[0120] The gunpowder is equivalent to an explosive cylinder during modeling, and the middle of the explosive cylinder needs to be aligned with the joint thread to be released;

[0121] The length l of the gunpowder is obtained according to the following formula:

[0122]

[0123] In the formula: m is the amount of gunpowder; ρ1 is the charge density of the gunpowder; R is the outer diameter of the explosive cylinder; r is the inner diameter of the explosive cylinder;

[0124] Calculate the powder size according to different powder amounts, and determine the geometric models of the stuck drill pipe - the thread of the joint to be loosened - the fluid domain for several different powder amounts.

[0125] The fluid domain of the drilling fluid is a cylindrical fluid domain, and the diameter of the cylindrical fluid domain is larger than the maximum outer diameter of the drill pipe.

[0126] In this embodiment, the method for determining the loaded state of the stuck drill pipe and the thread of the joint to be loosened before loosening includes:

[0127] The end face of the stuck lower drill pipe is completely constrained radially and axially; the end face of the upper connected drill pipe is free.

[0128] The hydrostatic pressure P generated by downhole fluids such as drilling fluid acts on the inside and outside of the drill pipe, and is calculated by the following formula:

[0129] P = ρ2gh

[0130] Where: ρ2 is the density of downhole fluids such as drilling fluid; g is the acceleration due to gravity; h is the well depth where the drill pipe is located.

[0131] The thread of the joint to be loosened is subjected to a make-up torque load radially, and is at the neutral point axially, and the neutral point is neither subjected to an upward force nor a hanging force.

[0132] In this embodiment, the method for performing a simulation analysis on the geometric models of the stuck drill pipe and the thread of the joint to be loosened includes:

[0133] Determine the material properties of the drill pipe according to the steel grade;

[0134] Perform geometric cleaning and divide the two-dimensional quadrilateral mesh of the thread surface;

[0135] Map from the thread surface to the non-thread drill pipe body to divide the three-dimensional hexahedron mesh, ensuring that the male and female thread meshes share the same nodes; and the mesh of the thread part is encrypted.

[0136] Create contact pairs for the joint shoulder surface and the thread engagement surface, set the contact type to surface-to-surface contact, use the penalty function method for tangential contact, and set the normal contact to hard contact;

[0137] Set coupling points on the non-thread end face of the upper drill pipe, and apply a make-up torque on its coupling points;

[0138] Set coupling points on the non-thread end face of the lower stuck drill pipe, and apply a fixed constraint on its coupling points;

[0139] Apply the hydrostatic pressure generated by the drilling fluid both inside and outside the drill pipe;

[0140] According to the simulation analysis results, analyze the connection performance and mechanical properties of the joint thread before loosening.

[0141] The applicant uses the simulation modeling method in this embodiment, taking a 2-7 / 8 drill pipe as the research object. The outer diameter of the drill pipe is 111.1 mm, the inner diameter is 41.3 mm, the coupling type is NC31, the thread model is V-0.038R, the taper is 1:6, the steel grade is S135, the elastic modulus is 206 GPa, the Poisson's ratio is 0.28, the yield strength is 968 MPa, the tensile strength is 1044 MPa, and the recommended make-up torque value from the drill pipe manufacturer is 11.5 kN·m. Considering the influence of the thread compound, the friction coefficient is set to 0.08.

[0142] In this embodiment, the method for analyzing the connection performance and mechanical properties before the joint thread becomes loose includes:

[0143] Extracting the stress characteristics and contact characteristics of the stuck drill pipe and the joint thread to be loosened under the make-up torque and static liquid column pressure;

[0144] The stress characteristics and contact characteristics include stress extreme values, distribution laws, and the interference amount of the shoulder surface, and the interference amount is the axial displacement value of the shoulder surface.

[0145] After the applicant applies a make-up torque of 11.5 kN·m, the stress of the drill pipe is mainly concentrated at the thread engagement. The stress of the pipe body part is relatively small. The maximum stress of 604.6 MPa appears at the root of the first thread tooth of the male thread near the shoulder, which is 62.46% of the yield strength. The error from the 60% described in the API standard is only 2.46%. The axial interference amount of the shoulder surface is 0.11 mm; on the basis of the make-up torque, with a well depth of 6000 m and a drilling fluid density of 1.5 g / cm 3 , an 88 MPa hydrostatic pressure is applied to the drill pipe. The maximum stress of the drill pipe joint rises to 618.3 MPa, and the axial interference amount of the shoulder surface is 0.11 mm;

[0146] The maximum stress in both loadings appears at the root of the first thread tooth of the male thread near the shoulder. The stress levels at the shoulder and the first few threads near the shoulder are relatively high, but all are lower than the material yield strength; this is consistent with the stress distribution trend of the drill pipe thread during actual operation, corresponding to the fact that failure cracks often appear at the first engaged thread of the drill pipe. The stress trend and values both illustrate the accuracy of the modeling method.

[0147] Embodiment 2

[0148] A safety evaluation method for detonation and thread loosening in oil and gas wells. Based on Example 1, the method for performing simulation analysis under detonation and thread loosening loads includes:

[0149] Performing explicit dynamic simulation analysis using the fluid-structure interaction method;

[0150] Based on the simulation analysis results of the stuck drill pipe and the thread of the joint to be loosened, they are used as the input conditions of the explicit dynamics finite element analysis of detonation loosening. The mesh type of the drill pipe is Lagrangian unit.

[0151] Mesh the fluid domain with gunpowder, and the mesh type of the fluid domain is Euler unit;

[0152] The gunpowder detonation time is 0s, and the detonation point is set at the top of the gunpowder;

[0153] Finite element simulations were performed on the models with different gunpowder amounts.

[0154] The applicant analyzed the Southwest Well A as an example. The drilling tool combination of the well was 3-1 / 2 drill pipe (H3029m) + 2-7 / 8 drill pipe (H5888m) + 2-7 / 8 drill collar (H5925m) + milling cone, mud density was 1.5g / cm3, drilling tool hanging weight was 105t, and it got stuck at a well depth of 5859.2m. The loosening position was 5850.33m above the stuck point at the first thread of the joint. The outer diameter of the pipe at this position was 73 .02mm, the outer diameter of the joint is 111.1mm, the inner diameter is 41.3mm, the buckle type is NC31, the thread model is V-0.038R, the taper is 1:6, and the steel grade is S135; after tightening, the pipe column is lifted up to make the loosening point the neutral point; when loosening, a qt700-2 explosive tube is used, the size is 35mm, and the initial explosive amount is 375g based on experience. The length of the explosive tube is about 82cm. After the blasting operation on site, the loosening is successful but the pipe column is cracked;

[0155] By comparing with the field data of the well, when the amount of explosives is 375g, the simulated maximum stress of the joint thread is 1032.1MPa, which is close to the tensile limit of the material. There is a risk of drill pipe breakage, and the contact stress of the circumferential path of the shoulder surface is zero, indicating that the drill pipe is separated. The actual situation is relatively consistent with the simulation, which verifies the reliability of the method for determining the amount of explosives for detonation loosening of oil and gas wells in this embodiment.

[0156] Example 3

[0157] A safety evaluation method for oil and gas well detonation loosening, based on Example 1 or 2, the method for evaluating the connection performance and mechanical properties of the joint thread after the gunpowder explosion includes:

[0158] Based on the simulation analysis results under detonation loosening load, the displacement-time curves of the joint thread shoulder surface, the circumferential path contact stress of the shoulder surface, and the maximum stress of the drill pipe under several different amounts of explosives were extracted;

[0159] Analyze the changes in the mechanical properties of the joint thread and the connection performance after the gunpowder explosion.

[0160] In this embodiment, the method for determining whether the joint thread is safely loosened under different amounts of explosive powder includes:

[0161] S601: If, after the gunpowder explodes, the displacement of the joint thread shoulder surface gradually oscillates with time and the circumferential path contact stress of the shoulder surface decreases, it is determined that the explosion causes the joint thread to vibrate and the shoulder surface of the threaded joint begins to separate, and the joint thread becomes loose at this gunpowder amount.

[0162] S602: If, after the gunpowder explodes, the joint thread becomes loose, the displacement of the joint thread shoulder surface gradually oscillates and decays with time, is lower than the displacement value at 0 s, and the circumferential path contact stress of the shoulder surface drops to zero, it is determined that the shoulder surface of the threaded joint is completely separated and the joint thread is completely unthreaded at this gunpowder amount.

[0163] S603: If, after the gunpowder explodes, the joint thread is completely unthreaded and the maximum stress is lower than the material yield limit, it is determined that the joint thread is safely unthreaded at this gunpowder amount.

[0164] S604: If multiple gunpowder amounts all meet the requirements for safely unthreading the joint thread, the minimum gunpowder amount is taken as the final safe unthreading gunpowder amount.

[0165] In this embodiment, based on the data of Well A in the southwestern stuck well site, the unthreading gunpowder amounts are set as 375 g, 365 g, 355 g, 345 g, 335 g, and 325 g, and the loosening behaviors of the drill pipe joints are studied respectively, with the aim of optimizing the safe unthreading gunpowder amount.

[0166] The displacement-time curves of the drill pipe thread shoulder surface under different gunpowder amounts are as Figure 2 shown, and the circumferential path contact stress curves of the drill pipe thread shoulder surface under different gunpowder amounts are as Figure 3 shown. At 0 ms, the initial displacement of the shoulder surface is 0.11 mm, indicating that an interference of 0.11 is generated on the shoulder surface under the make-up torque, and the initial circumferential path contact stress of the shoulder surface is about 185 MPa, indicating that the thread make-up is successful at this time; after 0 ms, the shoulder surface vibrates with the impact load generated by the explosion of the gunpowder, and the displacement oscillates with the explosion time. Under different gunpowder amounts, the vibration law of the shoulder surface displacement is the same, and the peak and trough appearance times in each period are relatively unified; and as the gunpowder amount increases, the circumferential path contact stress of the shoulder surface decreases. Therefore, when the gunpowder amounts are 375 g, 365 g, 355 g, 345 g, 335 g, and 325 g, the joint thread becomes loose.

[0167] The shoulder surface displacement reaches its maximum value at about 0.35 ms, and then gradually oscillates with time and approaches zero after 0.35 ms. The larger the amount of gunpowder, the faster the attenuation. At 1 ms, the shoulder surface displacements under different amounts of gunpowder are all lower than the initial interference of 0.11 mm, indicating that the interference generated by the tightening torque gradually decreases with the explosion of gunpowder. When the amounts of gunpowder are 325 g, 335 g, and 345 g, the circumferential path contact stresses of the shoulder surface are 88 MPa, 62 MPa, and 34 MPa respectively. At this time, the joint thread step surface changes from a close contact state to a loose state. When the amounts of gunpowder increase to 355 g, 365 g, and 375 g, the contact stress drops to zero. At this time, the joint thread step surface changes from a loose state to a completely separated state. Therefore, when the amounts of gunpowder are 355 g, 365 g, and 375 g, the shoulder surface is completely separated and the joint thread can be completely loosened.

[0168] The variation of the maximum stress of the drill pipe under different amounts of gunpowder is as Figure 4 shown. When the amounts of gunpowder are 365 g and 375 g, the maximum stresses of the joint thread are 998.5 MPa and 1032.0 MPa respectively, both of which are greater than the yield limit of the drill pipe of 968 MPa. At this time, plastic deformation occurs in the joint thread. For 375 g, it is even close to the tensile limit of the drill pipe of 1053 MPa, and there is a risk of fracture of the joint thread. Once fracture occurs, the difficulty of subsequent loosening and fishing operations will increase. When the amount of gunpowder is 355 g, the joint thread is completely loosened and the maximum stress is lower than the material yield limit, and safe loosening can be achieved. Therefore, the safe loosening amount of gunpowder for Well A stuck in the southwest when using the qt700-2 explosive cartridge is 355 g.

[0169] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A safety evaluation method for detonation and releasing of stuck pipe in oil and gas wells, characterized in that, Including: Step S1: Obtain the working conditions of the stuck drill pipe and the thread of the joint to be released, where the thread of the joint to be released is the thread of the first joint above the stuck point; the working conditions include the depth of the stuck point in the well, the density of the drilling fluid, the dimensions and steel grades of the drill pipe and the joint thread. Step S2: Establish a geometric model of the stuck drill pipe and the thread of the joint to be released, and geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder. Step S3: Determine the loaded state of the stuck drill pipe and the thread of the joint to be released before releasing the buckle, and conduct a simulation analysis on the geometric models of the stuck drill pipe and the thread of the joint to be released. Step S4: Using the simulation analysis results of the stuck drill pipe and the thread of the joint to be released as input conditions, conduct a simulation analysis on the geometric models of the stuck drill pipe - joint thread to be released - fluid domain under the detonation release load with several different amounts of gunpowder. Step S5: Based on the simulation analysis results under the detonation release load, evaluate the connection performance and mechanical properties of the joint thread after the gunpowder explodes. Step S6: Judge whether the joint thread can be safely released with different amounts of gunpowder, and determine the amount of gunpowder required for releasing the buckle.

2. The safety evaluation method for detonation and releasing stuck pipe in oil and gas wells according to claim 1, wherein The method for obtaining the working conditions of the stuck drill pipe and the thread of the joint to be released includes: Preliminarily determine the depth of the stuck point of the drill pipe through the following formula: In the formula: L is the preliminarily determined depth of the stuck point of the drill pipe; W is the unit mass of the drill pipe and its joint; E is the average elongation when lifting the drill string; P2 - P1 is the average pressure difference when lifting the drill string. Based on the preliminarily determined depth of the stuck point, use a pipe locator to measure the exact position of the stuck point. Determine the density of the drilling fluid at the stuck point according to the well site drilling log. Determine the dimensions and steel grades of the drill pipe and the thread of the joint to be released according to the wellbore structure data during drilling.

3. The safety evaluation method for detonation loosening of oil and gas wells according to claim 1, characterized in that The method for establishing a geometric model of the stuck drill pipe and the thread of the joint to be released includes: Take the wall thickness and radial dimension of the drill pipe as the true size of the drill pipe at the stuck point, and the male and female thread models of the joint to be released are consistent with the wellbore structure. Axially divide the model into upper and lower parts: The first part is the fixed end, including the lower stuck drill pipe to the joint thread to be released, and its length is the true length measured by the pipe locator. The second part is the free end, including the joint thread to be released to the upper drill pipe connected to the stuck drill pipe, and its length is 2 times the total length of the joint.

4. The safety evaluation method for detonation unthreading of oil and gas wells according to claim 1, characterized in that, The method for establishing geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder includes: On the basis of the geometric model of the stuck drill pipe and the thread of the joint to be released, add gunpowder and the drilling fluid domain to obtain the geometric model of the stuck drill pipe - joint thread to be released - fluid domain. The gunpowder is equivalent to an explosive cylinder during modeling, and the middle of the explosive cylinder needs to be aligned with the thread to be released. The length l of the gunpowder is obtained according to the following formula: In the formula: m is the amount of gunpowder; ρ1 is the charge density of the gunpowder; R is the outer diameter of the explosive cylinder; r is the inner diameter of the explosive cylinder. Calculate the gunpowder size according to different amounts of gunpowder, and determine the geometric models of the stuck drill pipe - joint thread to be released - fluid domain with several different amounts of gunpowder. The fluid domain of the drilling fluid is a cylindrical fluid domain, and the diameter of the cylindrical fluid domain is larger than the maximum outer diameter of the drill pipe.

5. According to the safety evaluation method for detonation release of oil and gas wells described in claim 1, the method for determining the loaded state of the stuck drill pipe and the thread of the joint to be released before releasing the buckle includes: The lower end face of the stuck drill pipe is completely radially and axially constrained; the upper connecting drill pipe end face is free; The hydrostatic pressure P generated by downhole fluids such as drilling fluid acts on the inside and outside of the drill pipe and is calculated by the following formula: P = ρ2gh Where: ρ2 is the density of downhole fluids such as drilling fluid; g is the acceleration due to gravity; h is the well depth where the drill pipe is located; The stuck drill pipe and the thread of the joint to be unfastened are subjected to a tightening torque load in the radial direction and the neutral point in the axial direction. The neutral point is neither subjected to an upward pulling force nor a hanging force.

6. The safety evaluation method for detonation unthreading of oil and gas wells according to claim 1, characterized in that, The method for simulating and analyzing the geometric models of the stuck drill pipe and the thread of the joint to be unfastened includes: Determine the drill pipe material properties according to the steel grade; Perform geometric cleaning and divide the two-dimensional quadrilateral mesh of the thread surface; Map from the thread surface to the non-thread drill pipe body and divide the three-dimensional hexahedron mesh to ensure that the male and female thread meshes share nodes; and the mesh of the thread part is encrypted; Create a contact pair for the joint shoulder surface and the thread meshing surface, set the contact type to surface-to-surface contact, use the penalty function method for tangential contact, and set the normal contact to hard contact; Set coupling points on the non-thread end face of the upper drill pipe and apply a tightening torque on its coupling points; Set coupling points on the non-thread end face of the lower stuck drill pipe and apply a fixed constraint on its coupling points; Apply the hydrostatic pressure generated by the drilling fluid on both the inside and outside of the drill pipe; According to the simulation analysis results, analyze the connection performance and mechanical properties of the joint thread before unfastening.

7. The safety evaluation method for detonation loosening of oil and gas wells according to claim 6, characterized in that, The method for analyzing the connection performance and mechanical properties of the joint thread before unfastening includes: Extract the stress characteristics and contact characteristics of the stuck drill pipe and the thread of the joint to be unfastened under the tightening torque and hydrostatic pressure; The stress characteristics and contact characteristics include stress extreme values, distribution laws, and the interference amount of the shoulder surface. The interference amount is the axial displacement value of the shoulder surface.

8. The safety evaluation method for detonation and releasing of stuck pipe in oil and gas wells according to claim 1, wherein The method for performing simulation analysis under the detonation unfastening load includes: Use the fluid-structure interaction method to perform explicit dynamics simulation analysis; Based on the simulation analysis results of the stuck drill pipe and the thread of the joint to be unfastened, use them as the input conditions for the explicit dynamics finite element analysis of detonation unfastening. The mesh type of the drill pipe is Lagrangian element; Divide the mesh of the fluid domain with gunpowder. The mesh type of the fluid domain is Euler element; The ignition time of the gunpowder is 0 s, and the ignition point is set at the top of the gunpowder; Perform finite element simulation on the models with several different gunpowder amounts.

9. The safety evaluation method for detonation and releasing of stuck pipe in oil and gas wells according to claim 1, characterized in that, The method for evaluating the connection performance and mechanical properties of the joint thread after gunpowder explosion includes: Based on the simulation analysis results under the detonation unfastening load, extract the displacement-time curve of the joint thread shoulder surface, the circumferential path contact stress of the shoulder surface, and the maximum drill pipe stress under several different gunpowder amounts; Analyze the changes in the mechanical properties and connection performance of the joint thread after gunpowder explosion.

10. The safety evaluation method for detonation and releasing stuck in oil and gas wells according to claim 1, characterized in that, The method for judging whether the joint thread is safely unfastened under different gunpowder amounts includes: S601. If, after the gunpowder explosion, the displacement of the joint thread shoulder surface oscillates gradually with time and the circumferential path contact stress of the shoulder surface decreases, it is determined that the explosion causes the joint thread to vibrate and the shoulder surface of the thread joint begins to separate, and the joint thread becomes loose under this gunpowder amount; S602. If the joint thread becomes loose after the gunpowder explosion, the displacement of the joint thread shoulder surface gradually oscillates and decays over time, being lower than the displacement value at 0 s, and the circumferential path contact stress of the shoulder surface drops to zero, then it is determined that the shoulder surface of the threaded joint is completely separated and the joint thread is completely loosened at this gunpowder quantity; S603. If the joint thread is completely loosened and the maximum stress is lower than the material yield limit after the gunpowder explosion, then it is determined that the joint thread is safely loosened at this gunpowder quantity; S604. If multiple gunpowder quantities all meet the requirements for the safe loosening of the joint thread, then the minimum gunpowder quantity is taken as the final safe loosening gunpowder quantity.

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