Method, device and equipment for predicting fatigue life of underground drilling tool and medium

Abstract

The invention discloses a method, a device, equipment and a medium for predicting the fatigue life of an underground drilling tool, and relates to the technical field of petroleum drilling tools. A drill bit rock breaking model and a rotary steering drill column dynamic model are constructed, and a well wall-drill column-drill bit-rock breaking coupled drill column dynamic model is constructed; performing transient dynamic simulation on the drilling parameters, calculating dynamic load spectrums at the two ends of the drilling tool, and constructing a finite element model; performing modal analysis and harmonic response analysis on the finite element model, calculating a characteristic value and a characteristic vector of the rotary steering structure, determining an inherent frequency, and judging whether the inherent frequency and an actual working frequency meet a resonance condition or not; if not, inputting the dynamic load spectrum into the finite element model, and predicting the fatigue life of the underground drilling tool; and if yes, converting time domain data of the dynamic load spectrum into frequency domain data to obtain power spectral density, performing spectral analysis to calculate power spectral density response, and predicting the fatigue life of the underground drilling tool by using the power spectral density response.

Description

Technical Field

[0001] This invention relates to the field of oil drilling tool technology, and in particular to a method, apparatus, equipment and medium for predicting the fatigue life of downhole drilling tools. Background Technology

[0002] Because downhole drilling tools operate for extended periods within a narrow wellbore, their upper end is driven by a top drive to rotate at high speed, while the lower end drives the drill bit to break rocks. Downhole drilling tools are constantly subjected to dynamic loads such as drilling pressure, torque, and bending moment, as well as intense coupled vibrations in the lateral, longitudinal, tangential, and torsional directions. After prolonged rock-breaking drilling, tool damage and fatigue failure are inevitable. Currently, fatigue life prediction for downhole drilling tools in conventional drilling processes uses static methods, which cannot accurately estimate the actual load on the tool. These methods only use uniform beam elements for calculations, failing to consider the actual structure and thus cannot accurately predict the fatigue life of the real structure. Furthermore, they do not comprehensively consider fatigue loss factors, increasing the complexity of fatigue life research and reducing the accuracy and efficiency of downhole drilling tool fatigue life prediction.

[0003] As can be seen from the above, how to comprehensively consider fatigue loss factors, reduce the complexity of fatigue life research process, and improve the accuracy and efficiency of fatigue life prediction for downhole drilling tools is a problem to be solved in this field. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method, apparatus, equipment, and medium for predicting the fatigue life of downhole drilling tools, which can comprehensively consider fatigue loss factors, reduce the complexity of the fatigue life research process, and improve the accuracy and efficiency of fatigue life prediction for downhole drilling tools. The specific solution is as follows:

[0005] In a first aspect, this application discloses a method for predicting the fatigue life of downhole drilling tools, including:

[0006] Construct a drill bit rock breaking model and a rotary steerable drill string dynamics model, and based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, construct a drill string dynamics model that couples wellbore-drill string-drill bit-rock breaking.

[0007] The drill string dynamics model is used to perform transient dynamic simulation on the pre-acquired drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool, and a finite element model of the downhole drilling tool is constructed based on the dynamic load spectrum.

[0008] Modal analysis and harmonic response analysis are performed on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and the corresponding natural frequencies are determined using the eigenvalues ​​and eigenvectors of the rotary guide structure. It is then determined whether the natural frequencies meet the resonance condition with the actual operating frequency.

[0009] If the natural frequency does not meet the resonance condition with the actual operating frequency, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool.

[0010] If the natural frequency and the actual operating frequency meet the resonance condition, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is then analyzed to calculate the power spectral density response. The fatigue life of the downhole drilling tool is then predicted using the power spectral density response.

[0011] Optionally, the construction of the drill bit rock breaking model and the rotary steerable drill string dynamics model includes:

[0012] Acquire actual working conditions, wellbore trajectory, and drill string assembly data for the target formation;

[0013] The PDC drill bit is treated as a rigid body, and the rock of the target formation is treated as an elastoplastic body. The contact relationship between the drill bit and the rock is established, and the rock breaking model of the drill bit is constructed using the rock breaking criterion.

[0014] Based on the actual working conditions, the wellbore trajectory, and the drill string assembly data, a dynamic model of a rotary steerable drill string with downhole drilling tools under wellbore constraints is established.

[0015] Optionally, the construction of a wellbore-drill string-drill bit-rock fracturing coupled drill string dynamics model based on the drill bit rock breaking model and the rotary steerable drill string dynamics model includes:

[0016] Based on the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the interaction mechanism between the upper longitudinal slender flexible drill string dynamic boundary and the lower transverse multi-cutting tooth drill bit rock breaking boundary at the connection point, and combined with the dynamic torque relationship established by the displacement and rotation degrees of freedom of the drill bit rock breaking model and the rotary steered drill string dynamic model, a drill string dynamic model coupling wellbore-drill string-drill bit-rock breaking is constructed.

[0017] Optionally, constructing the finite element model of the downhole drilling tool based on the dynamic load spectrum includes:

[0018] Draw a 3D structural diagram of downhole drilling tools and corresponding drill string assemblies;

[0019] Material properties are defined and meshes are generated. A finite element model of the downhole drilling tool is constructed based on the three-dimensional structural diagram of the downhole drilling tool and its corresponding drill string assembly and the dynamic load spectrum.

[0020] Optionally, performing modal analysis and harmonic response analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure includes:

[0021] Matrix calculations are performed on the finite element model to obtain the stiffness matrix and mass matrix;

[0022] Based on the stiffness matrix and the mass matrix, an eigenvalue problem is generated, and the eigenvalue problem is solved to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure.

[0023] Optionally, inputting the dynamic load spectrum into the finite element model to predict the fatigue life of the downhole drilling tool includes:

[0024] The dynamic stress spectrum under the dynamic load spectrum is input into the finite element model for calculation, and the fatigue life of the downhole drilling tool is predicted by combining the Miner linear damage accumulation calculation model under the number of cycles.

[0025] Optionally, if the natural frequency and the actual operating frequency meet the resonance condition, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. Spectral analysis is then performed on the power spectral density of the downhole drilling tool to calculate the power spectral density response. The fatigue life of the downhole drilling tool is then predicted using the power spectral density response. This includes:

[0026] If the natural frequency and the actual operating frequency meet the resonance condition, then the resonance frequency range between the natural frequency and the actual operating frequency is determined, and the time domain data of the dynamic load spectrum is converted into frequency domain data based on the resonance frequency range to obtain the power spectral density.

[0027] Based on the power spectral density, a power spectral density curve of the random dynamic load is plotted, and spectral analysis is performed on the power spectral density curve to calculate the power spectral density response.

[0028] The fatigue life of downhole drilling tools is predicted based on Miner's rule and the power spectral density response.

[0029] Secondly, this application discloses a fatigue life prediction device for downhole drilling tools, comprising:

[0030] The model building module is used to build a drill bit rock breaking model and a rotary steerable drill string dynamics model. Based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock breaking is constructed.

[0031] The dynamic load spectrum calculation module is used to perform transient dynamic simulation of the pre-acquired drilling parameters using the drill string dynamics model, so as to calculate the dynamic load spectrum at both ends of the drilling tool, and construct the finite element model of the downhole drilling tool based on the dynamic load spectrum.

[0032] The frequency resonance judgment module is used to perform modal analysis and harmonic response analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine the corresponding natural frequency using the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine whether the natural frequency meets the resonance condition with the actual operating frequency.

[0033] The first fatigue life prediction module is used to input the dynamic load spectrum into the finite element model if the natural frequency and the actual working frequency do not meet the resonance condition, so as to predict the fatigue life of the downhole drilling tool.

[0034] The second fatigue life prediction module is used to convert the time-domain data of the dynamic load spectrum into frequency-domain data to obtain the power spectral density if the natural frequency and the actual operating frequency meet the resonance condition, perform spectral analysis on the power spectral density of the downhole drilling tool to calculate the power spectral density response, and use the power spectral density response to predict the fatigue life of the downhole drilling tool.

[0035] Thirdly, this application discloses an electronic device, including:

[0036] Memory, used to store computer programs;

[0037] A processor is used to execute the computer program to implement the aforementioned method for predicting the fatigue life of downhole drilling tools.

[0038] Fourthly, this application discloses a computer storage medium for storing a computer program; wherein, when the computer program is executed by a processor, it implements the steps of the aforementioned disclosed method for predicting the fatigue life of downhole drilling tools.

[0039] As can be seen, this application provides a method for predicting the fatigue life of downhole drilling tools, including constructing a drill bit rock breaking model and a rotary steerable drill string dynamics model; constructing a drill string dynamics model coupling wellbore-drill string-drill bit-rock breaking based on the drill bit rock breaking model and the rotary steerable drill string dynamics model; performing transient dynamic simulation on pre-acquired drilling parameters using the drill string dynamics model to calculate the dynamic load spectrum at both ends of the drilling tool; constructing a finite element model of the downhole drilling tool based on the dynamic load spectrum; performing modal analysis and harmonic response analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary steerable structure; and utilizing the rotary steerable structure... The eigenvalues ​​and eigenvectors determine the corresponding natural frequencies, and it is determined whether the natural frequencies and the actual operating frequencies meet the resonance condition. If the natural frequencies and the actual operating frequencies do not meet the resonance condition, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool. If the natural frequencies and the actual operating frequencies meet the resonance condition, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is subjected to spectral analysis to calculate the power spectral density response, and the fatigue life of the downhole drilling tool is predicted using the power spectral density response. This application constructs a drill string dynamics model coupling the wellbore-drill string-drill bit-rock breaking process. It effectively considers the dynamic loads under the action of drill bit excitation and wellbore collision during rock breaking. Transient dynamic simulation is performed using the drill string dynamics model to calculate the dynamic load spectrum at both ends of the drilling tool. A finite element model of the downhole drilling tool is constructed, the eigenvalues ​​and eigenvectors of the rotary steering structure are calculated, and the corresponding natural frequencies are determined. The downhole resonance problem is considered, and it is determined whether the natural frequencies and the actual operating frequencies meet the resonance conditions. If the resonance conditions are met, the power spectral density of the downhole drilling tool is analyzed. Fatigue loss factors are comprehensively considered, and the fatigue life of the downhole drilling tool is predicted. This improves the accuracy and efficiency of downhole drilling tool fatigue life prediction and reduces the complexity of the fatigue life research process. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0041] Figure 1 This application discloses a flowchart of a method for predicting the fatigue life of downhole drilling tools.

[0042] Figure 2 This is a schematic diagram of a drill bit rock-breaking model disclosed in this application;

[0043] Figure 3 This is a nonlinear stress-strain curve of progressive damage disclosed in this application;

[0044] Figure 4 This is a schematic diagram of a rotary steerable drill string dynamics model disclosed in this application;

[0045] Figure 5 This is a schematic diagram of a drill string dynamics model of wellbore-drill string-drill bit-rock fracturing coupling disclosed in this application;

[0046] Figure 6 This application discloses a dynamic drill pressure spectrum at the drill bit boundary.

[0047] Figure 7 This application discloses a dynamic torque spectrum of a drill bit boundary.

[0048] Figure 8 This application discloses a first-order modal analysis contour plot;

[0049] Figure 9 This application discloses a second-order modal analysis contour plot;

[0050] Figure 10 This application discloses a third-order modal analysis contour plot;

[0051] Figure 11 This application discloses a fourth-order modal analysis contour plot;

[0052] Figure 12 This application discloses a fifth-order modal analysis contour plot;

[0053] Figure 13 This application discloses a sixth-order modal analysis contour plot;

[0054] Figure 14 This application discloses a dynamic stress cloud diagram for a latitude and longitude rotating guide.

[0055] Figure 15 This application discloses a fatigue life cloud map of a latitude and longitude rotary guide.

[0056] Figure 16 This application discloses a specific flowchart for predicting the fatigue life of a downhole drilling tool.

[0057] Figure 17 This is a schematic diagram of the structure of a downhole drilling tool fatigue life prediction device disclosed in this application.

[0058] Figure 18 This application provides a structural diagram of an electronic device. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Because downhole drilling tools operate for extended periods within a narrow wellbore, their upper end is driven by a top drive to rotate at high speed, while the lower end drives the drill bit to break rocks. Downhole drilling tools are constantly subjected to dynamic loads such as drilling pressure, torque, and bending moment, as well as intense coupled vibrations in the lateral, longitudinal, tangential, and torsional directions. After prolonged rock-breaking drilling, tool damage and fatigue failure are inevitable. Currently, fatigue life prediction for downhole drilling tools in conventional drilling processes uses static methods, which cannot accurately estimate the actual load on the tool. These methods only use uniform beam elements for calculations, neglecting the actual structure and failing to accurately predict the fatigue life of the real structure. Furthermore, they do not comprehensively consider fatigue loss factors, increasing the complexity of fatigue life research and reducing the accuracy and efficiency of downhole drilling tool fatigue life prediction. Therefore, how to comprehensively consider fatigue loss factors, reduce the complexity of fatigue life research, and improve the accuracy and efficiency of downhole drilling tool fatigue life prediction is a problem that needs to be solved in this field.

[0061] See Figure 1 As shown in the figure, this invention discloses a method for predicting the fatigue life of downhole drilling tools, which may specifically include:

[0062] Step S11: Construct a drill bit rock breaking model and a rotary steerable drill string dynamics model. Based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, construct a drill string dynamics model that couples wellbore-drill string-drill bit-rock breaking.

[0063] In this embodiment, when acquiring the actual working conditions, wellbore trajectory, and drill string assembly data of the target formation, the method further includes: determining the drill string assembly, inner and outer diameters, and material properties of the downhole drilling tools according to the actual drilling conditions of the target block; determining the wellbore size, well section length, wellbore curvature, and well inclination angle of the wellbore trajectory; determining drilling parameters such as rotational speed, drilling pressure, steering force, and tool face angle; and determining rock mechanics parameters such as lithology, elastic modulus, Poisson's ratio, and internal friction angle of the target formation. For example, based on the actual drilling conditions in a shale oil block, the drill string assembly used for rotary steerable drilling is determined as follows: Φ215.9mm PDC drill bit + Φ172mm rotary steerable drill + Φ127mm non-magnetic pressure drill pipe + screen connector + Φ172mm 7LZ172×7 / 8-4.5 straight screw + 411*410 check valve + 3 Φ127mm heavy-duty drill pipes + Φ165mm drilling shock absorber + 3 Φ127mm heavy-duty drill pipes + drill pipe. Drill string material properties: density 7850kg / L. The target formation has the following parameters: elastic modulus 210 GPa, Poisson's ratio 0.3, well depth 4478 m, wellbore size 215.9 mm, wellbore curvature 6° / 30 m, well inclination angle 60°, drilling parameters: top drive rotation speed 60 r / min + screw, drill pressure 200 kN, guide force 25 kN, and target formation lithology parameters: failure criterion using the Drucker-Prager model, elastic modulus 36 MPa, Poisson's ratio 0.34, density 2640 kg / m³. Damage strain 0.085 mm, failure displacement 0.055 mm, yield stress 80 MPa, internal friction angle 38.8°, and rheological stress ratio 0.8.

[0064] In this embodiment, the actual working conditions, wellbore trajectory, and drill string assembly data of the target formation are acquired. The PDC drill bit is treated as a rigid body, and the rock of the target formation is treated as an elasto-plastic body. A contact relationship between the drill bit and the rock is established, and a drill bit rock-breaking model is constructed using rock fracture criteria. Based on the actual working conditions, the wellbore trajectory, and the drill string assembly data, a rotary steerable drill string dynamics model with downhole drilling tools under wellbore constraints is established. Based on the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the interaction mechanism between the upper longitudinal slender flexible drill string dynamic boundary and the lower transverse multi-tooth drill bit rock-breaking boundary at the connection point, and combining the dynamic torque relationship established by the displacement and rotation degrees of freedom of the drill bit rock-breaking model and the rotary steerable drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock fracture is constructed.

[0065] In this embodiment, the specific process for constructing the drill bit rock breaking model and the rotary steerable drill string dynamics model is as follows: the PDC drill bit is regarded as a rigid body, and the rock is regarded as an elasto-plastic body. The rock breaking mechanism of the PDC drill bit is analyzed as first squeezing and then shearing to break the rock. The corresponding rock breaking criterion is selected as the constitutive model, the shear criterion is selected as the rock damage initiation criterion, and the material nonlinearity is selected to describe the progressive damage of the rock, thereby establishing the PDC drill bit rock breaking model. Based on the actual working conditions, drill string assembly, drilling parameters and wellbore trajectory, the random contact relationship between the drill string and the well wall and the pre-bending treatment of the rigid drill string in the curved wellbore are considered using beam theory and finite element method. The rotary steerable drill string dynamics model under wellbore constraints is established using the Lagrange equation.

[0066] The schematic diagram of the drill bit rock breaking model is as follows: Figure 2 As shown, the process of constructing the drill bit rock-breaking model is as follows: A three-dimensional structural diagram of the PDC drill bit is drawn. Since the rock strength is much lower than the drill bit strength, the drill bit is set as a rigid body and the rock is considered an elastoplastic body when establishing the drill bit rock-breaking model. The analysis process of drill bit rock breaking is equivalent to the force or displacement boundary of the rock, that is, the process of the rigid drill bit squeezing, shearing, and breaking the rock under the drive of drilling pressure and torque. The Drucker-Prager rock strength criterion, which combines the extended Drucker-Prager failure criterion and the linear elastic model, is used as the constitutive model to describe shale. Because it considers the influence of intermediate principal stress and hydrostatic pressure, it overcomes the main weaknesses of the traditional Mohr-Coulomb criterion. Its expression can be expressed as:

[0067] ;

[0068] in, , , There are three principal stresses. denoted as the internal friction angle in the Mohr-Coulomb criterion, and c as the cohesion in the Mohr-Coulomb criterion.

[0069] Assuming the equivalent plastic strain at the onset of damage is a function of the shear stress ratio and strain rate, the shear criterion is chosen as the damage initiation criterion for rocks to predict the onset of damage due to shear localization. The damage initiation criterion is satisfied when the following condition is met:

[0070] ;

[0071] in, Shear stress ratio, For equivalent plastic strain, for The derivative of .

[0072] The nonlinear stress-strain curve of progressive damage is as follows: Figure 3 As shown, the solid line represents the stress-strain response when there is damage, and the dashed line represents the stress-strain response when there is no damage. and These are the yield stress and equivalent plastic strain at the onset of damage, respectively, at which point the damage factor D = 0; This represents the equivalent plastic strain when the material completely fails, at which point the damage factor D = 1.

[0073] The schematic diagram of the rotary steerable drill string dynamics model is shown below. Figure 4 As shown, the process includes three parts: the finite element dynamics equations of the drill string, the boundary condition handling method, and the drill string-wellbore contact model. The specific process is as follows: Based on the finite element method, the actual bottom drill string of the rotary steerable drill string is discretized into N Timoshenko beam elements. Using the Lagrange equation as the fundamental theory of drill string dynamics, the expressions for the kinetic energy, potential energy, and generalized force of the drill string beam elements are derived. These expressions are then substituted into the Lagrange equations to derive the finite element dynamics equations of the drill string.

[0074] ;

[0075] in, For the kinetic energy of the beam element, Let be the potential energy of the beam element. For conservative forces in beam elements, For nonconservative forces in beam elements, Let t be the nodal displacement vector of the beam element, and t be time.

[0076] The actual working conditions of the rotary steerable drilling system are treated as corresponding boundary conditions, including the top drive boundary, drill pipe equivalent boundary, bottom drill string upper boundary, non-rotating outer sleeve equivalent boundary, rib pushing force boundary, and initial deformation treatment of the drill string in the curved wellbore.

[0077] The drill string-wellbore contact model assumes elastic deformation of a uniform, rigid wellbore, treating the contact as an instantaneous process and using constant contact stiffness to describe the contact force between the drill string and the wellbore. The contact model can be expressed as:

[0078] ;

[0079] ;

[0080] ;

[0081] in, For contact force, This refers to the gap between the drill string and the wellbore. For contact stiffness, The coefficient of friction, For tangential friction, The frictional torque caused by contact is denoted as r, and the outer diameter of the drill string is denoted as r.

[0082] In this embodiment, the drill string dynamics model of the wellbore-drill string-drill bit-rock fracturing coupling is as follows: Figure 5 As shown, the specific process for constructing the drill string dynamics model of wellbore-drill string-drill bit-rock breaking coupling is as follows: considering the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the relatively independent drill bit rock breaking model and drill string dynamics are coupled through the positive and negative torques of the drill bit to establish the drill string dynamics model of wellbore-drill string-drill bit-rock breaking coupling.

[0083] Specifically, considering the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the interaction mechanism between the upper longitudinal slender flexible drill string dynamic boundary and the lower transverse multi-cutting tooth drill bit rock breaking boundary at the "connection point" is clarified. The PDC drill bit rock breaking model and the rotary steerable drill string dynamic model are drilled, and the dynamic torque relationship is established through the six displacement and rotation degrees of freedom of the uppermost point of the drill bit and the lowermost point of the drill string. A drill string dynamic model coupling well wall-drill string-drill bit-rock breaking is established.

[0084] Step S12: Use the drill string dynamics model to perform transient dynamic simulation on the pre-acquired drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool, and construct a finite element model of the downhole drilling tool based on the dynamic load spectrum.

[0085] The process for calculating the dynamic load spectrum at both ends of the drilling tool is as follows: Using the established coupled drill string dynamics model, drilling parameters are applied: top drive speed 60 r / min + screw, drill pressure 200 kN, guiding force 25 kN; trajectory parameters: well depth 4478 m, wellbore size 215.9 mm, wellbore curvature 6° / 30 m, well inclination angle 60°. The implicit solution method, Newmark-β, is used to solve the model, performing dynamic simulation of the rotary steerable drilling process in shale formations. Based on the dynamic simulation results, the dynamic load spectrum at both ends of the rotary steerable tool is extracted, including triaxial dynamic forces and triaxial dynamic moments. The dynamic load spectrum is preprocessed, and a continuous segment of triaxial dynamic forces and triaxial dynamic moments with significant periodicity is extracted, considered as the working load under normal tool operating conditions, and used as the boundary input condition for fatigue life analysis.

[0086] In this embodiment, after calculating the dynamic load spectrum at both ends of the drilling tool, a three-dimensional structural diagram of the downhole drilling tool and its corresponding drill string assembly is drawn; material properties are defined and meshes are generated; and a finite element model of the downhole drilling tool is constructed based on the three-dimensional structural diagram of the downhole drilling tool and its corresponding drill string assembly and the dynamic load spectrum. For example, a 6.75-inch rotary steerable drilling system string should include four units: a steerable head unit, a geological survey unit, a central control unit, and an upper connecting drill pipe. The steerable head unit includes eight modules: a spindle, a non-rotating outer sleeve, a sliding bearing, an actuator, a primary circuit, a secondary circuit, an energy transmission system, and a flexible sub. The geological survey unit includes two modules: azimuth gamma and azimuth resistivity. The central control unit includes four modules: a pulse generator, a generator, a central control unit, and a directional probe. The upper connecting drill collar includes three non-magnetic pressure-bearing drill pipes below the screw drill string. Finite element meshes are generated for each of the above four units, the material properties of the elastomeric drill string are defined, a triaxial dynamic moment load spectrum is applied, and a solid finite element dynamic model of the downhole drilling tool is established.

[0087] In this embodiment, the established coupled drill string dynamics model is used to perform dynamic simulation of the drilling process under actual working conditions. The dynamic load spectrum at both ends of the downhole drilling tool is calculated, and the dynamic load spectrum is preprocessed. Load spectra with significant periodicity are extracted as boundary input conditions for fatigue analysis. A three-dimensional structural diagram of the downhole drilling tool and its drill string assembly is drawn, including the dynamic drill bit boundary dynamic pressure spectrum and the drill bit boundary dynamic torque spectrum. The material properties of the drill string are defined, and the drill string is treated as an elastic body. The drill string is meshed to obtain the dynamic load spectrum, and a solid finite element model of the downhole drilling tool is established. The dynamic drill bit boundary dynamic pressure spectrum is as follows: Figure 6 As shown, the dynamic torque spectrum at the drill bit boundary is as follows: Figure 7 As shown.

[0088] Step S13: Perform modal analysis and harmonic response analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and use the eigenvalues ​​and eigenvectors of the rotary guide structure to determine the corresponding natural frequencies, and determine whether the natural frequencies and the actual operating frequencies meet the resonance conditions.

[0089] In this embodiment, matrix calculations are performed on the finite element model to obtain the stiffness matrix and the mass matrix. Based on the stiffness matrix and the mass matrix, an eigenvalue problem is generated. The eigenvalue problem is solved to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure. The corresponding natural frequencies are determined using the eigenvalues ​​and eigenvectors of the rotary guide structure. It is then determined whether the natural frequencies and the actual operating frequencies meet the resonance condition.

[0090] In this embodiment, the established finite element model is used to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure to describe the stiffness and mass distribution of the model and determine the corresponding natural frequencies. For each natural frequency, the vibration mode of the model structure under different modes is analyzed. Combined with the analysis of actual drilling data, it is determined whether the natural frequency of the model meets the resonance condition with the actual working frequency, that is, whether the natural frequency is close to the actual working frequency, thereby determining whether resonance exists.

[0091] Specifically, using the established finite element model, the stiffness matrix and mass matrix are calculated to describe the stiffness and mass distribution of the model, respectively. Modal analysis is then performed, combining the stiffness and mass matrices into an eigenvalue problem, which is then solved to obtain the natural frequencies and corresponding modal shapes. The model's control equations are as follows:

[0092] ;

[0093] Where q is a generalized variable; [M] is the global mass matrix; [K] is the global stiffness matrix; and [C] is the global damping matrix.

[0094] The most common static loads applied during tool operation are used to perform harmonic response analysis, in order to verify whether the frequency at which the displacement peak occurs in the analysis is consistent with the natural frequencies of the modal analysis. The governing equations of motion for the model are as follows:

[0095] ;

[0096] Where q is a generalized variable; [M] is the global mass matrix; [K] is the global stiffness matrix; [C] is the global damping matrix; and {F} is the global external force vector.

[0097] When the actual operating frequency coincides with or is close to the natural frequencies of the tool, resonance occurs, generating significant equivalent stress that greatly impacts subsequent fatigue life. Conversely, if the frequency does not coincide and is far from the natural frequencies, the equivalent stress is close to zero and can be ignored, having no impact on subsequent fatigue life. Therefore, for each mode, the natural frequencies of the model structure under different modes are analyzed. Combined with actual drilling data analysis, it is determined whether the actual operating frequency of the tool is close to the natural frequencies of the model, thereby determining whether resonance exists. For example, taking the first six modal analysis cloud diagrams of a push-type rotary steered bottom drill string as an example, the first modal analysis cloud diagram is as follows: Figure 8 As shown, the second-order modal analysis contour plot is as follows: Figure 9 As shown, the third-order modal analysis contour plot is as follows: Figure 10 As shown, the fourth-order modal analysis contour plot is as follows: Figure 11 As shown, the 5th-order modal analysis contour plot is as follows: Figure 12 As shown, the 6th-order modal analysis contour plot is as follows: Figure 13As shown. The dynamic stress cloud diagram of the latitude-longitude rotating guide is as follows. Figure 14 As shown in the diagram. The fatigue life cloud map of the latitude and longitude rotary guide is as follows. Figure 15 As shown.

[0098] Step S14: If the natural frequency does not meet the resonance condition with the actual operating frequency, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool.

[0099] In this embodiment, if the natural frequency and the actual operating frequency do not meet the resonance condition, the dynamic stress spectrum under the dynamic load spectrum is input into the finite element model for calculation, and the fatigue life of the downhole drilling tool is predicted by combining the Miner linear damage accumulation calculation model under the number of cycles.

[0100] If resonance does not occur, the dynamic stress spectrum under the dynamic load spectrum is calculated using finite element simulation. A standard sample is taken from the inner wall of the raw material corresponding to the tool, and the material SN curve is obtained through mechanical testing. The fatigue life prediction of the rotary guide system is completed using the high-cycle fatigue criterion.

[0101] Specifically, the finite element simulation uses the dynamic stress spectrum under the dynamic load spectrum. A material mapping is established based on the material's SN experimental data, the material surface roughness is set, and the Miner linear damage accumulation calculation model, which belongs to the high-cycle fatigue criterion, is selected to predict the fatigue life of the rotary guide system. The result is the number of cycles of the dynamic load spectrum. The expression for the Miner linear damage accumulation criterion is:

[0102] ;

[0103] in, This indicates the damage to a part or component caused by the number of cycles under a certain stress level. ,in Let D be the number of cycles required to reach fatigue failure under this stress level. The total damage generated under k stress levels is denoted as D, and its defined failure criterion is:

[0104] .

[0105] Step S15: If the natural frequency and the actual operating frequency meet the resonance condition, the time domain data of the dynamic load spectrum is converted into frequency domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is analyzed to calculate the power spectral density response. The fatigue life of the downhole drilling tool is predicted using the power spectral density response.

[0106] In this embodiment, if the natural frequency and the actual operating frequency meet the resonance condition, the resonance frequency range between the natural frequency and the actual operating frequency is determined. Based on the resonance frequency range, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. The power spectral density curve of the random dynamic load is plotted according to the power spectral density, and spectral analysis is performed on the power spectral density curve to calculate the power spectral density response. Based on Miner's rule under cyclic stress and using the power spectral density response, the fatigue life of the downhole drilling tool is predicted. If resonance occurs, the resonance frequency range is determined, and the load excitation of the harmonic frequency is applied to the system model. The excitation conditions when the model reaches resonance in different directions are obtained, the distribution of vibration displacement when resonance occurs is clarified, the response amplitude and phase angle of the system at a specific harmonic frequency are analyzed, the system amplitude amplification is determined, the time domain data of the random dynamic load is converted into frequency domain data, the power spectral density of the applied load is obtained, random vibration load is added by configuring the power spectral density spectrum, and the PSD (Power Spectral Density) response is obtained. The material mapping is established based on the material SN experimental data, and the life cycle of the model is determined by statistical principles based on the linear fatigue damage accumulation theory.

[0107] Specifically, the distribution of vibration displacement at the occurrence of resonance is clearly defined, and the response amplitude and phase angle of the system at specific harmonic frequencies are analyzed to determine the amplitude amplification of the system. Time-series data is obtained by discretizing the time-domain data of the random dynamic load, and a discrete Fourier transform is calculated to convert the time-domain data into frequency-domain data. The square modulus of the result is then calculated to obtain the square of the amplitude of each frequency component, i.e., the power spectral density of the load. Power spectral density of random vibration load:

[0108] ;

[0109] ;

[0110] in, For power spectral density, Let be the autocorrelation function of the stochastic process. and They are respectively and The load value at time t. For a single input power spectral density value, the output of the model system is:

[0111] ;

[0112] in, Spectral density input, For spectral density response, For a single degree of freedom input, This is the output for the calculated single degree of freedom.

[0113] The specific process for this application is as follows: Figure 16 As shown, firstly, a drill bit rock-breaking model and a rotary steered drill string dynamics model are constructed respectively. Based on the drill bit rock-breaking model and the rotary steered drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock fracturing is constructed. Then, transient dynamic simulations are performed on drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool. Next, a three-dimensional structural diagram of the downhole drilling tool and its corresponding drill string assembly is drawn, material properties are defined, and meshes are generated to construct a finite element model of the downhole drilling tool. Then, modal analysis and harmonic response analysis are performed on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary steered structure, and the corresponding natural frequencies are determined using the eigenvalues ​​and eigenvectors of the rotary steered structure. The system determines whether the natural frequency and the actual operating frequency meet the resonance condition (i.e., whether resonance exists between the natural frequency and the actual operating frequency). If the natural frequency and the actual operating frequency do not meet the resonance condition (i.e., no resonance exists), the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool. If the natural frequency and the actual operating frequency meet the resonance condition (i.e., resonance exists), the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is then analyzed to calculate the power spectral density response, and the fatigue life of the downhole drilling tool is predicted using the power spectral density response.

[0114] In this embodiment, a drill bit rock-breaking model and a rotary steerable drill string dynamics model are constructed. Based on the drill bit rock-breaking model and the rotary steerable drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock breaking is constructed. The drill string dynamics model is used to perform transient dynamic simulations on pre-acquired drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool. Based on the dynamic load spectrum, a finite element model of the downhole drilling tool is constructed. Modal analysis and harmonic response analysis are performed on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary steerable structure. The eigenvalues ​​and eigenvectors of the rotary steerable structure are then used to determine the phase... The system determines whether the natural frequency and the actual operating frequency meet the resonance condition. If the natural frequency and the actual operating frequency do not meet the resonance condition, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool. If the natural frequency and the actual operating frequency meet the resonance condition, the time domain data of the dynamic load spectrum is converted into frequency domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is then analyzed to calculate the power spectral density response, and the fatigue life of the downhole drilling tool is predicted using the power spectral density response. This application constructs a drill string dynamics model coupling the wellbore, drill string, drill bit, and rock breaking processes. It effectively considers the dynamic loads caused by drill bit excitation and wellbore collision during rock breaking. Transient dynamic simulations are performed using the drill string dynamics model to calculate the dynamic load spectrum at both ends of the drilling tool. A finite element model of the downhole drilling tool is constructed, and the eigenvalues ​​and eigenvectors of the rotary steering structure are calculated. The corresponding natural frequencies are determined, and the downhole resonance problem is considered. It is determined whether the natural frequencies and the actual operating frequencies meet the resonance condition. If the resonance condition is met, spectral analysis of the power spectral density is performed. Fatigue loss factors are comprehensively considered to predict the fatigue life of the downhole drilling tool, improving the accuracy and efficiency of downhole drilling tool fatigue life prediction and reducing the complexity of the fatigue life research process.

[0115] See Figure 17 As shown in the figure, an embodiment of the present invention discloses a fatigue life prediction device for downhole drilling tools, which may specifically include:

[0116] Model building module 11 is used to build a drill bit rock breaking model and a rotary steerable drill string dynamics model, and to build a drill string dynamics model that couples wellbore-drill string-drill bit-rock breaking based on the drill bit rock breaking model and the rotary steerable drill string dynamics model.

[0117] The dynamic load spectrum calculation module 12 is used to perform transient dynamic simulation on the pre-acquired drilling parameters using the drill string dynamic model, so as to calculate the dynamic load spectrum at both ends of the drilling tool and construct a finite element model of the downhole drilling tool based on the dynamic load spectrum.

[0118] The frequency resonance judgment module 13 is used to perform modal analysis and harmonic response analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine the corresponding natural frequency using the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine whether the natural frequency meets the resonance condition with the actual operating frequency.

[0119] The first fatigue life prediction module 14 is used to input the dynamic load spectrum into the finite element model if the natural frequency and the actual working frequency do not meet the resonance condition, so as to predict the fatigue life of the downhole drilling tool.

[0120] The second fatigue life prediction module 15 is used to convert the time-domain data of the dynamic load spectrum into frequency-domain data to obtain the power spectral density if the natural frequency and the actual operating frequency meet the resonance condition, perform spectral analysis on the power spectral density of the downhole drilling tool to calculate the power spectral density response, and use the power spectral density response to predict the fatigue life of the downhole drilling tool.

[0121] In this embodiment, a drill bit rock-breaking model and a rotary steerable drill string dynamics model are constructed. Based on the drill bit rock-breaking model and the rotary steerable drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock breaking is constructed. The drill string dynamics model is used to perform transient dynamic simulations on pre-acquired drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool. Based on the dynamic load spectrum, a finite element model of the downhole drilling tool is constructed. Modal analysis and harmonic response analysis are performed on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary steerable structure. The eigenvalues ​​and eigenvectors of the rotary steerable structure are then used to determine the phase... The system determines whether the natural frequency and the actual operating frequency meet the resonance condition. If the natural frequency and the actual operating frequency do not meet the resonance condition, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool. If the natural frequency and the actual operating frequency meet the resonance condition, the time domain data of the dynamic load spectrum is converted into frequency domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is then analyzed to calculate the power spectral density response, and the fatigue life of the downhole drilling tool is predicted using the power spectral density response. This application constructs a drill string dynamics model coupling the wellbore, drill string, drill bit, and rock breaking processes. It effectively considers the dynamic loads caused by drill bit excitation and wellbore collision during rock breaking. Transient dynamic simulations are performed using the drill string dynamics model to calculate the dynamic load spectrum at both ends of the drilling tool. A finite element model of the downhole drilling tool is constructed, and the eigenvalues ​​and eigenvectors of the rotary steering structure are calculated. The corresponding natural frequencies are determined, and the downhole resonance problem is considered. It is determined whether the natural frequencies and the actual operating frequencies meet the resonance condition. If the resonance condition is met, spectral analysis of the power spectral density is performed. Fatigue loss factors are comprehensively considered to predict the fatigue life of the downhole drilling tool, improving the accuracy and efficiency of downhole drilling tool fatigue life prediction and reducing the complexity of the fatigue life research process.

[0122] In some specific embodiments, the model building module 11 may specifically include:

[0123] The acquisition module is used to acquire the actual working conditions, wellbore trajectory, and drill string assembly data of the target formation.

[0124] The drill bit rock breaking model construction module is used to establish the contact relationship between the drill bit and the rock of the target formation as an elastoplastic body, and to construct the drill bit rock breaking model using rock breaking criteria.

[0125] The rotary steerable drill string dynamics model building module is used to build a rotary steerable drill string dynamics model with downhole drilling tools under wellbore constraints based on the actual working conditions, the wellbore trajectory, and the drill string assembly data.

[0126] In some specific embodiments, the model building module 11 may specifically include:

[0127] The drill string dynamics model building module is used to construct a drill string dynamics model that couples wellbore, drill string, drill bit, and rock breaking based on the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the interaction mechanism between the upper longitudinal slender flexible drill string dynamic boundary and the lower transverse multi-cutting tooth drill bit rock breaking boundary, and the dynamic torque relationship built by the displacement and rotation degrees of freedom of the drill bit rock breaking model and the rotary steered drill string dynamics model.

[0128] In some specific embodiments, the dynamic load spectrum calculation module 12 may specifically include:

[0129] The drawing module is used to draw 3D structural diagrams of downhole drilling tools and their corresponding drill string assemblies.

[0130] The finite element model construction module is used to define material properties and generate meshes, and to construct a finite element model of the downhole drilling tool based on the three-dimensional structural diagram of the downhole drilling tool and the corresponding drill string assembly and the dynamic load spectrum.

[0131] In some specific embodiments, the frequency resonance determination module 13 may specifically include:

[0132] The matrix calculation module is used to perform matrix calculations on the finite element model to obtain the stiffness matrix and the mass matrix;

[0133] The solution module is used to generate an eigenvalue problem based on the stiffness matrix and the mass matrix, and solve the eigenvalue problem to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure.

[0134] In some specific embodiments, the first fatigue life prediction module 14 may specifically include:

[0135] The first prediction module is used to input the dynamic stress spectrum under the dynamic load spectrum into the finite element model for calculation, and combine it with the Miner linear damage accumulation calculation model under the number of cycles to predict the fatigue life of the downhole drilling tool.

[0136] In some specific embodiments, the second fatigue life prediction module 15 may specifically include:

[0137] The time-domain data conversion module is used to determine the resonance frequency range between the natural frequency and the actual operating frequency if the resonance condition is met, and to convert the time-domain data of the dynamic load spectrum into frequency-domain data based on the resonance frequency range to obtain the power spectral density.

[0138] The modal analysis and harmonic response analysis module is used to plot the power spectral density curve of the random dynamic load based on the power spectral density, and to perform spectral analysis on the power spectral density curve to calculate the power spectral density response.

[0139] The second prediction module is used to predict the fatigue life of downhole drilling tools based on Miner's law under cyclic stress and by utilizing the power spectral density response.

[0140] Figure 18 This is a schematic diagram of an electronic device provided in an embodiment of this application. The electronic device 20 may specifically include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input / output interface 25, and a communication bus 26. The memory 22 stores a computer program, which is loaded and executed by the processor 21 to implement the relevant steps in the downhole drilling tool fatigue life prediction method executed by the electronic device disclosed in any of the foregoing embodiments.

[0141] In this embodiment, the power supply 23 is used to provide operating voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and external devices, and the communication protocol it follows can be any communication protocol applicable to the technical solution of this application, and is not specifically limited here; the input / output interface 25 is used to acquire external input data or output data to the outside world, and its specific interface type can be selected according to specific application needs, and is not specifically limited here.

[0142] In addition, the memory 22, as a carrier for resource storage, can be a read-only memory, random access memory, disk or optical disk, etc. The resources stored on it include operating system 221, computer program 222 and data 223, etc., and the storage method can be temporary storage or permanent storage.

[0143] The operating system 221 manages and controls the various hardware devices and computer programs 222 on the electronic device 20 to enable the processor 21 to perform calculations and processing on the data 223 in the memory 22. The operating system 221 can be Windows, Unix, Linux, etc. The computer program 222, in addition to including a computer program capable of performing the downhole drilling tool fatigue life prediction method executed by the electronic device 20 as disclosed in any of the foregoing embodiments, may further include computer programs capable of performing other specific tasks. The data 223 may include data received by the downhole drilling tool fatigue life prediction device from external devices, as well as data collected by its own input / output interface 25.

[0144] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0145] Furthermore, this application also discloses a computer-readable storage medium storing a computer program. When the computer program is loaded and executed by a processor, it implements the steps of the downhole drilling tool fatigue life prediction method disclosed in any of the foregoing embodiments.

[0146] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0147] The above provides a detailed description of the method, apparatus, equipment, and storage medium for predicting the fatigue life of downhole drilling tools provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the fatigue life of downhole drilling tools, characterized in that, include: Construct a drill bit rock breaking model and a rotary steerable drill string dynamics model, and based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, construct a drill string dynamics model that couples wellbore-drill string-drill bit-rock breaking. The drill string dynamics model is used to perform transient dynamic simulation on the pre-acquired drilling parameters to calculate the dynamic load spectrum at both ends of the drilling tool, and a finite element model of the downhole drilling tool is constructed based on the dynamic load spectrum. Modal analysis and harmonic response analysis are performed on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and the corresponding natural frequencies are determined using the eigenvalues ​​and eigenvectors of the rotary guide structure. It is then determined whether the natural frequencies meet the resonance condition with the actual operating frequency. If the natural frequency does not meet the resonance condition with the actual operating frequency, the dynamic load spectrum is input into the finite element model to predict the fatigue life of the downhole drilling tool. If the natural frequency and the actual operating frequency meet the resonance condition, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. The power spectral density of the downhole drilling tool is then analyzed to calculate the power spectral density response. The fatigue life of the downhole drilling tool is then predicted using the power spectral density response.

2. The method for predicting the fatigue life of downhole drilling tools according to claim 1, characterized in that, The construction of the drill bit rock breaking model and the rotary steerable drill string dynamics model includes: Acquire actual working conditions, wellbore trajectory, and drill string assembly data for the target formation; The PDC drill bit is treated as a rigid body, and the rock of the target formation is treated as an elastoplastic body. The contact relationship between the drill bit and the rock is established, and the rock breaking model of the drill bit is constructed using the rock breaking criterion. Based on the actual working conditions, the wellbore trajectory, and the drill string assembly data, a dynamic model of a rotary steerable drill string with downhole drilling tools under wellbore constraints is established.

3. The method for predicting the fatigue life of downhole drilling tools according to claim 1, characterized in that, The drilling string dynamics model, which is a coupling of wellbore-drill string-drill bit-rock fracturing, is constructed based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, including: Based on the interaction between the active torque of the drill bit caused by the drill string drive and the reaction torque of the drill bit caused by the rock shear resistance, the interaction mechanism between the upper longitudinal slender flexible drill string dynamic boundary and the lower transverse multi-cutting tooth drill bit rock breaking boundary at the connection point, and combined with the dynamic torque relationship established by the displacement and rotation degrees of freedom of the drill bit rock breaking model and the rotary steered drill string dynamic model, a drill string dynamic model coupling wellbore-drill string-drill bit-rock breaking is constructed.

4. The method for predicting the fatigue life of downhole drilling tools according to claim 1, characterized in that, The construction of the finite element model of the downhole drilling tool based on the dynamic load spectrum includes: Draw a 3D structural diagram of downhole drilling tools and corresponding drill string assemblies; Material properties are defined and meshes are generated. A finite element model of the downhole drilling tool is constructed based on the three-dimensional structural diagram of the downhole drilling tool and its corresponding drill string assembly and the dynamic load spectrum.

5. The method for predicting the fatigue life of downhole drilling tools according to claim 1, characterized in that, The modal analysis and harmonic response analysis of the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure includes: Matrix calculations are performed on the finite element model to obtain the stiffness matrix and mass matrix; Based on the stiffness matrix and the mass matrix, an eigenvalue problem is generated, and the eigenvalue problem is solved to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure.

6. The method for predicting the fatigue life of downhole drilling tools according to claim 1, characterized in that, The step of inputting the dynamic load spectrum into the finite element model to predict the fatigue life of the downhole drilling tool includes: The dynamic stress spectrum under the dynamic load spectrum is input into the finite element model for calculation, and the fatigue life of the downhole drilling tool is predicted by combining the Miner linear damage accumulation calculation model under the number of cycles.

7. The method for predicting the fatigue life of downhole drilling tools according to any one of claims 1 to 6, characterized in that, If the natural frequency and the actual operating frequency meet the resonance condition, the time-domain data of the dynamic load spectrum is converted into frequency-domain data to obtain the power spectral density. Spectral analysis is performed on the power spectral density of the downhole drilling tool to calculate the power spectral density response. The fatigue life of the downhole drilling tool is predicted using the power spectral density response, including: If the natural frequency and the actual operating frequency meet the resonance condition, then the resonance frequency range between the natural frequency and the actual operating frequency is determined, and the time domain data of the dynamic load spectrum is converted into frequency domain data based on the resonance frequency range to obtain the power spectral density. Based on the power spectral density, a power spectral density curve of the random dynamic load is plotted, and spectral analysis is performed on the power spectral density curve to calculate the power spectral density response. The fatigue life of downhole drilling tools is predicted based on Miner's rule under cyclic stress and using the power spectral density response.

8. A device for predicting the fatigue life of downhole drilling tools, characterized in that, include: The model building module is used to build a drill bit rock breaking model and a rotary steerable drill string dynamics model. Based on the drill bit rock breaking model and the rotary steerable drill string dynamics model, a drill string dynamics model coupling wellbore-drill string-drill bit-rock breaking is constructed. The dynamic load spectrum calculation module is used to perform transient dynamic simulation of the pre-acquired drilling parameters using the drill string dynamics model, so as to calculate the dynamic load spectrum at both ends of the drilling tool, and construct the finite element model of the downhole drilling tool based on the dynamic load spectrum. The frequency resonance judgment module is used to perform modal analysis on the finite element model to calculate the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine the corresponding natural frequency using the eigenvalues ​​and eigenvectors of the rotary guide structure, and to determine whether the natural frequency meets the resonance condition with the actual operating frequency. The first fatigue life prediction module is used to input the dynamic load spectrum into the finite element model if the natural frequency and the actual working frequency do not meet the resonance condition, so as to predict the fatigue life of the downhole drilling tool. The second fatigue life prediction module is used to convert the time-domain data of the dynamic load spectrum into frequency-domain data to obtain the power spectral density if the natural frequency and the actual operating frequency meet the resonance condition, perform spectral analysis on the power spectral density of the downhole drilling tool to calculate the power spectral density response, and use the power spectral density response to predict the fatigue life of the downhole drilling tool.

9. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the downhole drilling tool fatigue life prediction method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, Used to store a computer program; wherein, when the computer program is executed by a processor, it implements the downhole drilling tool fatigue life prediction method as described in any one of claims 1 to 7.

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