Rotary steering fatigue life prediction method and system considering dynamic characteristics

Abstract

The application provides a rotary steering fatigue life prediction method and system considering dynamic characteristics. The method establishes a three-dimensional structure model based on a set target test structure, analyzes dangerous points based on a static finite element simulation model combined with a set test well section, and determines the static Mises stress of each point. A dynamic boundary load is introduced to construct a dynamic finite element simulation model to analyze the dynamic Mises stress of each point. The dynamic load addition coefficient of each point is calculated according to the dynamic maximum stress and the static stress. In addition, the dynamic load characteristics at each point are analyzed from the aspects of the drilling pressure, torque and bending moment. The fatigue characteristics of the structure corresponding to the dangerous point are analyzed according to the material. A linear damage accumulation operation model is designed, the above calculation results are comprehensively taken as inputs, and the fatigue index value is calculated for multiple rounds, so as to determine the fatigue life of the whole string tool. The scheme can overcome the defects of the prior art, such as incomplete angle calculation and insufficient accuracy, fully considers the dynamic load characteristics and the material characteristics of different structures, and realizes accurate prediction.

Description

Technical Field

[0001] This invention relates to the field of drilling tool reliability monitoring and evaluation technology, and in particular to a method and system for predicting the fatigue life of rotary steering tools that takes into account dynamic characteristics. Background Technology

[0002] Because rotary steerable tools rotate at high speed for extended periods within a narrow wellbore, they are subjected to coupled vibrations from the lateral, longitudinal, and torsional directions, as well as dynamic loads such as drilling pressure, torque, and bending moment. Prolonged use inevitably leads to tool damage and fatigue failure. To effectively assess the service life and application risks of rotary steerable tools and reduce the risk of fatigue failure, it is essential to comprehensively consider the severe operational loads on the tool at the time of manufacture and to conservatively predict its fatigue life.

[0003] Rotary steerable drill bits (SSDs) rotate at high speeds continuously within narrow wellbores, enduring coupled vibrations, complex loads, and random collisions. Due to the complexity of dynamic factors and nonlinear conditions, static finite element methods are insufficient for accurately estimating the tool's true loads. A dynamic finite element model considering dynamic characteristics is necessary to fully account for the stresses borne by the tool under dynamic loads. Due to the unique tool structure and working principle of static push-type rotary steerable systems, the steerable head contains complex mechanical structures such as upper and lower drive shafts, a non-rotating outer sleeve, and ribs. The drive shafts rotate at high speed along with the drill string body structure. The non-rotating outer sleeve is connected to the drive shaft via upper and lower sliding bearings and remains essentially stationary. The ribs, located outside the non-rotating outer sleeve, support the wellbore to provide the required guiding force to the drill bit. Fatigue load characteristics differ at different structures and locations; some locations are dominated by alternating positive and negative bending moments, while others are constantly subjected to tensile forces. Therefore, it is necessary to analyze the stress characteristics of each complex structure and clarify the stress ratio of the alternating loads at different locations to accurately describe the load history of the tool.

[0004] Existing research includes some methods for predicting drill string fatigue life. For example, patent document CN113065211B provides a method for predicting the fatigue life of bottom-end drill string assemblies based on drill string dynamics. This method uses conventional tool bottom-end drill string dynamics analysis to calculate the time-varying functions of nodal displacement and acceleration; it calculates the equivalent stress at the nodals and predicts the fatigue life of the bottom-end drill string based on the Walker model. Patent document CN103967428B provides a method for evaluating the fatigue failure risk of drill strings. It measures the wellbore structure, drill string assembly structure, and actual wellbore trajectory parameters of the target well to establish a finite element model of drill string dynamics; it solves for the buckling stress, dynamic bending stress, and dynamic axial force of each node section of the drill string, as well as the corrected dynamic bending stress; it solves for the fatigue frequency coefficient of each node section of the drill string; and it provides a graph showing the relationship between the fatigue frequency coefficient and the well depth, thereby evaluating whether the drill string has a high risk of fatigue failure. However, all of the above methods lack dynamic modeling and boundary condition processing for rotary steering systems, and also lack analysis of alternating load stress ratios for different dangerous locations. Therefore, they cannot reliably and accurately predict the fatigue life of rotary steering systems with complex operating mechanisms.

[0005] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for predicting the fatigue life of a rotary steering system considering dynamic characteristics. This method establishes a three-dimensional structural model based on a predetermined target test structure; analyzes critical points in a predetermined test well section using a static finite element simulation model to determine the static Mises stress at each critical point; introduces dynamic boundary loads to construct a dynamic finite element simulation model to analyze the dynamic Mises stress at each critical point; calculates the dynamic load additive coefficient at each critical point based on the dynamic maximum stress and static stress; further analyzes the dynamic load characteristics and load history at each point from multiple aspects, including drilling pressure, torque, and bending moment, to determine the stress ratio at each critical point; analyzes the fatigue characteristics of the material corresponding to the critical point; designs a linear damage accumulation calculation model; and integrates the above calculation results as inputs to calculate fatigue index values ​​in multiple rounds, thereby determining the fatigue life of the entire tool train. This solution overcomes the shortcomings of existing technologies, such as incomplete calculation perspectives and insufficient accuracy, by fully considering dynamic load characteristics and the load history of different critical points to achieve accurate prediction. In one embodiment, the method includes:

[0007] Structural model establishment steps: Select a target test structure for the rotary guide tool based on its working mechanism, establish a corresponding three-dimensional structural model based on the target test structure, and perform finite element mesh generation;

[0008] Hazard point analysis steps: Based on the static finite element simulation model and the set test well section, analyze the hazard points in the target test structure and determine the static Mises stress at each hazard point;

[0009] Dynamic simulation analysis steps: Introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each critical point;

[0010] Dynamic load analysis steps: Calculate the dynamic load addition factor corresponding to each critical point based on the dynamic maximum stress and static stress at each critical point;

[0011] Load history analysis steps: Analyze the dynamic load characteristics at different critical points from multiple aspects such as drilling pressure, torque, and bending moment, and classify and label them;

[0012] Material fatigue analysis steps: Perform fatigue tests on the material of the structure corresponding to the critical point to obtain material fatigue curve data characterizing fatigue properties;

[0013] Fatigue life decision-making steps: Taking the results of static finite element simulation, dynamic load addition coefficient, load characteristic identification and material fatigue curve data as input, a linear damage accumulation calculation model is designed as the fatigue analysis calculation model. The fatigue index values ​​of different dangerous points are calculated in multiple rounds using the fatigue analysis calculation model, and the target fatigue life prediction result of the rotary guide string tool is selected based on it.

[0014] In one optional embodiment, during the structural model building step, the selected rotary steering tool target test structure characterizes the entire rotary steering tool series, including multiple sub-functional structures among the steering head unit, geological survey unit, central control unit, and upper connecting drill pipe unit.

[0015] Furthermore, in one embodiment, in the hazard analysis step, a static finite element simulation model is constructed based on the elastic body equilibrium differential equation, wherein the elastic body equilibrium differential equation is as follows:

[0016]

[0017] Where σ is the stress; x, y, z are Cartesian coordinate vectors; F b It is a volume force.

[0018] Preferably, in one embodiment, in the dynamic simulation analysis step, the dynamic boundary load is the dynamic drilling pressure and counter-torque load at the drill bit when the maximum drilling pressure is applied to break the rock; the dynamic Mises stress spectrum of different test well sections at each dangerous point is calculated by dynamic simulation, and the maximum Mises stress value is extracted.

[0019] In one embodiment, during the dynamic simulation analysis step, based on the dynamic drilling pressure and counter-torque load data at the drill bit, a finite element simulation model of the rotational steering dynamics is established based on the Lagrange equation. The dynamic equation of the finite element simulation model is as follows:

[0020]

[0021] The Lagrange equation is:

[0022]

[0023] Where T is kinetic energy; U is potential energy; q is displacement vector; F is generalized force; t is time; [M] is global mass matrix; [K] is global stiffness matrix; [C] is global damping matrix; and {F} is global external force vector.

[0024] Furthermore, in one embodiment, in the dynamic simulation analysis step, the dynamic drilling pressure during the rock breaking process is calculated by adding a dynamic function that varies sinusoidally with the drilling pressure to the target drilling pressure, as shown in the following formula:

[0025] W b =W0(1+asin(nθ))

[0026] Among them, W b W0 is the actual drilling pressure at the drill bit; a is the drilling pressure fluctuation amplitude, which is related to the longitudinal vibration of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0027] In an optional embodiment, the drill bit counter-torque in the dynamic simulation analysis step includes the torque under drilling pressure, the torque under pushing force, and the friction torque along the drill string, as shown in the following formula:

[0028] T total =T w +T s +T f

[0029]

[0030] T s =μ s F s r b

[0031] Among them, T total T represents the actual torque at the drill bit. w T is the torque under drilling pressure; s The torque under the pushing force; T f The friction torque along the drill string needs to be calculated based on the mechanics theory of the drill string; G is the shear modulus; I z The polar moment of inertia of the beam element; le θ1 is the length of the lowest beam element; θ2 is the circumferential rotation angle of the drill bit node; θ3 is the circumferential rotation angle of the next node on the drill bit; ω is the drill bit rotation speed; δ is the critical rotation speed of the viscous phase; r b The outer diameter of the drill bit; μ s μ is the static friction coefficient. k d is the coefficient of kinetic friction; c γ is the attenuation coefficient; eq It represents the slip ratio.

[0032] Furthermore, in one embodiment, in the material fatigue analysis step, for the structure corresponding to the danger point, a material sample is collected from the matching position of its forging raw material, and an axial tensile and compressive fatigue test is performed using a high-frequency fatigue testing machine based on the principle of the lifting method of the material sample to complete the fatigue test; the matching position is determined according to the working characteristics of the current structure.

[0033] In a preferred embodiment, in the material fatigue analysis step, after the fatigue test is completed, a set stress level is selected based on the stress data from the rise and fall method test, and a group method test is performed in combination with the set confidence level requirements. The fatigue SN curve of the current material is plotted based on the fatigue test results and the group method test results, wherein the number of test specimens corresponds to the confidence level requirements.

[0034] Optionally, in one embodiment, in the fatigue life decision-making step, the Miner linear damage accumulation calculation model is designed by taking the integrated static finite element simulation results, dynamic load addition coefficient, load characteristic identifier, and material fatigue curve data as inputs, as follows:

[0035]

[0036] For different risk points, multiple rounds of targeted fatigue life prediction are conducted, and the minimum value among the fatigue index values ​​of different risk points is selected as the target fatigue life prediction result of the rotary guide string tool.

[0037] In the formula, n i N represents the number of cycles under a certain level of cyclic stress. i denoted as the number of cycles under a certain level of cyclic stress; D represents the sum of fatigue damage under various levels of stress.

[0038] Based on other aspects of the methods described in any one or more of the foregoing embodiments, the present invention also provides a storage medium storing program code that can implement the methods described in any one or more of the foregoing embodiments.

[0039] Based on the application aspects of the methods described in any one or more of the above embodiments, the present invention also provides a rotary guide fatigue life prediction system that considers dynamic characteristics, the system performing the methods described in any one or more of the above embodiments.

[0040] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0041] This invention provides a method and system for predicting the fatigue life of a rotary steering system that considers dynamic characteristics. The method establishes a three-dimensional structural model based on a predetermined target test structure. It analyzes critical points in a predetermined test section using a static finite element simulation model to determine the static Mises stress at each point. Furthermore, it introduces dynamic boundary loads to construct a dynamic finite element simulation model and analyzes the dynamic Mises stress at each point. The method calculates the dynamic load addition coefficient at each point based on the maximum dynamic stress and the static stress. This approach analyzes different critical points on the target test mechanism and then introduces dynamic boundary loads to calculate the dynamic stress, fully considering the dynamic load characteristics of the tool during application, and predicting the tool's load stress data more accurately and conservatively.

[0042] Furthermore, the dynamic load characteristics at various points are analyzed from multiple perspectives, including drilling pressure, torque, and bending moment; the material fatigue characteristics of the structure corresponding to the critical points are analyzed; and a Miner linear damage accumulation calculation model is designed to integrate the above calculation results as input to calculate fatigue index values, thereby determining the fatigue life of the entire tool series. By analyzing the dynamic load characteristics at various points from multiple perspectives and testing to determine the fatigue characteristics corresponding to the stress characteristics of each structure, the above operations can be effectively applied to rotary guide tools with complex structures, achieving accurate and reliable fatigue life prediction analysis.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0044] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0045] Figure 1 This is a flowchart illustrating a method for predicting the fatigue life of a rotary guide considering dynamic characteristics, provided in an embodiment of the present invention.

[0046] Figure 2 This is a schematic diagram of the location of the danger point determined by the static analysis of the rotary guide under the "latitude and longitude navigation" method provided in the embodiment of the present invention for predicting the fatigue life of rotary guides;

[0047] Figure 3 This is an example diagram of a standard fatigue specimen for material fatigue testing in the rotary guide fatigue life prediction method provided in this embodiment of the invention;

[0048] Figure 4 This is an example diagram of the measured SN fatigue curve in the rotary guide fatigue life prediction method provided in this embodiment of the invention;

[0049] Figure 5 This is a schematic diagram of the fatigue life cloud map of a static push-type rotary guide using the fatigue life prediction method for rotary guides provided in the embodiments of the present invention.

[0050] Figure 6 This is a schematic diagram of the structure of a rotary guide fatigue life prediction system considering dynamic characteristics, provided in another embodiment of the present invention. Detailed Implementation

[0051] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples. Those skilled in the art will then fully understand how the present invention uses technical means to solve technical problems and achieve technical effects, and will be able to implement the present invention specifically based on the above-described implementation process. It should be noted that, as long as there is no conflict, the various embodiments and features of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0052] Although the flowchart describes the operations as sequential processes, many of these operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. A process can terminate when its operation is complete, but it may also have additional steps not included in the diagram. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0053] Computer equipment includes user equipment and network equipment. User equipment or clients include, but are not limited to, computers, smartphones, and PDAs (Personal Digital Assistants); network equipment includes, but is not limited to, a single network server, a server group consisting of multiple network servers, or a cloud based on cloud computing consisting of a large number of computers or network servers. Computer equipment can operate independently to implement this invention, or it can connect to a network and implement this invention through interaction with other computer devices within the network. The network in which the computer equipment resides includes, but is not limited to, the Internet, wide area networks (WANs), metropolitan area networks (MANs), local area networks (LANs), and VPN networks.

[0054] The terms “first,” “second,” etc., may be used herein to describe various units, but these units should not be limited by these terms; they are used merely to distinguish one unit from another. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items. When a unit is referred to as “connected” or “coupled” to another unit, it may be directly connected or coupled to said other unit, or there may be intermediate units present.

[0055] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are also intended to include the plural. It should also be understood that the terms “comprising” and / or “including” as used herein specify the presence of the stated features, integers, steps, operations, units, and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components, and / or combinations thereof.

[0056] Rotary steerable drilling rigs are the most advanced directional drilling equipment in the world today, representing the highest level of drilling technology. Because they rotate at high speed for extended periods within a narrow wellbore, they are subjected to coupled vibrations from the lateral, longitudinal, and torsional directions, as well as dynamic loads such as drilling pressure, torque, and bending moment. After prolonged use, tool damage and fatigue failure are inevitable. Static push-type rotary steerable drilling rigs are the most widely used type in China. To effectively assess the service life and application risks of rotary steerable drilling rigs and reduce the risk of fatigue failure, it is essential to comprehensively consider the severe operating loads on the tool at the time of manufacture and conservatively predict its fatigue life.

[0057] To achieve fatigue life prediction for rotary steerable drilling tools, the following technical challenges need to be overcome: (1) Rotary steerable drilling tools rotate at high speed in a narrow wellbore, bearing coupled vibrations, complex loads, and random collisions. Due to the complexity of dynamic factors and nonlinear conditions, static finite element methods are no longer sufficient to accurately estimate the actual load on the tool. It is necessary to establish a dynamic finite element model that considers dynamic characteristics and fully considers the stress borne by the tool under dynamic loads. (2) Due to the special tool structure and working principle of the static push-type rotary steerable system, its guide head contains complex mechanical structures such as upper and lower drive shafts, non-rotating outer sleeves, and ribs. The drive shafts rotate at high speed following the drill string body structure. The non-rotating outer sleeves are connected to the drive shafts through upper and lower sliding bearings and remain basically stationary. The ribs are outside the non-rotating outer sleeves to support the well wall in order to provide the required guiding force to the drill bit. The fatigue load characteristics are different in different structures and locations. Some locations are mainly subjected to alternating positive and negative bending moments, while some locations are always subjected to tensile forces. Therefore, it is necessary to analyze the stress characteristics of each complex structure and clarify the stress ratio of the alternating loads at different locations in order to accurately describe the load history of the tool.

[0058] Existing research includes some methods for predicting drill string fatigue life. For example, patent document CN113065211B provides a method for predicting the fatigue life of bottom-end drill string assemblies based on drill string dynamics. This method uses conventional tool bottom-end drill string dynamics analysis to calculate the time-varying functions of nodal displacement and acceleration; it calculates the equivalent stress at the nodals and predicts the fatigue life of the bottom-end drill string based on the Walker model. Patent document CN103967428B provides a method for evaluating the fatigue failure risk of drill strings. It measures the wellbore structure, drill string assembly structure, and actual wellbore trajectory parameters of the target well to establish a finite element model of drill string dynamics; it solves for the buckling stress, dynamic bending stress, and dynamic axial force of each node section of the drill string, as well as the corrected dynamic bending stress; it solves for the fatigue frequency coefficient of each node section of the drill string; and it provides a graph showing the relationship between the fatigue frequency coefficient and the well depth, thereby evaluating whether the drill string has a high risk of fatigue failure. The above schemes are for predicting the fatigue life of bottom-end drill strings using conventional tools, not for fatigue prediction methods for rotary steerable systems. Several points need to be emphasized based on this: First, conventional tools themselves have simple structures and lack modeling and boundary condition handling processes for rotary steering systems. Second, for such simple structures as conventional tools, calculations only use beam elements with uniform cross-sections, without considering the actual structure, making it impossible to accurately predict the fatigue life of tools with many minute features, whether conventional or complex rotary steering tools. Third, there is a lack of analysis on alternating loads and stress ratios for different critical locations.

[0059] The above-mentioned solutions all lack modeling and boundary condition processing for rotary steering systems, as well as stress ratio analysis of alternating loads at different dangerous locations. Furthermore, the working principles and structures of different types of rotary steering systems vary greatly, and their stress characteristics and load histories are also different. Therefore, the existing methods cannot be directly applied to various rotary steering tools, cannot meet the requirements for fatigue life prediction of rotary steering tools, and are difficult to reliably and accurately predict the fatigue life of rotary steering systems with complex operating mechanisms.

[0060] To address the aforementioned problems, this invention provides a method and system for predicting the fatigue life of a rotary guide considering dynamic characteristics. This invention improves upon the system in at least the following ways: First, it provides a detailed modeling and boundary condition processing procedure for the rotary guide system; second, it uses solid elements to consider the minute features of all tool positions; third, it fully considers the stress amplification effect borne by the tool under dynamic loads and proposes a new method for calculating the dynamic load amplification factor; fourth, it proposes a fatigue life calculation approach that calculates fatigue life in multiple rounds and compares the results to find the minimum value, taking into account different load histories and stress ratios.

[0061] This invention enables reliable prediction of the fatigue life of rotary steering systems under dynamic loads. It establishes a finite element simulation method for rotary steering dynamics that considers dynamic boundaries. The amplification of dynamic loads caused by downhole vibrations is effectively accounted for by using the ratio of dynamic maximum stress to static stress, thus reflecting the dynamic characteristics of the rotary steering system. Furthermore, fatigue life assessments are performed separately for different critical locations with varying stress and load histories, effectively considering the stress characteristics of different structural locations and enabling more accurate prediction of tool fatigue life. Moreover, the fatigue life prediction method proposed in this invention can be applied to various drilling tools without being limited by tool type, effectively assessing the service life and application status of drilling tools and reducing the risk of fatigue failure.

[0062] In establishing a static push-type rotary guide fatigue life prediction method, the present invention mainly considers the following two challenging issues:

[0063] (1) Rotary steerable drill bits are always rotating at high speed in narrow wellbores, and are subjected to coupled vibration, complex loads and random collisions. Due to the complexity of dynamic factors and nonlinear conditions, static finite element method can no longer accurately estimate the actual load of the tool. It is necessary to establish a dynamic finite element model that considers dynamic characteristics and fully considers the stress borne by the tool under dynamic load.

[0064] (2) Due to the special tool structure and working principle of the static push-type rotary steering system, its guide head contains complex mechanical structures such as upper and lower drive shafts, non-rotating outer sleeve, and ribs. The drive shaft rotates at high speed along with the drill string body structure. The non-rotating outer sleeve is connected to the drive shaft through two sliding bearings and remains basically stationary. The ribs are located outside the non-rotating outer sleeve to support the well wall in order to provide the required guiding force to the drill bit. The fatigue load characteristics are different in different structures and locations. Some locations are mainly subjected to alternating positive and negative bending moments, while other locations are always subjected to tensile forces. Therefore, by analyzing the stress characteristics of each complex structure, the stress ratio of the alternating load at different locations can be clarified, and the load history of the tool can be accurately described.

[0065] The following describes the detailed flow of the method according to an embodiment of the present invention with reference to the accompanying drawings, the steps of which can be executed in a computer system containing, for example, a set of computer-executable instructions. Although the logical order of the steps is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0066] Example 1:

[0067] Figure 1 This diagram illustrates a flow chart of the rotary guide fatigue life prediction method considering dynamic characteristics provided in Embodiment 1 of the present invention. (Refer to...) Figure 1 As can be seen, the method includes the following steps.

[0068] Structural model establishment steps: Select a target test structure for the rotary guide tool based on its working mechanism, establish a corresponding three-dimensional structural model based on the target test structure, and perform finite element mesh generation;

[0069] Hazard point analysis steps: Based on the static finite element simulation model and the set test well section, analyze the significant stress concentration points in the target test structure as hazard points, and determine the static Mises stress at each hazard point;

[0070] Dynamic simulation analysis steps: Introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each critical point;

[0071] Dynamic load analysis steps: Calculate the dynamic load addition factor corresponding to each critical point based on the dynamic maximum stress and static stress at each critical point;

[0072] Load history analysis steps: Analyze the dynamic load characteristics and load history at different critical points from multiple aspects such as drilling pressure, torque, and bending moment, determine the stress ratio at each critical point and classify and label it;

[0073] Material fatigue analysis steps: Perform fatigue tests on the material of the structure corresponding to the critical point to obtain material fatigue curve data characterizing fatigue properties;

[0074] Fatigue life decision-making steps: Taking the results of static finite element simulation, dynamic load addition coefficient, load characteristic identification and material fatigue curve data as input, a linear damage accumulation calculation model is designed as the fatigue analysis calculation model. The fatigue index values ​​of different dangerous points are calculated in multiple rounds using the fatigue analysis calculation model, and the target fatigue life prediction result of the rotary guide string tool is selected based on it.

[0075] The rotary steering fatigue life prediction method considering dynamic characteristics provided in the above embodiments of the present invention can establish a rotary steering dynamics finite element simulation method considering dynamic boundaries for predicting the fatigue life of rotary steering under dynamic loads. The dynamic load amplification phenomenon caused by downhole vibration is effectively considered by the ratio of dynamic maximum stress to static stress, thus taking into account the dynamic characteristics of the rotary steering. In addition, fatigue life assessment is performed separately for different stress and load histories at different critical points, effectively considering the stress characteristics of different structural locations, and can more accurately predict the fatigue life of rotary steering tools.

[0076] Preferably, in one embodiment, in the structural model establishment step, the selected rotary guide tool target test structure characterizes the entire rotary guide tool string, including: multiple sub-functional structures in the guide head unit, geological survey unit, central control unit, and upper connecting drill pipe unit.

[0077] Specifically, in optional embodiments, the method of the present invention is effectively applicable to push-type rotary guide tools and other rotary guide tools. For the rotary guide tool, a target test structure is selected based on its operating mechanism. The target test structure includes four units: a guide head unit, a geological measurement unit, a central control unit, and an upper connecting drill pipe. The guide 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 short section. The geological measurement 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 multiple non-magnetic pressure-bearing drill pipes below the screw drill bit. Finite element mesh generation is performed for each of the above four units.

[0078] Furthermore, a hazard point analysis step is performed, which analyzes the hazard points in the target test structure based on the static finite element simulation model combined with the set test well section, and determines the static Mises stress at each hazard point.

[0079] In this embodiment of the invention, by applying the maximum permissible boundary load specified in the tool manual, namely the maximum drilling pressure of 20t and the torque of 21kN·m, a static finite element simulation model is constructed to analyze the high stress hazard points of the entire tool string in the horizontal well section and the curved well section under the actual required dogleg degree.

[0080] In practical applications, in-depth research and development of rotary guides is usually required to accurately understand and set the boundary conditions of the rotary guide structure. Before static analysis, the present invention sets the boundary conditions or contact conditions of the rotary guide structure according to the following approach. In the above steps, the threaded connections between modules are bonded. Inside the guide head unit, the upper and lower spindles establish a contact pair due to the presence of a 40kN·m preload torque. The inner and outer alloy plates between the male and female bearings establish a contact pair. The spherical surfaces and shear keyways inside the male bearing establish a contact pair. The anti-extrusion rubber inside the male bearing is made of a superelastic material.

[0081] In a preferred embodiment, the static boundary load is the maximum drilling pressure and torque allowed to be applied in the tool manual, and the test well section (construction well section) is selected as a curved well section with a maximum dogleg angle of 8° / 30m and a horizontal well section with a 90° well inclination, which are actually required in the project.

[0082] Furthermore, in one embodiment, in the hazard analysis step, a static finite element simulation model is constructed based on the elastic body equilibrium differential equation, wherein the elastic body equilibrium differential equation is as follows:

[0083]

[0084] Where σ is the stress; x, y, z are Cartesian coordinate vectors; F b It is a volume force.

[0085] Based on this, static simulation analysis was conducted to identify significant high-stress hazard points in the entire tool series under different well sections.

[0086] Specifically, when analyzing dangerous points based on the static finite element simulation model, multiple static simulations are performed under different construction parameters according to the set common demand target working conditions. The simulation calculation results are analyzed to determine several significant stress concentration points in several structures, which are the dangerous points.

[0087] First, identify several locations with significantly high stress as critical points. Then, correlate and extract the stresses corresponding to these critical points under the desired target working condition and record them.

[0088] This process involves simulation calculations based on different target working conditions. A single structural location may yield static stress calculation results for multiple different working conditions. In practical applications, under different common target working conditions and different construction parameters, high stress points are always a limited number of recurring locations. Therefore, these recurring, common high stress concentration locations are designated as danger points. Of course, for some working conditions with special requirements, locations where more than one working condition's stress result reaches the danger index can be flexibly set as danger points for subsequent calculations, improving the comprehensiveness of the analysis. Next, the dynamic simulation analysis step is executed, introducing dynamic boundary loads, constructing a dynamic finite element simulation model, and analyzing the dynamic Mises stress at each danger point.

[0089] In this step, dynamic boundary loads are applied to the drill bit, and a dynamic finite element simulation model is constructed. In a preferred embodiment, the dynamic boundary loads are the dynamic drilling pressure and counter-torque loads at the drill bit when the highest drilling pressure is applied to break the rock. The remaining calculation parameters are the same as those in the static simulation analysis process, mainly including all boundary condition settings, construction well sections, tool structures, material parameters, etc. The dynamic Mises stress spectrum of different test well sections at each dangerous point is calculated through dynamic simulation, and the maximum Mises stress value is extracted.

[0090] In this context, the actual drilling pressure at the drill bit during rock breaking fluctuates numerically as the drill bit twists and breaks the rock. This dynamic drilling pressure should be expressed as a dynamic function that varies sinusoidally with the drilling pressure, added to the target drilling pressure. Specifically:

[0091] W b =W0(1+asin(nθ)) (2)

[0092] In the formula, W b W0 is the actual drilling pressure at the drill bit; a is the drilling pressure fluctuation amplitude, which is related to the longitudinal vibration of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0093] The drill bit counter-torque comprises three parts: the torque under drilling pressure, the torque under pushing force, and the friction torque along the drill string, specifically:

[0094] T total =T w +T s +T f (3)

[0095]

[0096] T s =μ s F s r b (5)

[0097] Among them, T total T represents the actual torque at the drill bit. w T is the torque under drilling pressure; s The torque under the pushing force; T f The friction torque along the drill string needs to be calculated based on the mechanics theory of the drill string; G is the shear modulus; I z The polar moment of inertia of the beam element; l e θ1 is the length of the lowest beam element; θ2 is the circumferential rotation angle of the drill bit node; θ3 is the circumferential rotation angle of the next node on the drill bit; ω is the drill bit rotation speed; δ is the critical rotation speed of the viscous phase; r b The outer diameter of the drill bit; μ s μ is the static friction coefficient. k d is the coefficient of kinetic friction; c γ is the attenuation coefficient; eq It represents the slip ratio.

[0098] Furthermore, after applying dynamic boundary loads, a finite element simulation model of the rotational steering dynamics is established based on the Lagrange equations. The Lagrange equations and the dynamic equations can be expressed as follows:

[0099]

[0100]

[0101] Where T is kinetic energy; U is potential energy; q is displacement vector; F is generalized force; t is time; [M] is global mass matrix; [K] is global stiffness matrix; [C] is global damping matrix; and {F} is global external force vector.

[0102] Based on this, a dynamic load addition analysis step is performed to calculate the dynamic load addition coefficient corresponding to each critical point based on the dynamic maximum stress and static stress at each critical point.

[0103] Specifically, in a preferred embodiment, the ratio of the maximum dynamic Mises stress to the static Mises stress at each critical point is calculated as a dynamic load amplification (addition) factor, so that the additive effect of dynamic load can be considered on the basis of fixed load in the later stage, thereby realizing the prediction of the fatigue life of the rotary guide.

[0104] Furthermore, a load history analysis step is performed to analyze and classify the dynamic load characteristics at different danger points from multiple aspects such as drilling pressure, torque, and bending moment.

[0105] In a preferred embodiment, the fatigue load history at each critical point is analyzed, specifically the load characteristics of drilling pressure, torque, and bending moment at different critical points are analyzed, and the stress ratio of alternating loads at different critical points is determined to characterize the load characteristics; it is determined whether the dynamic load at different critical points is always unidirectional stress or alternating stress with positive and negative directions. The stress ratio of always unidirectional stress is 0, and the stress ratio with positive and negative directions is -1.

[0106] For example, the spindle of the guide head unit is mainly subjected to loads from drilling pressure, torque, and bending moment. Critical points 1 and 2 are both located in the middle of the spindle, primarily subjected to alternating positive and negative bending moments, occasional negative torque, and consistently unidirectional drilling pressure. This location is primarily affected by high-frequency alternating bending moments, leading to fatigue issues. To conservatively describe the load history of the bending moment, the stress ratio at this location is selected as -1 in the fatigue analysis. For the thread relief groove, due to the presence of thread preload torque, this location is consistently subjected to unidirectional tensile loads; therefore, the stress ratio at this location is selected as 0 in the fatigue analysis.

[0107] Next, the material fatigue analysis step is performed. Fatigue tests are conducted on the material of the structure corresponding to the critical point to obtain material fatigue curve data that characterizes fatigue properties.

[0108] In an optional embodiment, in the material fatigue analysis step, for the structure corresponding to the danger point, material samples are collected from the matching position of its forging raw material, and axial tensile and compressive fatigue tests are performed using a high-frequency fatigue testing machine based on the principle of rising and falling of the material samples to complete the fatigue test; the matching position is determined according to the current operating characteristics of the structure.

[0109] In the material fatigue analysis step, after the fatigue test is completed, the stress level is selected based on the stress data of the rise and fall method test, and a group method test is carried out in combination with the set confidence level requirements. The fatigue SN curve of the current material is plotted based on the fatigue test results and the group method test results. The number of test specimens is matched with the confidence level requirements.

[0110] In practical applications, high-cycle axial fatigue tests are performed on the forging raw materials processed by the tool to obtain the SN fatigue curve; standard samples are taken from the inner wall of the raw material corresponding to the tool, and axial tensile and compressive fatigue tests are performed using a high-frequency fatigue testing machine at room temperature. The SN fatigue curve is plotted according to the lifting method and the group method.

[0111] In this invention, considering that the raw material for spindle machining is bar stock, and that the mechanical properties of the bar stock are not uniform between the outer and inner surfaces after heat treatment, with the internal properties being inferior to the outer surface properties, and given that the spindle's structural limitations primarily allow for machining of areas with poorer internal mechanical properties, and similar situations may exist for other functional structures, this invention addresses the issue of not using the official standard SN fatigue curve for each functional structure. Instead, it selects sampling locations at corresponding positions on the raw material; for example, for the spindle, sampling is performed at the corresponding position on the internal spindle forging raw material to create standard fatigue specimens for high-cycle fatigue testing, thus verifying the material's true SN fatigue curve.

[0112] Furthermore, high-cycle fatigue testing uses a high-frequency fatigue testing machine to conduct axial tension-compression fatigue tests. In practical applications, the testing machine is set to meet the requirements of the 0.5 grade force value and constant amplitude dynamic force in the JJG556-2011 Verification Procedure for Axial Loading Fatigue Testing Machines.

[0113] Based on the tensile properties of the material, calculate the median load and load amplitude, set the testing machine parameters, and conduct a fatigue test under this stress. For example, if the test passes 10... 7 If the stress level is increased by one step, the stress level is decreased by one step; the difference between the increased and decreased stress levels shall not exceed 3%-5% of the estimated fatigue limit, until the set confidence level requirement is met, such as 95% confidence level. The fatigue limit is calculated according to the following formula (8):

[0114]

[0115] Where m is the total number of effective tests (including both failure and pass data points); p is the test stress level number; σ i For the i-th stress level, v i The number of tests is denoted by _i_th stress level.

[0116] Furthermore, after the fatigue limit test, based on the stress obtained from the stress leveling method, a group method test is conducted at corresponding stress levels, for example, selecting stress levels 4-5 for group method testing, until each group meets the set confidence level requirement, such as 95% confidence level. The number of group method levels is determined based on the life distribution. Based on the results of the stress leveling method and the group method, SN curves are plotted. According to the 95% confidence level requirement, the number of samples should meet the following requirements:

[0117]

[0118] Where s / x is the coefficient of variation; δ max For the error limit; u p β is the standard normal skewness; n is the number of samples; β is the standard correction coefficient.

[0119] Furthermore, the fatigue life decision-making step is executed. Taking the static finite element simulation results, dynamic load addition coefficient, load characteristic identification and material fatigue curve data as input, a linear damage accumulation calculation model is designed as the fatigue analysis calculation model. The fatigue index values ​​of different dangerous points are calculated in multiple rounds using the fatigue analysis calculation model, and the target fatigue life prediction result of the rotary guide string tool is selected based on it.

[0120] In the fatigue life decision-making process, based on the determined target well section, load amplification factor, stress ratio and material SN curve, the fatigue life at each critical point is calculated in multiple rounds using the fatigue life analysis calculation model based on Miner's linear damage accumulation theory.

[0121] In the fatigue life decision-making step, the Miner linear damage accumulation calculation model is designed by taking the static finite element simulation results, dynamic load addition coefficient, load characteristic label, and material fatigue curve data as inputs, as follows:

[0122]

[0123] In the formula, n i N represents the number of cycles under a certain level of cyclic stress. i denoted as the number of cycles under a certain level of cyclic stress; D represents the sum of fatigue damage under various levels of stress.

[0124] The fatigue life at each of the aforementioned danger points is compared, and the minimum life value is selected. The minimum value among the fatigue index values ​​at different danger points is selected as the target fatigue life prediction result for the rotary guide string tool.

[0125] The present invention will be further described below with reference to specific embodiments. The scope of the present invention is not limited to the embodiments, but is defined in the claims.

[0126] Taking a certain model of rotary steerable drilling system based on the push-and-hold principle as an example, the fatigue life prediction analysis of rotary steerable drilling tools is achieved by following the steps below:

[0127] Step 1: Select a target test structure for the rotary guide tool based on its working mechanism, establish a corresponding three-dimensional structural model based on the target test structure, draw a three-dimensional structural diagram of the static push-type rotary guide tool string, and perform finite element mesh generation.

[0128] Specifically, the 6.75-inch "Jingwei Navigator" rotary steerable drilling system should consist of four units: a steerable head unit, a geological survey unit, a central control unit, and an upper connecting drill pipe. The steerable head unit comprises eight modules: a spindle, a non-rotating outer sleeve, a sliding bearing, an actuator, primary circuitry, secondary circuitry, energy transmission, and a flexible sub. The geological survey unit includes two modules: azimuth gamma and azimuth resistivity. The central control unit comprises four modules: a pulse generator, a generator, a central control unit, and a directional probe. The upper connecting drill collar consists of three non-magnetic pressure-bearing drill pipes below the screw drill string. Finite element meshing is performed for each of these four units.

[0129] Step 2: Apply nominal static boundary loads, construct a static finite element simulation model, analyze the high stress hazard points of the entire tool string in the horizontal well section and the curved well section under the actual required dogleg, and calculate the Mises stress at each hazard point;

[0130] A static finite element simulation model was constructed based on the elastic body equilibrium differential equation to analyze the high stress hazard points of the entire tool string in the horizontal well section and the curved well section under the actual required dogleg degree.

[0131] Step two further includes: the threaded connection between each module is bonded; inside the guide head module, the upper and lower spindles establish a contact pair due to the presence of a preload torque of 40 kN·m; the inner and outer alloy plates between the male and female bearings establish a contact pair; the spherical surfaces inside the male bearing and the anti-shear keyway establish a contact pair; and the anti-extrusion rubber inside the male bearing is made of a super-elastic material.

[0132] The static boundary loads are the maximum allowable drilling pressure of 20t and torque of 21kN·m as specified in the tool manual. The selected well sections are curved sections with a maximum dogleg angle of 8° / 30m and horizontal sections with a 90° inclination, which are actually required in the project.

[0133] A static finite element simulation model is established based on the differential equations of elastic body equilibrium. The differential equations of elastic body equilibrium can be expressed as:

[0134]

[0135] Where σ is the stress; x, y, z are Cartesian coordinate vectors; F b The stress is volumetric force; the obvious high-stress hazard points of the entire tool string in different well sections are analyzed through static simulation.

[0136] Through static simulation analysis, three high-stress hazard points were identified in the entire tool string of the "Jingwei Leading" rotary steerable drilling system. All three points are located within the spindle of the steer head, specifically at the spindle insertion hole, the lower diameter change position of the insertion hole, and the threaded retraction groove. The distribution of these hazard points is as follows: Figure 2 As shown;

[0137] The calculated Mises stresses at the three critical points in the 8° / 30m curved section are 162.3MPa, 140.8MPa, and 267.7MPa, respectively, and in the 90° horizontal section are 99.1MPa, 90.6MPa, and 241.2MPa, respectively.

[0138] Step 3: Apply dynamic boundary loads to the drill bit, construct a dynamic finite element simulation model, and calculate the maximum dynamic Mises stress at each critical point obtained from the static simulation location in Step 2.

[0139] The dynamic boundary load is the dynamic drilling pressure and counter-torque load at the drill bit when the maximum drilling pressure is applied to break the rock. All other calculation parameters are the same as those in the static simulation in step two. The dynamic Mises stress spectrum at different well sections and dangerous points is calculated through dynamic simulation, and the maximum Mises stress value is extracted.

[0140] In this context, the actual drilling pressure at the drill bit during rock breaking fluctuates numerically as the drill bit twists and breaks the rock. This dynamic drilling pressure should be expressed as a dynamic function that varies sinusoidally with the drilling pressure, added to the target drilling pressure. Specifically:

[0141] W b =W0(1+asin(nθ)) (2)

[0142] In the formula, W b W0 is the actual drilling pressure at the drill bit; a is the drilling pressure fluctuation amplitude, which is related to the longitudinal vibration of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0143] The drill bit counter-torque comprises three parts: the torque under drilling pressure, the torque under pushing force, and the friction torque along the drill string, specifically:

[0144] T total =T w +T s +T f (3)

[0145]

[0146] T s =μ s F s r b (5)

[0147] Among them, T total T represents the actual torque at the drill bit. w T is the torque under drilling pressure; s The torque under the pushing force; T f The friction torque along the drill string needs to be calculated based on the mechanics theory of the drill string; G is the shear modulus; Iz The polar moment of inertia of the beam element; l e θ1 is the length of the lowest beam element; θ2 is the circumferential rotation angle of the drill bit node; θ3 is the circumferential rotation angle of the next node on the drill bit; ω is the drill bit rotation speed; δ is the critical rotation speed of the viscous phase; r b The outer diameter of the drill bit; μ s μ is the static friction coefficient. k d is the coefficient of kinetic friction; c γ is the attenuation coefficient; eq It represents the slip ratio.

[0148] Furthermore, after applying dynamic boundary loads, a finite element simulation model of the rotational steering dynamics is established based on the Lagrange equations. The Lagrange equations and the dynamic equations can be expressed as follows:

[0149]

[0150]

[0151] Where T is kinetic energy; U is potential energy; q is displacement vector; F is generalized force; t is time; [M] is global mass matrix; [K] is global stiffness matrix; [C] is global damping matrix; and {F} is global external force vector.

[0152] Through dynamic simulation analysis, three dangerous points were identified in the "Jingwei Navigation" rotary steerable drilling system. The maximum dynamic Mises stresses in the 8° / 30m curved well section were 184.4MPa, 169.7MPa, and 321.2MPa, respectively, while the maximum dynamic Mises stresses in the 90° horizontal well section were 123.3MPa, 112.6MPa, and 291.3MPa, respectively.

[0153] Step 4: Calculate the ratio of the maximum dynamic stress to the static stress at each critical point, and use it as the dynamic load amplification factor;

[0154] Using the results of dynamic and static simulations in curved and horizontal well sections, the ratio of the maximum dynamic Mises stress to the static Mises stress at each critical point was calculated and used as the dynamic load amplification factor. The ratio of the maximum dynamic Mises stress to the static Mises stress at the three critical points of the "Jingwei Leading" rotary steerable drilling system was calculated to be 1.20, as shown in the table below. Therefore, 1.20 was used as the dynamic load amplification factor to facilitate the later prediction of the rotary steerable's fatigue life by considering the additive effect of dynamic loads on top of fixed loads.

[0155]

[0156] Step 5: Analyze the fatigue load history at each critical point in order to determine the stress ratio of the alternating load at different critical points;

[0157] Analyze the load characteristics of drilling pressure, torque, and bending moment at different danger points to determine whether the dynamic load at different danger points is always unidirectional stress or alternating stress with positive and negative directions. The stress ratio is 0 for always unidirectional stress and -1 for stress with positive and negative directions.

[0158] Specifically, the guide head spindle is mainly subjected to loads from drilling pressure, torque, and bending moment. Critical points 1 and 2 are both located in the middle of the spindle, primarily subjected to alternating positive and negative bending moments, occasional negative torque, and consistently unidirectional drilling pressure. This location is primarily affected by high-frequency alternating bending moments, leading to fatigue issues. To conservatively describe the load history of the bending moment, the stress ratio at this location is selected as -1 in the fatigue analysis. Critical point 3 is located at the thread relief groove. Due to the presence of thread preload torque, this location is consistently subjected to unidirectional tensile loads; therefore, the stress ratio at this location is selected as 0 in the fatigue analysis.

[0159] Step 6: Perform high-circulation axial fatigue tests on the forging raw materials processed by the tool to obtain the SN fatigue curve;

[0160] Standard samples were taken from the inner wall of the raw material corresponding to the tool, and axial tensile and compressive fatigue tests were conducted using a high-frequency fatigue testing machine at room temperature. The SN fatigue curves were plotted according to the lifting method and the group method.

[0161] The raw material for the spindle machining is bar stock. After heat treatment, the mechanical properties of the bar stock are uneven between its outer and internal surfaces, with the internal properties being inferior to the outer surface properties. However, due to the structural limitations of the spindle, machining primarily utilizes areas with poorer internal mechanical properties. Therefore, instead of using the official standard SN fatigue curve, samples are taken from corresponding locations within the raw material and the spindle itself to create standard fatigue specimens for high-cycle fatigue testing. Figure 3 As shown, the actual SN fatigue curve of the test material is displayed.

[0162] Furthermore, high-cycle fatigue testing utilizes a high-frequency fatigue testing machine to perform axial tension-compression fatigue testing. The testing machine must meet the requirements of JJG556-2011, the verification procedure for axial loading fatigue testing machines, for force values ​​of grade 0.5 and constant amplitude dynamic forces. Based on the tensile properties of the material, the median load and load amplitude are calculated, and the testing machine parameters are set. Fatigue testing is then conducted under this stress. If the test passes 10... 7 If the stress level is increased by one step, the stress level is decreased by one step; the difference between the increased and decreased stress levels shall not exceed 3%-5% of the estimated fatigue limit, until the 95% confidence level requirement is met:

[0163]

[0164] Where m is the total number of effective tests (including both failure and pass data points); p is the test stress level number; σ i For stress level i; v i The number of tests is denoted by _i_th stress level.

[0165] Furthermore, after the fatigue limit test, based on the stress obtained from the stress increase / decrease method, 4-5 corresponding stress levels are selected for group testing until each group meets the 95% confidence level requirement. The number of stress levels in the group method is determined based on the life distribution. Based on the results of the stress increase / decrease method and the group method, SN curves are plotted, as shown below. Figure 4 As shown. Based on the 95% confidence level requirement, the number of samples should meet the following requirements:

[0166]

[0167] Where s / x is the coefficient of variation; δ max For the error limit; u p β is the standard normal skewness; n is the number of samples; β is the standard correction coefficient.

[0168] Step 7: Based on the determined target well section, load amplification factor, stress ratio and material SN curve, use the fatigue life analysis module to calculate the fatigue life at each critical point in multiple rounds; compare the fatigue life at each critical point and select the minimum value as the final fatigue life of the tool.

[0169] Step seven further includes: based on the target well section, load amplification factor, stress ratio and material SN curve determined in steps one to six, calculating the fatigue life at each critical point in multiple rounds based on Miner's linear damage accumulation theory.

[0170] Specifically, the static finite element simulation results, load amplification factor, material model, and symmetrical cyclic loading (R=-1) or pulsating loading (R=0) are input into the fatigue analysis program. Based on Miner's linear damage accumulation theory, the number of cycles for the multi-directional load is calculated, thereby determining the fatigue life of the guide head spindle. The fatigue life at each critical point is calculated in two rounds. The fatigue life at the three critical points of the spindle is shown in [reference needed]. Figure 5 .

[0171] Miner's linear damage accumulation theory can be expressed as:

[0172]

[0173] Where, n i N represents the number of cycles under a certain level of cyclic stress. i denoted as the number of cycles under a certain level of cyclic stress; D represents the sum of fatigue damage under various levels of stress.

[0174] Then, the predicted fatigue life at each of the aforementioned danger points is compared, and the minimum life value is selected as the expected fatigue life before the tool leaves the factory.

[0175] For static push-type rotary steerable drilling systems, the fatigue life prediction method for rotary steerable systems considering dynamic characteristics provided in this invention can conservatively estimate tool fatigue life by taking into account the added effect of dynamic loads caused by downhole vibrations, based on the static finite element simulation results. Furthermore, to address the issue of different stress and load histories at different critical points, load characteristic analysis is performed separately, effectively considering the stress characteristics of different structural locations, and enabling more accurate prediction of tool fatigue life. For different load histories and stress ratios, a fatigue life calculation approach involves multiple rounds of fatigue life calculations and comparisons to obtain the minimum value. Simultaneously, this lays a theoretical foundation for fatigue life prediction of other types of rotary steerable drilling systems.

[0176] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0177] It should be noted that, in other embodiments of the present invention, the method can also combine one or more of the above embodiments to obtain a new method for predicting the fatigue life of rotary guide tools that considers dynamic characteristics, so as to achieve accurate prediction of the fatigue life of rotary guide tools in all aspects.

[0178] It should be noted that, based on the methods in any one or more embodiments of the present invention described above, the present invention also provides a storage medium storing program code that can implement the methods described in any one or more embodiments, and when the code is executed by the operating system, it can implement the rotary guide fatigue life prediction method considering dynamic characteristics as described above.

[0179] Example 2:

[0180] The methods described in detail in the above-disclosed embodiments of the present invention can be implemented using various forms of devices or systems. Therefore, based on other aspects of the methods described in any one or more of the above embodiments, the present invention also provides a rotary guide fatigue life prediction system considering dynamic characteristics. This system is used to execute the rotary guide fatigue life prediction method considering dynamic characteristics described in any one or more of the above embodiments. Specific embodiments are given below for detailed description.

[0181] Specifically, Figure 6 The diagram shows a schematic representation of the rotary guide fatigue life prediction system considering dynamic characteristics provided in an embodiment of the present invention. Figure 6 As shown, the system includes:

[0182] The structural model building module is configured to select a target test structure for the rotary guide tool based on its working mechanism, build a corresponding three-dimensional structural model based on the target test structure, and perform finite element mesh generation.

[0183] The hazard point analysis module is configured to analyze the hazard points in the target test structure based on the static finite element simulation model combined with the set test well section, and determine the static Mises stress at each hazard point.

[0184] The dynamic simulation analysis module is configured to introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each critical point.

[0185] The dynamic load analysis module is configured to calculate the dynamic load addition coefficient corresponding to each critical point based on the dynamic maximum stress and static stress at each critical point.

[0186] The load history analysis module is configured to analyze and classify the dynamic load characteristics at different critical points from multiple aspects such as drilling pressure, torque, and bending moment.

[0187] The material fatigue analysis module is configured to perform fatigue tests on the material of the structure corresponding to the critical point and obtain material fatigue curve data that characterizes fatigue properties.

[0188] The fatigue life decision module is configured to take as input the results of integrated static finite element simulation, dynamic load addition coefficient, load characteristic identification and material fatigue curve data, and design a linear damage accumulation calculation model as the fatigue analysis calculation model. The fatigue analysis calculation model is used to calculate the fatigue index values ​​of different dangerous points in multiple rounds, and the target fatigue life prediction result of the rotary guide string tool is selected based on it.

[0189] In one optional embodiment, the target test structure of the rotary guide tool selected by the structural model building module represents the entire rotary guide tool string, including multiple sub-functional structures among the guide head unit, geological survey unit, central control unit, and upper connecting drill pipe unit.

[0190] Furthermore, in one embodiment, the hazard analysis module constructs a static finite element simulation model based on the elastic body equilibrium differential equation, which is as follows:

[0191]

[0192] Where σ is the stress; x, y, z are Cartesian coordinate vectors; F b It is a volume force.

[0193] Preferably, in one embodiment, the dynamic simulation analysis module sets the dynamic boundary load to the dynamic drilling pressure and counter-torque load at the drill bit when the maximum drilling pressure is applied for rock breaking; it calculates the dynamic Mises stress spectrum of different test well sections at each dangerous point through dynamic simulation, and extracts the maximum Mises stress value.

[0194] In one embodiment, the dynamic simulation analysis module is configured to establish a finite element simulation model of rotational steering dynamics based on the dynamic drilling pressure and counter-torque load data at the drill bit and the Lagrange equation. The dynamic equation of the finite element simulation model is as follows:

[0195]

[0196] The Lagrange equation is:

[0197]

[0198] Where T is kinetic energy; U is potential energy; q is displacement vector; F is generalized force; t is time; [M] is global mass matrix; [K] is global stiffness matrix; [C] is global damping matrix; and {F} is global external force vector.

[0199] Furthermore, in one embodiment, the dynamic simulation analysis module's dynamic drilling pressure during the rock-breaking process is configured to add a dynamic function that varies sinusoidally with the drilling pressure to the target drilling pressure, as shown in the following formula:

[0200] W b =W0(1+asin(nθ))

[0201] Among them, W b W0 is the actual drilling pressure at the drill bit; a is the drilling pressure fluctuation amplitude, which is related to the longitudinal vibration of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0202] In an optional embodiment, the drill bit counter-torque used in the dynamic simulation analysis module includes the torque under drilling pressure, the torque under pushing force, and the friction torque along the drill string, as shown in the following formula:

[0203] T total =T w +T s +T f

[0204]

[0205] T s =μs F s r b

[0206] Among them, T total T represents the actual torque at the drill bit. w T is the torque under drilling pressure; s The torque under the pushing force; T f The friction torque along the drill string needs to be calculated based on the mechanics theory of the drill string; G is the shear modulus; I z The polar moment of inertia of the beam element; l e θ1 is the length of the lowest beam element; θ2 is the circumferential rotation angle of the drill bit node; θ3 is the circumferential rotation angle of the next node on the drill bit; ω is the drill bit rotation speed; δ is the critical rotation speed of the viscous phase; r b The outer diameter of the drill bit; μ s μ is the static friction coefficient. k d is the coefficient of kinetic friction; c γ is the attenuation coefficient; eq It represents the slip ratio.

[0207] Furthermore, in one embodiment, the material fatigue analysis module is configured to collect material samples from the matching position of the forging raw material of the structure corresponding to the danger point, and perform axial tensile and compressive fatigue tests using a high-frequency fatigue testing machine based on the lifting method principle of the material samples to complete the fatigue test; the matching position is determined according to the operating characteristics of the current structure.

[0208] In a preferred embodiment, after the fatigue test is completed, the material fatigue analysis module selects a set stress level based on the stress data from the rise and fall method test, performs a group method test in combination with the set confidence level requirements, and plots the fatigue SN curve of the current material based on the fatigue test results and the group method test results, wherein the number of test samples corresponds to the confidence level requirements.

[0209] Optionally, in one embodiment, the fatigue life decision module takes the comprehensive static finite element simulation results, dynamic load additive coefficient, load characteristic identifier, and material fatigue curve data as input, and designs the Miner linear damage accumulation calculation model as follows:

[0210]

[0211] For different risk points, multiple rounds of targeted fatigue life prediction are conducted, and the minimum value among the fatigue index values ​​of different risk points is selected as the target fatigue life prediction result of the rotary guide string tool.

[0212] In the formula, n i N represents the number of cycles under a certain level of cyclic stress. idenoted as the number of cycles under a certain level of cyclic stress; D represents the sum of fatigue damage under various levels of stress.

[0213] In the rotary guide fatigue life prediction system considering dynamic characteristics provided in this embodiment of the invention, each module or unit structure can operate independently or in combination according to actual data processing and computational analysis needs to achieve the corresponding technical effects.

[0214] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should be extended to equivalent substitutions of these features as understood by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0215] The phrase "an embodiment" in the specification means that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, the phrase "an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0216] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for predicting the fatigue life of a rotary guide considering dynamic characteristics, characterized in that, The method includes: Structural model establishment steps: Select a target test structure for the rotary guide tool based on its working mechanism, establish a corresponding three-dimensional structural model based on the target test structure, and perform finite element mesh generation; Hazard point analysis steps: Based on the static finite element simulation model and the set test well section, analyze the hazard points in the target test structure and determine the static Mises stress at each hazard point; Dynamic simulation analysis steps: Introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each critical point; Dynamic load analysis steps: Calculate the dynamic load addition factor corresponding to each critical point based on the dynamic maximum stress and static stress at each critical point; Load history analysis steps: Analyze the dynamic load characteristics at different critical points from multiple aspects such as drilling pressure, torque, and bending moment, and classify and label them; Material fatigue analysis steps: Perform fatigue tests on the material of the structure corresponding to the critical point to obtain material fatigue curve data characterizing fatigue properties; Fatigue life decision-making steps: Taking the results of static finite element simulation, dynamic load addition coefficient, load characteristic identification and material fatigue curve data as input, a linear damage accumulation calculation model is designed as the fatigue analysis calculation model. The fatigue index values ​​of different critical points are calculated in multiple rounds using the fatigue analysis calculation model. Based on the model, the target fatigue life prediction result of the rotary guide string tool is selected. In the dynamic simulation analysis step, the dynamic drill pressure during the rock breaking process is calculated by adding a dynamic function that varies sinusoidally with the drill pressure to the target drill pressure, as shown in the following formula: in, W b This represents the actual drilling pressure at the drill bit. W 0 is the target drilling pressure; a The amplitude of drilling pressure fluctuation is related to the degree of longitudinal vibration of the drill bit. n As a motivating factor; θ For the drill bit's rotation angle; In the dynamic simulation analysis step, the drill bit counter-torque includes the torque under drilling pressure, the torque under pushing force, and the friction torque along the drill string, as shown in the following formula: in, T total This represents the actual torque at the drill bit. T w This refers to the torque under drilling pressure. T s The torque under the action of the pushing force; T f The friction torque along the drill string is calculated based on the drill string mechanics theory. G Shear modulus; I z The polar moment of inertia of the beam element; l e The length of the lowest beam element; θ 1 represents the circumferential rotation angle of the drill bit node; θ 2 represents the circumferential rotation angle of a node on the drill bit; ω This refers to the drill bit rotation speed; δ The critical speed for the viscous phase; r b The outer diameter of the drill bit; μ s The coefficient of static friction; μ k The coefficient of kinetic friction; d c The attenuation coefficient; γ eq It represents the slip ratio.

2. The method according to claim 1, characterized in that, In the structural model establishment step, the selected rotary steering tool target test structure characterizes the entire rotary steering tool series, including multiple sub-functional structures in the steering head unit, geological survey unit, central control unit, and upper connecting drill pipe unit.

3. The method according to claim 1, characterized in that, In the hazard analysis step, a static finite element simulation model is constructed based on the elastic body equilibrium differential equation, which is as follows: in, The stress is represented by x, y, and z, which are Cartesian coordinate vectors. F b It is a volume force.

4. The method according to claim 1, characterized in that, In the dynamic simulation analysis step, the dynamic boundary load is the dynamic drilling pressure and counter-torque load at the drill bit when the maximum drilling pressure is applied to break the rock; the dynamic Mises stress spectrum of different test well sections at each dangerous point is calculated by dynamic simulation, and the maximum Mises stress value is extracted.

5. The method according to claim 1, characterized in that, In the dynamic simulation analysis step, based on the dynamic drilling pressure and counter-torque load data at the drill bit, a finite element simulation model of the rotational steering dynamics is established based on the Lagrange equation. The dynamic equation of the finite element simulation model is as follows: The Lagrange equation is: in, T Kinetic energy; U Potential energy; q It is a displacement vector; F For generalized force; t For time; [ M [ is the global quality matrix;] K [ is the global stiffness matrix;] C ] is the global damping matrix; { F } represents the global external force vector.

6. The method according to claim 1, characterized in that, In the material fatigue analysis step, for the structure corresponding to the danger point, material samples are collected from the matching position of its forging raw material. Based on the material samples, axial tensile and compressive fatigue tests are carried out using a high-frequency fatigue testing machine according to the principle of the lifting method to complete the fatigue test; the matching position is determined according to the current operating characteristics of the structure.

7. The method according to claim 1, characterized in that, In the material fatigue analysis step, after the fatigue test is completed, the stress level is selected based on the stress data of the rise and fall method test, and a group method test is carried out in combination with the set confidence level requirements. The fatigue SN curve of the current material is plotted based on the fatigue test results and the group method test results. The number of test specimens is matched with the confidence level requirements.

8. The method according to claim 1, characterized in that, In the fatigue life decision-making process, the Miner linear damage accumulation calculation model is designed by taking the results of static finite element simulation, dynamic load addition coefficient, load characteristic label, and material fatigue curve data as inputs, as follows: For different risk points, multiple rounds of targeted fatigue life prediction are conducted, and the minimum value among the fatigue index values ​​of different risk points is selected as the target fatigue life prediction result of the rotary guide string tool. In the formula, n i The number of cycles under a certain level of cyclic stress; N i D represents the number of cycles of life under a certain level of cyclic stress; D is the sum of fatigue damage under all levels of stress. D i For the first i Fatigue damage under stress level.

9. A storage medium, characterized in that, The storage medium stores program code capable of implementing the method as described in any one of claims 1 to 8.

10. A rotary guide fatigue life prediction system considering dynamic characteristics, characterized in that, The system performs the method as described in any one of claims 1 to 8.

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