Rotary steering fatigue life prediction method and system considering dynamic characteristics

Abstract

The invention provides a rotary steering fatigue life prediction method and system considering dynamic characteristics, and the method comprises the steps: building a three-dimensional structure model based on a set target test structure, analyzing dangerous points based on a statics finite element simulation model in combination with a set test well section, and determining the static Mises stress of each point; introducing a dynamic boundary load to construct a dynamic finite element simulation model, and analyzing the dynamic Mises stress of each point; calculating a dynamic load addition coefficient of each point according to the dynamic maximum stress and the static stress; in addition, dynamic load characteristics at all points are analyzed from multiple aspects of bit pressure, torque and bending moment; analyzing fatigue characteristics according to the material of the structure corresponding to the dangerous point; and designing a linear damage accumulation operation model, integrating the calculation results to calculate a fatigue index value for multiple input rounds, and further determining the fatigue life of the whole string of tools. According to the scheme, the defects of incomplete operation angles and insufficient accuracy in the prior art can be overcome, and accurate prediction is realized by fully considering dynamic load characteristics and material characteristics of different structures.

Description

Technical Field

[0001] The present invention relates to the technical field of reliability monitoring and evaluation of drilling tools, and particularly to a method and system for predicting the fatigue life of a rotary steerable system considering dynamic characteristics. Background Art

[0002] Since the rotary steerable system is always rotating at a high speed in a long and narrow wellbore for a long time, it is subjected to coupled vibrations such as lateral, longitudinal, and torsional vibrations, as well as dynamic loads such as drilling pressure, torque, and bending moment. After long-term use, tool damage, fatigue damage, etc. are inevitable. In order to effectively evaluate the service life and application risks of the rotary steerable system and reduce the risk of fatigue failure, it is very necessary to comprehensively consider the harsh construction loads of the tool when the tool leaves the factory and conservatively predict the fatigue life of the tool.

[0003] The rotary steerable drilling tool is always rotating at a high speed in a long and narrow wellbore, and is subjected to coupled vibrations, complex loads, and random collisions. Due to the complexity of dynamic factors and non-linear conditions, the static finite element method can no longer meet the requirement of accurately estimating the true loads of the tool. It is necessary to establish a dynamic finite element model considering dynamic characteristics and fully consider the stresses borne by the tool under dynamic loads. Due to the special tool structure and working principle of the static push-steering rotary steerable system, there are complex mechanical structures such as upper and lower drive shafts, non-rotating outer sleeves, and wing ribs in its steering head. The drive shaft rotates at a high speed following the drill string body structure. The non-rotating outer sleeve is connected to the drive shaft through two upper and lower sliding bearings and basically remains stationary. The wing ribs are used to support the wellbore outside the non-rotating outer sleeve to provide the required steering force for the drill bit. The fatigue load characteristics are different at different structures and positions. Some positions are mainly subjected to positive and negative alternating bending moments, and some positions are always subjected to tensile forces. Therefore, it is necessary to analyze the force characteristics of each complex structure and clarify the stress ratio of the alternating loads at different positions in order to accurately describe the load history borne by the tool.

[0004] There are some methods for predicting the fatigue life of drill tools in existing research. For example, a method for predicting the fatigue life of a bottom hole assembly based on drill string dynamics provided in the patent document CN113065211B calculates the functions of node displacement, acceleration, etc. changing with time through the dynamic analysis of the bottom hole assembly of conventional tools; calculates the equivalent stress of the nodes, and predicts the fatigue life of the bottom hole assembly according to the Walker model. The patent document CN103967428B provides a method for evaluating the risk of drill string fatigue failure, measures the wellbore structure, drill string assembly structure and actual wellbore trajectory parameters of the target well, and establishes a finite element model of drill string dynamics; solves the buckling stress, dynamic bending stress and dynamic axial force of each node section of the drill string and corrects the dynamic bending stress; solves the fatigue frequency coefficient of each node section of the drill string; gives a relationship diagram between the fatigue frequency coefficient and the well depth, so as to evaluate whether the drill string has a high risk of fatigue failure. The above-mentioned schemes lack the dynamic modeling and boundary condition processing process for the rotary steerable system, and also lack the analysis of the alternating load stress ratio at different dangerous positions, and cannot realize reliable and accurate fatigue life prediction for the rotary steerable with a complex operation mechanism.

[0005] The information disclosed in the background art section of the present invention is only intended to deepen the understanding of the general background art of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for predicting the fatigue life of a rotary steerable 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 dangerous point; introduces dynamic boundary loads to construct a dynamic finite element simulation model, and analyzes the dynamic Mises stress of each dangerous point; calculates the dynamic load addition coefficient of each dangerous point according to the dynamic maximum stress and static stress; in addition, analyzes the dynamic load characteristics and load history at each point from multiple aspects of weight on bit, torque, and bending moment, and determines the stress ratio at each dangerous point; analyzes the fatigue characteristics of the material corresponding to the structure of the dangerous point; designs a linear damage accumulation operation model, and uses the above calculation results as input to calculate the fatigue index value in multiple rounds, and then determines the fatigue life of the entire string of tools. This scheme can overcome the defects of incomplete operation angle and insufficient accuracy in the prior art, fully consider the dynamic load characteristics and the load history of different dangerous points to achieve accurate prediction; in one embodiment, the method includes:

[0007] Step of establishing a structure model: Select a target test structure according to the operation mechanism for the rotary steerable tool, establish a corresponding three-dimensional structure model based on the target test structure, and perform finite element mesh division;

[0008] Steps for analyzing dangerous points: Based on the static finite element simulation model and the set test well section, analyze the dangerous points in the target test structure and determine the static Mises stress at each dangerous point.

[0009] Steps for dynamic simulation analysis: Introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each dangerous point.

[0010] Steps for dynamic addition analysis: Calculate the dynamic load addition coefficient corresponding to the dangerous point according to the dynamic maximum stress and static stress at each dangerous point.

[0011] Steps for load history analysis: Analyze the dynamic load characteristics at different dangerous points from multiple aspects such as weight on bit, torque, and bending moment and classify and label them.

[0012] Steps for material fatigue analysis: Conduct fatigue tests on the materials corresponding to the structures of the dangerous points to obtain material fatigue curve data characterizing fatigue characteristics.

[0013] Steps for fatigue life decision-making: Using the static finite element simulation results, dynamic load addition coefficient, load characteristic labels, and material fatigue curve data as inputs, design a linear damage accumulation operation model as the fatigue analysis operation model, use the fatigue analysis operation model to calculate the fatigue index values of different dangerous points in multiple rounds, and select the target fatigue life prediction result of the rotary steerable tool string based on it.

[0014] In an optional embodiment, in the step of establishing the structural model, the selected target test structure of the rotary steerable tool represents the rotary steerable tool string, including: multiple sub-functional structures such as a steering head unit, a geological measurement unit, a central control unit, and an upper connecting drill pipe unit.

[0015] Further, in an embodiment, in the step of analyzing dangerous points, a static finite element simulation model is constructed based on the elastic body equilibrium differential equation, and the elastic body equilibrium differential equation is as follows:

[0016]

[0017] where σ is stress; x, y, z are Cartesian three-coordinate vectors; F b is the body force.

[0018] Preferably, in an embodiment, in the step of dynamic simulation analysis, the dynamic boundary load is the dynamic weight on bit and reverse torque load at the drill bit when applying the maximum weight on bit for rock breaking; calculate the dynamic Mises stress spectrum at each dangerous point in different test well sections through dynamic simulation and extract the maximum Mises stress value among them.

[0019] In one embodiment, in the dynamic simulation analysis step, based on the dynamic weight on bit and reverse torque load data at the drill bit, a finite element simulation model of rotary steerable dynamics is established based on the Lagrange equation. The dynamic equation of the finite element simulation model of dynamics is as follows:

[0020]

[0021] The Lagrange equation is:

[0022]

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

[0024] Furthermore, in one embodiment, in the dynamic simulation analysis step, the dynamic weight on bit during the rock breaking process is a dynamic function that varies sinusoidally with the weight on bit on the basis of the target weight on bit, as follows:

[0025] W b =W 0 (1 + asin(nθ))

[0026] where W b is the actual weight on bit at the drill bit; W 0 is the target weight on bit; a is the amplitude of the weight on bit fluctuation, which is related to the longitudinal vibration degree of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0027] In an alternative embodiment, in the dynamic simulation analysis step, the reverse torque of the drill bit includes the torque under the action of the weight on bit, the torque under the action of the pushing force, and the frictional torque along the drill string, as follows:

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

[0029]

[0030] T s =μ s F s r b

[0031] where T total is the actual torque at the drill bit; T w is the torque under the action of the weight on bit; T s is the torque under the action of the pushing force; T f is the frictional torque along the drill string, which needs to be calculated according to the pipe string mechanics theory; G is the shear modulus; Iz is the polar moment of inertia of the beam element; l e is the length of the lowermost beam element; θ 1 is the circumferential rotation angle of the drill bit node; θ 2 is the circumferential rotation angle of the previous node of the drill bit; ω is the rotational speed of the drill bit; δ is the critical rotational speed of the viscous phase; r b is the outer diameter of the drill bit; μ s is the static friction coefficient; μ k is the dynamic friction coefficient; d c is the attenuation coefficient; γ eq is the slip rate.

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

[0033] In a preferred embodiment, in the material fatigue analysis step, after the fatigue test is completed, a stress of a set level is selected based on the stress data tested by the staircase method, and a group method test is performed in combination with the set confidence requirement. A fatigue S-N curve of the current material is drawn based on the fatigue test results and the group method test results, wherein the number of specimens corresponding to the test matches the confidence requirement.

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

[0035]

[0036] For different critical points, multiple rounds of targeted fatigue life predictions are respectively performed, and the minimum value is selected from the fatigue index values of different critical points as the target fatigue life prediction result of the rotary steerable string tool;

[0037] In the formula, n i is the number of cycles under a cyclic stress of a certain level; N i is the number of life cycles under a cyclic stress of a certain level; D is the sum of fatigue damages under cyclic stresses of each level.

[0038] Based on other aspects of the method described in any one or more of the above embodiments, the present invention further provides a storage medium, on which program code capable of implementing the method described in any one or more of the above embodiments is stored.

[0039] In terms of the application aspects of the method described in any one or more of the above embodiments, the present invention further provides a rotary steerable fatigue life prediction system considering dynamic characteristics, and this system executes the method 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] A rotary steerable fatigue life prediction method and system considering dynamic characteristics provided by the present invention establish a three-dimensional structure model based on a set target test structure, analyze dangerous points based on a static finite element simulation model in combination with a set test well section, and determine the static Mises stress at each point; further introduce dynamic boundary loads to construct a dynamic finite element simulation model to analyze the dynamic Mises stress at each point; calculate the dynamic load addition coefficient at each point according to the dynamic maximum stress and static stress; this solution analyzes different dangerous points for the target test mechanism and then introduces dynamic boundary loads to calculate dynamic stress, fully considering the dynamic load characteristics of the tool during application, and more accurately and conservatively predicting the load stress data of the tool;

[0042] In addition, analyze the dynamic load characteristics at each point from multiple aspects such as weight on bit, torque, and bending moment; analyze the fatigue characteristics of the material corresponding to the structure of the dangerous point; design a Miner linear damage accumulation operation model and use the above calculation results as input to calculate the fatigue index value, and then determine the fatigue life of the entire string of tools. By analyzing the dynamic load characteristics at each point from multiple aspects and testing to determine the fatigue characteristics corresponding to the force characteristics of each structure, based on the above operations, it can be effectively applied to rotary steerable tools with complex structures, and achieve accurate and reliable fatigue life prediction analysis.

[0043] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will become obvious from the specification, or be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. Brief Description of the Drawings

[0044] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings:

[0045] Figure 1 is a flowchart of the rotary steerable fatigue life prediction method considering dynamic characteristics provided by an embodiment of the present invention;

[0046] Figure 2 is a schematic diagram of the position of the dangerous points determined by the static analysis of "Jingwei Pilot" rotary steerable in the rotary steerable fatigue life prediction method provided by an embodiment of the present invention;

[0047] Figure 3 It is an exemplary diagram of a standard fatigue specimen for material fatigue testing in the rotary steerable fatigue life prediction method provided by an embodiment of the present invention;

[0048] Figure 4 It is an exemplary diagram of a measured S-N fatigue curve in the rotary steerable fatigue life prediction method provided by an embodiment of the present invention;

[0049] Figure 5 It is a schematic diagram of a fatigue life nephogram of a static push-steer rotary steerable using the rotary steerable fatigue life prediction method provided by an embodiment of the present invention;

[0050] Figure 6 It is a schematic structural diagram of a rotary steerable fatigue life prediction system considering dynamic characteristics provided by another embodiment of the present invention. Detailed implementation manners

[0051] The following will describe in detail the implementation manners of the present invention in conjunction with the accompanying drawings and embodiments, so that the implementers of the present invention can fully understand how to apply technical means to solve technical problems and achieve the implementation process of technical effects, and specifically implement the present invention according to the above implementation process. It should be noted that as long as there is no conflict, the various embodiments in the present invention and the various features of each embodiment can be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.

[0052] Although the flowchart describes the operations as sequential processing, many of the operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. When the operations are completed, the processing can be terminated, but there can also be additional steps not included in the drawings. The processing can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0053] Computer devices include user devices and network devices. Among them, user devices or clients include, but are not limited to, computers, smart phones, PDAs (Personal Digital Assistants), etc.; network devices include, but are not limited to, a single network server, a server group composed of multiple network servers, or a cloud composed of a large number of computers or network servers based on cloud computing. The computer device can run alone to implement the present invention, or can be connected to the network and implement the present invention through interaction with other computer devices in the network. The network where the computer device is located includes, but is not limited to, the Internet, wide area network, metropolitan area network, local area network, VPN network, etc.

[0054] The terms "first", "second", etc. may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one element from another. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items. When an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intervening elements.

[0055] The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments. Unless the context clearly dictates otherwise, the singular forms "a", "an" used herein are also intended to include the plural. It should also be understood that the terms "comprises" and / or "comprising" specify the presence of the stated features, integers, steps, operations, elements, and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0056] Rotary steerable systems are the world's most advanced oil directional drilling equipment, representing the highest level of current drilling technology. Since rotary steerable systems are always rotating at high speed for a long time in narrow wellbores, they are subjected to coupled vibrations such as lateral, longitudinal, and torsional vibrations, as well as dynamic loads such as drill pressure, torque, and bending moment. After long-term use, tool damage, fatigue damage, etc. are inevitable. Among them, the static push-against rotary steerable system is the most widely used in China. In order to effectively evaluate the service life and application risks of rotary steerable systems and reduce the risk of fatigue failure, it is very necessary to comprehensively consider the severe construction loads of the tools when they leave the factory and conservatively predict the fatigue life of the tools.

[0057] To achieve fatigue life prediction of rotary steerable systems, the following technical difficulties need to be overcome: (1) Rotary steerable drilling tools are always rotating at high speed in long and narrow wellbores, subject to coupled vibration, complex loads, and random collisions. Due to the excessive complexity of dynamic factors and non-linear conditions, the static finite element method can no longer meet the requirement of accurately estimating the true loads on the tools. A dynamic finite element model considering dynamic characteristics needs to be established, fully taking into account the stresses borne by the tools under dynamic loads. (2) Due to the special tool structure and working principle of the static push-steering rotary steerable system, there are complex mechanical structures such as upper and lower drive shafts, non-rotating outer sleeves, and wing ribs in its steering head. The drive shaft rotates at high speed following the drill string body structure. The non-rotating outer sleeve is connected to the drive shaft through upper and lower sliding bearings and remains basically stationary. The wing ribs are used to support the wellbore outside the non-rotating outer sleeve to provide the required steering force for the drill bit. The fatigue load characteristics are different at different structures and positions. At some positions, the loads are mainly alternating bending moments of positive and negative directions, while at some positions, they are always under tensile action. Therefore, it is necessary to analyze the stress characteristics of each complex structure and clarify the stress ratios of the alternating loads at different positions, so as to accurately describe the load history borne by the tools.

[0058] There are some methods for predicting the fatigue life of drilling tools in existing research. For example, a method for predicting the fatigue life of the bottom hole assembly based on drill string dynamics provided by patent document CN113065211B calculates the functions of node displacement, acceleration, etc. changing with time through the dynamic analysis of the conventional tool bottom hole assembly; calculates the equivalent stress of the nodes, and predicts the fatigue life of the bottom hole assembly according to the Walker model. Patent document CN103967428B provides a method for evaluating the risk of drill string fatigue failure, measures the wellbore structure, drill string assembly structure, and actual wellbore trajectory parameters of the target well, and establishes a dynamic finite element model of the drill string; solves the buckling stress, dynamic bending stress, and dynamic axial force of each node section of the drill string, as well as the modified dynamic bending stress; solves the fatigue frequency coefficient of each node section of the drill string; gives the relationship diagram between the fatigue frequency coefficient and the well depth, so as to evaluate whether the drill string has a high risk of fatigue failure. The above solutions are for predicting the fatigue life of the bottom hole assembly of conventional tools, not for the fatigue prediction method of rotary steerable systems. Based on this, several aspects need to be emphasized. First, the conventional tools themselves have a simple structure and lack the modeling and boundary condition processing process for rotary steerable systems. Second, for the simple structure of conventional tools, only beam elements with uniform cross-sections are used for calculation, without considering the real structure, and it is impossible to accurately predict the fatigue life of tools with many small features, whether they are conventional tools or complex rotary steerable tools. Third, there is a lack of analysis of alternating loads and stress ratios at different dangerous positions.

[0059] The above schemes lack the modeling and boundary condition processing process for the rotary steering system, and also lack the analysis of the alternating load stress ratio for different dangerous positions. The working principles and structures of different types of rotary steering are quite different, and their force characteristics and load histories are different. Therefore, the existing methods cannot be directly applied to various types of rotary steering tools, and cannot meet the requirements of fatigue life prediction of rotary steering tools. It is difficult to achieve reliable and accurate fatigue life prediction for rotary steering with complex operating mechanisms.

[0060] To solve the above problems, the present invention provides a method and system for predicting fatigue life of rotary guide considering dynamic characteristics. The present invention improves at least in the following aspects: first, a detailed modeling and boundary condition processing process of rotary guide system is given; second, solid units are used to consider the tiny features of all positions of the tool; third, the stress addition effect of the tool under dynamic load is fully considered, and a new method for calculating dynamic load magnification factor is proposed; fourth, a fatigue life calculation idea is proposed to calculate fatigue life for multiple rounds and compare the minimum value according to the different load history and stress ratio.

[0061] The method of the present invention can reliably predict the fatigue life of rotary guide under dynamic load, establishes a rotary guide dynamic finite element simulation method considering dynamic boundaries, and amplifies the dynamic load caused by downhole vibration through the ratio of dynamic maximum stress to static stress, effectively considering the dynamic characteristics of rotary guide; in addition, fatigue life assessment is performed separately for different stress and load histories at different dangerous points, effectively considering the force characteristics at different structural positions, and more accurately predicting the fatigue life of the tool. In addition, the fatigue life prediction method proposed in the present invention can be applied to various types of drilling tools, and is not limited by the type of tool. It can effectively evaluate the service life and application of drilling tools and reduce the risk of fatigue failure.

[0062] The present invention mainly considers the following two difficult problems when establishing the fatigue life prediction method of static push-type rotary guide:

[0063] (1) The rotary steerable drilling tool always rotates at high speed in the narrow wellbore, and is subjected to coupled vibration, complex loads and random collisions. Due to the complexity of dynamic factors and nonlinear conditions, the static finite element method can no longer accurately estimate the real 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 loads;

[0064] (2) Due to the special tool structure and working principle of the static push - type rotary steerable system, there are complex mechanical structures such as upper and lower drive shafts, non - rotating outer sleeves, and wing ribs in its steering head. The drive shaft rotates at high speed following the drill string body structure. The non - rotating outer sleeve is connected to the drive shaft through upper and lower sliding bearings and basically remains stationary. The wing ribs are used to support the wellbore outside the non - rotating outer sleeve to provide the required steering force for the drill bit. The fatigue load characteristics are different at different structures and positions. Some positions are mainly subjected to positive and negative alternating bending moments, and some positions are always under tensile action. Therefore, by analyzing the force characteristics of each complex structure and clarifying the stress ratios of the alternating loads at different positions, the load history of the tool can be accurately described.

[0065] Next, the detailed process of the method of the embodiment of the present invention will be described in detail based on the accompanying drawings. The steps shown in the flowchart of the accompanying drawings can be executed in a computer system including, 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 can be executed in a different order than here.

[0066] Embodiment 1:

[0067] Figure 1 The flow schematic diagram of the rotary steerable fatigue life prediction method considering dynamic characteristics provided by Embodiment 1 of the present invention is shown. Referring to Figure 1 it can be seen that the method includes the following steps.

[0068] Structural model establishment step: For the rotary steerable tool, select the target test structure according to the operation mechanism, establish the corresponding three - dimensional structural model based on the target test structure, and perform finite - element mesh division;

[0069] Dangerous point analysis step: Based on the static - mechanics finite - element simulation model combined with the set test well section, analyze the significant stress concentration points in the target test structure as dangerous points, and determine the static Mises stress at each dangerous point;

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

[0071] Dynamic addition analysis step: Calculate the dynamic load addition coefficient corresponding to the dangerous point according to the dynamic maximum stress and static stress at each dangerous point;

[0072] Load history analysis step: Analyze the dynamic load characteristics and load history at different dangerous points from aspects such as weight - on - bit, torque, and bending moment, determine the stress ratio at each dangerous point, and classify and label them;

[0073] Steps for material fatigue analysis: Conduct fatigue tests on the materials corresponding to the structures at the critical points to obtain the material fatigue curve data characterizing the fatigue properties.

[0074] Steps for fatigue life decision-making: Using the static finite element simulation results, dynamic load addition coefficient, load characteristic identification, and material fatigue curve data as inputs, design a linear damage accumulation operation model as the fatigue analysis operation model. Use the fatigue analysis operation model to calculate the fatigue index values of different critical points in multiple rounds, and select the target fatigue life prediction result of the rotary steerable string tool based on it.

[0075] By using the method for predicting the fatigue life of a rotary steerable tool considering dynamic characteristics provided in the above embodiments of the present invention, a method for predicting the fatigue life of a rotary steerable tool under dynamic loads can be established. A dynamic finite element simulation method for a rotary steerable tool considering dynamic boundaries is established, and the dynamic load amplification phenomenon caused by downhole vibration is considered effectively through the ratio of dynamic maximum stress to static stress, taking into account the dynamic characteristics of the rotary steerable tool. In addition, for the different stresses and load histories at different critical point positions, fatigue life assessments are carried out separately, effectively considering the force characteristics at different structural positions, and the fatigue life of the rotary steerable tool can be predicted more accurately.

[0076] Preferably, in one embodiment, in the step of establishing the structural model, the selected target test structure of the rotary steerable tool represents the rotary steerable string tool, including multiple sub-functional structures such as a steering head unit, a geological survey unit, a central control unit, and an upper connecting drill pipe unit.

[0077] Specifically, in an optional embodiment, the method of the present invention can be effectively applied to push-type rotary steerable tools and other rotary steerable tools. According to the operation mechanism of the rotary steerable tool, the target test structure is selected. The target test structure includes 4 units: a steering head unit, a geological survey unit, a central control unit, and an upper connecting drill pipe. The steering head unit includes 8 modules such as a main shaft, a non-rotating outer sleeve, a sliding bearing, an actuator, a primary circuit, a secondary circuit, energy transmission, and a flexible sub-joint. The geological survey unit includes 2 modules such as an azimuth gamma and an azimuth resistivity. The central control unit includes 4 modules such as a pulser, a generator, a central control, and a directional probe. The upper connecting drill collar includes multiple non-magnetic pressure-bearing drill pipes below the positive displacement motor. Finite element mesh division is carried out for the above 4 units respectively.

[0078] Furthermore, perform the critical point analysis step, and analyze the critical points in the target test structure based on the static finite element simulation model combined with the set test well section to determine the static Mises stress at each critical point.

[0079] In the embodiments of the present invention, by applying the maximum allowable boundary load specified in the tool instruction manual, that is, the maximum weight on bit of 20t and the torque of 21kN·m, a static finite element simulation model is constructed to analyze the high-stress dangerous points of the entire string of tools in the horizontal well section and the curved well section with the actual required dogleg severity.

[0080] In practical applications, it is usually necessary to conduct in-depth research on rotary steerable systems to accurately understand and set the boundary conditions of the rotary steerable structure. Before the static analysis in the embodiments of the present invention, the boundary conditions or contact conditions of the rotary steerable structure are set and processed according to the following ideas. In the above steps, the threaded connections between modules are processed using binding. Inside the steering head unit, contact pairs are established between the upper and lower main shafts due to the existence of a pre-tightening torque of 40kN·m, contact pairs are established between the inner and outer alloy sheets of the male and female bearings, contact pairs are established between the inner spherical surfaces and shear key grooves inside the male bearing, and the anti-extrusion rubber inside the male bearing is set as a hyperelastic material.

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

[0082] Further, in one embodiment, in the dangerous point analysis step, a static finite element simulation model is constructed based on the equilibrium differential equation of the elastic body, and the equilibrium differential equation of the elastic body is as follows:

[0083]

[0084] where σ is the stress; x, y, z are the Cartesian three coordinate vectors; F b is the body force.

[0085] Based on this, the obvious high-stress dangerous points of the entire string of tools in different well sections are analyzed through static simulation.

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

[0087] First, several positions with significant high stress are determined as dangerous points, and then the stresses corresponding to these dangerous points under the required target working conditions are associated and extracted and recorded.

[0088] In this process, simulation calculations are carried out based on different required target working conditions. For a single structural position, static stress operation results of multiple different working conditions may be obtained. In actual applications, under different common required target working conditions and different construction parameters, in fact, the high-stress points always repeatedly appear at a limited number of positions. Therefore, these several common high-stress concentration positions that repeatedly appear are taken as dangerous points. Of course, for some working conditions with special requirements, it is also possible to flexibly set that the positions where the stress results of more than one working condition reach the dangerous index are all taken as dangerous points to carry out subsequent calculations, so as to improve the comprehensiveness of the analysis. Next, perform the dynamic simulation analysis step, introduce the dynamic boundary load, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each dangerous point.

[0089] In this step, apply the dynamic boundary load of the drill bit and construct a dynamic finite element simulation model. In a preferred embodiment, when applying the highest bit weight to break rock, the dynamic boundary load is the dynamic bit weight and the reaction torque load applied to the drill bit. All other 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. Through dynamic simulation, calculate the dynamic Mises stress spectra of each dangerous point at different test well sections, and extract the maximum Mises stress value among them.

[0090] Among them, during the rock-breaking process, the actual bit weight at the drill bit fluctuates numerically with the rock-breaking process of the drill bit's torsion. This dynamic bit weight should be expressed as adding a dynamic function that varies sinusoidally with the bit weight on the basis of the target bit weight. Specifically:

[0091] W b =W 0 (1 + asin(nθ)) (2)

[0092] In the formula, W b is the actual bit weight at the drill bit; W 0 is the target bit weight; a is the amplitude of the bit weight fluctuation, which is related to the longitudinal vibration degree of the drill bit; n is the excitation factor; θ is the bit rotation angle.

[0093] The reaction torque of the drill bit includes three parts, namely the torque under the action of the bit weight, the torque under the action of the pushing force, and the frictional torque along the drill string. Specifically:

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

[0095]

[0096] T s =μ s F s rb (5)

[0097] Among them, T total is the actual torque at the drill bit; T w is the torque under the action of the weight on bit; T s is the torque under the action of the pushing force; T f is the frictional torque along the drill string, which needs to be calculated according to the pipe string mechanics theory; G is the shear modulus; I z is the polar moment of inertia of the beam element; l e is the length of the lowermost beam element; θ 1 is the circumferential rotation angle of the drill bit node; θ 2 is the circumferential rotation angle of the node above the drill bit; ω is the rotational speed of the drill bit; δ is the critical rotational speed of the viscous phase; r b is the outer diameter of the drill bit; μ s is the static friction coefficient; μ k is the dynamic friction coefficient; d c is the attenuation coefficient; γ eq is the slip rate.

[0098] Furthermore, after forming the dynamic boundary load, based on the Lagrange equation, a finite element simulation model for rotary steerable dynamics is established. Among them, the Lagrange equation and the dynamic equation can be expressed as follows:

[0099]

[0100]

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

[0102] Based on this, perform the dynamic addition analysis step, and calculate the dynamic load addition coefficient corresponding to the critical points according to the dynamic maximum stress and static stress at each critical point.

[0103] Specifically, in a preferred embodiment, calculate the ratio of the dynamic maximum Mises stress to the static Mises stress at each critical point as the dynamic load amplification (addition) coefficient, so as to consider the addition effect of the dynamic load on the basis of the fixed load in the later stage and realize the prediction of the fatigue life of the rotary steerable.

[0104] Furthermore, perform the load history analysis step, and analyze the dynamic load characteristics at different critical points from multiple aspects such as the weight on bit, torque, and bending moment and classify and identify them.

[0105] In a preferred embodiment, the fatigue load history at each critical point is analyzed. Specifically, the load characteristics of the weight on bit, torque, and bending moment at different critical points are analyzed to determine the stress ratio of the alternating load at different critical points to characterize the load characteristics. It is determined whether the dynamic load at different critical points is always unidirectional stress or alternating stress that changes in positive and negative directions. The stress ratio of the stress that is always unidirectional is 0, and the stress ratio of the stress that has positive and negative direction changes is -1.

[0106] For example, the main shaft of the guide head unit is mainly subjected to the loads of the weight on bit, torque, and bending moment. Among them, critical point 1 and critical point 2 are both located in the middle of the main shaft and are mainly subjected to positive and negative alternating bending moments, occasionally negative torque, and always unidirectional weight on bit. Fatigue problems are mainly caused by the high-frequency alternating bending moment at this position. In order to conservatively describe the load history of the bending moment, the stress ratio here is selected as -1 in the fatigue analysis. For the thread relief groove, due to the existence of the thread pre-tightening torque, this position is always subjected to a unidirectional tensile load, so the stress ratio here is selected as 0 in the fatigue analysis.

[0107] Next, the material fatigue analysis step is performed. Fatigue tests are carried out on the materials of the structures corresponding to the critical points to obtain the material fatigue curve data characterizing the fatigue characteristics.

[0108] In an alternative embodiment, in the material fatigue analysis step, for the structure corresponding to the critical point, material specimens are collected from the matching position of the forging raw material. Based on the material specimens, axial tensile and compressive fatigue tests are carried out using a high-frequency fatigue testing machine according to the up-and-down method principle to complete the fatigue test; the matching position is determined according to the operating characteristics of the current structure.

[0109] In the material fatigue analysis step, after the fatigue test is completed, a stress of a set level is selected from the stress data tested by the up-and-down method, and a group method test is carried out in combination with the set confidence requirement. The fatigue S-N curve of the current material is drawn according to the fatigue test results and the group method test results, where the number of specimens corresponding to the test matches the confidence requirement.

[0110] In practical applications, high-cycle axial fatigue tests are carried out on the forging raw materials of the tool to obtain the S-N fatigue curve; standard specimens are taken at the inner wall position of the raw material corresponding to the tool, and axial tensile and compressive fatigue tests are carried out using a high-frequency fatigue testing machine at room temperature. The S-N fatigue curve is drawn according to the up-and-down method and the group method.

[0111] Among them, considering that the raw material for the spindle machining is bar stock, and the mechanical properties of the outer surface and the interior of the bar stock are non-uniform after material heat treatment, with the interior properties being inferior to those of the outer surface. However, due to the structural limitations of the spindle, its machining mainly uses the positions with relatively poor interior mechanical properties; similar situations may exist in the application of other functional structures; therefore, in the present invention, instead of using the official standard S-N fatigue curve for each functional structure, samples are taken at corresponding positions of the raw material. For example, for the spindle, samples are taken at the corresponding positions of the raw material of the interior spindle forging, and made into standard fatigue specimens for high-cycle fatigue tests to test the true S-N fatigue curve of the material.

[0112] Furthermore, a high-frequency fatigue testing machine is used for the high-cycle fatigue test to conduct axial tension-compression fatigue tests. In actual application, the testing machine is set to meet the requirements of Class 0.5 force value and equal-amplitude dynamic force in the JJG556-2011 Verification Regulation for Axial Loading Fatigue Testing Machines.

[0113] According to the tensile properties of the material, the median load and load amplitude are calculated, the parameters of the testing machine are set, and fatigue tests are conducted under this stress. For example, if it passes 10 7 then the stress level is increased by one level, otherwise it is decreased by one level. The stress level difference for increase or decrease does 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 (both failed and passed data points are included); p is the number of stress level series in the test; σ i is the stress level of the i-th level, and v i is the number of tests at the stress level of the i-th level.

[0116] Furthermore, after the fatigue limit test is completed, according to the stress of the up-and-down method, corresponding stresses are selected thereon for the group method test. For example, 4-5 stress levels are selected for the group method test until each group meets the set confidence level requirement and ends, such as 95% confidence level. The number of levels of the group method is determined according to the life distribution. Based on the results of the up-and-down method and the group method, an S-N curve is plotted. According to the 95% confidence level requirement, the number of specimens should meet the following requirements:

[0117]

[0118] where s / x is the coefficient of variation; δ max is the error limit; u p is the standard normal deviate; n is the number of subsamples; β is the standard correction coefficient.

[0119] Furthermore, perform the fatigue life decision-making step. Taking the static finite element simulation results, dynamic load addition coefficient, load characteristic identification, and material fatigue curve data as inputs, design a linear damage accumulation operation model as the fatigue analysis operation model. Use the fatigue analysis operation model to calculate the fatigue index values of different critical points in multiple rounds, and select the target fatigue life prediction result of the rotary steerable string tool based on them.

[0120] In the fatigue life decision-making step, according to the determined target well section, load amplification factor, stress ratio, and material S-N curve, use the fatigue life analysis operation model to calculate the fatigue life at each critical point in multiple rounds based on the Miner linear damage accumulation theory.

[0121] Among them, in the fatigue life decision-making step, taking the static finite element simulation results, dynamic load addition coefficient, load characteristic identification, and material fatigue curve data as inputs, design the Miner linear damage accumulation operation model as follows:

[0122]

[0123] In the formula, n i is the number of cycles under a certain level of cyclic stress; N i is the number of life cycles under a certain level of cyclic stress; D is the sum of fatigue damages under each level of stress.

[0124] Compare the fatigue lives at the above-mentioned critical points, and select the minimum life value among them; select the minimum value from the fatigue index values of different critical points as the target fatigue life prediction result of the rotary steerable string tool;

[0125] The present invention will be further described below in conjunction with the implementation cases. The scope of the present invention is not limited by the embodiments, and the scope of the present invention is set forth in the claims.

[0126] Taking a certain model of rotary steerable drilling system of "Jingwei Pilot" based on the pushing principle as an example, the fatigue life prediction analysis of the rotary steerable drilling tool is realized according to the following operations:

[0127] Step 1: Select the target test structure for the rotary steerable tool according to the operation mechanism, establish the corresponding three-dimensional structure model based on the target test structure, draw the three-dimensional structure diagram of the static pushing-type rotary steerable string tool, and perform finite element mesh division.

[0128] Specifically, the entire string of tools for the 6.75-inch "Jingwei Pilot" rotary steerable drilling system should include 4 units: the steering head unit, the geological survey unit, the central control unit, and the upper connecting drill pipe. The steering head unit includes 8 modules such as the main shaft, non-rotating outer sleeve, sliding bearing, actuator, primary circuit, secondary circuit, energy transmission, and flexible sub. The geological survey unit includes 2 modules such as azimuth gamma and azimuth resistivity. The central control unit includes 4 modules such as the pulser, generator, central control, and directional probe. The upper connecting drill collar includes 3 non-magnetic pressure-bearing drill pipes below the positive displacement motor. Finite element mesh generation is performed for the above 4 units respectively.

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

[0130] Based on the equilibrium differential equation of the elastic body, construct a static finite element simulation model, and analyze the high-stress critical points of the entire string of tools in the horizontal well section and the curved well section with the actual required dogleg severity;

[0131] The said Step 2 further includes: using bonded treatment for the threaded connections between modules. Inside the steering head module, contact pairs are established between the upper and lower main shafts due to the existence of a pre-tightening torque of 40 kN·m, contact pairs are established between the inner and outer alloy sheets of the male and female bearings, contact pairs are established between the inner spherical surfaces and shear keyways inside the male bearing, and the anti-extrusion rubber inside the male bearing is set as a hyperelastic material.

[0132] The static boundary load is the maximum allowable weight on bit of 20 t and torque of 21 kN·m specified in the tool manual. The construction well section is selected as the curved well section with the maximum actual required dogleg severity of 8° / 30 m and the horizontal well section with a well inclination of 90°.

[0133] Based on the equilibrium differential equation of the elastic body, establish a static finite element simulation model. Among them, the equilibrium differential equation of the elastic body can be expressed as:

[0134]

[0135] where σ is the stress; x, y, z are the Cartesian three coordinate vectors; F b is the body force; through static simulation, analyze the obvious high-stress critical points of the entire string of tools under different well sections.

[0136] Through static simulation analysis, it is found that there are 3 high-stress critical points in the entire string of tools of the "Jingwei Pilot" rotary steerable drilling system, all in the upper main shaft of the steering head, respectively located at the main shaft socket position, the reduced diameter position below the socket, and the thread relief groove position. The distribution of the critical points is as Figure 2 shown;

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

[0138] Step 3: Apply the dynamic boundary load of the drill bit, construct a dynamic finite element simulation model, and calculate the dynamic maximum Mises stress at each dangerous point obtained by the static simulation positioning in Step 2.

[0139] The dynamic boundary load is the dynamic drill pressure and reverse torque load applied to the drill bit when applying the maximum bit weight for rock breaking. All other calculation parameters are the same as those in the static simulation in Step 2. Calculate the dynamic Mises stress spectra at different well sections and each dangerous point through dynamic simulation, and extract the maximum Mises stress value.

[0140] Among them, during the rock breaking process, the actual drill pressure at the drill bit fluctuates numerically with the drill bit's torsional rock breaking process. This dynamic drill pressure should be expressed as adding a dynamic function that varies sinusoidally with the drill pressure to the target drill pressure. Specifically:

[0141] W b =W 0 (1 + asin(nθ)) (2)

[0142] In the formula, W b is the actual drill pressure at the drill bit; W 0 is the target drill pressure; a is the drill pressure fluctuation amplitude, which is related to the longitudinal vibration degree of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0143] The reverse torque of the drill bit consists of three parts, namely the torque under the action of the drill pressure, the torque under the action of the pushing force, and the frictional 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 is the actual torque at the drill bit; T w is the torque under the action of the drill pressure; T s is the torque under the action of the pushing force; T fThe frictional torque along the drill string needs to be calculated according to the theory of drill string mechanics; G is the shear modulus; I z is the polar moment of inertia of the beam element; l e is the length of the lowermost beam element; θ 1 is the circumferential rotation angle of the bit node; θ 2 is the circumferential rotation angle of the node above the bit; ω is the bit rotation speed; δ is the critical rotation speed of the viscous phase; r b is the outer diameter of the bit; μ s is the static friction coefficient; μ k is the dynamic friction coefficient; d c is the attenuation coefficient; γ eq is the slip rate.

[0148] Furthermore, after forming the dynamic boundary load, based on the Lagrange equation, a finite element simulation model for the dynamics of rotary steerable drilling is established. Among them, the Lagrange equation and the dynamic equation can be expressed as follows:

[0149]

[0150]

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

[0152] Through dynamic simulation analysis, 3 dangerous points of the "Jingwei Pilot" rotary steerable drilling system are obtained. The dynamic maximum Mises stresses in the 8° / 30m curved well section are 184.4 MPa, 169.7 MPa, and 321.2 MPa respectively, and the dynamic maximum Mises stresses in the 90° horizontal well section are 123.3 MPa, 112.6 MPa, and 291.3 MPa respectively.

[0153] Step 4: Calculate the ratio of the dynamic maximum stress to the static stress at each dangerous point as the dynamic load amplification factor;

[0154] Using the results of dynamic simulation and static simulation in the curved well section and horizontal well section, calculate the ratio of the dynamic maximum Mises stress to the static Mises stress at each dangerous point, and use it as the dynamic load amplification factor. The ratios of the dynamic maximum Mises stress to the static Mises stress at the 3 dangerous points of the "Jingwei Pilot" rotary steerable drilling system are 1.20, as shown in the following table. Therefore, 1.20 is used as the dynamic load amplification factor to facilitate the consideration of the additive effect of dynamic loads on the basis of fixed loads in the later stage for the prediction of the fatigue life of rotary steerable drilling.

[0155]

[0156] Step 5: Analyze the fatigue load history at each dangerous point to determine the stress ratio of the alternating loads on different dangerous points;

[0157] Analyze the load characteristics of the weight on bit, torque, and bending moment on different dangerous points, and determine whether the dynamic loads on different dangerous points are always unidirectional stresses or alternating stresses that change in positive and negative directions. The stress ratio for unidirectional stresses is 0, and the stress ratio for alternating stresses with positive and negative changes is -1.

[0158] Specifically, the main shaft of the guide head is mainly subjected to the loads of the weight on bit, torque, and bending moment. Among them, Dangerous Point 1 and Dangerous Point 2 are both located in the middle of the main shaft, mainly subjected to positive and negative alternating bending moments, occasionally negative torque, and always unidirectional weight on bit. This position is mainly subjected to high-frequency alternating bending moments, resulting in fatigue problems. For conservative description of the load history of the bending moment, the stress ratio here is selected as -1 in the fatigue analysis. Dangerous Point 3 is located at the thread relief groove. Due to the existence of the pre-tightening torque of the thread, this position is always subjected to a unidirectional tensile load, so the stress ratio here is selected as 0 in the fatigue analysis.

[0159] Step 6: Conduct high-cycle axial fatigue tests on the forged raw materials processed by the tool to obtain the S-N fatigue curve;

[0160] Take standard specimens at the inner wall position of the raw materials corresponding to the tool, and conduct axial tension-compression fatigue tests using a high-frequency fatigue testing machine at room temperature. Draw the S-N fatigue curve according to the up-and-down method and the group method.

[0161] Among them, the raw material for machining the main shaft is a bar. After heat treatment of the material, the mechanical properties of the outer surface and the inside of the bar are uneven, and the internal properties are inferior to the outer surface properties. However, due to the structural limitations of the main shaft, its machining mainly uses the position with poor internal mechanical properties. Therefore, instead of using the official standard S-N fatigue curve, samples are taken at the corresponding position of the main shaft inside the raw material and made into standard fatigue specimens for high-cycle fatigue tests, as Figure 3 shown, to test the true S-N fatigue curve of the material.

[0162] Furthermore, for the high-cycle fatigue test, use a high-frequency fatigue testing machine to conduct axial tension-compression fatigue tests. The testing machine needs to meet the requirements of the 0.5-level force value and equal-amplitude dynamic force in the verification regulation of the axial loading fatigue testing machine JJG556-2011. Calculate the median load and load amplitude according to the tensile properties of the material, set the parameters of the testing machine, and conduct fatigue tests at this stress. For example, if it passes 10 7 then increase the stress level by one level, otherwise decrease the stress level by one level. The stress level difference for increase or decrease does not exceed 3%-5% of the estimated fatigue limit until the 95% confidence level requirement is met. The fatigue limit is calculated according to formula (8):

[0163]

[0164] Among them, m is the total number of valid tests (both failure and passing data points are counted); p is the number of levels of test stress; σ i is the stress level at the i-th level; v i is the number of tests at the stress level of the i-th level.

[0165] Furthermore, after the fatigue limit test, according to the stress of the up-and-down method, select the corresponding 4-5 levels of stress for the group method test until each group meets the 95% confidence level requirement. The number of levels of the group method is determined according to the life distribution. According to the results of the up-and-down method and the group method, draw the S-N curve, as Figure 4 shown. According to the 95% confidence level requirement, the number of specimens should meet the following requirements:

[0166]

[0167] Among them, s / x is the coefficient of variation; δ max is the error limit; u p is the standard normal deviate; n is the number of subsamples; β is the standard correction coefficient.

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

[0169] The above Step 7 further includes: Based on the determined target well section, load amplification factor, stress ratio, and material S-N curve in Steps 1 to 6, calculate the fatigue life at each critical point in multiple rounds based on the Miner linear damage accumulation theory.

[0170] Specifically, input the static finite element simulation results, load amplification factor, material model, and symmetric cyclic loading (R = -1) or pulsating loading (R = 0) into the fatigue analysis program. Based on the Miner linear damage accumulation theory, solve the number of cyclic periods of the multi-directional load, and then determine the fatigue life of the guide head spindle. Calculate the fatigue life at each critical point in 2 rounds. The fatigue lives at the 3 critical point positions of the spindle are shown in Figure 5 .

[0171] Among them, the Miner linear damage accumulation theory can be expressed as:

[0172]

[0173] Among them, n i is the number of cycles under the cyclic stress of a certain level; N iN is the number of life cycles under cyclic stress of a certain level; D is the sum of fatigue damages under cyclic stress of each level.

[0174] Furthermore, compare the predicted fatigue lives at the above-mentioned dangerous points, and select the minimum life value as the expected fatigue life before the tool leaves the factory.

[0175] For the static push-against rotary steerable drilling system, the method for predicting the fatigue life of a rotary steerable system considering dynamic characteristics provided by the embodiments of the present invention can, on the basis of the static finite element simulation results, consider the additive effect of dynamic loads caused by downhole vibrations, and can conservatively estimate the tool fatigue life. In addition, for the problem that the stresses and load histories at different dangerous point positions are different, the load characteristics are analyzed separately, effectively considering the stress characteristics of different structural positions, and can more accurately predict the tool fatigue life. For the differences in load history and stress ratio, the fatigue life is calculated in multiple rounds and the minimum value is taken as the fatigue life calculation idea. At the same time, it lays a theoretical foundation for the fatigue life prediction of other types of rotary steerable drilling systems.

[0176] For the foregoing method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all 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 be combined with one or more of the above embodiments to obtain a new method for predicting the fatigue life of a rotary steerable system considering dynamic characteristics, so as to comprehensively achieve the accurate prediction of the fatigue life of the rotary steerable tool.

[0178] It should be noted that based on the method in any one or more of the above embodiments of the present invention, the present invention also provides a storage medium, on which program codes capable of implementing the methods described in any one or more of the above embodiments are stored. When the codes are executed by an operating system, the method for predicting the fatigue life of a rotary steerable system considering dynamic characteristics as described above can be implemented.

[0179] Embodiment 2:

[0180] In the embodiments of the present invention disclosed above, the method has been described in detail. The method of the present invention can be implemented by various forms of devices or systems. Therefore, based on other aspects of the method described in any one or more of the above embodiments, the present invention also provides a rotary steerable fatigue life prediction system considering dynamic characteristics, which is used to execute the rotary steerable 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 shows a schematic structural diagram of the rotary steerable fatigue life prediction system considering dynamic characteristics provided in the embodiments of the present invention. As Figure 6 shown, the system includes:

[0182] A structural model establishment module, configured to select a target test structure for the rotary steerable tool according to the operation mechanism, establish a corresponding three-dimensional structural model based on the target test structure, and perform finite element mesh division;

[0183] A dangerous point analysis module, configured to analyze the dangerous points in the target test structure based on the static finite element simulation model in combination with the set test well section, and determine the static Mises stress at each dangerous point;

[0184] A dynamic simulation analysis module, configured to introduce dynamic boundary loads, construct a dynamic finite element simulation model, and analyze the dynamic Mises stress at each dangerous point;

[0185] A dynamic addition analysis module, configured to calculate the dynamic load addition coefficient corresponding to the dangerous point according to the dynamic maximum stress and static stress at each dangerous point;

[0186] A load history analysis module, configured to analyze the dynamic load characteristics at different dangerous points from multiple aspects of weight on bit, torque, and bending moment and classify and identify them;

[0187] A material fatigue analysis module, configured to perform fatigue tests on the materials corresponding to the dangerous points to obtain material fatigue curve data characterizing fatigue characteristics;

[0188] A fatigue life decision module, configured to take the static finite element simulation results, dynamic load addition coefficients, load characteristic identifications, and material fatigue curve data as inputs, design a linear damage accumulation operation model as the fatigue analysis operation model, use the fatigue analysis operation model to calculate the fatigue index values of different dangerous points in multiple rounds, and select the target fatigue life prediction result of the entire rotary steerable tool based on it.

[0189] In an alternative embodiment, the target test structure of the rotary steerable tool selected by the structure model building module represents the entire rotary steerable tool string, including multiple sub-functional structures in the steering head unit, geological survey unit, central control unit, and upper connecting drill pipe unit.

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

[0191]

[0192] where σ is the stress; x, y, z are the Cartesian three coordinate vectors; F b is the body force.

[0193] Preferably, in one embodiment, when the dynamic simulation analysis module sets the dynamic boundary load to apply the maximum drilling pressure for rock breaking, the dynamic drilling pressure and reverse torque load at the drill bit are applied; the dynamic Mises stress spectra at different test well sections of each hazard point are calculated through dynamic simulation, and the maximum Mises stress value is extracted therefrom.

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

[0195]

[0196] The Lagrange equation is:

[0197]

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

[0199] Furthermore, in one embodiment, the dynamic drilling pressure of the dynamic simulation analysis module during the rock breaking process is configured to adopt a dynamic function that adds a sine variation with the drilling pressure on the basis of the target drilling pressure, as follows:

[0200] W b = W 0 (1 + asin(nθ))

[0201] where W b is the actual drilling pressure at the drill bit; W 0is the target WOB; a is the WOB fluctuation amplitude, which is related to the longitudinal vibration degree of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

[0202] In an optional embodiment, the reverse torque of the drill bit adopted by the dynamic simulation analysis module includes the torque under the action of the WOB, the torque under the action of the pushing force, and the frictional torque along the drill string, as shown in the following formula:

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

[0204]

[0205] T s = μ s F s r b

[0206] Among them, T total is the actual torque at the drill bit; T w is the torque under the action of the WOB; T s is the torque under the action of the pushing force; T f is the frictional torque along the drill string, which needs to be calculated according to the pipe string mechanics theory; G is the shear modulus; I z is the polar moment of inertia of the beam element; l e is the length of the lowermost beam element; θ 1 is the circumferential rotation angle of the drill bit node; θ 2 is the circumferential rotation angle of the node above the drill bit; ω is the drill bit rotation speed; δ is the critical rotation speed of the viscous phase; r b is the outer diameter of the drill bit; μ s is the static friction coefficient; μ k is the dynamic friction coefficient; d c is the attenuation coefficient; γ eq is the slip rate.

[0207] Furthermore, in an embodiment, the material fatigue analysis module is configured to collect material specimens from the matching position of the forgings raw materials for the structure corresponding to the critical point, and perform axial tension-compression fatigue tests on the material specimens using a high-frequency fatigue testing machine based on the staircase method principle 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 the stress of a set level on it according to the stress data tested by the staircase method, combines the set confidence requirement to perform the group method test, and draws the fatigue S-N curve of the current material according to the fatigue test results and the group method test results, where the number of specimens corresponding to the test matches the confidence requirement.

[0209] Optionally, in one embodiment, the fatigue life decision-making module takes the comprehensive static finite element simulation results, dynamic load addition coefficient, load characteristic identification, and material fatigue curve data as inputs, and designs the Miner linear damage accumulation operation model as follows:

[0210]

[0211] For different critical points, multiple rounds of targeted fatigue life predictions are carried out respectively, and the minimum value is selected from the fatigue index values of different critical points as the target fatigue life prediction result of the rotary steerable string tool;

[0212] In the formula, n i is the number of cycles under a certain level of cyclic stress; N i is the number of life cycles under a certain level of cyclic stress; D is the sum of fatigue damages under the action of stresses at each level.

[0213] In the rotary steerable fatigue life prediction system considering dynamic characteristics provided by the embodiments of the present invention, each module or unit structure can operate independently or in combination according to actual data processing requirements and operation analysis requirements to achieve corresponding technical effects.

[0214] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps, or materials disclosed herein, but should extend to equivalent alternatives of these features understood by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are only for the purpose of describing specific embodiments and do not mean to limit.

[0215] The phrase "one embodiment" mentioned in the specification means that the specific features, structures, or characteristics described in connection with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrase "one embodiment" that appears throughout the specification does not necessarily refer to the same embodiment.

[0216] Although the disclosed embodiments of the present invention are as above, the above content is only an embodiment adopted for the convenience of understanding the present invention and is not intended to limit the present invention. Any person skilled in the technical field to which the present invention pertains can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A method for predicting fatigue life of a rotary guide considering dynamic characteristics, characterized in that: The method comprises: Structural model establishment step: selecting a target test structure for the rotary guide tool according to the operation mechanism, establishing a corresponding three-dimensional structural model based on the target test structure, and performing finite element meshing; Danger point analysis step: based on the static finite element simulation model combined with the set test well section, analyzing the dangerous points in the target test structure, and determining the static Mises stress at each dangerous point; Dynamic simulation analysis steps: introduce dynamic boundary loads, build a dynamic finite element simulation model, and analyze the dynamic Mises stress at each dangerous point; Dynamic addition analysis steps: Calculate the dynamic load addition coefficient corresponding to the dangerous point according to the dynamic maximum stress and static stress at each dangerous point; Load history analysis steps: Analyze the dynamic load characteristics at different dangerous points from the aspects of drilling pressure, torque and bending moment, and classify and mark them; Material fatigue analysis steps: perform fatigue tests on the materials of the structure corresponding to the dangerous point to obtain material fatigue curve data representing fatigue characteristics; Fatigue life decision steps: Comprehensive static finite element simulation results, dynamic load addition coefficient, load characteristic identification and material fatigue curve data are used as input, and 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 results of the entire string of rotary guide tools are selected based on it.

2. The method according to claim 1, characterized in that In the structural model building step, the selected rotary steering tool target test structure represents the entire string of rotary steering tools, including: a steering head unit, a geological measurement unit, a central control unit and multiple sub-functional structures in an upper connected drill rod unit.

3. The method according to claim 1, characterized in that In the dangerous point analysis step, a static finite element simulation model is constructed based on the elastic body equilibrium differential equation, and the elastic body equilibrium differential equation is as follows: Where σ is stress; x, y, z are Cartesian coordinate vectors; F b is the 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 on the drill bit when the highest drilling pressure is applied to break rock. 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.

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

6. The method according to claim 1, characterized in that In the dynamic simulation analysis step, the dynamic drilling pressure in the rock breaking process is calculated by adding a dynamic function with sinusoidal changes in drilling pressure on the basis of the target drilling pressure, as shown in the following formula: W b =W0(1+and(nθ)) Among them, W b is the actual drilling pressure at the drill bit; W0 is the target drilling pressure; a is the fluctuation amplitude of the drilling pressure, which is related to the longitudinal vibration degree of the drill bit; n is the excitation factor; θ is the drill bit rotation angle.

7. The method according to claim 1, characterized in that In the dynamic simulation analysis step, the drill bit anti-torque includes the torque under the bit pressure, the torque under the push force and the friction torque along the drill string, as shown in the following formula: T total =T w +T s +T f T s =μ s F s r b Among them, T total is the actual torque at the drill bit; T w is the torque under the drilling pressure; T s is the torque under the pushing force; T f is the friction torque along the drill string, which needs to be calculated according to the string mechanics theory; G is the shear modulus; I z is the polar moment of inertia of the beam element; l e is the length of the lower beam unit; θ1 is the circumferential rotation angle of the drill node; θ2 is the circumferential rotation angle of the previous node on the drill; ω is the drill speed; δ is the critical speed of the viscous phase; r b is the outer diameter of the drill bit; μ s is the static friction coefficient; μ k is the coefficient of kinetic friction; d c is the attenuation coefficient; γ eq is the slip rate.

8. The method according to claim 1, characterized in that In the material fatigue analysis step, for the structure corresponding to the dangerous point, material samples are collected from the matching position of the forging raw material, and an axial tension and compression fatigue test is carried out on the material sample based on the lifting method principle using a high-frequency fatigue testing machine to complete the fatigue test; the matching position is determined according to the operating characteristics of the current structure.

9. The method according to claim 1, characterized in that: In the material fatigue analysis step, after the fatigue test is completed, a set level of stress is selected based on the stress data of the lifting method test, and a group method test is performed in combination with the set confidence requirements. The fatigue SN curve of the current material is drawn based on the fatigue test results and the group method test results, where the number of corresponding test specimens matches the confidence requirements.

10. The method according to claim 1, characterized in that In the fatigue life decision step, the static finite element simulation results, dynamic load addition coefficient, load characteristic identification and material fatigue curve data are used as input to design the Miner linear damage accumulation calculation model as follows: For different dangerous points, multiple rounds of targeted fatigue life prediction are carried out respectively, and the minimum value among the fatigue index values ​​of different dangerous points is selected as the target fatigue life prediction result of the entire string of rotary guide tools; Where n i N is the number of cycles under a certain level of cyclic stress; i is the number of life cycles under a certain level of cyclic stress; D is the sum of fatigue damage under each level of stress.

11. A storage medium, characterized in that: The storage medium stores program codes that can implement the method as claimed in any one of claims 1 to 10.

12. A rotary guide fatigue life prediction system considering dynamic characteristics, characterized in that: The system executes the method according to any one of claims 1 to 10.

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