A method for evaluating sucker rod wear

Abstract

This invention discloses a method for evaluating sucker rod wear, relating to the field of sucker rod technology. The method includes the following steps: acquiring real-time sucker rod operating condition data using a downhole intelligent sensor array; calculating the well fluid density using a weighted average method; obtaining a coupling judgment index based on hydrodynamic lubrication theory and comparing it with a preset threshold to determine the rod-tube friction coefficient; calculating the lateral normal pressure by combining the wellbore dogleg degree and the rod-tube friction coefficient; obtaining the basic wear amount for a single stroke using a corrosion-coupled wear method, and then obtaining a crack correction wear factor through crack propagation theory to correct the basic wear amount, resulting in a corrected wear amount for a single stroke; calculating the total wear amount and safety factor based on the corrected wear amount for a single stroke; introducing allowable stress and coupled damage theory to obtain a coupled damage coefficient to correct the safety factor, obtaining the basic safety and reliability level, and comparing it with a preset range to achieve wear state evaluation, thereby realizing the wear evaluation of the sucker rod.

Description

Technical Field

[0001] This invention relates to the field of sucker rod technology, specifically to a method for evaluating sucker rod wear. Background Technology

[0002] In the production process of mechanically operated wells in oilfields, the sucker rod, as the core component for transmitting power and lifting well fluid, needs to undergo reciprocating relative motion with the tubing in the complex downhole environment for extended periods. Affected by factors such as well fluid properties, wellbore trajectory, and load fluctuations, it is highly susceptible to wear. Sucker rod wear not only leads to a decrease in its cross-sectional strength and a shortened fatigue life, but can also cause problems such as rod string breakage and shortened pump inspection cycles, severely impacting oilfield production efficiency and increasing production costs.

[0003] Traditional methods typically use the Auchinger formula to calculate the wear of the sucker rod during a single stroke. This method is based on the theory of mechanical wear and calculates the basic wear of the sucker rod during a single stroke by substituting parameters such as the lateral normal pressure between the sucker rod and the tubing, the contact area, the relative speed of the rod and tubing, and the material hardness into the Auchinger formula. Ultimately, the basic wear of the sucker rod during a single stroke directly reflects the degree of wear of the sucker rod within that single stroke.

[0004] However, traditional methods only focus on quantifying mechanical wear factors and do not consider the dynamic impact of crack propagation on the sucker rod surface. In the actual downhole environment, crack propagation accelerates material shedding and changes wear characteristics, making it difficult for the calculated single-stroke wear amount to match the actual downhole wear state. Ultimately, this cannot provide accurate and reliable basic data for subsequent sucker rod wear evaluation, affecting the validity of the evaluation results. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for evaluating sucker rod wear, thereby resolving the problems existing in the background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for evaluating sucker rod wear, comprising the following steps:

[0007] S1: Real-time data on sucker rod operating conditions is acquired through a downhole intelligent sensor array, and the well fluid density is calculated by weighted average method based on the sucker rod operating conditions data.

[0008] S2: Based on the well fluid density, the operating data of the sucker rod are calculated using the hydrodynamic lubrication theory to obtain a coupling judgment index. The coupling judgment index is then compared with a preset threshold to obtain the rod-tube friction coefficient.

[0009] S3: Perform mechanical analysis on the operating data of the sucker rod to calculate the dogleg degree of the wellbore trajectory. By combining the friction coefficient of the rod and tubing and the dogleg degree of the wellbore trajectory, calculate the lateral normal pressure between the sucker rod and the tubing.

[0010] S4: Based on the lateral normal pressure and Hertzian contact theory, the initial contact area of ​​the sucker rod single stroke is calculated. The corrosion-wear coupling effect is introduced to correct the initial contact area of ​​the sucker rod single stroke, thus obtaining the effective contact area of ​​the sucker rod single stroke. Based on the sucker rod operating data, the crack propagation theory is used to calculate and obtain the crack-corrected wear factor. By combining the effective contact area of ​​the sucker rod single stroke and the crack-corrected wear factor, the basic wear amount of the sucker rod single stroke is corrected to obtain the crack-corrected wear amount of the sucker rod single stroke. The crack-corrected wear amount of the single stroke is corrected according to the coupling judgment index to obtain the total wear amount of the sucker rod single stroke.

[0011] S5: The total wear of the sucker rod is calculated based on the total wear of the sucker rod in a single stroke. The safety factor is calculated based on the total wear of the sucker rod. Based on the total wear of the sucker rod, the allowable stress and coupled damage theory are used to calculate the coupled damage coefficient. The safety factor is corrected based on the coupled damage coefficient, and the basic safety and reliability level is calculated. The basic safety and reliability level is compared with a preset range to obtain the evaluation result, thereby realizing the wear evaluation of the sucker rod.

[0012] Preferably, the step of calculating the well fluid density by using a weighted average method based on the sucker rod operating data includes the following specific steps:

[0013] The formula for calculating well fluid density is:

[0014]

[0015] in, This refers to the density of the well fluid, expressed in kg / m³. 3 It is a core physical quantity describing the mass distribution of well fluid. The density of the formation water, To correct the crude oil density, The water content of the well fluid is dimensionless and ranges from 0 to 1. Its physical meaning is the mass proportion of formation water in the well fluid. The crude oil mass fraction, For solid particles, This represents the volume fraction of solid particles.

[0016] Preferably, the step of calculating the coupling judgment index based on the well fluid density and using hydrodynamic lubrication theory to analyze the operating data of the sucker rod includes the following steps:

[0017] The formula for calculating the minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is:

[0018]

[0019] in, The minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is a core indicator for determining whether the oil film can separate the metal surface of the sucker rod. The radius of curvature of the sucker rod and tubing along the direction of motion reflects the geometric fit of the contact surfaces in the direction of motion, and is expressed in meters (m). This is the equivalent radius of curvature of the sucker rod and tubing in the vertical direction of motion, expressed in meters (m). Let be the well fluid viscosity coefficient, describing the characteristic of well fluid viscosity changing with pressure. Based on typical well fluid experiments, its value is taken as 3.0 × 10⁻⁶. , This refers to the real-time dynamic viscosity of the well fluid, expressed in Pa·s. The instantaneous velocity of the relative motion between the rod and the tube is expressed in m / s. The equivalent radius of curvature of the sucker rod contact surface, in meters. This is the corrected elastic modulus of the sucker rod and tubing materials, expressed in Pa. This refers to the lateral normal force between the sucker rod and the oil rod;

[0020] The formula for calculating the initial roughness ratio is:

[0021]

[0022] in, The dynamic roughness of the sucker rod surface reflects the degree of microscopic unevenness on the sucker rod surface, and is measured in meters (m). For the dynamic roughness of the inner wall surface of the oil pipe, The initial roughness ratio, physically defined as "the ratio of oil film thickness to the sum of surface roughness peak heights";

[0023] The formula for calculating the real-time flow rate of well fluid is:

[0024]

[0025] in, This is the real-time flow rate of the well fluid, reflecting its flow state within the tubing, expressed in m / s. Real-time liquid production rate, unit: m³ 3 / s, This refers to the inner diameter of the oil pipe, in meters (m). The diameter of the sucker rod. It is the Reynolds number;

[0026] The formula for calculating the coupling judgment index is:

[0027]

[0028] in, The water content coupling coefficient is... As a coupling judgment index, This refers to the real-time flow rate of the well fluid. The initial roughness ratio, This is a velocity direction correction term.

[0029] Preferably, the step of performing mechanical analysis on the sucker rod operating data to calculate the wellbore trajectory dogleg includes the following steps:

[0030] Mechanical analysis was performed on the sucker rod operating data to calculate the wellbore trajectory dogleg. The formula for calculating the wellbore trajectory dogleg is as follows:

[0031]

[0032] in, For the wellbore trajectory dogleg degree, The borehole curvature angle between two adjacent survey points. The depth of the well is the depth of two adjacent inclination measurement points.

[0033] Preferably, the step of calculating the lateral normal force between the sucker rod and tubing by combining the rod-tubing friction coefficient and the wellbore trajectory dogleg degree includes the following steps:

[0034] The formula for calculating the axial force of the sucker rod micro-segment is:

[0035]

[0036] in, The pump mounting depth is in meters (m). This refers to the tension in the upper section of the sucker rod string. The density of the sucker rod material is taken as 7850 kg / m³. 3 , Let be the cross-sectional area of ​​the sucker rod. For well fluid density, Given the current well depth, It is the acceleration due to gravity. For time indexing, The well inclination angle;

[0037] Lateral normal force is the result of the combined action of the component of the rod string axial force in the wellbore inclination direction and friction. By incorporating the amplification effect of dogleg, the formula for calculating lateral normal force is:

[0038]

[0039] in, Lateral positive pressure indicates well depth. ,time The normal load when the sucker rod is in contact with the tubing. This represents the total axial force acting on the micro-segment of the sucker rod. For well depth The angle between the wellbore and the vertical direction, expressed in rad. The coefficient of friction between the sucker rod and the tubing is denoted as . For well depth The dogleg degree at the location, quantifying the amplification effect of local borehole curvature on normal pressure, The dogleg amplification factor quantifies the influence of wellbore trajectory dogleg on lateral normal pressure. A factor of 0.015 is used for vertical sections, 0.02 for gently inclined sections, and 0.025 for sharp bends. The unit is 30 m / °. For correction factor, The reference friction coefficient is .

[0040] Preferably, the initial contact area of ​​the sucker rod during a single stroke is corrected by introducing the corrosion-wear coupling effect to obtain an effective contact area, including the following specific steps:

[0041] The initial contact area of ​​the sucker rod during a single stroke is corrected by introducing the corrosion-wear coupling effect, thus obtaining the effective contact area. The formula for calculating the effective contact area of ​​the sucker rod during a single stroke is as follows:

[0042]

[0043] in, This represents the initial contact area of ​​the sucker rod during a single stroke. This represents the corrosion rate of the well fluid on the surface of the sucker rod per unit time, reflecting the decrease in contact area due to corrosion. This represents the cumulative time the sucker rod has been in operation. This represents the attenuation coefficient of mechanical wear on the contact area. The corrosion attenuation coefficient is the coefficient of the contact area. To calculate the cumulative number of contacts, The number of contacts that significantly increases surface roughness. The corrosion-wear synergy coefficient, This refers to the effective contact area of ​​the sucker rod during a single stroke.

[0044] Preferably, the calculation of the crack correction wear factor based on sucker rod operating data and using crack propagation theory includes the following specific steps:

[0045] The formula for calculating the crack-corrected wear factor is:

[0046]

[0047] in, The crack-corrected wear factor combines temperature and crack length (dimensionless) to reflect the ease or difficulty of material wear. This refers to the real-time temperature of the contact area between the sucker rod and the tubing, expressed in Kelvin (K). This is the temperature sensitivity coefficient, with a value of 0.5. This refers to the length of the cracks that have already formed on the surface of the sucker rod. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. The crack influence coefficient quantifies the amplification effect of crack length on the wear factor, and is set to a value of 0.3. The reference wear factor coefficient is set to 20.

[0048] Preferably, the basic wear amount of the sucker rod single stroke is corrected by combining the initial contact area of ​​the sucker rod single stroke and the crack correction wear factor to obtain the crack correction wear amount of the sucker rod single stroke, including the following specific steps:

[0049] The formula for calculating the wear amount corrected by cracking in a single stroke of the sucker rod is:

[0050]

[0051] in, Correcting wear on single-stroke cracks in sucker rods. To correct the wear factor for cracks, for , is the ratio of lateral normal force to contact area. The relative instantaneous velocity between the sucker rod and the tubing. The cumulative time of contact between the rod and tube within a single stroke, expressed in seconds. The Brinell hardness is the material of the inner wall of the oil pipe.

[0052] Preferably, the calculation of the coupled damage coefficient based on the total wear of the sucker rod using allowable stress and coupled damage theory includes the following specific steps:

[0053] The formula for calculating the coupling damage coefficient is:

[0054]

[0055] in, The coupling damage coefficient reflects the overall failure risk resulting from the synergistic effect of various factors. The dynamic wear-corrosion coupling coefficient is used to quantify the synergistic amplification effect of wear and corrosion. This represents the dynamic stress-crack coupling coefficient, quantifying the accelerating effect of stress on crack propagation. This is the dynamic wear threshold. The total wear of the sucker rod during the time interval 0 to t. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. This represents the dynamic crack length on the surface of the sucker rod. This is the ratio of the stress range of the sucker rod. To accumulate corrosion depth, The wear-stress-corrosion coupling coefficient is set to 0.15. This is the dynamic corrosion threshold. This represents the maximum allowable stress of the sucker rod. This represents the yield strength of the material.

[0056] Preferably, the step of correcting the safety factor based on the coupling damage coefficient to calculate the basic safety and reliability level includes the following specific steps:

[0057] The safety factor calculated earlier is corrected by using the coupling damage coefficient:

[0058]

[0059] in, To correct the single-dimensional security, For uncorrected single-dimensional security, For dynamic sensitivity coefficient, The dynamic coupling damage threshold. The coupling damage coefficient;

[0060] The formula for calculating the basic safety and reliability level is:

[0061]

[0062] in, Based on the level of security and reliability, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, These are dynamic weighting coefficients.

[0063] This invention provides a method for evaluating sucker rod wear, which involves machine learning and deep learning technologies, and has the following beneficial effects:

[0064] (1) The calculation of single-stroke corrected wear effectively makes up for the shortcomings of traditional methods. Traditional wear calculation often ignores the dynamic influence of well fluid corrosion and crack propagation and only calculates with fixed parameters, which is out of touch with the actual working conditions downhole. This step constructs a contact area model coupled with corrosion and wear to quantify the attenuation effect of corrosion on the contact area. At the same time, combined with the crack propagation theory, the crack length is associated with the wear factor to form a correction factor, which allows the wear factor to be adjusted in real time with the crack change, greatly improving the accuracy of single-stroke wear calculation and laying a reliable data foundation for subsequent safety evaluation.

[0065] (2) The multi-factor coupled damage evaluation system solves the problem of the one-sidedness of traditional single-factor evaluation. Traditional evaluation often analyzes factors such as wear and corrosion separately without considering the synergistic amplification effect between factors, which easily underestimates or overestimates the failure risk. However, this method integrates the synergistic attenuation of wear and corrosion and the accelerated propagation effect of stress and cracks by dynamically coupling the damage coefficient, and then corrects the safety of each dimension, so that the evaluation results are more in line with the actual downhole condition of the sucker rod, providing a more accurate basis for operation and maintenance decisions.

[0066] (3) By introducing crack propagation theory to dynamically correct the wear factor, the influence of surface crack length on material wear characteristics is effectively quantified. This innovation breaks through the limitation of the wear factor taking a fixed value in the traditional model, and can reflect the material damage evolution process of the sucker rod under alternating loads in real time. By establishing a correlation model between crack length and wear factor, the accuracy of single-stroke wear calculation is significantly improved, making the calculation results more consistent with the actual working conditions downhole, and providing a more reliable data basis for preventive maintenance and life prediction of sucker rods. Attached Figure Description

[0067] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0068] Figure 1 This is a flowchart of the steps in the sucker rod wear evaluation method proposed in this invention;

[0069] Figure 2 This is a step hierarchy diagram of obtaining lateral normal pressure in a sucker rod wear evaluation method proposed in this invention;

[0070] Figure 3 This is a step hierarchy diagram of the method for evaluating sucker rod wear proposed in this invention to obtain the total wear amount of the sucker rod. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Please see Figures 1-3 The present invention provides a technical solution: a method for evaluating sucker rod wear.

[0073] S1: Real-time data on sucker rod operating conditions is acquired through a downhole intelligent sensor array, and the well fluid density is calculated by weighted averaging of the sucker rod operating conditions data.

[0074] This step aims to collect real-time and comprehensive data on sucker rod operating conditions that affect wear through a downhole intelligent sensor array. Unlike traditional static data acquisition (such as fixing well fluid density and ignoring local wellbore bending characteristics), which suffers from a disconnect from actual operating conditions, this step ensures that the input data for the subsequent wear evaluation model closely matches the real downhole operating conditions through multi-dimensional parameter acquisition and dynamic quantitative calculation, significantly improving the accuracy and reliability of the evaluation results.

[0075] An integrated downhole intelligent sensor array is adopted, which integrates the following functional modules. The selection and arrangement of each module are determined based on the on-site working conditions of the oilfield (such as well depth, temperature range, and well fluid corrosivity):

[0076] The temperature sensor is a PT100 platinum resistance temperature sensor with a measurement range of -50~150℃ and an accuracy of ±0.5℃. It is placed on the outer wall of the sucker rod coupling (near the contact surface with the inner wall of the tubing) to collect the temperature T of the contact surface between the sucker rod and the tubing in real time.

[0077] The pressure sensor is a diffused silicon piezoresistive pressure sensor with a measurement range of 0~30MPa and an accuracy of ±0.2%FS. It is placed above the plunger of the oil pump to indirectly assist in verifying the rationality of the well fluid dynamic viscosity calculation (pressure changes reflect the flow state of the well fluid and are related to dynamic viscosity), and at the same time provide a bottom hole pressure reference.

[0078] The water cut sensor is an RF capacitive water cut sensor with a measurement range of 0~100% and an accuracy of ±1.5%. It is placed on the inner wall of the tubing (near the oil pump outlet) to collect the water cut of the well fluid in real time. Based on the experimental law that when the water cut exceeds 74%, the well fluid changes from oil-in-water to water-in-oil, the lubrication performance drops sharply, and the wear intensifies, the water cut is the core input for dynamically calculating the well fluid density.

[0079] The dogleg measurement module is based on an integrated design of a triaxial accelerometer and gyroscope, with a measurement range of 0~10° / 30m and an accuracy of ±0.1° / 30m. One module is deployed every 100m along the sucker rod string. For the well depth between two measurement points, a spline interpolation algorithm is used to estimate the dogleg, more accurately reflecting the continuous variation characteristics of the wellbore trajectory. It is used to acquire the wellbore inclination angle of the wellbore trajectory. Azimuth and the wellbore curvature angle of adjacent measuring points And calculate the degree of sycophancy using a built-in algorithm. The greater the dogleg angle, the greater the axial and lateral forces on the sucker rod, and the greater the wear depth.

[0080] By coordinating wellhead and downhole sensors, the pumping unit stroke s (measurement range 0~6m, accuracy ±0.01m), stroke frequency n (measurement range 0~10min⁻¹, accuracy ±0.1min⁻¹), and real-time production rate Q (measurement range 0~100m) are collected. 3 / d, accuracy ±2%), where stroke s and stroke n are used to calculate the relative motion velocity U of the rod and tubing, and real-time production Q is used to calculate the well fluid flow velocity v. The acquisition frequency is synchronized with the pumping unit stroke cycle (acquiring once per stroke) to ensure that the parameters match the rod and tubing motion state. The well fluid density is obtained by calculating the operating data of the pumping rod using the weighted average method.

[0081] The formula for calculating well fluid density is:

[0082]

[0083] in, This refers to the density of the well fluid, expressed in kg / m³. 3 It is a core physical quantity describing the mass distribution of well fluid. The density of the formation water, To correct the crude oil density, The water content of the well fluid is dimensionless and ranges from 0 to 1. Its physical meaning is the mass proportion of formation water in the well fluid. The crude oil mass fraction, For solid particles, This represents the volume fraction of solid particles.

[0084] It should be noted that the formula for calculating the corrected crude oil density is as follows: ,in, The density of crude oil is taken as 850 kg / m³. 3 , For well fluid temperature, For the bottom hole pressure, The coefficient of volumetric expansion of crude oil is taken as 0.0015. The compressibility factor of crude oil is taken as 0.0005. The formula for calculating the density of formation water is: , Formation water salinity, The formula for calculating the water content of well fluid, where salinity is the influence coefficient, is: , This refers to the volumetric water content. This represents the volume fraction of solid particles. The formula for calculating the crude oil mass fraction, where solid phase particle density is given, is: =1- - .

[0085] The well fluid density calculation formula uses a "weighted average" logic to convert the dynamically changing water cut into well fluid density that can be directly used for mechanical calculations, realizing a quantitative correlation between "well fluid properties and mechanical parameters". Its core innovation lies in breaking through the traditional static density assumption, enabling the subsequent calculation of rod buoyancy and axial force to be updated in real time with changes in well fluid water cut, providing accurate fluid dynamic parameters to support the calculation of dynamic lateral positive pressure.

[0086] All collected parameters are uploaded in real time to the surface data processing terminal via downhole cable (or wireless transmission module, adapted to deep well conditions). The terminal performs the following preprocessing on the data: adopts the 3σ criterion to remove parameters that exceed the reasonable range to avoid abnormal data affecting subsequent calculations; uses linear interpolation to supplement parameters between adjacent measuring points to ensure that parameters are continuously distributed with well depth; and synchronizes the acquisition time of all parameters with the pumping unit stroke cycle (the start time of the above stroke is the time zero point) to ensure time matching of subsequent steps.

[0087] S2: Based on the well fluid density, the operating data of the sucker rod are calculated using the hydrodynamic lubrication theory to obtain a coupling judgment index. The coupling judgment index is then compared with a preset threshold to obtain the rod-tube friction coefficient.

[0088] This step aims to achieve wear and lubrication status judgment based on the coupling characteristics of hydrodynamic lubrication theory and wellbore conditions, by linking multiple factors such as "oil film thickness, surface roughness, well fluid flow rate, and well type". It can accurately distinguish between three states: "good lubrication (no wear)", "partial wear" and "metal wear". Its core is to solve the technical defects of traditional wear evaluation that rely only on mechanical load and ignore the dynamic influence of lubrication medium.

[0089] Based on the well fluid density, the operating data of the sucker rod are calculated using the hydrodynamic lubrication theory to obtain a coupling judgment index.

[0090] First, the real-time dynamic viscosity of the well fluid needs to be calculated in stages. When the viscosity is less than 74%, the formula for calculating the dynamic viscosity of the water-in-oil well fluid is: ,in, The dynamic viscosity of pure crude oil is taken as 0.08. The temperature influence coefficient is taken as 0.015. The factor representing the influence of water-in-oil well fluid density is taken as 0.02. The coefficient representing the influence of water cut in water-in-oil well fluids is taken as 0.5. Here is the density of the well fluid, and here is... When the viscosity is >74%, the formula for calculating the dynamic viscosity of water-in-oil well fluid is: , Let be the dynamic viscosity of pure water, taken as 0.001. The factor representing the influence of water-in-oil well fluid density is taken as 0.0005. The coefficient representing the influence of water cut in water-in-oil well fluid is set to 2.0.

[0091] The formula for calculating the minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is:

[0092]

[0093] in, The minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is a core indicator for determining whether the oil film can separate the metal surface of the sucker rod. The radius of curvature of the sucker rod and tubing along the direction of motion reflects the geometric fit of the contact surfaces in the direction of motion, and is expressed in meters (m). This is the equivalent radius of curvature of the sucker rod and tubing in the vertical direction of motion, expressed in meters (m). Let be the well fluid viscosity coefficient, describing the characteristic of well fluid viscosity changing with pressure. Based on typical well fluid experiments, its value is taken as 3.0 × 10⁻⁶. , This refers to the real-time dynamic viscosity of the well fluid, expressed in Pa·s. The instantaneous velocity of the relative motion between the rod and the tube is expressed in m / s. The equivalent radius of curvature of the sucker rod contact surface, in meters. This is the corrected elastic modulus of the sucker rod and tubing materials, expressed in Pa. This refers to the lateral normal force between the sucker rod and the oil rod.

[0094] It should be noted that the lateral normal force N(x,t) depends on step S3, and the lateral normal force N(x,t) in step S3 depends on the minimum thickness h0 of the oil film between the contact surface of the sucker rod and the tubing in step S2. This creates a "parameter-dependent loop," which can be solved using the "iterative method" commonly used in engineering calculations. The formula for calculating the corrected elastic modulus of the equivalent materials of the sucker rod and tubing is as follows: ,in, This is the equivalent elastic modulus of the rod / tube material under normal temperature and pressure. This refers to the temperature decay coefficient of the elastic modulus of steel. The contact surface temperature, For the bottom hole pressure, and Poisson's ratio, representing the materials of the sucker rod and tubing, respectively. and These are the elastic moduli of the sucker rod and tubing materials, respectively. The formula for calculating the instantaneous velocity of the relative motion between the rod and tubing is as follows: ,in, For the pumping unit stroke, For the stroke.

[0095] This formula, based on hydrodynamic lubrication theory, couples geometric parameters, fluid parameters, motion parameters, material parameters, and load parameters to quantitatively calculate the minimum oil film thickness in the contact area. Its core value lies in breaking through the limitations of traditional qualitative judgments of lubrication status by providing a quantitative... This reflects the actual load-bearing capacity of the oil film, providing a quantitative basis for subsequent judgments on "whether metal-to-metal contact has occurred." If the oil film is too small, it cannot cover the rough peaks, inevitably leading to metal wear; if... If it is large enough, good lubrication can be achieved.

[0096] The formula for calculating the initial roughness ratio is:

[0097]

[0098] in, The dynamic roughness of the sucker rod surface reflects the degree of microscopic unevenness on the sucker rod surface, and is measured in meters (m). For the dynamic roughness of the inner wall surface of the oil pipe, The initial roughness ratio is physically defined as "the ratio of the oil film thickness to the sum of the surface roughness peak heights".

[0099] It should be noted that the surface roughness of the sucker rod... ,in, Let be the initial dynamic roughness of the sucker rod, where Similarly, the calculation of the dynamic roughness of the inner wall surface of the oil pipe is based on this formula, which takes into account the influence of wear time on roughness.

[0100] The formula for calculating the real-time flow rate of well fluid is:

[0101]

[0102] in, This is the real-time flow rate of the well fluid, reflecting its flow state within the tubing, expressed in m / s. Real-time liquid production rate, unit: m³ 3 / s, This refers to the inner diameter of the oil pipe, in meters (m). The diameter of the sucker rod. It is the Reynolds number.

[0103] The formula for calculating the coupling judgment index is:

[0104]

[0105] in, The water content coupling coefficient is... As a coupling judgment index, This refers to the real-time flow rate of the well fluid. The initial roughness ratio, This is a velocity direction correction term.

[0106] It should be noted that the formula for calculating the moisture content coupling coefficient is as follows: ,in, The volumetric water content is given. The velocity direction correction term is 1.1 during the upstroke and 0.9 during the downstroke.

[0107] The core innovation of the coupling judgment index lies in coupling the initial roughness ratio with the well fluid velocity, which solves the defect of the traditional roughness ratio ignoring the dynamic influence of flow velocity, and the judgment result is more in line with the actual flow field environment downhole.

[0108] The lubrication status of the sucker rod is obtained by comparing the coupling judgment index with a preset threshold. By statistically analyzing the correlation between wear patterns of different well types, a differentiated threshold is set according to the well type, as follows:

[0109] Vertical wells have a gentle wellbore trajectory (usually with an inclination angle of <15°), low rod and tubing contact pressure, the lowest risk of eccentric wear, and lower requirements for oil film stability. When the value is greater than the first threshold, the initial first threshold for a vertical well is 2.8, indicating good lubrication of the sucker rod (no wear). When the value is between the first and second thresholds, it indicates that the sucker rod has some wear. The initial second threshold for vertical wells is 0.9, indicating metal wear on the sucker rod. For deviated wells with an inclination angle of 15° to 45°, moderate rod-tube contact pressure, and moderate risk of wear, higher oil film stability is required. The initial first threshold for deviated wells is 3.2, and the initial second threshold is 1.0. For horizontal wells with an inclination angle > 45°, long rod-tube contact time, high pressure, and the highest risk of wear, the initial first threshold for horizontal wells is 3.5, and the initial second threshold is 1.1.

[0110] By introducing moisture content to correct the threshold, the formulas for calculating the first and second thresholds are as follows:

[0111] ;

[0112] ;

[0113] in, The first threshold for the initial well pattern. The second threshold for the initial well pattern. To correct the first threshold of well type, To correct the second threshold of the well type.

[0114] When the sucker rod is under metal wear, the friction coefficient between the rod and tubing is 0.22~0.28; when partially worn, the friction coefficient is 0.10~0.15. In the field of mechanically operated oil wells, the friction coefficient between the sucker rod (mostly 30CrMo steel) and the tubing (mostly N80 steel) is a mature research parameter. This friction coefficient range conforms to the common experimental data of steel-to-steel friction in the industry. However, the above friction coefficient range does not consider material hardness and sand content in the well fluid. Multiple parameters are introduced to correct it. The formula for calculating the rod-tubing friction coefficient is:

[0115]

[0116] in, This represents the midpoint of the friction coefficient range corresponding to the lubrication condition. This refers to the Brinell hardness of the sucker rod. The Brinell hardness of the oil pipe is given. This refers to the sand content of the well fluid. The standard well fluid sand content value is taken as 1%. The standard Brinell hardness value is taken as 300 HB. is the coefficient of friction between the rod and the tube.

[0117] The coefficient of friction of the rod tube is determined based on the lubrication condition of the sucker rod.

[0118] S3: Perform mechanical analysis on the operating data of the sucker rod to calculate the dogleg degree of the wellbore trajectory. By combining the friction coefficient of the rod and tubing and the dogleg degree of the wellbore trajectory, calculate the lateral normal pressure between the sucker rod and the tubing.

[0119] This step aims to construct a three-in-one dynamic lateral normal pressure calculation method integrating wellbore trajectory, rod mechanics, and layered iteration. It accurately quantifies the contact normal load between the sucker rod and tubing at different well depths and times. Its core solution addresses two major technical shortcomings of traditional static normal pressure calculation: first, it ignores the amplification effect of wellbore trajectory dogleg on contact pressure; second, it does not consider the force difference above and below the neutral point of the sucker rod. The neutral point is the boundary between tension and compression of the rod string. Below this point, pressure easily leads to instability and more severe wear. The dynamic lateral normal pressure N(x,t) calculated in this step provides the core load input for the subsequent single-stroke correction wear calculation and provides a mechanical basis for the friction coefficient value in the wear state judgment step. It is a key bridge connecting wellbore conditions and wear quantification.

[0120] Mechanical analysis was performed on the sucker rod operating data to calculate the wellbore trajectory dogleg. The formula for calculating the wellbore trajectory dogleg is as follows:

[0121]

[0122] in, Dogleg angle, measured in degrees per 30 meters, is an industry-standard indicator describing the local curvature of a wellbore trajectory. Physically, it represents the curvature angle of the wellbore trajectory within a 30-meter well depth range. The borehole curvature angle between two adjacent survey points. The value is the well depth (m) between two adjacent inclination measurement points. The value is based on the arrangement spacing of the dogleg measurement modules. 30 is a conversion factor used to convert the "bending angle per meter of well depth" into the dogleg degree commonly used in the oilfield industry.

[0123] It should be noted that the method for calculating the wellbore curvature angle is as follows: ,in, , The inclination angle of adjacent measuring points. The azimuth difference between adjacent measuring points is ±0.1. This formula quantifies the "spatial curvature characteristics" of the wellbore trajectory into a dogleg degree that can be directly used for mechanical analysis, thus solving the defect of traditional wear evaluation that only considers the well inclination angle and ignores the local curvature of the wellbore.

[0124] The lateral normal pressure between the sucker rod and tubing is calculated by combining the friction coefficient of the rod and tubing and the dogleg degree of the wellbore trajectory.

[0125] The formula for calculating the axial force of the sucker rod micro-segment is:

[0126]

[0127] in, The pump mounting depth is in meters (m). This refers to the tension in the upper section of the sucker rod string. The density of the sucker rod material is taken as 7850 kg / m³. 3 , Let be the cross-sectional area of ​​the sucker rod. For well fluid density, Given the current well depth, It is the acceleration due to gravity. For time indexing, It is the well inclination angle.

[0128] Lateral normal force is the result of the combined action of the component of the rod string axial force in the wellbore inclination direction and friction. By incorporating the amplification effect of dogleg, the formula for calculating lateral normal force is:

[0129]

[0130] in, Lateral positive pressure indicates well depth. ,time The normal load when the sucker rod is in contact with the tubing. This represents the total axial force acting on the micro-segment of the sucker rod. For well depth The angle between the wellbore and the vertical direction, expressed in rad. The coefficient of friction between the sucker rod and the tubing is denoted as . For well depth The dogleg degree at the location, quantifying the amplification effect of local borehole curvature on normal pressure, The dogleg amplification factor quantifies the influence of wellbore trajectory dogleg on lateral normal pressure. A factor of 0.015 is used for vertical sections, 0.02 for gently inclined sections, and 0.025 for sharp bends. The unit is 30 m / °. For correction factor, The reference friction coefficient is .

[0131] It should be noted that the coefficient of friction between the sucker rod and the tubing in the formula is... In essence, the friction coefficient is used to quantify the characteristics of the contact interface under different lubrication conditions and to dynamically correct the basic normal pressure, rather than directly using the friction coefficient to calculate the normal pressure.

[0132] The core innovation of this formula lies in the fact that it is the first time to use the dogleg degree of the wellbore trajectory as a correction term for the lateral normal pressure. By using the experimental law related to the dogleg degree amplification factor, the quantitative mapping of wellbore curvature and contact pressure is realized.

[0133] The sucker rod neutralization point is a technical term used in the petroleum industry. It's the point where the forces acting on the sucker rod are zero; that is, the tension and compression forces on the sucker rod are balanced. Specifically, during the upstroke, the entire sucker rod string is under tension, and there is no neutralization point. However, during the downstroke, due to upward friction, the pressure on the bottom plunger, and the downward force of gravity on the rod and fluid, a point of zero force is created on the sucker rod string—the neutralization point. The neutralization point divides the sucker rod string into two parts: the upper part is always under tension, while the lower part is always under compression.

[0134] The formula for calculating the dynamic frictional resistance between the plunger and the bushing during the movement of the oil pump plunger is as follows:

[0135]

[0136] in, Where is the diameter of the pump cylinder. This refers to the clearance between the plunger and the bushing. This refers to the dynamic frictional resistance between the plunger and the bushing during the movement of the oil pump plunger. Standard viscosity, This represents the real-time dynamic viscosity of the well fluid.

[0137] The hydraulic resistance of the well fluid through the traveling valve is:

[0138]

[0139] in, The hydraulic resistance of the well fluid passing through the traveling valve acts downwards on the plunger, measured in N (N). Number of traveling valves This refers to the cross-sectional area of ​​the pump plunger, expressed in m². The cross-sectional area of ​​the valve seat bore of the moving valve is... The real-time dynamic viscosity of the well fluid. For well fluid density, This refers to the sucker rod stroke, measured in meters (m). This refers to the number of strokes of the sucker rod.

[0140] The formula for calculating the dynamic viscous resistance coefficient of the well fluid against the downward movement of the rod string is as follows:

[0141] ;

[0142] ;

[0143] ;

[0144] in, This represents the viscous resistance coefficient of the well fluid against the downward movement of the rod string. This represents the maximum downward speed of the sucker rod string. To correct for the well fluid flow coefficient, dimensionless, It is the ratio of the tubing inner diameter to the sucker rod diameter. The real-time dynamic viscosity of the well fluid. This refers to the sucker rod stroke. This refers to the number of strokes of the sucker rod.

[0145] Therefore, it is necessary to first calculate the neutralization point location, and then iteratively calculate the lateral normal force based on the differential parameters of the upper and lower segments. The formula for calculating the neutralization point location is:

[0146]

[0147] in, The neutralization point is located at a depth representing the distance from the wellhead to the neutralization point, in meters (m). The dynamic frictional resistance between the plunger and the bushing during the movement of the oil pump plunger, expressed in N. The hydraulic resistance of the well fluid passing through the traveling valve, This represents the dynamic viscous resistance coefficient of the well fluid against the downward movement of the rod string. Let be the cross-sectional area of ​​the sucker rod. For well fluid density, The density of the sucker rod material.

[0148] It should be noted that the formula for calculating the density of the sucker rod material is: ,in, Let x be the temperature at well depth. is the coefficient of thermal expansion of steel.

[0149] This formula uses local forces ( , The balance between the effective gravity difference of the pole and the column is used to accurately locate the neutral point, avoiding the errors caused by traditional empirical estimation methods (such as taking 2 / 3 of the pump hanging depth), and providing an accurate boundary for subsequent layered iterations.

[0150] Based on the neutralization point, the sucker rod string is divided into the upper section (x < 0.05). ) and the next paragraph (x> Lateral normal force was calculated using different iteration parameters:

[0151] Above the neutral point, the length of the micro-element segment is 10m, and the lateral friction coefficient of metal wear is 0.18~0.25; the lateral friction coefficient of partial wear is 0.08~0.12. The lateral normal pressure is calculated iteratively from the wellhead downwards in the upper section, and the difference in normal pressure between adjacent micro-elements is <5%.

[0152] Below the neutral point, starting from the pump end load, the vertical well section is divided into 5m micro-element segments. Convergence is achieved when the positive pressure difference between micro-elements is <3%. The gently inclined section is divided into 3m micro-element segments. Convergence occurs when the positive pressure difference between micro-elements is <2%. The sharply curved section is divided into 2m micro-element segments. Convergence occurs when the positive pressure difference between micro-elements is <1%. If the positive pressure difference between adjacent micro-elements is >15%, it is further subdivided into 1m micro-element segments, and the lateral positive pressure is iteratively calculated until x= This ensures continuous positive pressure at the neutralization point.

[0153] Through the above iterative calculations, the final output is a two-dimensional lateral positive pressure distribution curve of well depth and time, with the time dimension synchronized with the pumping unit stroke cycle (updated every 0.1s).

[0154] S4: Based on the lateral normal pressure and Hertzian contact theory, calculate the initial contact area of ​​the sucker rod single stroke. Introduce the corrosion-wear coupling effect to correct the initial contact area of ​​the sucker rod single stroke, and obtain the effective contact area of ​​the sucker rod single stroke. Based on the sucker rod operating data, use crack propagation theory to calculate and obtain the crack-corrected wear factor. By combining the effective contact area of ​​the sucker rod single stroke and the crack-corrected wear factor, correct the basic wear amount of the sucker rod single stroke to obtain the crack-corrected wear amount of the sucker rod single stroke. Correct the crack-corrected wear amount of the single stroke according to the coupling judgment index to obtain the total wear amount of the sucker rod single stroke.

[0155] This step aims to construct a three-in-one single-stroke corrected wear calculation model integrating contact geometry, corrosion coupling, and crack correlation, accurately quantifying the wear depth of the sucker rod within a single pumping stroke. Its core solution addresses two major technical deficiencies in traditional wear calculation: first, it ignores the mechanism by which eccentric wear removes slow corrosion products and accelerates corrosion of the wear surface in the synergistic aggravation effect of well fluid corrosion and mechanical wear; second, it does not consider the dynamic influence of crack propagation on the wear factor.

[0156] The contact area is the core geometric parameter for calculating wear. Traditional models only consider the area change caused by mechanical wear. This invention introduces the attenuation effect of corrosion on the contact area. Based on the lateral normal pressure, the corrosion-coupled wear method is used to calculate the basic wear of the sucker rod in a single stroke.

[0157] First, based on the lateral normal force and Hertzian contact theory, the initial contact area of ​​the sucker rod during a single stroke is calculated. The formula for calculating the initial contact area of ​​the sucker rod during a single stroke is as follows:

[0158] ;

[0159] ;

[0160] in, This represents the initial contact area of ​​the sucker rod during a single stroke. This is the maximum axial wear length. This represents the maximum lateral wear width. This refers to the axial length of the sucker rod coupling. The equivalent radius of curvature, It is a lateral normal force. This is the modified elastic modulus of the sucker rod and tubing materials.

[0161] It should be noted that the formula for calculating the equivalent radius of curvature is: , The inner diameter of the oil pipe. This refers to the diameter of the sucker rod.

[0162] The formula for calculating the corrosion rate of the well fluid on the surface of the sucker rod per unit time is:

[0163]

[0164] in, The corrosion rate of the sucker rod surface by the well fluid per unit time, expressed in mm / year. The water content of the well fluid is dimensionless and ranges from 0 to 1. Its physical meaning is the mass proportion of formation water in the well fluid. Let x be the temperature at well depth. The pressure at depth x. The salinity of the well fluid at depth x is given.

[0165] It should be noted that this calculation formula was derived by conducting indoor corrosion rate experiments and establishing an empirical model, analyzing the corrosion of sucker rods downhole, and obtaining the mathematical expression of this relationship through numerical fitting methods.

[0166] The initial contact area of ​​the sucker rod during a single stroke is corrected by introducing the corrosion-wear coupling effect, thus obtaining the effective contact area. The formula for calculating the effective contact area of ​​the sucker rod during a single stroke is as follows:

[0167]

[0168] in, This represents the initial contact area of ​​the sucker rod during a single stroke. This represents the corrosion rate of the well fluid on the surface of the sucker rod per unit time, reflecting the decrease in contact area due to corrosion. This represents the cumulative time the sucker rod has been in operation. This represents the attenuation coefficient of mechanical wear on the contact area. The corrosion attenuation coefficient is the coefficient of the contact area. To calculate the cumulative number of contacts, The number of contacts that significantly increases surface roughness. The corrosion-wear synergy coefficient, This refers to the effective contact area of ​​the sucker rod during a single stroke.

[0169] The core innovation of this formula lies in the fact that the corrosion-wear coupling mechanism is quantified as a contact area correction term for the first time, which solves the problem of area calculation error caused by mechanical wear in traditional models.

[0170] As oil pumping progresses, the wear of the sucker rod gradually increases, the cross-sectional area gradually decreases, and the stress in the sucker rod section gradually increases. Under the action of complex alternating cyclic loads, the damaged rod string will undergo fatigue fracture. After the sucker rod string wears, the cross-sectional area changes, and the cross-sectional stress also changes. The fatigue strength of the sucker rod string can be checked using the Auginger formula.

[0171] Based on sucker rod operating data, a crack-corrected wear factor is calculated using crack propagation theory. The wear factor K is a core parameter in the Archard formula. Traditional models use a fixed value, but this invention introduces a crack-corrected wear factor. The calculation formula for the crack-corrected wear factor is as follows:

[0172]

[0173] in, The crack-corrected wear factor combines temperature and crack length (dimensionless) to reflect the ease or difficulty of material wear. This refers to the real-time temperature of the contact area between the sucker rod and the tubing, expressed in Kelvin (K). This is the temperature sensitivity coefficient, with a value of 0.5. This refers to the length of the cracks that have already formed on the surface of the sucker rod. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. The crack influence coefficient quantifies the amplification effect of crack length on the wear factor, and is set to a value of 0.3. The reference wear factor coefficient is set to 20.

[0174] It should be noted that the formula for calculating the length of cracks that have already formed on the surface of the sucker rod is: ,in, The initial crack length is... Let be the crack propagation factor, taken as 0.0002. For the material's yield strength, for , , Let be the cross-sectional area of ​​the sucker rod. It is a lateral normal force. This refers to the effective contact area of ​​the sucker rod during a single stroke. To calculate the cumulative number of contacts, This represents the rate at which well fluid corrodes the surface of the sucker rod per unit time.

[0175] The formula for calculating the critical length at which a crack propagates to cause the bar to fracture is:

[0176]

[0177] in, This refers to the critical length at which the crack propagates, leading to the breakage of the rod. The fracture toughness of the sucker rod is taken as 60 MPa·m1 / 2. For the largest contact area .

[0178] By combining the effective contact area of ​​the sucker rod single stroke and the crack correction wear factor, the basic wear amount of the sucker rod single stroke is corrected, and the crack correction wear amount of the sucker rod single stroke is obtained.

[0179] The formula for calculating the wear amount corrected by cracking in a single stroke of the sucker rod is:

[0180]

[0181] in, Correcting wear on single-stroke cracks in sucker rods. To correct the wear factor for cracks, for , is the ratio of lateral normal force to contact area. The relative instantaneous velocity between the sucker rod and the tubing. The cumulative time of contact between the rod and tube within a single stroke, expressed in seconds. The Brinell hardness is the material of the inner wall of the oil pipe.

[0182] The core innovation of this formula lies in quantifying the crack-wear synergistic effect as a wear factor correction term, thus solving the problem of underestimating the wear amount caused by neglecting cracks in traditional models.

[0183] The wear amount of a single-stroke crack is corrected based on the coupling judgment index, resulting in the final corrected wear amount for the single stroke. During partial wear, an oil film exists, reducing the wear amount. The calculation formula for the corrected wear amount during the sucker rod movement is as follows:

[0184]

[0185] in, This represents the final corrected wear amount during the sucker rod's movement. Correcting wear on single-stroke cracks in sucker rods. For well fluid flow rate, This is a correction factor for lubrication conditions.

[0186] It should be noted that the formula for calculating the lubrication condition correction factor is: ,in, The first threshold for lubrication status. The second threshold for lubrication status is the same as step S2. When lubrication is good and smooth, the lubrication status correction coefficient is 0, and when metal wears, the lubrication status correction coefficient is 1.

[0187] The sucker rod single stroke includes the upstroke and the downstroke. The wear amount of each stroke is calculated separately and then summed.

[0188]

[0189] in, This represents the total wear of the sucker rod during a single stroke. This is to correct the wear during the final upward stroke of the sucker rod during its movement. This is to correct the wear during the final downstroke of the sucker rod during its movement. This is the correction factor for wear during the downstroke.

[0190] It should be noted that the formula for calculating the final wear correction factor of the downstroke is as follows: ,in, The lateral normal force during the downstroke. This is the lateral positive pressure during the upstroke.

[0191] S5: The total wear of the sucker rod is calculated based on the total wear of the sucker rod in a single stroke. The safety factor is calculated based on the total wear of the sucker rod. Based on the total wear of the sucker rod, the allowable stress and coupled damage theory are used to calculate the coupled damage coefficient. The safety factor is corrected based on the coupled damage coefficient, and the basic safety and reliability level is calculated. The basic safety and reliability level is compared with a preset range to obtain the evaluation result, thereby realizing the wear evaluation of the sucker rod.

[0192] This step aims to solve the problems of neglecting the synergistic failure effect between factors and the disconnect between safety status and life prediction in traditional wear evaluation by constructing a complete technical system of multi-factor coupled damage measurement, single-dimensional safety correction, and comprehensive safety and reliability quantification. The core output is the safety and reliability level after coupling correction (0~100 points), which provides a quantitative decision basis for the preventive maintenance of sucker rods.

[0193] The total wear of the sucker rod is calculated based on the final corrected wear amount during the single stroke of the sucker rod. The formula for calculating the total wear of the sucker rod within the time interval 0 to t is as follows:

[0194]

[0195] in, The total wear of the sucker rod during the time interval 0 to t. This represents the total wear of the sucker rod during a single stroke. This represents the number of up and down stroke cycles completed by the pumping unit within the time interval 0 to t. This refers to the length of the cracks that have already formed on the surface of the sucker rod. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. The corrosion acceleration factor is 0.8.

[0196] The safety factor is calculated based on the total wear of the sucker rod, and the stress safety factor is calculated accordingly. Wear safety Crack safety Corrosion safety The stress range ratio exceeding 85% is considered a dangerous threshold with a stress safety factor of 0; less than 60% is considered a safe threshold with a stress safety factor of 100. The closer the wear is to the limit, the lower the wear safety score. The crack safety factor exceeds 0.5. Time-based scaling acceleration, less than 0.5 The safety factor for cracks is 100, and the score is 0 when the corrosion depth exceeds the limit.

[0197] Allowable stress is the benchmark for the mechanical safety of the sucker rod. Considering the influence of well fluid corrosion, the formula for calculating the maximum allowable stress of the sucker rod is:

[0198]

[0199] in, This represents the maximum allowable stress of the sucker rod. The minimum tensile strength of the sucker rod. The maximum and minimum loads of this micro-element segment are... This represents the cross-sectional area of ​​the sucker rod after wear. This refers to the sucker rod utilization factor. This represents the rate at which well fluid corrodes the surface of the sucker rod per unit time.

[0200] It should be noted that the formula for calculating the cross-sectional area of ​​the sucker rod after wear is as follows: ,in, This represents the cross-sectional area of ​​the sucker rod.

[0201] The formula for calculating the stress range ratio of the sucker rod is:

[0202]

[0203] in, This is the ratio of the stress range of the sucker rod. This represents the maximum load on this micro-element segment. This represents the minimum load on this infinitesimal element segment. This represents the maximum allowable stress of the sucker rod. This represents the cross-sectional area of ​​the sucker rod after wear.

[0204] When the stress range ratio is between 60% and 85%, the formula for calculating the stress safety factor is:

[0205]

[0206] in, For stress safety, This is the ratio of the stress range of the sucker rod.

[0207] The formula for calculating wear safety factor is:

[0208]

[0209] in, For wear and tear safety, This is the dynamic wear threshold. The total wear of the sucker rod during the time interval 0 to t.

[0210] It should be noted that the dynamic wear threshold is determined based on the lubrication condition, and the value is taken when lubrication is smooth. Take when partially worn Take when metal wears out 15, This refers to the diameter of the sucker rod.

[0211] The formula for calculating the crack safety factor is:

[0212]

[0213] in, For crack safety, This refers to the length of the cracks that have already formed on the surface of the sucker rod. This is the critical length at which the crack propagates to cause the rod to break.

[0214] The formula for calculating corrosion safety is:

[0215]

[0216] in, For corrosion safety, The cumulative corrosion depth is obtained by integrating the corrosion rate. This represents the dynamic corrosion threshold.

[0217] It should be noted that the formula for calculating the dynamic corrosion threshold is: ,in, The water content of the well fluid. This refers to the diameter of the sucker rod.

[0218] Based on the total wear of the sucker rod, the coupling damage coefficient is calculated using allowable stress and coupled damage theory.

[0219] Based on the coupled damage theory, wear damage and corrosion damage are quantified into coupled damage coefficients. The formula for calculating the dynamic coupled damage coefficient is as follows:

[0220]

[0221] in, The coupling damage coefficient reflects the overall failure risk resulting from the synergistic effect of various factors. The dynamic wear-corrosion coupling coefficient is used to quantify the synergistic amplification effect of wear and corrosion. This represents the dynamic stress-crack coupling coefficient, quantifying the accelerating effect of stress on crack propagation. This is the dynamic wear threshold. The total wear of the sucker rod during the time interval 0 to t. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. This represents the dynamic crack length on the surface of the sucker rod. This is the ratio of the stress range of the sucker rod. To accumulate corrosion depth, The wear-stress-corrosion coupling coefficient is set to 0.15. This is the dynamic corrosion threshold. This represents the maximum allowable stress of the sucker rod. This represents the yield strength of the material.

[0222] It should be noted that the formula for calculating the wear-corrosion coupling coefficient is as follows: ,in, Given the water cut of the well fluid, the formula for calculating the dynamic stress-crack coupling coefficient is: ,in, The ratio of sucker rod stress range is given by the coefficients in the formula, which are obtained through numerical fitting of wear and corrosion experiments.

[0223] Based on the aforementioned coupling damage coefficient, the safety factor is corrected, and the basic safety and reliability level is calculated. The calculation process is as follows:

[0224] The safety factor calculated earlier is corrected by using the coupling damage coefficient:

[0225]

[0226] in, To correct the single-dimensional security, For uncorrected single-dimensional security, For dynamic sensitivity coefficient, The dynamic coupling damage threshold. This represents the coupling damage coefficient.

[0227] It should be noted that the dynamic sensitivity coefficient The wear sensitivity coefficient is 0.05 for vertical wells, 0.06 for deviated wells, and 0.07 for horizontal wells. Crack sensitivity coefficient Corrosion sensitivity coefficient The dynamic coupling damage thresholds are 0.03 for vertical wells, 0.03 for inclined wells, and 0.02 for horizontal wells, and 1.2 for vertical wells, 1.1 for inclined wells, and 1.0 for horizontal wells.

[0228] The formula for calculating the basic safety and reliability level is:

[0229]

[0230] in, Based on the level of security and reliability, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, These are dynamic weighting coefficients.

[0231] It should be noted that, 0.3 for vertical wells, 0.3 for inclined wells, and 0.25 for horizontal wells. 0.15 for vertical wells, 0.25 for inclined wells, and 0.3 for horizontal wells. 0.35 for vertical wells, 0.3 for inclined wells, and 0.3 for horizontal wells. 0.20 for vertical wells, 0.15 for inclined wells, and 0.15 for horizontal wells.

[0232] Monte Carlo simulation can effectively solve probabilistic problems under complex functional relationships. It is suitable for rod safety analysis with many influencing factors and complex relationships. Monte Carlo simulation is used to evaluate the safety of sucker rod wear during use. The Monte Carlo simulation needs to cover the fluctuations of key parameters. Five core random parameters are selected, and their distribution types and fluctuation ranges are as follows:

[0233] The number of impacts follows a normal distribution with a fluctuation range of ±5%; the corrosion rate follows a log-normal distribution; the lateral normal pressure follows a normal distribution with a fluctuation range of ±8%; and the wear-corrosion coupling coefficient... It follows a normal distribution, with a fluctuation range of ±10%, and the stress-crack coupling coefficient is... It follows a normal distribution with a fluctuation range of ±10%.

[0234] Input the pre-set data and set the number of simulations. Iteration time step In each iteration, parameter values ​​are randomly selected from the above distribution, and calculations are performed. Record 500 scores, and take the 2.5% quantile and the 97.5% quantile of the 500 scores to form a 95% confidence interval.

[0235] The basic safety and reliability level is compared with a preset range to obtain the evaluation result, thereby realizing the wear evaluation of the sucker rod.

[0236] The relationship between the evaluation results and the corresponding safety level is as follows: Safety Level: >80 (probability of failure <10%), relatively safe level: 60< <80 (failure probability 10%~30%), more dangerous level: 30< <60 (failure probability 30%~80%), Danger level: For sucker rod strings with a failure probability of <30 (>80%), there is basically no risk of strength failure and they can continue to work. For sucker rod strings with a relatively dangerous level, there is a certain safety risk, which can be judged based on their lifespan. For sucker rod strings with a dangerous level, the rod string must be removed and treated to prevent rod string breakage.

[0237] This technical solution discloses a method for evaluating sucker rod wear. The method first collects multi-dimensional dynamic parameters using a downhole intelligent sensor array. Then, based on hydrodynamic lubrication theory, it determines the lubrication state of the sucker rod. Combining the wellbore trajectory dogleg degree with the sucker rod neutralization point through layered iteration, it calculates the corrected lateral normal pressure. Next, it corrects the contact area through corrosion-wear coupling and the wear factor through crack propagation correlation, accurately obtaining the corrected wear amount for a single stroke. Finally, based on allowable stress and coupled damage theory, it corrects the safety factor and combines Monte Carlo simulation to output the corrected safety and reliability level with a confidence interval. This achieves a comprehensive evaluation of the sucker rod wear state and life prediction, effectively overcoming the limitations of traditional evaluation methods that ignore the synergistic effects of multiple factors and the influence of parameter fluctuations, providing a scientific basis for preventative maintenance of sucker rods.

[0238] The single-stroke corrected wear calculation effectively overcomes the shortcomings of traditional methods. Traditional wear calculations often ignore the dynamic effects of well fluid corrosion and crack propagation, using only fixed parameters, which is out of touch with actual downhole conditions. This step constructs a corrosion-wear coupled contact area model to quantify the attenuation effect of corrosion on the contact area. At the same time, combined with crack propagation theory, crack length is correlated with wear factor to form a correction factor, allowing the wear factor to be adjusted in real time as the crack changes, which greatly improves the accuracy of single-stroke wear calculation and lays a reliable data foundation for subsequent safety assessment.

[0239] The multi-factor coupled damage evaluation system solves the problem of the one-sidedness of traditional single-factor evaluation. Traditional evaluations often analyze factors such as wear and corrosion in isolation, without considering the synergistic amplification effect between factors, which easily underestimates or overestimates the failure risk. However, this method integrates the synergistic attenuation of wear and corrosion and the accelerated propagation effect of stress and cracks by dynamically coupling the damage coefficient, and then corrects the safety factor of each dimension, so that the evaluation results are more in line with the actual downhole condition of the sucker rod, providing a more accurate basis for operation and maintenance decisions.

[0240] By introducing crack propagation theory to dynamically correct the wear factor, the influence of surface crack length on material wear characteristics is effectively quantified. This innovation overcomes the limitation of traditional models that use fixed values ​​for the wear factor, and can reflect the material damage evolution process of sucker rods under alternating loads in real time. By establishing a correlation model between crack length and wear factor, the accuracy of single-stroke wear calculation is significantly improved, making the calculation results more consistent with actual downhole operating conditions, and providing a more reliable data foundation for preventive maintenance and life prediction of sucker rods.

[0241] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0242] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating sucker rod wear, characterized in that: Includes the following steps: S1: Real-time data on sucker rod operating conditions is acquired through a downhole intelligent sensor array, and the well fluid density is calculated by weighted average method based on the sucker rod operating conditions data. S2: Based on the well fluid density, the operating data of the sucker rod are calculated using the hydrodynamic lubrication theory to obtain a coupling judgment index. The coupling judgment index is then compared with a preset threshold to obtain the rod-tube friction coefficient. S3: Perform mechanical analysis on the operating data of the sucker rod to calculate the dogleg degree of the wellbore trajectory. By combining the friction coefficient of the rod and tubing and the dogleg degree of the wellbore trajectory, calculate the lateral normal pressure between the sucker rod and the tubing. S4: Based on the lateral normal pressure and Hertzian contact theory, the initial contact area of ​​the sucker rod single stroke is calculated. The corrosion-wear coupling effect is introduced to correct the initial contact area of ​​the sucker rod single stroke, thus obtaining the effective contact area of ​​the sucker rod single stroke. Based on the sucker rod operating data, the crack propagation theory is used to calculate and obtain the crack-corrected wear factor. By combining the effective contact area of ​​the sucker rod single stroke and the crack-corrected wear factor, the basic wear amount of the sucker rod single stroke is corrected to obtain the crack-corrected wear amount of the sucker rod single stroke. The crack-corrected wear amount of the single stroke is corrected according to the coupling judgment index to obtain the total wear amount of the sucker rod single stroke. S5: The total wear of the sucker rod is calculated based on the total wear of the sucker rod in a single stroke. The safety factor is calculated based on the total wear of the sucker rod. Based on the total wear of the sucker rod, the allowable stress and coupled damage theory are used to calculate the coupled damage coefficient. The safety factor is corrected based on the coupled damage coefficient, and the basic safety and reliability level is calculated. The basic safety and reliability level is compared with a preset range to obtain the evaluation result, thereby realizing the wear evaluation of the sucker rod. The formula for calculating the effective contact area of ​​the sucker rod during a single stroke is: ； in, This represents the initial contact area of ​​the sucker rod during a single stroke. This represents the corrosion rate of the well fluid on the surface of the sucker rod per unit time, reflecting the decrease in contact area due to corrosion. This represents the cumulative time the sucker rod has been in operation. This represents the attenuation coefficient of mechanical wear on the contact area. The corrosion attenuation coefficient is the coefficient of the contact area. To calculate the cumulative number of contacts, The number of contacts that significantly increases surface roughness. The corrosion-wear synergy coefficient, The effective contact area of ​​the sucker rod during a single stroke; The formula for calculating the crack-corrected wear factor is: ； in, The crack-corrected wear factor combines temperature and crack length to reflect the ease or difficulty of material wear. Real-time temperature of the contact area between the sucker rod and the tubing, in Kelvin (K). This is the temperature sensitivity coefficient, with a value of 0.

5. This refers to the length of the cracks that have already formed on the surface of the sucker rod. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. Crack influence coefficient, quantifying the amplification effect of crack length on the wear factor, with a value of 0.

3. The baseline wear factor coefficient is set to 20. The formula for calculating the wear amount corrected by cracking in a single stroke of the sucker rod is: ； in, Correcting wear on single-stroke cracks in sucker rods. To correct the wear factor for cracks, for , is the ratio of lateral normal force to contact area. The relative instantaneous velocity between the sucker rod and the tubing. The cumulative time of contact between the rod and tube within a single stroke, expressed in seconds. The Brinell hardness is the material of the inner wall of the oil pipe.

2. The method for evaluating sucker rod wear according to claim 1, characterized in that: The calculation of well fluid density using the weighted average method based on the sucker rod operating data includes the following specific steps: The formula for calculating well fluid density is: ； in, This refers to the density of the well fluid, in units of... kg / m3 It is a core physical quantity describing the mass distribution of well fluid. The density of the formation water, To correct the crude oil density, The water content of the well fluid is dimensionless and ranges from 0 to 1. Its physical meaning is the mass proportion of formation water in the well fluid. The crude oil mass fraction in the well fluid. For solid particles, This represents the mass fraction of solid particles in the well fluid.

3. The method for evaluating sucker rod wear according to claim 2, characterized in that: The process of calculating the coupling judgment index based on the well fluid density and using hydrodynamic lubrication theory to analyze the sucker rod operating data includes the following steps: The formula for calculating the minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is: ； in, The minimum thickness of the oil film between the contact surface of the sucker rod and the tubing is a core indicator for determining whether the oil film can separate the metal surface of the sucker rod. The radius of curvature of the sucker rod and tubing along the direction of motion reflects the geometric fit of the contact surfaces in the direction of motion, and is expressed in meters (m). This is the equivalent radius of curvature of the sucker rod and tubing in the vertical direction of motion, expressed in meters (m). Let be the well fluid viscosity coefficient, describing the characteristic of well fluid viscosity changing with pressure. Based on typical well fluid experiments, its value is taken as 3.0 × 10⁻⁶. , This refers to the real-time dynamic viscosity of the well fluid, expressed in Pa·s. The instantaneous velocity of the relative motion between the rod and the tube is expressed in m / s. The equivalent radius of curvature of the sucker rod contact surface, in meters. This is the corrected elastic modulus of the sucker rod and tubing materials, expressed in Pa. This refers to the lateral normal force between the sucker rod and the oil rod; The formula for calculating the initial roughness ratio is: ； in, The dynamic roughness of the sucker rod surface reflects the degree of microscopic unevenness on the sucker rod surface, and is measured in meters (m). For the dynamic roughness of the inner wall surface of the oil pipe, The initial roughness ratio, physically defined as "the ratio of oil film thickness to the sum of surface roughness peak heights"; The formula for calculating the real-time flow rate of well fluid is: ； in, This is the real-time flow rate of the well fluid, reflecting its flow state within the tubing, expressed in m / s. Real-time liquid production rate, in m³ 3 / s, This refers to the inner diameter of the oil pipe, in meters (m). The diameter of the sucker rod. It is the Reynolds number; The formula for calculating the coupling judgment index is: ； in, The water content coupling coefficient is... As a coupling judgment index, This refers to the real-time flow rate of the well fluid. The initial roughness ratio, This is a velocity direction correction term.

4. The method for evaluating sucker rod wear according to claim 3, characterized in that: The mechanical analysis of sucker rod operating data to calculate the wellbore trajectory dogleg includes the following steps: Mechanical analysis was performed on the sucker rod operating data to calculate the wellbore trajectory dogleg. The formula for calculating the wellbore trajectory dogleg is as follows: ； in, For the wellbore trajectory dogleg degree, The borehole curvature angle between two adjacent survey points. The depth of the well is the depth of two adjacent inclination measurement points.

5. The method for evaluating sucker rod wear according to claim 4, characterized in that: The calculation of the lateral normal force between the sucker rod and tubing by combining the friction coefficient of the rod and tubing and the dogleg degree of the wellbore trajectory includes the following steps: The formula for calculating the axial force of the sucker rod micro-segment is: ； in, The pump mounting depth is in meters (m). This refers to the tension in the upper section of the sucker rod string. The density of the sucker rod material is taken as 7850 kg / m³. 3， Let be the cross-sectional area of ​​the sucker rod. For well fluid density, Given the current well depth, It is the acceleration due to gravity. For time indexing, The well inclination angle; Lateral normal force is the result of the combined action of the component of the rod string axial force in the wellbore inclination direction and friction. By incorporating the amplification effect of dogleg, the formula for calculating lateral normal force is: ； in, Lateral positive pressure indicates well depth. ,time The normal load when the sucker rod is in contact with the tubing. This represents the total axial force acting on the micro-segment of the sucker rod. For well depth The angle between the wellbore and the vertical direction, expressed in rad. The coefficient of friction between the sucker rod and the tubing is denoted as . For well depth The dogleg degree at the location, quantifying the amplification effect of local borehole curvature on normal pressure, The dogleg amplification factor quantifies the influence of wellbore trajectory dogleg on lateral normal pressure. A factor of 0.015 is used for vertical sections, 0.02 for gently inclined sections, and 0.025 for sharp bends. The unit is 30 m / °. For correction factor, The reference friction coefficient is .

6. The method for evaluating sucker rod wear according to claim 5, characterized in that: The process of calculating the coupled damage coefficient based on the total wear of the sucker rod using allowable stress and coupled damage theory includes the following specific steps: The formula for calculating the coupling damage coefficient is: ； in, The coupling damage coefficient reflects the overall failure risk resulting from the synergistic effect of various factors. The dynamic wear-corrosion coupling coefficient is used to quantify the synergistic amplification effect of wear and corrosion. This represents the dynamic stress-crack coupling coefficient, quantifying the accelerating effect of stress on crack propagation. This is the dynamic wear threshold. The total wear of the sucker rod during the time interval 0 to t. This refers to the critical length at which the crack propagates, leading to the breakage of the rod. This represents the dynamic crack length on the surface of the sucker rod. This is the ratio of the stress range of the sucker rod. To accumulate corrosion depth, The wear-stress-corrosion coupling coefficient is set to 0.

15. This is the dynamic corrosion threshold. This represents the maximum allowable stress of the sucker rod. This represents the yield strength of the material.

7. The method for evaluating sucker rod wear according to claim 6, characterized in that: The process of correcting the safety factor based on the coupling damage coefficient to calculate the basic safety and reliability includes the following specific steps: The safety factor calculated earlier is corrected by using the coupling damage coefficient: ； in, To correct the single-dimensional security, For uncorrected single-dimensional security, For dynamic sensitivity coefficient, The dynamic coupling damage threshold. The coupling damage coefficient; The formula for calculating the basic safety and reliability level is: ； in, Based on the level of security and reliability, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, To correct the stress safety factor, These are dynamic weighting coefficients.

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