Beam-pumping unit tail bearing fault diagnosis method
By analyzing the displacement curve and dynamometer diagram of the beam pumping unit, the tail bearing fault was determined, solving the problems of high cost and low efficiency in the existing technology, realizing rapid and accurate fault diagnosis, and ensuring the safe operation of the pumping unit.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-11-21
- Publication Date
- 2026-05-22
Smart Images
Figure CN122071949A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fault diagnosis technology for beam pumping units, specifically relating to a fault diagnosis method for the tail bearing of a beam pumping unit. Background Technology
[0002] my country has over 200,000 pumping units of various types, with beam pumping units accounting for more than 90% of the total in operation in oilfields. Pumping units include both surface and downhole equipment. While remote diagnostic methods based on dynamometer card changes can be used to diagnose the operating conditions of downhole equipment, current technology does not apply this method to surface equipment fault diagnosis. In field operation, beam pumping units frequently experience vibration, shaking, abnormal noises, and even rollovers due to the susceptibility of their tail bearings to failure. Failure to detect and address these issues promptly during inspections can negatively impact the stable operation of oil and gas production. Tail bearing failure is a common surface fault type in pumping units. Currently, tail bearing diagnosis relies primarily on manual on-site inspections, video inspections, and drone inspections. These methods all suffer from varying degrees of high cost, low efficiency, and delayed fault detection, affecting the safe operation of the pumping unit and consequently the normal operation of oil and gas production. Summary of the Invention
[0003] The purpose of this invention is to provide a method for diagnosing the faults of the tail bearings of a beam pumping unit, in order to solve the technical problems of high cost and low efficiency of on-site inspections and the inability to detect faults in the tail bearings of pumping units in a timely manner.
[0004] To solve the above-mentioned technical problems, the present invention provides a method for diagnosing faults in the tail bearing of a beam pumping unit, comprising the following steps:
[0005] Obtain the head displacement curve and indicator diagram of the beam pumping unit. When the head displacement curve and indicator diagram simultaneously meet the following conditions during a certain stroke, the tail bearing of the pumping unit is determined to be faulty:
[0006] Burrs appear at the corresponding points in the latter half of the donkey head's upward travel in the donkey head displacement curve;
[0007] Typical characteristics appear in the latter half of the load stabilization line during the upward process of the pumping unit's indicator diagram; specifically, when a displacement value corresponds to at least two load values in the latter half of the load stabilization line during the upward process of the indicator diagram, it is determined that typical characteristics appear in the latter half of the load stabilization line during the upward process of the indicator diagram.
[0008] Furthermore, when the absolute value of the difference between the displacement of a point corresponding to the second half of the upward stroke of the donkey head in the donkey head displacement curve and the average displacement of the two adjacent points is greater than or equal to the total displacement of the donkey head in one stroke, it is determined that a burr has appeared at the point corresponding to the second half of the upward stroke of the donkey head in the donkey head displacement curve.
[0009] Furthermore, the typical features include return trip and twist;
[0010] When the deviations of all load values corresponding to a displacement value in the typical characteristics from the load values corresponding to the normal indicator diagram are all less than the set load deviation threshold, the typical characteristic is a return stroke; otherwise, the typical characteristic is a twist.
[0011] A typical characteristic is that the tail bearing failure during twisting is more severe than that during return.
[0012] Furthermore, the normal indicator diagram is the indicator diagram of the pumping unit when no fault has occurred or the theoretical indicator diagram of the pumping unit.
[0013] Furthermore, an alarm will be triggered when the donkey head displacement decreases or remains unchanged during the upward phase of the donkey head displacement curve.
[0014] Furthermore, an alarm is triggered when the displacement of the pumping unit's pumping head increases or remains unchanged during the downward phase of the pumping head displacement curve.
[0015] Furthermore, when the maximum value of the donkey head load curve in this stroke is greater than the maximum value of the load curve in the previous stroke, and the degree of the greater value is greater than or equal to the first set threshold, an alarm is triggered.
[0016] Furthermore, when the maximum value of the donkey head load curve of the stroke is greater than the maximum value of the load curve within a set time period before the stroke, and the degree of the greater value is greater than or equal to the second set threshold, an alarm is triggered.
[0017] This invention is a pioneering invention with the following beneficial effects: It applies the remote diagnostic method using dynamometer diagrams, originally used for downhole equipment fault diagnosis, to surface equipment fault diagnosis. Furthermore, research reveals that when the tail bearing of a pumping unit fails, it causes wear on the shaft or bearing housing, leading to changes in the length of the pumping unit's four-link linkage. Because the tail bearing operates at low speed and not in a full rotation, it experiences only tension in the first half of the upward stroke and only compression in the first half of the downward stroke. The relative movement between the shaft and the balls is minimal; only near the top and bottom dead centers does the relative movement between the shaft and the balls increase. At this point, due to the tail bearing failure, the displacement of the pumping unit becomes abnormal, with burrs appearing on the displacement curve near the top and bottom dead centers. Corresponding changes occur in the displacement curve and dynamometer diagram, including: burrs appearing at points corresponding to the latter half of the upward stroke in the displacement curve; and typical characteristics appearing in the latter half of the load stability line during the upward stroke of the pumping unit's dynamometer diagram. This invention determines that a typical characteristic has appeared in the latter half of the load stability line during the upward process of the dynamometer diagram when a displacement value corresponds to at least two load values. This forms a method for diagnosing the tail bearing of a pumping unit using the donkey head displacement curve and the dynamometer diagram. It eliminates the need for inspection personnel to conduct on-site inspections, and can easily, quickly, and promptly detect tail bearing failures in the pumping unit, ensuring the normal operation of the pumping unit. Attached Figure Description
[0018] Figure 1 This is an equivalent model diagram of a beam pumping unit according to an embodiment of the present invention;
[0019] Figure 2 This is a theoretical donkey head displacement curve diagram of an embodiment of the method of the present invention;
[0020] Figure 3 This is a theoretical donkey head load curve diagram of an embodiment of the method of the present invention;
[0021] Figure 4 This is a theoretical indicator diagram of the oil pumping unit according to an embodiment of the method of the present invention;
[0022] Figure 5 These are the donkey head displacement curve and donkey head load curve diagrams when the tail bearing of the first pumping unit fails in the method embodiment of the present invention.
[0023] Figure 6 This is a diagram showing the operation of the pumping unit during the return stroke in an embodiment of the method of the present invention;
[0024] Figure 7 This is a diagram showing the operation of the pumping unit when twisting occurs in an embodiment of the method of the present invention;
[0025] Figure 8 This is a flowchart of a method for diagnosing faults in the tail bearing of a beam pumping unit according to an embodiment of the present invention. Detailed Implementation
[0026] This invention applies the remote diagnostic method using dynamometer diagrams, originally used for downhole equipment diagnosis, to fault diagnosis of surface equipment. Research reveals that when the tail bearing of a pumping unit fails, the donkey head displacement curve and dynamometer diagram exhibit corresponding changes, including: burrs appearing at points corresponding to the latter half of the donkey head's upward stroke in the displacement curve; and typical characteristics appearing in the latter half of the load stability line during the upward stroke of the pumping unit's dynamometer diagram. This invention determines that typical characteristics have appeared in the latter half of the load stability line during the upward stroke of the dynamometer diagram when one displacement value corresponds to at least two load values. This forms a method for diagnosing the tail bearing of a pumping unit using the donkey head displacement curve and dynamometer diagram, eliminating the need for on-site inspections and enabling simple, quick, and timely detection of tail bearing faults, thus ensuring the normal operation of the pumping unit.
[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0028] Method Implementation Examples:
[0029] The beam pumping unit is a type of four-bar pumping unit, and its equivalent model is as follows: Figure 1 As shown, AB is the crank of the pumping unit, with AB2 as the crank's rotation angle 0. The crank rotates counterclockwise with an angular velocity ω. The movement of point B on the crank varies with time t and the crank's rotation angle, exhibiting a sinusoidal characteristic. B1 and B2 in the figure represent different positions of point B.
[0030] The method for detecting faults in the tail bearing of an oil pumping unit according to the present invention, such as... Figure 8 As shown, it includes the following steps:
[0031] Step 1: Obtain the displacement curve and indicator diagram of the pumping unit for one stroke.
[0032] Sensors mounted on the walking beam of the pumping unit acquire the donkey head displacement curve as a function of crank angle during one stroke, and the dynamometer diagram of the pumping unit is obtained based on the donkey head displacement curve. One stroke consists of a top stroke and a bottom stroke, during which the crank pin rotates one revolution, and the crank angle changes from 0 to 2π.
[0033] In this embodiment, N (256) points are taken at equal intervals within one stroke, and the displacement value and load value of each point are collected synchronously. Then, the points are plotted to draw the donkey head displacement curve of the pumping unit. Then, the pumping unit indicator diagram is obtained based on the donkey head displacement curve of the pumping unit and the donkey head load of the corresponding point.
[0034] As the crank angle ranges from 0 to π+α, the pumping unit's "donkey head" moves upward, and the donkey head displacement curve monotonically increases. At this point, the donkey head load equals the weight of the rod column plus the weight of the liquid column above the piston. The donkey head reaches its highest position when the crank angle is π+α. As the crank angle ranges from π+α to 2π, the pumping unit's "donkey head" moves downward, and the donkey head displacement curve monotonically decreases. The donkey head load equals the weight of the rod column, and reaches its lowest point when the crank angle is 2π (i.e., 0).
[0035] Under normal operating conditions of the pumping unit, multiple sets of data are collected within one stroke. The theoretical donkey head displacement curve obtained by plotting points is a non-standard sine curve, such as... Figure 2 As shown; the obtained theoretical load curve is a "trapezoidal line", as shown. Figure 3 As shown. The theoretical indicator diagram is obtained as follows. Figure 4 As shown, it is a parallelogram. BC represents the load stability line during the upward process, and DA represents the load stability line during the downward process.
[0036] This invention reveals that in the early stages of tail bearing failure, because the tail bearing operates at low speed and not in a full revolution, the load curve of the pumping unit usually does not change significantly. However, the displacement curve of the pumping unit typically exhibits burrs before and after the loading and unloading processes. The upward or downward lines of the indicator diagram will show points of overlap and twisting. Furthermore, due to the low-speed, non-full-revolution operation, the burrs on the displacement curve may appear intermittently in the early stages; for example, the aforementioned changes may occur during a certain stroke, but return to normal in the next stroke, rather than appearing continuously. Once this phenomenon occurs, combined with verification from abnormal sounds on-site, a bearing failure requires planned maintenance to prevent serious mechanical accidents. Therefore, this invention can determine whether the tail bearing of the pumping unit is faulty by obtaining the displacement curve and indicator diagram of the pumping unit.
[0037] Step 2: Determine whether burrs appear at the corresponding points in the latter half of the donkey head's upward movement in the donkey head displacement curve.
[0038] When the tail bearing fails, it causes wear on the shaft or bearing housing, resulting in a change in the length of the four-link of the pumping unit. Because the tail bearing operates at low speed and not in a full rotation, it is only subjected to tension in the first half of the upward movement of the pumping unit and only to pressure in the first half of the downward movement. There is little relative movement between the shaft and the balls. Only when approaching the top dead center does the relative movement between the shaft and the balls increase. At this point, due to the failure of the tail bearing, the displacement of the pumping unit will be abnormal, and burrs will appear on the displacement curve when approaching the top dead center (the second half of the upward movement).
[0039] In this embodiment, the method for determining whether a burr appears at the corresponding point of the second half of the upward stroke of the donkey head displacement curve is as follows: when the absolute value of the difference between the displacement of a certain point at the corresponding point of the second half of the upward stroke of the donkey head displacement curve and the average displacement of two adjacent points is greater than or equal to the ratio of the total displacement of the donkey head in one stroke to the absolute value of the difference between the displacement of a certain point at the corresponding point of the second half of the upward stroke of the donkey head displacement curve, it is determined that a burr appears at the corresponding point of the second half of the upward stroke of the donkey head displacement curve.
[0040] In this embodiment, the threshold for displacement burr is set to 1%. When the calculated ratio exceeds this displacement amplitude deviation threshold, obvious burrs can be seen on the donkey head displacement curve. Figure 5 The diagram shows the displacement curve, load curve, and indicator diagram of the pumping unit when the tail bearing fails. Figure 5 The green curve in the middle is the donkey head displacement curve. Its horizontal axis is the product of angular velocity ω and time t, and the vertical axis is the donkey head displacement. It can be clearly seen in the figure that the displacement curve has burrs near the bottom dead center, that is, before and after loading. Figure 5 The gray curve represents the load curve of the donkey head, with its horizontal axis representing the product of angular velocity ω and time t, and its vertical axis representing the load. Since the load curve shows no abnormal changes, this invention does not require the use of the load curve for diagnosis. The red curve in the figure represents the dynamometer diagram, with its horizontal axis representing the displacement of the donkey head and its vertical axis representing the load.
[0041] The displacement curve of the donkey's head shows the corresponding points of the latter half of the upward stroke during the donkey's head movement as follows: Figure 2 The points on the theoretical displacement curve are between (π+α) / 2 and π+α.
[0042] Step 3: Determine whether the load stabilization line in the upward process of the pumping unit indicator diagram shows a return or twist (typical characteristics).
[0043] When the tail bearing of the pumping unit fails, the length of the four-link rod of the pumping unit will change. Because the tail bearing operates at low speed and not in a full revolution, it is only subjected to tension in the first half of the upward movement of the pumping unit and only to compression in the first half of the downward movement. There is little relative movement between the shaft and the balls. Only when approaching the top dead center and bottom dead center does the relative movement between the shaft and the balls increase. At this time, due to the failure of the tail bearing, the displacement of the pumping unit will be abnormal. The displacement curve of the pumping unit will show burrs when approaching the top dead center. The change in displacement will be reflected on the indicator diagram as a return or twisting in the second half of the load stability line during the upward movement.
[0044] When the tail bearing is damaged, the displacement of the donkey head becomes abnormal while the load on the donkey head remains unchanged. Therefore, the corresponding position on the indicator diagram of the pumping unit will also change. Specifically, obvious typical features appear in the latter half of the upward line BC. These typical features include two types: return and twisting. As long as one of them appears, it can be determined that a typical feature has appeared, and the diagnosis of the tail bearing failure of the pumping unit can be completed.
[0045] In this embodiment, the method for determining whether a return or twist occurs in the latter half of the load stability line during the upward process of the indicator diagram is as follows: when a displacement value corresponds to at least two load values in the latter half of the load stability line during the upward process of the indicator diagram, it is determined that a return or twist has occurred in the latter half of the load stability line during the upward process of the indicator diagram.
[0046] When burrs appear at the corresponding point in the second half of the upward stroke of the donkey head displacement curve and twisting occurs in the second half of the load stability line during the upward stroke of the indicator diagram, it indicates that the tail bearing is in serious condition. When burrs appear at the corresponding point in the second half of the upward stroke of the donkey head displacement curve and reversal occurs in the second half of the load stability line during the upward stroke of the indicator diagram, it indicates that the tail bearing is in relatively minor condition.
[0047] Therefore, this embodiment further distinguishes between return stroke and torque on the indicator diagram, allowing for the determination of the tail bearing's fault severity based on whether return stroke or torque occurs on the indicator diagram. The specific method for distinguishing between return stroke and torque is as follows:
[0048] When the deviation of all load values corresponding to a displacement value in the typical characteristics from the load value corresponding to that displacement value during the normal upward process of the indicator diagram is less than the set load deviation threshold, the typical characteristic is a return trip; otherwise, the typical characteristic is a twist.
[0049] In this embodiment, the load deviation threshold is set to 2%. When the deviation of at least one load value corresponding to a displacement value in the typical feature is greater than the set load deviation threshold of 2%, a noticeable twisting phenomenon can be seen on the indicator diagram. When the deviation of all load values from the load value corresponding to the displacement value in the normal upward process of the indicator diagram is less than the set load deviation threshold of 2%, a noticeable return phenomenon can be seen on the indicator diagram.
[0050] Figure 6 and Figure 7 These are two indicator diagrams showing a failure in the tail bearing of an oil pumping unit. The diagrams show either the down-traverse or up-traverse line experiencing a return or twisting. Figure 6 During the upward movement, a significant reversal occurred in the latter half of the load stability line. Figure 7 During the upward movement, the latter half of the load stability line showed obvious twisting.
[0051] In this embodiment, all thresholds are obtained by statistical analysis of the displacement and load changes of the pumping unit when a tail bearing failure occurs. For example, the threshold for displacement burr severity is set by obtaining multiple displacement curves when the tail bearing of the pumping unit fails, calculating the deviation between the displacement value at the corresponding burr location and the normal displacement value, obtaining the average value of all deviations, and setting the threshold for displacement burr severity based on the average value.
[0052] Step 4: When all the above conditions are met, it is determined that the tail bearing of the pumping unit has failed.
[0053] This invention obtains the displacement curve of the pumping unit's head, the load curve of the head, and the indicator diagram during one stroke. When these curves show specific changes, it determines that the tail bearing of the pumping unit has failed. This eliminates the need for manual inspection, saving manpower and improving efficiency. At the same time, it can perform real-time detection, enabling timely detection of tail bearing failures and preventing safety accidents.
[0054] In addition, the oil pumping unit tail bearing fault diagnosis method of the present invention also alarms when the following situations occur:
[0055] 1. When the donkey head displacement curve shows a decrease or no change in the donkey head displacement during the upward movement of the donkey head;
[0056] 2. The donkey head displacement curve shows either an increase or no change in displacement during the downward movement of the donkey head in the pumping unit;
[0057] 3. The maximum value of the load curve of the donkey head at a certain moment is greater than the maximum value of the load curve within N strokes set before the certain moment, and the degree of the greater is greater than or equal to the first set degree threshold of 10%.
[0058] 4. The maximum value of the donkey head load curve at a certain moment is greater than the maximum value of the load curve within a set time period before that moment, and the degree of the difference is greater than or equal to the second set threshold of 10%.
[0059] If any of the above situations occur, it indicates that the pumping unit is malfunctioning and an alarm needs to be triggered. Staff should conduct inspections to ensure the normal operation of the pumping unit.
[0060] In this embodiment, the normal donkey head displacement curve, load curve, and indicator diagram are the donkey head displacement curve, donkey head load curve, and indicator diagram when the pumping unit has not malfunctioned or under theoretical conditions.
[0061] The present invention provides a method for diagnosing the tail bearing fault of a beam pumping unit. This method diagnoses the tail bearing based on changes in the head displacement curve, load curve, and indicator diagram of the pumping unit. A fault is identified when the head displacement curve exhibits burrs before and after unloading, the head load curve shows no abnormal changes, or the indicator diagram shows a return stroke or twisting on the upward line. This method eliminates the need for on-site inspections by maintenance personnel, offering a simple and quick diagnostic process, saving manpower, improving diagnostic efficiency, and ensuring the normal operation of the pumping unit. Furthermore, the invention proposes methods for determining whether burrs appear on the displacement curve and for determining whether a return stroke or twisting occurs on the indicator diagram, which improves the accuracy of tail bearing diagnosis and prevents misdiagnosis. Additionally, the present invention provides an alarm when abnormalities occur in the head displacement curve and head load curve, ensuring the normal operation of the pumping unit and eliminating safety hazards caused by pumping unit malfunctions.
Claims
1. A method for diagnosing faults in the tail bearing of a beam pumping unit, characterized in that, Includes the following steps: Obtain the head displacement curve and indicator diagram of the beam pumping unit. When the head displacement curve and indicator diagram simultaneously meet the following conditions during a certain stroke, the tail bearing of the pumping unit is determined to be faulty: Burrs appear at the corresponding points in the latter half of the donkey head's upward travel in the donkey head displacement curve; Typical characteristics appear in the latter half of the load stabilization line during the upward process of the pumping unit's indicator diagram; specifically, when a displacement value corresponds to at least two load values in the latter half of the load stabilization line during the upward process of the indicator diagram, it is determined that typical characteristics appear in the latter half of the load stabilization line during the upward process of the indicator diagram.
2. The method for diagnosing faults in the tail bearing of a beam pumping unit according to claim 1, characterized in that, When the absolute value of the difference between the displacement of a point corresponding to the second half of the upward stroke of the donkey head and the average displacement of the two adjacent points in the donkey head displacement curve is greater than or equal to the set displacement burr degree threshold, it is determined that a burr has appeared at the corresponding point in the second half of the upward stroke of the donkey head displacement curve.
3. The method for diagnosing the fault of the tail bearing of a beam pumping unit according to claim 1, characterized in that, The typical characteristics include return journey and twisting; When the deviation of all load values corresponding to a displacement value in the typical characteristics from the load value corresponding to the normal indicator diagram is less than the set load deviation threshold, the typical characteristic is a return trip; Otherwise, the typical characteristic is twisting; A typical characteristic is that the tail bearing failure during twisting is more severe than that during return.
4. The method for diagnosing faults in the tail bearing of a beam pumping unit according to claim 3, characterized in that, The normal indicator diagram refers to the indicator diagram of the pumping unit when no fault has occurred or the theoretical indicator diagram of the pumping unit.
5. The method for diagnosing faults in the tail bearing of a beam pumping unit according to any one of claims 1-4, characterized in that, An alarm will be triggered when the donkey head displacement decreases or remains unchanged during the upward phase of the donkey head displacement curve.
6. The method for diagnosing faults in the tail bearing of a beam pumping unit according to any one of claims 1-4, characterized in that, An alarm will sound when the displacement of the pumping unit's head increases or remains unchanged during the downward phase of the head displacement curve.
7. The method for diagnosing faults in the tail bearing of a beam pumping unit according to any one of claims 1-4, characterized in that, An alarm is triggered when the maximum value of the donkey head load curve in the stroke exceeds the maximum value of the load curve in the previous stroke, and the degree of excess is greater than or equal to the first set threshold.
8. The method for diagnosing faults in the tail bearing of a beam pumping unit according to any one of claims 1-4, characterized in that, An alarm is triggered when the maximum value of the donkey head load curve during the stroke is greater than the maximum value of the load curve within a set time period prior to the stroke, and the degree of the excess is greater than or equal to the second set threshold.