Beam-pumping unit chassis fracture diagnosis method

Abstract

The invention belongs to the technical field of oil pumping unit fault diagnosis, and particularly relates to a beam-pumping unit chassis fracture diagnosis method. Comprising the following steps: acquiring a horse head displacement curve, a horse head load curve and an indicator diagram of the beam-pumping unit, if the horse head displacement curve, the horse head load curve and the indicator diagram of a certain stroke meet the following corresponding conditions at the same time, it is judged that the chassis of the beam-pumping unit is broken; the load descending speed of a load shedding line in the horse head load curve is slower than the load descending speed of a load shedding line in a normal horse head load curve; the slowing degree exceeds a first set degree threshold value; burrs appear near the highest position corresponding point of the horse head in the horse head displacement curve, and the point displacement value of at least a continuous first set point number is not changed; and the displacement change trend of at least continuous points of a second set point number on the load shedding line in the indicator diagram is opposite to or unchanged with the change trend of the load shedding line in the normal indicator diagram. The breakage of the chassis of the oil pumping unit can be found simply, quickly and timely, and the normal operation of the oil pumping unit can be ensured.

Description

Technical Field

[0001] This invention belongs to the field of oil pumping unit fault diagnosis technology, specifically relating to a method for diagnosing chassis fracture in 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 vibrations, shaking, abnormal noises, and even overturning due to chassis (surface equipment) fractures. Failure to detect these issues promptly during inspections can negatively impact the stable operation of oil and gas production. Current technology primarily relies on on-site inspections, such as manual inspections, to detect the condition of the pumping unit chassis. However, this method is time-consuming, labor-intensive, and inefficient. Furthermore, real-time inspections are impossible, making it difficult to detect chassis fractures immediately. Furthermore, negligence by inspection personnel can lead to missed faults, creating safety hazards and affecting the stable operation of oil and gas production. Summary of the Invention

[0003] The purpose of this invention is to provide a method for diagnosing chassis fractures in beam pumping units, thereby solving the technical problem that the inability to detect chassis fractures in a timely manner during on-site inspections can affect the stable operation of oil and gas production.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for diagnosing chassis fracture of a beam pumping unit, comprising the following steps:

[0005] Obtain the head displacement curve, head load curve, and indicator diagram of the beam pumping unit. If the head displacement curve, head load curve, and indicator diagram of a certain stroke simultaneously meet the following corresponding conditions, the chassis of the beam pumping unit is determined to be fractured:

[0006] The load decrease rate of the unloading line in the donkey head load curve is slower than the load decrease rate of the unloading line in the normal donkey head load curve, and the degree of slowing down exceeds the first set threshold.

[0007] In the donkey head displacement curve, burrs appear near the highest point of the donkey head and the displacement value of points with at least a first set number of consecutive points remains unchanged; the first set number of points is greater than or equal to two.

[0008] The displacement change trend of at least a second set number of points on the load shedding line in the dynamometer diagram is opposite to or unchanged from the change trend of the load shedding line in the normal dynamometer diagram; the second set number of points is greater than or equal to two.

[0009] Furthermore, the load descent rate of the donkey head load curve unloading line is measured by its slope. Correspondingly, the ratio obtained by subtracting the slope of the unloading line in the normal donkey head load curve from the slope of the unloading line of the donkey head load curve using this stroke, and then dividing the difference by the slope of the unloading line in the normal donkey head load curve, is used as the degree of slowdown in the load descent rate.

[0010] Furthermore, when the absolute value of the difference between the displacement of a point near the highest point 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 ratio of the total displacement of the donkey head in one stroke, it is determined that a burr appears in the donkey head displacement curve near the highest point of the donkey head.

[0011] Furthermore, the normal indicator diagram is the indicator diagram or theoretical indicator diagram when the pumping unit is not malfunctioning.

[0012] Furthermore, the normal donkey head load curve is the donkey head load curve when the pumping unit does not malfunction or the theoretical donkey head load curve.

[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 set strokes, and the degree of the greater value is greater than or equal to the second set threshold, an alarm is triggered.

[0016] Furthermore, when the maximum value of the donkey head load curve during this stroke is greater than the maximum value of the load curve within a set time period before this stroke, and the degree of the excess is greater than or equal to the third set threshold, an alarm is triggered.

[0017] This invention is a pioneering invention, and its beneficial effects are as follows: This invention applies diagnostic methods originally used for downhole equipment to the diagnosis of surface equipment. The research of this invention found that: when the chassis of a beam pumping unit breaks, it is often accompanied by loose chassis fixing bolts. The four-link frame breaks at a certain point in the middle, breaking into two sections. When the pumping head moves downward, it causes the rear half of the frame to tilt upward around the break point. The upward tilt is limited by the degree of fracture and the degree of looseness of the fixing bolts. When tilting upward, the pumping head accelerates downward. After tilting upward to the limit position, the displacement stops for a short time and then continues to move downward, accompanied by shaking. The length of the frame changes before and after tilting upward, resulting in burrs and translation of the displacement curve. At the same time, because the load change cannot be fully transmitted to the walking beam and pumping head through the chassis during the upward tilting process of the rear half of the frame AO around point O, the load change decreases more slowly when the pumping head moves downward. The changes in displacement and load are reflected in the indicator diagram as a broken line twist. The donkey head displacement curve, donkey head load curve, and indicator diagram all exhibit corresponding characteristics. During unloading, the load reduction rate of the donkey head load curve is slower than normal, and this slowdown exceeds a certain level. The donkey head displacement curve shows burrs near the highest point of the donkey head and continuous points with unchanged displacement values ​​exceeding a first set number of points (the first set number of points is greater than or equal to two). The indicator diagram shows a broken line twist on the unloading line. Furthermore, this invention determines the occurrence of a broken line twist by observing the displacement change trend of at least a second set number of points on the unloading line of the indicator diagram, which is either opposite to or unchanged from the normal trend of the unloading line. Based on these findings, this invention proposes a technical solution for diagnosing the pumping unit chassis based on the changes in the donkey head displacement curve, donkey head load curve, and indicator diagram. This eliminates the need for on-site inspections and can easily, quickly, and promptly detect chassis fractures, 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 load curve and donkey head displacement curve diagrams when the pumping unit chassis breaks according to an embodiment of the present invention.

[0023] Figure 6This is a diagram of the pumping unit when the pumping unit chassis breaks according to an embodiment of the present invention.

[0024] Figure 7 This is a diagram of another pumping unit when the pumping unit chassis breaks according to an embodiment of the present invention.

[0025] Figure 8 This is a flowchart of a method for diagnosing chassis fracture in a beam pumping unit according to an embodiment of the present invention. Detailed Implementation

[0026] This invention applies diagnostic methods originally used for downhole equipment to the diagnosis of surface equipment. The invention's research found that chassis fractures in beam pumping units are often accompanied by loose chassis fixing bolts. Figure 1 As shown, the frame AD, which is equivalent to a four-bar linkage, breaks at a certain point O in the middle, and the frame AD becomes AO+OD. When the donkey head moves downward, it causes the rear half of the frame AO to tilt upward around point O. The upward tilt is limited by the degree of fracture and the degree of looseness of the fixing bolts. When tilting upward, the donkey head accelerates downward. After tilting to the limit position, the displacement stops briefly and then moves downward again, accompanied by shaking. The length change of the frame from AD length to AO+OD length and back to AD length, the length change of the four-bar linkage frame AD causes the displacement of the donkey head to change, resulting in burrs and translation on the displacement curve. At the same time, because the load change cannot be fully transmitted to the walking beam and donkey head through the chassis during the upward tilt of the rear half of the frame AO around point O, the load change decreases more slowly when the donkey head moves downward. The changes in displacement and load are reflected in the indicator diagram as a broken line twist. Based on this discovery, the present invention identifies the corresponding characteristics of the donkey head displacement curve, donkey head load curve, and indicator diagram when the chassis breaks, including: the donkey head load curve shows a slower load reduction rate during unloading compared to normal conditions, and this slowdown exceeds a certain level; the donkey head displacement curve shows burrs near the highest point of the donkey head and continuous displacement values ​​exceeding a first set number of points that remain unchanged, where the first set number of points is greater than or equal to two; and the indicator diagram shows a broken line twist on the unloading line, to determine whether the pumping unit has experienced a chassis breakage fault. Furthermore, the present invention determines the occurrence of a broken line twist by observing that the displacement change trend of at least a second set number of points on the unloading line of the indicator diagram is opposite to or unchanged from the normal trend of the unloading line. Based on this discovery, the present invention proposes a technical solution for diagnosing the pumping unit chassis based on the changes in the donkey head displacement curve, donkey head load curve, and indicator diagram. This eliminates the need for on-site inspection and can easily, quickly, and promptly detect chassis breakage, 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] Point C of the walking beam oscillates under the influence of the crank and connecting rod. Affected by the extreme position angle α and the characteristics of the four-bar linkage, the pumping unit moves upward within the crank angle θ1 (0~π+α), and the pumping unit head is at its highest position when the crank angle is π+α. Within the crank angle θ2 (π+α~2π), the pumping unit moves downward. The relationship between the stroke speed ratio coefficient k and the extreme position angle α is as follows:

[0031]

[0032] Under the influence of the quick-return characteristic of the stroke ratio k, the walking beam inclination angle ψ and the donkey head displacement S vary with time t and crank angle θ, approximating a non-standard sinusoidal characteristic. Crank angle θ = ωt, where ω is the crank angular velocity and t is time. Since the motion trajectory of the four-bar linkage can be determined through the constraints and geometric relationships between the links, the crank angle determines a corresponding walking beam inclination angle, and the walking beam inclination angle has a linear relationship with the donkey head displacement. Where S is the donkey head displacement, ψ is the inclination angle of the walking beam, and r is the length of the walking beam's forearm.

[0033] By calculating multiple sets of data and plotting the results, it can be observed that the theoretical donkey head displacement curve is a smooth sine wave. At π+α, the donkey head displacement curve reaches its highest point, and the donkey head is also at its highest position. At 0 or 2π, the donkey head displacement curve reaches its lowest point, and the donkey head is at its lowest position. Figure 2 As shown, an inclination sensor is installed on the walking beam. Each rotation of the crank causes the walking beam to move up and down once. The inclination sensor collects N sets of inclination change data at the same time, and calculates and generates a real-time displacement curve of the walking beam. The waveform of the walking beam displacement curve can be used to determine whether the walking beam displacement is normal, thereby identifying any malfunctions in the pumping unit.

[0034] Under theoretical conditions, when the pumping unit moves upward, the load on the pumping head mainly includes the weight of the rod and the weight of the liquid column above the piston. When the pumping unit moves downward, the load on the pumping head mainly consists of the weight of the rod in the liquid column. Theoretically, the loads on the pumping head during upward and downward movements are two horizontal lines. The transition from upward to downward and from downward to upward movements, based on the loads on the pumping head at the upward and downward suspension points, is further superimposed with the change in the elastic load of the rod, forming a trapezoidal curve, as shown below. Figure 3 As shown.

[0035] The theoretical indicator diagram only considers the static load borne by the donkey head suspension point and the elastic deformation of the pipe rod caused by the static load; the load-displacement curve is a parallelogram. For example... Figure 4 As shown.

[0036] When a pumping unit experiences a chassis fracture, the displacement curve of the pumping head, the load curve of the pumping head, and the indicator diagram will show regular changes. Therefore, this invention uses the changes in these three curves to remotely diagnose the pumping unit chassis fracture. Figure 8 As shown, the specific steps are as follows:

[0037] Step 1: Obtain the pumping unit's pumping head operation data during one stroke, and obtain the pumping head displacement curve, pumping head load curve, and indicator diagram for that stroke.

[0038] A stroke consists of a topstroke and a bottomstroke. Plot the head displacement curve as a function of crank angle (ωt) and the head load curve as a function of crank angle (ωt) for this stroke. Simultaneously, plot the indicator diagram of the head load as a function of head displacement for this stroke.

[0039] In this embodiment, N (256) points are taken at equal intervals within a stroke to plot the donkey head displacement curve and donkey head load curve of that stroke, and an indicator diagram is plotted based on the donkey head displacement curve and donkey head load curve.

[0040] Step 2: Determine whether there are burrs on the donkey head displacement curve near point π+α (the point corresponding to the highest position of the donkey head) and whether the displacement value of at least the first set number of consecutive points remains unchanged.

[0041] When the pumping unit chassis breaks, Figure 1 As shown, the frame AD, which is equivalent to a four-bar linkage, breaks at a certain point O in the middle, and the frame AD becomes AO+OD. When the donkey head moves downward, it causes the rear half of the frame AO to tilt upward with point O as the center. The upward tilt is limited by the degree of fracture and the degree of looseness of the fixing bolts. When tilting upward, the donkey head accelerates downward. After tilting upward to the limit position, the displacement stops for a short time and then continues to move downward with shaking. The length change of the frame from AD length to AO+OD length and then back to AD length. The length change of the four-bar linkage frame AD causes the displacement of the donkey head to change, resulting in burrs and translation in the displacement curve.

[0042] In this embodiment, the method for determining whether the donkey head displacement curve has burrs is as follows: calculate the absolute value of the difference between the displacement amplitude at a certain point and the average value of the displacement amplitudes of the two adjacent points before and after it, divide the absolute value of the difference by the stroke displacement value to obtain a ratio. If the obtained ratio is greater than or equal to the set displacement burr degree threshold, it is determined that the donkey head displacement curve has burrs near the point π+α; otherwise, no burrs have appeared.

[0043] The threshold for displacement burr severity is set to 0.5%. The first set number of points is greater than or equal to two; in this embodiment, the first set number of points is three.

[0044] When the above conditions are met, such as Figure 5 As shown by the red curve in the middle, its horizontal axis is the crank angle (ωt), and its vertical axis is the donkey head displacement. The donkey head displacement curve shows burrs near the point corresponding to the highest position of the donkey head (π+α in the figure) and the displacement value remains unchanged for points that exceed the first set number of points consecutively.

[0045] Step 3: Determine whether the load curve of the donkey head shows a slowdown in the rate of load reduction on the unloading line and whether the degree of slowdown exceeds the first set threshold.

[0046] Because during the upward tilting of the rear half of the frame AO around point O, load changes cannot be fully transmitted through the chassis to the walking beam and the donkey head, resulting in a slower load descent rate when the donkey head descends. In this embodiment, the method for determining whether the load curve shows a slower load descent rate on the unloading line and that the degree of slowdown exceeds a first set threshold is as follows: First, the slope of the unloading line for this stroke is compared with the slope of the unloading line of the normal load curve. If the slope of the unloading line for this stroke is greater than the slope of the unloading line of the normal load curve (both slopes are negative), it indicates that the load descent rate on the unloading line is slower. Further determination is then made as to whether the degree of slowdown exceeds the first set threshold.

[0047] In this embodiment, the degree of slowdown in load speed is the ratio obtained by subtracting the slope of the unloading line of the donkey head load curve using this stroke from the slope of the unloading line of the normal donkey head load curve and then dividing by the slope of the unloading line of the normal donkey head load curve. If this ratio is greater than or equal to the first set threshold, then the degree of slowdown in the load descent speed of the donkey head load curve exceeds the first set threshold.

[0048] When the above conditions are met, it indicates that the rate of load reduction of the donkey head during unloading is slower than normal, and a load reduction line can be clearly seen on the donkey head load curve. Figure 3 The slope of the curve becomes gentler where the load decreases. For example... Figure 5 As shown by the blue curve, the horizontal axis represents the crank angle (ωt), and the vertical axis represents the load.

[0049] Step 4: Determine whether there are broken or twisted lines on the load reduction line in the indicator diagram.

[0050] The changes in displacement and load are reflected on the indicator diagram as a twisted line.

[0051] In this embodiment, when the displacement change trend of at least a second set number of points on the load reduction line in the indicator diagram is opposite to or unchanged from the normal change trend, it is determined that a broken line twist has occurred on the load reduction line.

[0052] In this embodiment, the displacement on the unloading line gradually decreases. When the displacement of points above the second set number increases or remains unchanged, it is determined that a broken line twist has occurred. The second set number is greater than or equal to two. In this embodiment, the second set number is three. In actual use, it can be adaptively set according to the total number of points in one stroke.

[0053] A dynamometer diagram that meets the conditions is as follows: Figure 6 and Figure 7 As shown, the horizontal axis represents the displacement of the donkey's head, and the vertical axis represents the load. The sloping part of the red line in the figure is the loading line, and the remaining relatively horizontal part is the upward line; the sloping part of the green line is the unloading line, and the remaining relatively horizontal part is the downward line. Figure 6 and Figure 7 It is clearly visible that in the initial stage, the displacement of the green unloading line decreases as the load decreases, and then suddenly a vertical line appears where the load decreases but the displacement remains unchanged. The unloading line as a whole presents a twisted and zigzag pattern.

[0054] In this embodiment, all thresholds were obtained by analyzing the changes in the displacement and load of the pumping unit's chassis when it fractured using statistical methods. For example, to set a threshold for the degree of displacement burrs, multiple sets of displacement curves of the pumping unit's chassis when it fractured were obtained. The displacement value at the location where the burr occurred was compared with the normal displacement value to obtain a degree of deviation. Then, the average of all the deviation degrees was calculated to obtain the set threshold for the degree of displacement burrs.

[0055] Step 5: When all the above conditions are met, it is determined that the pumping unit chassis is broken.

[0056] In addition, the method for diagnosing pumping unit chassis fracture of the present invention also triggers an alarm when the following conditions occur:

[0057] 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;

[0058] 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;

[0059] 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 second set degree threshold of 10%.

[0060] 4. At a certain moment, the maximum value of the donkey head load curve 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 third set threshold.

[0061] 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.

[0062] 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.

[0063] The above-described method for diagnosing chassis fracture in a beam pumping unit enables remote assessment of the unit's chassis condition using the pumping unit's head displacement curve, load curve, and dynamometer diagram. This eliminates the need for on-site inspections, saving manpower and allowing for real-time assessment. It ensures timely detection of chassis fractures, eliminating safety hazards caused by delayed detection, guaranteeing the normal operation of oil and gas extraction, and protecting equipment and personnel safety at the extraction site.

Claims

1. A method for diagnosing chassis fracture in a beam pumping unit, characterized in that, Includes the following steps: Obtain the head displacement curve, head load curve, and indicator diagram of the beam pumping unit. If the head displacement curve, head load curve, and indicator diagram of a certain stroke simultaneously meet the following corresponding conditions, the chassis of the beam pumping unit is determined to be fractured: The load decrease rate of the unloading line in the donkey head load curve is slower than the load decrease rate of the unloading line in the normal donkey head load curve, and the degree of slowing down exceeds the first set threshold. The donkey head displacement curve shows burrs near the highest point of the donkey head and the point displacement value remains unchanged for at least the first set number of consecutive points. The first set number of points is greater than or equal to two; The displacement change trend of at least the second set number of consecutive points on the load reduction line in the indicator diagram is opposite to or unchanged from the change trend of the load reduction line in the normal indicator diagram. The second set number of points is greater than or equal to two.

2. The method for diagnosing chassis fracture of a beam pumping unit according to claim 1, characterized in that, The load descent rate of the donkey head load curve unloading line is measured by its slope. Correspondingly, the ratio obtained by subtracting the slope of the unloading line in the normal donkey head load curve from the slope of the unloading line of the donkey head load curve using this stroke, and then dividing the difference by the slope of the unloading line in the normal donkey head load curve, is the degree of slowing down of the load descent rate.

3. The method for diagnosing chassis fracture 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 near the highest point 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 appears in the donkey head displacement curve near the highest point of the donkey head.

4. The method for diagnosing chassis fracture of a beam pumping unit according to claim 1, characterized in that, A normal indicator diagram is the indicator diagram or theoretical indicator diagram when the pumping unit is not malfunctioning.

5. The method for diagnosing chassis fracture of a beam pumping unit according to claim 2, characterized in that, The normal donkey head load curve is the donkey head load curve when the pumping unit does not malfunction or the theoretical donkey head load curve.

6. The method for diagnosing chassis fracture of a beam pumping unit according to any one of claims 1-5, 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.

7. The method for diagnosing chassis fracture of a beam pumping unit according to any one of claims 1-5, 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.

8. The method for diagnosing chassis fracture of a beam pumping unit according to any one of claims 1-5, characterized in that, An alarm is triggered when the maximum value of the load curve of the donkey head in this stroke is greater than the maximum value of the load curve in the previous stroke, and the degree of the excess is greater than or equal to the second set threshold.

9. The method for diagnosing chassis fracture of a beam pumping unit according to any one of claims 1-5, 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 the previous set time period, and the degree of the excess is greater than or equal to the third set threshold.

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