Method and system for simulating power curve of oil pumping unit under working condition

Abstract

The invention discloses a power curve simulation method and system of an oil pumping unit under a working condition. The method comprises the following steps: establishing a model of a relation between suspension center displacement and time by utilizing a model for accurately calculating the suspension center displacement; a stroke of the oil pumping unit is divided into a suspension center loading section, an ascending section after loading is completed, a suspension center unloading section and a descending section after unloading is completed, and a model of the relationship between suspension center loads and time is established; establishing a relationship between the suspension center load and the suspension center displacement, and drawing an indicator diagram curve of the rod pumped well; and calculating the torque and power of the pumping unit according to the indicator diagram curve, drawing a power curve, and extracting working condition characteristics. According to the method, the elastic modulus of the sucker rod is considered, a simple mathematical calculation model for representing the relation between the polished rod load and the displacement of the rod-pumped well under the normal working condition is invented, and a simple mathematical model for calculating the power of the pumping unit under the normal working condition is established on the basis; and rapid and effective simulation of the pumping unit power curve under different pumping rod elasticity moduli and different pumping unit working systems is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of oil production with a pumping unit, and in particular relates to a power curve simulation method and system for a pumping unit under working conditions. Background Art

[0002] At present, working condition diagnosis is mostly based on the dynamometer diagram. The investment cost of the Internet of Things for the dynamometer diagram is high, which does not meet the development needs of low-cost Internet of Things. The acquisition cost of the power electrical parameters of the pumping unit is low, but there is a lack of corresponding methods for diagnosing working conditions using power electrical parameters. Therefore, simulating the power curve, understanding the shape of the power curve, and extracting the working condition characteristics contained in the power curve are indispensable links for using electrical parameters to diagnose working conditions. However, the research on using power curves to directly diagnose complex working conditions at home and abroad is not mature yet and needs to be carried out urgently.

[0003] The power curve has a complex shape. To extract the working condition characteristics contained in the power curve, the power curves of different working conditions must be simulated first. In order to calculate the power curve, it is necessary to first calculate the load and displacement of the suspension point based on the structure and working system of the pumping unit, and establish the power diagram model of the pumping unit. Currently, the commonly used power diagram analysis technology is mostly based on solving the one-dimensional rod column wave equation proposed by Gibbs. Complex variable function theory is used to solve this mathematical physics equation. The principle is complex and difficult to implement. In addition, the model is not easy to modify, and it is difficult to consider other complex working conditions on its basis.

[0004] The diagnosis technology of pumping well working condition is mainly based on power diagram diagnosis. Power diagram diagnosis mostly uses analytical or numerical methods to solve the one-dimensional rod column wave equation proposed by Gibbs. The principle is complex and the implementation coefficient is high. It cannot take into account the working conditions of ground equipment and lacks a method for diagnosing pumping unit faults based on power electrical parameters. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for simulating the power curve of an oil pump under working conditions, so as to solve the problems that the prior art has complex principles, high difficulty in implementation, inability to consider the working conditions of ground equipment, and lacks diagnosis of oil pump faults based on power electrical parameters.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for simulating a power curve of an oil pump under working conditions, comprising:

[0008] A model of the relationship between suspension point displacement and time is established using a model that accurately calculates suspension point displacement;

[0009] A stroke of the pumping unit is divided into the suspension point loading section, the rising section after loading, the suspension point unloading section, and the descending section after unloading. A model of the relationship between the suspension point load and time is established.

[0010] Establish the relationship between the suspension point load and the suspension point displacement, and draw the work diagram curve of the pumping well;

[0011] Calculate the torque and power of the pumping unit according to the power diagram curve, draw the power curve, and extract the working condition characteristics.

[0012] Optionally, a model for the exact calculation of suspension point displacements can be used to model the relationship between suspension point displacements and time:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019] Among them, S A is the suspension point displacement, m; r is the crank radius, m; ω is the crank angular velocity, rad / s; t is the time the crank rotates when calculating the displacement, s; a is the forearm length, m; b is the rear arm length, m; v A is the speed of the suspension point, m / s; a A is the acceleration of the suspension point, m / s 2 .

[0020] Optionally, the suspension point loading section, the rising section after loading is completed, the suspension point unloading section, and the descending section after unloading are respectively:

[0021] The first item represents the process in which the suspension point starts to move upward from the bottom dead center, the sucker rod is stretched and loaded but the pump piston remains stationary; the second item represents the process in which the sucker rod is loaded and moves to the top dead center with the liquid on the pump piston; the third item represents the process in which the suspension point starts to move downward after reaching the top dead center, the sucker rod contracts and unloads, and the pump piston remains stationary; the fourth item represents the process in which the sucker rod is unloaded, and the suspension point and the rod column form a whole and move downward in a unified manner.

[0022] Optional, time-dependent model of the suspension load:

[0023] Under static load, the maximum total load acting on the suspension point during the upstroke is:

[0024] W up =W r_up +W l_up =f r ρ s gL+(f p -fr )Lρ l g=f r (ρ s -ρ l )gL+f p ρ l gL (1)

[0025] During the downstroke, the floating valve opens, and the liquid column load acts on the oil pipe through the fixed valve. The minimum total load acting on the suspension point during the downstroke is:

[0026] W down =f r (ρ s -ρ l )gL (2)

[0027] Establish the relationship between total load and crank rotation phase angle:

[0028]

[0029] According to formula (3), draw the relationship curve between the hanging point load of the pumping unit and time;

[0030] Among them, W r_up -Gravity of the sucker rod in the air, N; g-acceleration due to gravity, m / s; f r -Sucker rod cross-sectional area, m 2 ρ s - density of sucker rod; L-length of sucker rod string, m; q r -The mass of the sucker rod per meter, kg / m; W r_down -Load of the sucker rod string acting on the suspension point during the downstroke, N; ρ l -density of the mixed fluid of crude oil and formation water in the plunger; f p - Cross-sectional area of ​​the plunger, m 2 ;k rod -Elastic tensile modulus of the sucker rod, Pa; S a -Displacement of suspension point, m.

[0031] Optionally, establish the relationship between the suspension point load and the suspension point displacement with time as the pivot:

[0032] The suspension point starts to move, and the load continues to increase as the sucker rod stretches. After the loading is completed, the sucker rod lifts the liquid on the plunger and moves upward, and the load remains unchanged. The load law of the downstroke is exactly the opposite of the upstroke. The larger the elastic coefficient of the sucker rod, the less likely the sucker rod is to stretch, the larger the effective stroke of the pump, and the higher the pump efficiency.

[0033] Optional, pumping unit torque calculation:

[0034] Net torque M of crank-balanced pumping unitnet Equal to the oil well load torque M p Minus crank balance torque M c The net torque of the oil pump is mainly composed of the suspension point torque and the crank balance torque. For the standard power curve, in a complete stroke of bottom dead center-top dead center-bottom dead center, the suspension point torque is a sine curve, and the area enclosed by the torque of the upstroke is larger than the area enclosed by the suspension point torque of the downstroke; the crank balance torque is a cosine curve, which outputs torque in the upstroke and absorbs torque in the downstroke; the net torque presents a symmetrical double-peak structure, the bottom dead center appears in the trough, the top dead center appears in a valley adjacent to the trough, and the trough of the bottom dead center is lower than the valley of the top dead center.

[0035] Optional, pumping unit power calculation:

[0036] The relationship between the motor input power and the torque transmitted to the crankshaft is:

[0037]

[0038] Where: N r —motor input power, kW;

[0039] M motor —Torque transmitted from the motor to the crankshaft, N·m;

[0040] n m —Motor speed, r / min; i—total transmission ratio; η—transmission efficiency, η=0.85~0.89;

[0041] The motor input power is expressed as:

[0042]

[0043] The input power of the motor is proportional to the net torque of the pumping unit.

[0044] Optionally, during the upstroke, the balance block rotates from top to bottom to output power; the suspension point moves from bottom to top to consume power; the motor outputs power, and when the crank rotates and shifts horizontally, the motor power reaches the first peak value, and the crank continues to rotate, and the motor power reaches the lowest valley value at the top dead center.

[0045] Optionally, in the downstroke, the balance weight rotates from bottom to top, consuming power; the suspension point moves from top to bottom, outputting power, and the motor continues to output power. When the crank rotates to the opposite horizontal position, the power reaches a second peak.

[0046] In a second aspect, the present invention provides a power curve simulation system for an oil pump under working conditions, comprising:

[0047] A suspension point displacement and time relationship model establishment module is used to establish a suspension point displacement and time relationship model using a model for accurately calculating the suspension point displacement;

[0048] The module for establishing the model of the relationship between the suspension point load and time is used to divide a stroke of the pumping unit into a suspension point loading section, a rising section after loading, a suspension point unloading section, and a descending section after unloading, and establishes a model of the relationship between the suspension point load and time;

[0049] The power diagram curve output module is used to establish the relationship between the suspension point load and the suspension point displacement and draw the power diagram curve of the pumping well;

[0050] The power curve output module is used to calculate the torque and power of the pumping unit according to the power diagram curve, draw the power curve, and extract the working condition characteristics.

[0051] Compared with the prior art, the present invention has the following technical effects:

[0052] The present invention takes the elastic modulus of the sucker rod into consideration and invents a simple mathematical calculation model for characterizing the relationship between the suspension point load and displacement under normal operating conditions of the pumping well. On this basis, a simple mathematical model for calculating the pumping unit power under normal operating conditions is established, which can realize fast and effective simulation of the pumping unit power curve under different sucker rod elastic moduli and different pumping unit working systems. It is independent of solving complex wave equations and realizes fast simulation of the pumping unit power curve under normal operating conditions. On this basis, corrections can be made to further realize the simulation of complex working conditions, which provides theoretical support for realizing electrical parameter diagnosis of oil well working conditions and is of great significance for realizing cost reduction and efficiency improvement in oil fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Flowchart of the simulation of the pumping unit power curve.

[0054] Figure 2 Structural diagram of a beam pumping unit.

[0055] Figure 3 Comparison of displacement curves of three suspension point motion models.

[0056] Figure 4 Curve of the suspension point load changing with time.

[0057] Figure 5 Dynamometer diagram of different sucker rod elastic coefficients.

[0058] Figure 6 Torque curve of oil pumping unit.

[0059] Figure 7 The shape of the pumping unit power curve.

[0060] Figure 8 Power curves at different impulse times.

[0061] Fig. 9 Power curves for different crank radii. DETAILED DESCRIPTION

[0062] The present invention is further described below in conjunction with the accompanying drawings:

[0063] See also Figures 1 to 9 The present invention provides a method and system for simulating the power curve of an oil pump under working conditions. On this basis, a simple mathematical model for calculating the power of an oil pump under normal working conditions is established to achieve rapid and effective simulation of the power curve of the oil pump under different sucker rod elastic moduli and different oil pump working systems.

[0064] The suspension loads of the pumping unit during operation mainly include: static load, dynamic load and friction load. The static load is mainly composed of the sucker rod column load, the liquid column load acting on the plunger, the sinking pressure load and the wellhead back pressure load. The dynamic load is mainly composed of inertia load and vibration load. The friction load is mainly composed of the friction between the sucker rod column and the liquid column, the friction between the liquid column and the oil pipe, and the resistance generated by the liquid passing through the swimming valve.

[0065] Since the sinking pressure and the wellhead back pressure cause the hanging point load in opposite directions and can offset each other partially, these two items can be ignored in general approximate calculations. The device of the present invention gives priority to the law of the hanging point load under the action of static load.

[0066] Firstly, a model of the relationship between suspension point displacement and time is established using a model that accurately calculates suspension point displacement;

[0067] Secondly, one stroke of the pumping unit is divided into the hanging point loading section, the rising section after loading is completed, the hanging point unloading section, and the descending section after unloading is completed. A simple segmented method for calculating the hanging point load is proposed, and a model of the relationship between the hanging point load and time is established. With time as the pivot, the relationship between the hanging point load and displacement is established, and the power diagram curve of the pumping well is drawn.

[0068] Finally, the torque and power of the pumping unit are calculated, the power curve is drawn, and the operating characteristics are extracted.

[0069] Establish the relationship between the displacement of the pumping unit suspension point and time

[0070] The beam pumping unit is a four-bar linkage mechanism consisting of the line connecting the beam fulcrum and the center of the crank shaft as the fixed rod, and the crank, connecting rod and beam rear arm as the three movable rods. Figure 2 ). Understanding the displacement, velocity and load transformation rules of the pumping unit suspension point is the basis for studying the dynamics of the pumping unit, conducting pumping design and analyzing its working conditions.

[0071] The models for calculating suspension point displacement mainly include simplified simple harmonic vibration model, simplified crank slider motion model and accurate calculation model. Figure 3 The motion laws of the suspension points of three models, namely, precise calculation, simplified crank slider, and simplified simple harmonic oscillation, are compared. The displacements of the suspension point motions of the three models are consistent with each other. To calculate the torque of the oil pump, it is necessary to know the angle of the connecting rod structure during the movement of the oil pump. Only the precise model can solve these parameters during the simulation process. Therefore, in the following analysis, the device of the present invention adopts a precise calculation model.

[0072] Establish the relationship between the suspension point load and displacement

[0073] If only the static load is considered and the influence of the submergence pressure and the wellhead back pressure on the suspension point load is ignored, the maximum total load acting on the suspension point during the upstroke is:

[0074] W up =W r_up +W l_up =f r ρ s gL+(f p -f r )Lρ l g=f r (ρ s -ρ l )gL+f p ρ l gL (1)

[0075] In the downstroke, since the floating valve is open, the liquid column load acts on the oil pipe through the fixed valve instead of on the suspension point. The minimum total load acting on the suspension point in the downstroke is:

[0076] W down =f r (ρ s -ρ l )gL (2)

[0077] Assuming that the tubing is anchored, considering the effect of the elastic expansion and contraction of the sucker rod on the load, the relationship between the total load and the crank rotation phase angle is established:

[0078]

[0079] Among them, W r_up -Gravity of the sucker rod in the air, N; g-acceleration due to gravity, m / s; f r -Sucker rod cross-sectional area, m 2 ρ s -Density of sucker rod (material steel), 7850kg / m 3 ; L- sucker rod length, m; q r -The mass of the sucker rod per meter, kg / m; W r_down -Load of the sucker rod string acting on the suspension point during the downstroke, N; ρl -The density of the mixed fluid of crude oil and formation water in the plunger, which is 800 kg / m 3 ;f p - Cross-sectional area of ​​the plunger, m 2 ;k rod -Elastic tensile modulus of the sucker rod, Pa; S a -Displacement of suspension point, m.

[0080] The calculation formula for the static load of the suspension point in formula (3) consists of four items: the first item represents the process in which the suspension point starts to move upward from the bottom dead center, the sucker rod is stretched and loaded, but the pump piston is still at rest; the second item represents the process in which the sucker rod is loaded and moves to the top dead center with the liquid on the pump piston; the third item represents the process in which the suspension point starts to move downward after reaching the top dead center, the sucker rod contracts and unloads, and the pump piston is still at rest; the fourth item represents the process in which the sucker rod is unloaded, the suspension point and the rod column form a whole and move downward in a unified manner. Based on the above theory, the relationship curve between the suspension point load and time of the pumping unit is drawn as follows: Figure 4 As shown:

[0081] After establishing the relationship between the suspension point load and displacement and time, the work diagram of the pumping unit can be drawn, such as Figure 5 As shown in the figure: At the beginning of the suspension point movement, the load increases as the sucker rod stretches. After the loading is completed, the sucker rod lifts the liquid on the plunger and moves upward, and the load remains unchanged; the load law of the downstroke is exactly the opposite of the upstroke. The typical indicator diagram is a standard parallelogram. The larger the elastic coefficient of the sucker rod, the less likely the sucker rod is to stretch, the larger the effective stroke of the pump, and the more conducive to improving the pump efficiency.

[0082] Pumping unit torque calculation:

[0083] Net torque M of crank-balanced pumping unit net Equal to the oil well load torque (load torque) M p Minus crank balance torque M c (Zhang Qi, 2000), under the condition of known suspension point displacement and load, the torque of the pumping unit can be calculated. Figure 6 As shown in the figure, under the condition of only considering crank balance, the net torque of the pumping unit is mainly composed of suspension point torque and crank balance torque. For the standard power curve, in a complete stroke of bottom dead center-top dead center-bottom dead center, the suspension point torque is an approximate sine curve, and the area enclosed by the torque of the upper stroke is larger than the area enclosed by the suspension point torque of the lower stroke; the crank balance torque is a cosine curve, which outputs torque in the upper stroke and absorbs torque in the lower stroke; after combining the two, the net torque presents a symmetrical double-peak structure, the bottom dead center appears near the trough, the top dead center appears a concave valley adjacent to the trough, and the trough of the bottom dead center is lower than the concave valley of the top dead center.

[0084] Pumping unit power calculation

[0085] The relationship between the motor input power and the torque transmitted to the crankshaft is:

[0086]

[0087] Where: N r —motor input power, kW;

[0088] M motor —Torque transmitted from the motor to the crankshaft, N·m;

[0089] n m —Motor speed, r / min; i—total transmission ratio; η—transmission efficiency, η=0.85~0.89.

[0090] Therefore, the motor input power can be expressed as:

[0091]

[0092] It can be seen from formula (5) that the input power of the motor is proportional to the net torque of the pumping unit. If the transmission coefficient is a constant, the shapes of the two are basically the same. Figure 3-9 It is a dual coordinate curve graph. The smooth blue curve is the torque curve. In order to distinguish the torque curve, some "interference" is added to the red power curve to represent the real power curve.

[0093] like Figure 7 As shown in the figure, the standard power curve is a curve with two approximately equal peaks. In the upstroke, the balance block rotates from top to bottom and outputs power; the suspension point moves from bottom to top and consumes power; in order to maintain balance, the motor outputs power, and the motor power reaches the first peak near the horizontal displacement of the crank rotation. The crank continues to rotate, and the motor power reaches the lowest valley near the top dead center. In the downstroke, the balance block rotates from bottom to top and consumes power; the suspension point moves from top to bottom and outputs power. In order to maintain balance, the motor continues to output power, and the power reaches the second peak when the crank rotates to the opposite horizontal position.

[0094] Effect of strokes and crank radius on power curve

[0095] Figure 8 The influence of impulse frequency on power curve is simulated. The impulse frequency affects the power curve period. The faster the impulse frequency, the shorter the curve period. Fig. 9 The influence of crank radius on power curve was simulated. Adjusting crank radius will change pump stroke. Increasing rotation radius will increase stroke and increase power curve peak.

[0096] In yet another embodiment of the present invention, a power curve simulation system for an oil pumping unit under working conditions is provided, which can be used to implement the power curve simulation method for an oil pumping unit under the working conditions described above. Specifically, the system includes:

[0097] A suspension point displacement and time relationship model establishment module is used to establish a suspension point displacement and time relationship model using a model for accurately calculating the suspension point displacement;

[0098] The module for establishing the model of the relationship between the suspension point load and time is used to divide a stroke of the pumping unit into a suspension point loading section, a rising section after loading, a suspension point unloading section, and a descending section after unloading, and establishes a model of the relationship between the suspension point load and time;

[0099] The power diagram curve output module is used to establish the relationship between the suspension point load and the suspension point displacement and draw the power diagram curve of the pumping well;

[0100] The power curve output module is used to calculate the torque and power of the pumping unit according to the power diagram curve, draw the power curve, and extract the working condition characteristics.

[0101] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for simulating the power curve of an oil pump under working conditions, characterized in that: include: Model the relationship between suspension point displacement and time; A stroke of the pumping unit is divided into the suspension point loading section, the rising section after loading, the suspension point unloading section, and the descending section after unloading. A model of the relationship between the suspension point load and time is established. Based on the above two models, the relationship between the suspension point load and the suspension point displacement is established, and the work diagram curve of the pumping well is drawn; Calculate the torque and power of the pumping unit according to the power diagram curve, draw the power curve, and extract the working condition characteristics.

2. The method for simulating the power curve of an oil pump under working conditions according to claim 1, characterized in that: The model of the relationship between suspension point displacement and time is established by accurately calculating the suspension point displacement: Among them, S A is the suspension point displacement, m; r is the crank radius, m; ω is the crank angular velocity, rad / s; t is the time the crank rotates when calculating the displacement, s; a is the forearm length, m; b is the rear arm length, m; v A is the speed of the suspension point, m / s; a A is the acceleration of the suspension point, m / s 2 .

3. The power curve simulation method of the oil pumping unit under working conditions according to claim 1 is characterized in that: The suspension point loading section, the rising section after loading is completed, the suspension point unloading section, and the descending section after unloading are as follows: The first item represents the process in which the suspension point starts to move upward from the bottom dead center, the sucker rod is stretched and loaded but the pump piston remains stationary; the second item represents the process in which the sucker rod is loaded and moves to the top dead center with the liquid on the pump piston; the third item represents the process in which the suspension point starts to move downward after reaching the top dead center, the sucker rod contracts and unloads, and the pump piston remains stationary; the fourth item represents the process in which the sucker rod is unloaded, and the suspension point and the rod column form a whole and move downward in a unified manner.

4. The method for simulating the power curve of an oil pump under working conditions according to claim 3, characterized in that: Model of the relationship between suspension point load and time: Under static load, the maximum total load acting on the suspension point during the upstroke is: W up =W r_up +W l_up =f r ρ s gL+(f p -f r )Lρ l g=f r (ρ s -ρ l )gL+f p ρ l gL (1) During the downstroke, the floating valve opens, and the liquid column load acts on the oil pipe through the fixed valve. The minimum total load acting on the suspension point during the downstroke is: W down =f r (r s -r l )gL (2) Establish the relationship between total load and crank rotation phase angle: According to formula (3), draw the relationship curve between the hanging point load of the pumping unit and time; Among them, W r_up -Gravity of the sucker rod string in the air, N; g-acceleration due to gravity, m / s; Sucker rod cross-sectional area, m 2 ; Density of sucker rod; L-length of sucker rod string, m; q r -The mass of the sucker rod per meter, kg / m; W r_down -Load of the sucker rod string acting on the suspension point during the downstroke, N; ρ l - Density of the mixed fluid of crude oil and formation water in the plunger; Cross-sectional area of ​​the plunger, m 2 ; Elastic tensile modulus of the sucker rod, Pa; S a -Displacement of suspension point, m.

5. The method for simulating the power curve of an oil pump under working conditions according to claim 1, characterized in that: With time as the pivot, the relationship between suspension point load and suspension point displacement is established: The suspension point starts to move, and the load continues to increase as the sucker rod stretches. After the loading is completed, the sucker rod lifts the liquid on the plunger and moves upward, and the load remains unchanged. The load law of the downstroke is exactly the opposite of the upstroke. The larger the elastic coefficient of the sucker rod, the less likely the sucker rod is to stretch, the larger the effective stroke of the pump, and the higher the pump efficiency.

6. The method for simulating the power curve of an oil pump under working conditions according to claim 1, characterized in that: Pumping unit torque calculation: Net torque M of crank-balanced pumping unit net Equal to the oil well load torque M p Minus crank balance torque M c The net torque of the oil pump is mainly composed of the suspension point torque and the crank balance torque. For the standard power curve, in a complete stroke of bottom dead center-top dead center-bottom dead center, the suspension point torque is a sine curve, and the area enclosed by the torque of the upstroke is larger than the area enclosed by the suspension point torque of the downstroke; the crank balance torque is a cosine curve, which outputs torque in the upstroke and absorbs torque in the downstroke; the net torque presents a symmetrical double-peak structure, the bottom dead center appears in the trough, the top dead center appears in a valley adjacent to the trough, and the trough of the bottom dead center is lower than the valley of the top dead center.

7. The method for simulating the power curve of an oil pump under working conditions according to claim 1, characterized in that: Pumping unit power calculation: The relationship between the motor input power and the torque transmitted to the crankshaft is: Where: N r —motor input power, kW; M motor —Torque transmitted from the motor to the crankshaft, N·m; n m —Motor speed, r / min; i—total transmission ratio; η—transmission efficiency, η=0.85~0.89; The motor input power is expressed as: The input power of the motor is proportional to the net torque of the pumping unit.

8. The method for simulating the power curve of an oil pump under working conditions according to claim 7, characterized in that: During the upstroke, the balance block rotates from top to bottom and outputs power; the suspension point moves from bottom to top and consumes power; the motor outputs power, and when the crank rotates and shifts horizontally, the motor power reaches the first peak value, and the crank continues to rotate, and the motor power reaches the lowest valley value at the top dead center.

9. The method for simulating the power curve of an oil pump under working conditions according to claim 7, characterized in that: During the downstroke, the balance block rotates from bottom to top, consuming power; the suspension point moves from top to bottom, outputting power. The motor continues to output power, and when the crank rotates to the opposite horizontal position, the power reaches a second peak.

10. The power curve simulation system of the oil pump under working conditions is characterized by: include: A suspension point displacement and time relationship model establishment module is used to establish a suspension point displacement and time relationship model using a model for accurately calculating the suspension point displacement; The module for establishing the model of the relationship between the suspension point load and time is used to divide a stroke of the pumping unit into a suspension point loading section, a rising section after loading, a suspension point unloading section, and a descending section after unloading, and establishes a model of the relationship between the suspension point load and time; The power diagram curve output module is used to establish the relationship between the suspension point load and the suspension point displacement and draw the power diagram curve of the pumping well; The power curve output module is used to calculate the torque and power of the pumping unit according to the power diagram curve, draw the power curve, and extract the working condition characteristics.

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