Studying the flow field inside the pump, especially the mixed-phase flow field, is the key to improving the performance of the deep well pump. With the maturity of PIV technology, LDV technology and ultrasonic technology, these advanced flow field testing techniques can be used to perform high-precision measurements without disturbing the flow field. In Canada, people have used these advanced technologies to study the flow field of deep well pumps. The University of Petroleum (Beijing) Marine Mechanics Laboratory has applied PIV (Particle Imaging Velocity Measurement Technology) to conduct experimental research on this problem. The main content is to measure the inflow of pumps at different flow rates. The distribution law of the field, and compare the similarities and differences of the flow field in the deep well pump during single-phase and mixed-phase flow.
1 particle imaging speed measurement and image processing technology
The basic principle of particle imaging velocity measurement (PIV) technology is to use the scattering effect of particles scattered in a fluid to record the position of the particles in the flow field at different times by optical means, thereby obtaining the displacement of the particles. With respect to the followability of the flow field, the velocity and instantaneous motion parameters of the fluid at the location of the particle are measured.
Using PIV technology, the number of particles in the flow field can be recorded on the same image by multiple exposures in chronological order, or recorded on different graphics by high-speed cameras. Using the relevant physics and mechanics assumptions and laws, and according to the corresponding mathematical model, a series of numerical operations can be used to obtain parameters (particle displacement, velocity, etc.) that reflect the characteristics of the flow field. Generally, a PIV system is mainly composed of a lighting system, a PIV image recording storage system, and a PIV processing system.
2 small gas-liquid two-phase deep well pump simulation test device
The deep well pump works underground and its working medium is not single-phase, so it is difficult to actually test the flow field of the deep well pump working in the field. In addition, because the oil well formation conditions in each oilfield are very complicated, it is difficult to find general rules. Therefore, a small gas-liquid two-phase deep well pump simulation test device was established in the laboratory, as shown in Figure 1.
The simulation test device is mainly composed of a hydraulic control system and a pneumatic control system. In order to carry out the visualization study, the pump and plunger of the deep well pump model are made of plexiglass, the pump diameter is 57mm, the plunger length is 0.3m, the simulated stroke is 0~0.6m, and the stroke is 0~6 times/s. The internal pressure is 0.7 MPa.
3 test process
Industrial white oil similar in density and viscosity to crude oil was used as a test medium, and GDX501 polystyrene beads close to the density of white oil were used as tracer particles. The strong light source caused by the 10W krypton laser generator and the corresponding optical path system is used as the illumination source of the PIV imaging, and the PIV image is taken by video or photography. According to different working conditions, PIV images were recorded and photographed in the pump, cylinder, plunger and other parts of the deep well pump under single-phase and gas-liquid two-phase flow medium conditions, for further analysis and processing.
4 experimental results and analysis
Due to the research results of the flow field of the fixed valve part of the deep well pump, and the PIV image processing procedure of the gas-liquid two-phase flow is not perfect, the emphasis here is on analyzing the deep well pump swimming valve and column when the flowing medium is single-phase fluid. The flow field at the plug.
4.1 Deep well pump valve movement law
It was found in the experiment that the movement law of the pump valve of the deep well pump is not exactly the same as that of the resident. Its movement is accompanied by two kinds of rotary motions in addition to the linear motion in the vertical direction. When the plunger movement speed is small, the valve ball rotates up and down around the horizontal axis; when the plunger movement speed is large, the valve ball rotates horizontally around the vertical axis and revolves along the inner hole corner of the valve seat, that is, the valve seat hole center axis. The angular velocity of rotation is related to the speed of movement of the plunger. The greater the speed of the plunger, the greater the angular velocity of rotation of the ball. The special movement form of the valve ball is mainly related to the special characteristics of the valve ball and the valve seat structure and the impact of the fluid.
The deep well pump valve is a spherical valve member that will detach from the boundary layer at the rear when the fluid flows around it, while producing a lateral excitability. Due to the symmetry of the ball, this lateral excitability will move back and forth around the "equator" of the ball, so that the ball is not always on the axis of the seat bore, but is offset by a distance and abuts against the seat Rotating on the corners, this is the "revolution" phenomenon.
In addition, due to the instability of the fluid flow and the deviation of the valve ball, the asymmetry of the flow of the fluid relative to the valve ball will cause a certain deflection to the valve ball, so that the lateral force does not act on the center of the ball, but on the horizontal surface. There is a certain degree of eccentricity, so that the valve ball has a rotation in the horizontal plane, that is, "rotation" phenomenon. The above conclusions were obtained in the case of pure liquid. In the gas-liquid mixed phase flow, due to the presence of air bubbles, the flow field disturbance is more severe, and the bubble has a certain impact on the valve ball. At this time, the ball movement is more complicated, in addition to the rotary motion, there is a sharp jump up and down.
4.2 PIV image processing results of single-phase flow swimming valve ball
It can be seen from the flow field velocity vector of the swimming valve part of the deep well pump that the flow field around the ball of the swimming valve is not symmetrically distributed, and the boundary layer of the left valve gap continues to the top of the near ball to fall off. This means that the forces on the sides of the fixed valve gap are unbalanced against the ball, which causes the ball to rotate. With the increase of the stroke, the fluid flow rate increases, the boundary layer of the valve ball breaks off earlier, and the flow field asymmetry around the valve ball still exists, so the eccentricity of the valve ball is more intense, which is observed during the test. The law of valve motion is consistent.
It can be seen that due to the lateral impact force of the fluid on the valve ball, the ball is deviated from the axis, and the effect of its "rotation" makes the ball have a certain lag time when it is opened and closed, thus making the pump The pumping efficiency is reduced, resulting in pump stroke loss. In addition, due to the non-streamlined shape of the valve seat, the suction resistance is increased, the hysteresis time of the valve ball is also increased, and the disturbance of the valve ball is increased. The drift and disturbance of the valve ball have a great relationship with the shape of the valve ball and the valve seat. In order to make the valve ball as close as possible to the vertical movement in the ideal state, and to reduce the overcurrent resistance of the valve gap, the valve can be improved. The hood and seat are designed so that the bonnet limits the bounce height of the ball. While ensuring the maximum flow area, the ball is only allowed to move vertically up and down, and the valve cover and the seat shape are designed to be streamlined to reduce the overcurrent resistance. These improvements can reduce the disturbance of the ball and shorten the lag time of opening and closing, so as to improve the pump efficiency.
In addition, it can be seen from the flow field rotation of the portion that there are two distinct vortices between the bottom end of the plunger of the swimming valve suction port and the pump cylinder. This is because when the plunger performs the downstroke movement, the bottom end of the plunger has a certain area, so that the liquid that presses the bottom thereof flows downward during the downward movement. At this time, the swimming valve ball is in an open state, and the liquid at the lower end of the swimming valve ball is pressed into the swimming valve gap, and enters the plunger inner cavity, causing liquid backflow at the bottom end portion of the plunger to form a vortex. These two vortices greatly increase the overcurrent resistance of the liquid and also increase the disturbance of the ball of the ball. In order to eliminate the vortex and reduce the overcurrent resistance, the cross-sectional area of ​​the bottom of the plunger can be minimized and the shape of the plunger can be bell-shaped, thereby reducing the overcurrent resistance.
4.3 PIV image processing results at the exit of the single-phase flow plunger
The flow field velocity vector at the outlet of the plunger tip under the action of a single-phase flow. It can be seen from the figure that the flow field characteristics of the plunger tip outlet are as follows: the internal flow of the plunger is in a symmetrical flow state, and the flow line distribution is relatively uniform. This shows that the internal flow of the plunger is stable and is substantially laminar flow, which can be seen more clearly from the flow field rotation at the outlet of the plunger. However, at the outlet of the plunger, due to the reduction of the cross-sectional cross section and the change in the shape of the cross-section, the fluid produces a horizontal velocity component at the outlet of the plunger, especially at the corner where a vortex occurs, thereby generating a negative pressure, which is increased. Flow resistance. As the number of strokes increases, the vortex at the corner of the plunger outlet is also continuously strengthened, and the overcurrent resistance at the outlet is correspondingly increased. In order to reduce the generation of vortex, it can be seen from the analysis of this part that if the corner of the plunger outlet is designed to be streamlined or chamfered at this location, the vortex should be minimized, thereby reducing the overcurrent resistance at the portion.
5 suggestions
The following improvements should be made to the deep well pump:
(1) The ball is a major component of the deep well pump and is also a consumable part, which determines the efficiency of the pump and the pump cycle. It is recommended to use eccentric spherical ball for the mixed-phase deep well pump, drop valve ball for deep well pump with narrow flow channel, and cone valve ball with sealing rubber for deep well pump with sand pumping well.
(2) Under the condition of ensuring the maximum over-flow area, the flow-through type should be adopted as much as possible for the cross-sectional shape of the valve ball cover to reduce the over-current resistance.
(3) When designing the structure of the plunger, it should be considered to design the suction port at the lower end of the plunger to be streamlined or bell-shaped to reduce its suction resistance. While ensuring that the plunger outlet has a maximum flow cross section, the plunger outlet flow passage is also designed to be streamlined to reduce the overcurrent resistance at the plunger outlet.
1 particle imaging speed measurement and image processing technology
The basic principle of particle imaging velocity measurement (PIV) technology is to use the scattering effect of particles scattered in a fluid to record the position of the particles in the flow field at different times by optical means, thereby obtaining the displacement of the particles. With respect to the followability of the flow field, the velocity and instantaneous motion parameters of the fluid at the location of the particle are measured.
Using PIV technology, the number of particles in the flow field can be recorded on the same image by multiple exposures in chronological order, or recorded on different graphics by high-speed cameras. Using the relevant physics and mechanics assumptions and laws, and according to the corresponding mathematical model, a series of numerical operations can be used to obtain parameters (particle displacement, velocity, etc.) that reflect the characteristics of the flow field. Generally, a PIV system is mainly composed of a lighting system, a PIV image recording storage system, and a PIV processing system.
2 small gas-liquid two-phase deep well pump simulation test device
The deep well pump works underground and its working medium is not single-phase, so it is difficult to actually test the flow field of the deep well pump working in the field. In addition, because the oil well formation conditions in each oilfield are very complicated, it is difficult to find general rules. Therefore, a small gas-liquid two-phase deep well pump simulation test device was established in the laboratory, as shown in Figure 1.
The simulation test device is mainly composed of a hydraulic control system and a pneumatic control system. In order to carry out the visualization study, the pump and plunger of the deep well pump model are made of plexiglass, the pump diameter is 57mm, the plunger length is 0.3m, the simulated stroke is 0~0.6m, and the stroke is 0~6 times/s. The internal pressure is 0.7 MPa.
3 test process
Industrial white oil similar in density and viscosity to crude oil was used as a test medium, and GDX501 polystyrene beads close to the density of white oil were used as tracer particles. The strong light source caused by the 10W krypton laser generator and the corresponding optical path system is used as the illumination source of the PIV imaging, and the PIV image is taken by video or photography. According to different working conditions, PIV images were recorded and photographed in the pump, cylinder, plunger and other parts of the deep well pump under single-phase and gas-liquid two-phase flow medium conditions, for further analysis and processing.
4 experimental results and analysis
Due to the research results of the flow field of the fixed valve part of the deep well pump, and the PIV image processing procedure of the gas-liquid two-phase flow is not perfect, the emphasis here is on analyzing the deep well pump swimming valve and column when the flowing medium is single-phase fluid. The flow field at the plug.
4.1 Deep well pump valve movement law
It was found in the experiment that the movement law of the pump valve of the deep well pump is not exactly the same as that of the resident. Its movement is accompanied by two kinds of rotary motions in addition to the linear motion in the vertical direction. When the plunger movement speed is small, the valve ball rotates up and down around the horizontal axis; when the plunger movement speed is large, the valve ball rotates horizontally around the vertical axis and revolves along the inner hole corner of the valve seat, that is, the valve seat hole center axis. The angular velocity of rotation is related to the speed of movement of the plunger. The greater the speed of the plunger, the greater the angular velocity of rotation of the ball. The special movement form of the valve ball is mainly related to the special characteristics of the valve ball and the valve seat structure and the impact of the fluid.
The deep well pump valve is a spherical valve member that will detach from the boundary layer at the rear when the fluid flows around it, while producing a lateral excitability. Due to the symmetry of the ball, this lateral excitability will move back and forth around the "equator" of the ball, so that the ball is not always on the axis of the seat bore, but is offset by a distance and abuts against the seat Rotating on the corners, this is the "revolution" phenomenon.
In addition, due to the instability of the fluid flow and the deviation of the valve ball, the asymmetry of the flow of the fluid relative to the valve ball will cause a certain deflection to the valve ball, so that the lateral force does not act on the center of the ball, but on the horizontal surface. There is a certain degree of eccentricity, so that the valve ball has a rotation in the horizontal plane, that is, "rotation" phenomenon. The above conclusions were obtained in the case of pure liquid. In the gas-liquid mixed phase flow, due to the presence of air bubbles, the flow field disturbance is more severe, and the bubble has a certain impact on the valve ball. At this time, the ball movement is more complicated, in addition to the rotary motion, there is a sharp jump up and down.
4.2 PIV image processing results of single-phase flow swimming valve ball
It can be seen from the flow field velocity vector of the swimming valve part of the deep well pump that the flow field around the ball of the swimming valve is not symmetrically distributed, and the boundary layer of the left valve gap continues to the top of the near ball to fall off. This means that the forces on the sides of the fixed valve gap are unbalanced against the ball, which causes the ball to rotate. With the increase of the stroke, the fluid flow rate increases, the boundary layer of the valve ball breaks off earlier, and the flow field asymmetry around the valve ball still exists, so the eccentricity of the valve ball is more intense, which is observed during the test. The law of valve motion is consistent.
It can be seen that due to the lateral impact force of the fluid on the valve ball, the ball is deviated from the axis, and the effect of its "rotation" makes the ball have a certain lag time when it is opened and closed, thus making the pump The pumping efficiency is reduced, resulting in pump stroke loss. In addition, due to the non-streamlined shape of the valve seat, the suction resistance is increased, the hysteresis time of the valve ball is also increased, and the disturbance of the valve ball is increased. The drift and disturbance of the valve ball have a great relationship with the shape of the valve ball and the valve seat. In order to make the valve ball as close as possible to the vertical movement in the ideal state, and to reduce the overcurrent resistance of the valve gap, the valve can be improved. The hood and seat are designed so that the bonnet limits the bounce height of the ball. While ensuring the maximum flow area, the ball is only allowed to move vertically up and down, and the valve cover and the seat shape are designed to be streamlined to reduce the overcurrent resistance. These improvements can reduce the disturbance of the ball and shorten the lag time of opening and closing, so as to improve the pump efficiency.
In addition, it can be seen from the flow field rotation of the portion that there are two distinct vortices between the bottom end of the plunger of the swimming valve suction port and the pump cylinder. This is because when the plunger performs the downstroke movement, the bottom end of the plunger has a certain area, so that the liquid that presses the bottom thereof flows downward during the downward movement. At this time, the swimming valve ball is in an open state, and the liquid at the lower end of the swimming valve ball is pressed into the swimming valve gap, and enters the plunger inner cavity, causing liquid backflow at the bottom end portion of the plunger to form a vortex. These two vortices greatly increase the overcurrent resistance of the liquid and also increase the disturbance of the ball of the ball. In order to eliminate the vortex and reduce the overcurrent resistance, the cross-sectional area of ​​the bottom of the plunger can be minimized and the shape of the plunger can be bell-shaped, thereby reducing the overcurrent resistance.
4.3 PIV image processing results at the exit of the single-phase flow plunger
The flow field velocity vector at the outlet of the plunger tip under the action of a single-phase flow. It can be seen from the figure that the flow field characteristics of the plunger tip outlet are as follows: the internal flow of the plunger is in a symmetrical flow state, and the flow line distribution is relatively uniform. This shows that the internal flow of the plunger is stable and is substantially laminar flow, which can be seen more clearly from the flow field rotation at the outlet of the plunger. However, at the outlet of the plunger, due to the reduction of the cross-sectional cross section and the change in the shape of the cross-section, the fluid produces a horizontal velocity component at the outlet of the plunger, especially at the corner where a vortex occurs, thereby generating a negative pressure, which is increased. Flow resistance. As the number of strokes increases, the vortex at the corner of the plunger outlet is also continuously strengthened, and the overcurrent resistance at the outlet is correspondingly increased. In order to reduce the generation of vortex, it can be seen from the analysis of this part that if the corner of the plunger outlet is designed to be streamlined or chamfered at this location, the vortex should be minimized, thereby reducing the overcurrent resistance at the portion.
5 suggestions
The following improvements should be made to the deep well pump:
(1) The ball is a major component of the deep well pump and is also a consumable part, which determines the efficiency of the pump and the pump cycle. It is recommended to use eccentric spherical ball for the mixed-phase deep well pump, drop valve ball for deep well pump with narrow flow channel, and cone valve ball with sealing rubber for deep well pump with sand pumping well.
(2) Under the condition of ensuring the maximum over-flow area, the flow-through type should be adopted as much as possible for the cross-sectional shape of the valve ball cover to reduce the over-current resistance.
(3) When designing the structure of the plunger, it should be considered to design the suction port at the lower end of the plunger to be streamlined or bell-shaped to reduce its suction resistance. While ensuring that the plunger outlet has a maximum flow cross section, the plunger outlet flow passage is also designed to be streamlined to reduce the overcurrent resistance at the plunger outlet.
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