Experimental Study on Flow Field in Deep Well Pump

Studying the pump flow field, especially the mixed-phase flow field, is the key to improve the performance of deep well pump. With the PIV technology, LDV technology and ultrasonic technology has matured, people have been able to use these advanced flow field test technology without interfering with the flow field of high-precision measurements. In Canada, people have been using these advanced technologies to study the flow field of deep well pumps. The Ocean University of Beijing (Beijing) Laboratory for Ocean Mechanics conducted a pilot study on this issue using PIV (Particle Imaging Velocimetry) technology. Its main content is to measure the pump flow Field distribution law, and compared single-phase and mixed-phase flow when the deep well pump flow field similarities and differences.
1 particle imaging speed and image processing technology

Particle imaging velocimetry (PIV) the basic principle of ① is the use of scattered particles in the scattering of light on the role of the optical method to record the particles at different times in the flow field position, in order to get the particle displacement, based on the particles Following the flow field, the velocity and instantaneous motion parameters of the fluid at the location of the particle are measured.

With PIV technology, numerous particle events in the flow field can be recorded in the same image in multiple exposures in chronological order, as well as recorded on different graphs using high-speed cameras. The parameters (particle displacement, velocity, etc.) that reflect the characteristics of the flow field can be obtained through a series of numerical calculations using the relevant assumptions and laws of physics and mechanics and according to the corresponding mathematical model. Generally, the 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

Deep well pumps work underground and their working medium is not single-phase, so it is difficult to actually test the flow field of deep well pumps working in the field. In addition, due to the complex formation conditions of oil wells in various oil fields, it is difficult to find a general law. Therefore, a small-scale gas-liquid two-phase deep well pump simulation test device has been set up in the laboratory, as shown in FIG. 1.

The simulation test device mainly consists of hydraulic control system and pneumatic control system. For visualization, deep well pump model cylinder and plunger are made of plexiglass with a pump diameter of 57 mm, a plunger length of 0.3 m, a simulated stroke of 0 to 0.6 m and a stroke of 0 to 6 times / s, the internal pressure of 0.7 MPa working conditions.

3 test process

Using industrial white oil with similar density and viscosity to crude oil as test medium, GDX501 polystyrene beads with density close to white oil were used as tracer particles. A strong light source caused by a 10 W neon laser generator and a corresponding light path system is used as an illumination source for PIV imaging and a PIV image is taken by way of video recording or photography. According to different working conditions, PIV images were recorded and photographed for deep well pump cylinder, pump valve and plunger under single-phase and gas-liquid two-phase flow conditions for further analysis and treatment.

4 experimental results and analysis

Due to the research on the flow field in the fixed valve of deep well pump, and the gas-liquid two-phase flow PIV image processing program is not perfect, the emphasis here is on the analysis of deep well pump moving valve and column Plug site flow field.

4.1 deep well pump valve movement

In the test, we found that the movement pattern of deep well pump valve is not exactly the same as the living people's understanding of it. Its movement is accompanied by two kinds of rotating motions in addition to the linear motion in the vertical direction. When the movement speed of the plunger is small, the valve ball rotates up and down around the horizontal axis. When the movement speed of the plunger is large, the valve ball rotates horizontally about the vertical axis and revolves around the hole center of the valve seat hole. The angular velocity of rotation is related to the movement speed of the plunger. The greater the movement speed of the plunger, the greater the angular rotation speed of the valve ball. The special ball valve movement mainly with the valve ball, seat structure of the particularity and fluid impact. Deep well pump valve is a spherical valve, when the fluid flows around it, will occur in the rear of the detachment of the detachment phenomenon, while producing a lateral excitation force. Due to the symmetry of the valve ball, this lateral force of motion will move circumferentially around the "equator" of the valve ball so that the valve ball does not always lie on the axis of the valve bore hole but is offset a distance away from the valve seat Corner rotation, 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 degree of deflection to the valve ball so that the lateral force does not act on the ball center but on the horizontal plane There is a certain degree of eccentricity, so that the ball in the ball there is a rotation, the "rotation" phenomenon. The above conclusion is obtained in the case of pure liquid. In the gas-liquid mixed phase flow, due to the presence of bubbles, the disturbance of the flow field is more severe, and the bubble has a certain impact on the valve ball. At this time, the valve ball movement is more complicated. In addition to the rotational movement, there is also a violent fluctuation. 4.2 Single-phase flow valve ball PIV image processing results

It can be seen from the velocity vector of the flow field in the deep well pump moving valve that the flow field around the floating valve ball is not symmetrical and the boundary layer on the left valve gap continues to fall off near the top of the valve ball. This shows that the fluid on both sides of the fixed valve clearance force on the valve ball is not balanced, so that the valve ball to produce rotational movement. With the increase of impulse and the increase of fluid velocity, the valve ball boundary layer departs earlier and the asymmetry of the flow field around the valve ball still exists. Therefore, the eccentricity of valve ball is more intense, which is similar to that observed in the experiment Valve ball movement is consistent.

It can be seen that the lateral deviation of the valve ball from the axis due to the lateral impact of the fluid on the valve ball and the effect of its "rotation" cause the valve ball to have a certain lag time when the valve ball is opened and closed, Pumping efficiency is reduced, resulting in pump stroke loss. In addition, due to non-streamlined valve seat shape, making inhalation resistance increases, but also to increase the valve ball lag time, and to increase the ball valve disturbance. This valve ball drift and disturbance and valve ball and valve seat shape has a great relationship, in order to make the ball as close as possible under the ideal vertical movement up and down, and in order to reduce the valve gap flow resistance, you can improve the valve The hood and seat design allow the valve housing to limit the bounce height of the valve ball. In ensuring the maximum flow area at the same time as far as possible to make the vertical movement of the ball only up and down, and the valve cover and seat design streamlined, in order to reduce the flow resistance. These improvements can reduce the valve ball disturbance and shorten the opening and closing of the lag time, so as to achieve the purpose of improving pump efficiency.

In addition, it can be seen from the curl of the flow field in this part that there are two obvious vortices between the bottom end of the plunger of the swimming valve and the pump barrel. This is because when the plunger performs the down stroke movement, the bottom end of the plunger flows down due to a certain area of ​​the bottom end of the plunger, so that the liquid pressing the bottom thereof during the downward movement is downward. At this moment, the floating valve ball is in the open state, and the liquid at the lower end of the floating valve ball is pressed into the floating valve gap and enters the plunger cavity to cause liquid backflow at the bottom part of the plunger to form a vortex. Both of these vortices greatly increase the overcurrent resistance of the liquid and also increase the disturbance of the traveling valve ball. In order to eliminate the vortex and reduce the over-current resistance, the piston bottom cross-sectional area can be minimized, and make it bell-shaped appearance, thereby reducing the over-current resistance.

4.3 Single-phase flow plunger exit PIV image processing results

Flow field velocity at the top of plunger at single-phase flow. As can be seen from the figure, the top of the plunger outlet presents the following characteristics of the flow field: the internal flow of the plunger symmetrical flow state, and streamline distribution more evenly. This shows that the internal plunger flow stability, the general laminar flow state, which is from the exit of the plunger flow field curvature can be more clearly seen. However, at the exit of the plunger, due to the reduction of the cross section of the flow and the change of the shape of the cross section, the fluid produces a horizontal velocity component at the exit of the plunger, especially at the corner where vortices appear, creating negative pressure and increasing Flow resistance. With the increase of the stroke, the vortex at the corner of the outlet of the plunger is also continuously strengthened, and the overcurrent resistance at the outlet also increases correspondingly. In order to reduce the vortex generation, it can be seen from the analysis of this part that if the corner of the outlet of the plunger is designed to be streamlined or chamfering is to be made in this part, the vortex should be minimized so as to reduce the overcurrent resistance at this part.

5 suggestions

Deep well pump should make the following improvements:

(1) The valve ball is a major part of the deep well pump, which is also a wearing part. It determines the efficiency of the pump and the pump cycle. It is suggested to use eccentric ball valve for the mixed-flow deep well pump, drop-shaped ball valve for the deep well with small flow passage and conical valve ball with the seal rubber for the deep well pump with sand for oil well.

(2) Under the condition that the maximum flow area is guaranteed, the shape of the overcurrent section of the valve dome should be minimized to reduce the overcurrent resistance.

(3) In designing the structure of the plunger, consideration should be given to designing the suction inlet at the lower end of the plunger to be streamlined or flared to reduce its suction resistance. While ensuring the maximum overcurrent section at the outlet of the plunger, the outlet passage of the plunger is also designed to be streamlined to reduce the overcurrent resistance at the outlet of the plunger.

Department of Mechanical and Electrical Engineering, Petroleum University of Petroleum, Beijing 102200, China

About the author: Lin Sheng (1971-), male, received a master's degree from the University of Petroleum (Beijing) in 1996 and is currently pursuing a doctorate in Mechanics Institute, Chinese Academy of Sciences. (1) DONG Shuping. Particle imaging velocimetry (PIV) and its image processing technology. Internal data of Department of Mechatronic Engineering, University of Petroleum (Beijing).

references:

[1] Galway GW et al. Flow of complex mixtures in pipelines [M]. Beijing: Petroleum Industry Press, 1983.

[2] Shi Xi Xiting H. boundary layer theory [M] Beijing: Science Press, 1993.

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