**Abstract:**
Understanding the internal flow field of a pump, especially the multiphase flow field, is crucial for improving pump performance. To achieve this, the University of Petroleum (Beijing) developed a simulation test device designed for gas-liquid two-phase flow hydraulic pumps. The system includes a single-phase flow testing unit and a multiphase flow testing unit. The former can accurately simulate various downhole conditions and liquid flow states within the pump, while the latter enables the simulation of different oil-gas ratios. To quantitatively measure the transient flow field without interference, image processing techniques are used to visualize velocity vectors and curl fields in the planar flow field. Advanced particle image velocimetry (PIV) technology is employed due to its high precision, spatial resolution, and fast dynamic response.
Oil pumps are essential equipment in oilfield development. Enhancing their performance can significantly increase crude oil output and improve the economic benefits of oilfield operations. Current pump development focuses on three main areas: (1) analyzing valve movement mechanics through simplification of motion and stress conditions; (2) innovating pump structures based on functional design requirements, such as developing sand-resistant and gas-resistant heavy-duty oil pumps; and (3) studying pump efficiency and related factors through laboratory tests and observations. For example, research conducted at Daqing Petroleum Institute used pressure and displacement sensors to measure inlet and outlet pressure curves, ball valve pressure drop, and power diagrams.
Despite these efforts, the fundamental issue—pump flow field dynamics—remains underexplored. Understanding the flow field inside the pump is key to solving issues related to valve movement, structural rationality, and performance optimization. With advancements in PIV, LDV, and ultrasound technologies, non-intrusive, high-precision flow field measurements have become possible. Although some studies have been conducted in Canada, no published results are available. Therefore, applying advanced technologies like PIV to study internal pump flow fields is a promising direction for future development. In line with this, the Offshore Engineering Laboratory at the University of Petroleum (Beijing) initiated visualization studies of the internal flow field, combining both theoretical and experimental approaches.
**Design of Pump Simulation Test Device**
Since the working medium in downhole pumping is not always single-phase, actual flow field testing is challenging. To save time and cost, the simulation test device must include gas and liquid sources, visualization conditions, and the ability to observe and record both single-phase and gas-liquid two-phase flow characteristics. The entire pump chamber should be transparent for visual analysis. Additionally, a data acquisition and processing system is needed to handle the rapid changes in the flow field. A variable rod drive system is also required to observe the effects of pump stroke on the flow field.
**Structure Design of Simulation Test Device**
To simulate the up-and-down reciprocation of the plunger and polished rod in real oil pumps, a suitable power system is essential. One approach involves using a motor-driven donkey head system, but this is costly and impractical for laboratories. Another method uses a motor-driven rope system with a pulley to move the plunger up and down, but it requires balancing weights and micro-motors, which pose challenges. These systems cannot fully simulate pump inlet and outlet pressures or adjust flow rates. To overcome these limitations, a hydraulic control system and a pneumatic control system were implemented. The hydraulic system controls the plunger’s reciprocating motion and inlet/outlet pressure, while the pneumatic system manages the multiphase flow intake.
**Power Cylinder Hydraulic System**
The power cylinder hydraulic system consists of a power cylinder, travel switches, two-way solenoid valves, a relief valve, an oil pump, and a governor valve. It operates by driving the piston up and down to move the polished rod. When the polished rod hits the limit switch, the solenoid valve reverses, allowing the piston to move in the opposite direction. The speed control valve adjusts the stroke, and the relief valve regulates the pressure inside the cylinder.
**Suction Pump Pressure Compensation System**
This system includes an oil tank, pump, sequence valve, accumulator, pressure gauge, pressure tank, and relief valve. The pump continuously operates, and the relief valve maintains a set pressure. If the inlet pressure exceeds the regulated level, the relief valve opens to reduce it. If the pressure drops too low, the pump refills the pressure tank. Two accumulators help stabilize the pressure, ensuring consistent operation.
**Pneumatic Control System**
The pneumatic system comprises a gas pump, gas flow meter, electromagnetic switch, check valve, and travel switch. During the stroke, the electromagnetic switch opens, allowing gas to enter the pump. When the polished rod hits the on-stroke switch, the switch closes, stopping the gas flow. On the downstroke, the switch reopens, allowing gas to be supplied again.
**Features of the Simulation Test Device**
The device is divided into two parts: the single-phase flow test unit and the multiphase flow test unit. The single-phase unit includes a power cylinder, plexiglass pump cylinder, plunger, and hydraulic control system. It simulates underground conditions with stable strokes and accurate fluid flow. The multiphase unit includes a pump, gas flow meter, electromagnetic switch, and water tank, enabling precise simulation of different oil-gas ratios. Both units are made of plexiglass for easy observation. The system is lightweight, reliable, and user-friendly, making it a unique and innovative solution compared to existing devices.
**Image Acquisition and Processing System**
To capture transient flow field data without interference, PIV technology is used. It offers high precision, spatial resolution, and fast dynamic response, allowing detailed analysis of velocity vectors and curl fields. The system includes a lighting source, a recording device, and image processing software. In this setup, a 10W neon laser illuminates the flow, a video recorder captures images, and custom PIV software processes the data to extract velocity and other flow parameters. This system provides valuable insights into complex flow behaviors that traditional methods cannot achieve.
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