As an important mechanical oil recovery process, the screw pump oil recovery system has the advantages of low investment, simple equipment structure, convenient operation, obvious energy-saving effect, strong adaptability, etc., and has been more and more widely used in oil field production.
xx Oilfield has promoted the application of screw pump oil production system since 1999, and gradually applied it as an energy-saving lifting equipment in a large area of thin oil reservoirs. Since 2004, it has gradually changed its concept and explored the application of screw pump oil production systems. The application of heavy oil and high water cut blocks has obvious effects of increasing oil and reducing water and has become another new way for efficient development of heavy oil and heavy water flooded areas.
1. Working principle of screw pump for oil extraction
The main working principle of screw pump oil recovery is that external power drives the rod column to rotate clockwise and then drives the rotor in the downhole screw pump to move in the stator rubber bushing. When the rotor moves, the suction end forms a sealed cavity, and the axial direction moves to the discharge end, the oil enters the sealing cavity under the action of the pressure difference at the suction end and moves upwards, and is pushed from the suction end to the discharge end. The continuous formation, upward movement and disappearance of the sealing cavity will displace oil, sand, and water, waiting for the medium to lift to the ground together.
2. Composition of screw pump oil production system
At present, the screw pump used in an oil field is mainly based on the ground-driven single screw pump oil production system (hereinafter referred to as the screw pump oil production system), which consists of four parts:
1) Electric control part: including electric control box and cables;
2) Ground driving part: including gearbox and driving motor, wellhead dynamic seal, support frame, square card, etc.;
3) Downhole part: drive rod, screw pump stator, rotor;
4) Supporting tools: including special wellhead, polished rod, rod centralizer, pipe centralizer, anchor, etc.
3 Characteristics and application of screw pump oil production system
The main technical characteristics of the screw pump oil production system are as follows:
1) Small one-time investment. Compared with electric submersible pumps, hydraulic piston pumps and beam-type (chain-type) pumping units, screw pumps have the lowest one-time investment.
2) Low energy consumption. Due to the stable load and small mechanical loss when the screw pump is working, the pump efficiency can reach 70%, and the system efficiency is high. It is the mechanical oil recovery method with the lowest energy consumption at present.
3) Low noise, safety and environmental protection.
4) Small footprint. The surface driving device of the screw pump has a simple structure, is located above the wellhead, and occupies a small area.
5) Easy to manage. The movable parts of the screw pump ground driving device are mainly belts, dynamic seals, and gearboxes, which are very convenient for inspection and have less management workload. At the same time, it is small in size, easy to install and maintain, and low in daily maintenance costs.
6) Strong adaptability. The screw pump is a positive displacement pump with low sensitivity to thick, sand, wax, and gas. It can be used normally for heavy oil wells, high sand content wells, and high gas content wells whose suction viscosity is lower than 10,000mPa·s.
7) The liquid discharge is stable. Since the screw pump only rotates, the suction end continuously enters the liquid with a constant flow, which avoids the pulsation interference of the conventional oil well pump, helps to suppress the sand production in the formation, and helps to reduce the interaction between water and oil phase in the high mobility ratio two-phase flow Infestation, play a role in reducing water output.
4. Carried out research on the mechanism of cold recovery of heavy oil PCP
Through the study of the mechanism of screw pump cold recovery, the following important understandings have been obtained:
1) Heavy oil has abnormal viscosity due to its non-Newtonian fluid properties.
2) The uniform suction movement of the rod pump avoids the intermittent start and stop of the heavy oil network structure, which makes the heavy oil form a continuous oil belt and reduces the water output.
3) Under the condition of small production pressure difference of the screw pump, the high oil-water mobility ratio of the heavy oil reservoir itself is alleviated, so that the water production decreases and the oil production increases.
4) Heavy oil reservoirs have a threshold pressure gradient, which decreases with the increase of permeability and increases significantly with the increase of crude oil viscosity.
5. Expand the oil recovery technology of the screw pump and expand the application range of the screw pump
At present, in addition to the large-scale implementation of the conventional screw pump oil recovery system in an oil field, the test and research of special screw pumps have been actively carried out, which has expanded the application range of screw pumps.
1) Electric heating screw pump oil production process
The electric heating screw pump oil production process integrates the screw pump and the electric heating device, which can not only give full play to the characteristics of energy saving, lifting and easy management of the screw pump but also can uniformly heat the heavy oil through the heating cable to improve the flow of heavy oil and oil production parts Working conditions, prolong service life, ensure the normal production of oil wells, suitable for popularization and application.
The system adopts the skin principle to convert electrical energy into heat energy, so that the whole hollow sucker rod generates skin heat, heats the crude oil in the tubing throughout, reduces the viscosity of crude oil, prevents waxing of the tubing, and reduces the load of the screw pump and the torque of the sucker rod, to ensure the normal exploitation of the “three high” oilfields.
2) Negative pressure oil recovery screw pump
Due to the impact of edge and bottom water, some oil wells have single-layer water flooding before or after the implementation of screw pumps, which seriously affects the production of oil wells. According to the characteristics of negative pressure oil production technology and the technical requirements of screw pump oil production in an oilfield, a 341+441 negative pressure oil production screw pump was selected, relying on the pressure to be transmitted step by step, and the seals were set in sequence to ensure the water shutoff packer and Effective fit between special anchors for screw pumps.
3) Apply screw pump to extract oil to realize mechanical finding of blocked water
Some oil wells have unclear water-producing layers, and water-seeking operations are required. According to the characteristics of the string for the water-blocking process, combined with the oil production process of the screw pump, the mechanical water-blocking screw pump oil production process test was carried out. The test results show that the oil recovery process is completely