As a mechanical oil production equipment, screw pump has advantages that other pumping equipment cannot replace. It is mainly suitable for the exploitation of gas wells with heavy oil, sand and high gas content, and has the important characteristics of small volume, convenient installation, no pollution, low energy consumption and easy popularization.
in recent years, with the development of high-viscosity crude oil exploitation and tertiary oil recovery, screw pump has been widely used, and the workload of screw pump wells has been increasing, and the operation technology has been developing.
I. composition of screw pump oil production system
according to the basic structural form of screw pump, it can be divided into single barrel type and series type, and according to the driving mode, it can be divided into two types: surface driving and underground driving. The ground-driven screw pump mainly has two forms: belt drive and direct drive. Downhole drive screw pump can be divided into two forms: electric drive and hydraulic drive. At present, the surface-driven downhole elastic screw pump oil production system is widely used in oil fields.
the ground-driven downhole single screw pump is mainly composed of four parts: the electric control part, the ground-driven part, the downhole screw pump and supporting tools, as shown in Figure 1-1.
Figure 1-1 Schematic Diagram of Single Screw Pump Oil Production in Ground Driven Downhole
1- Electric Control Box; 2- motor; 3- belt; 4- square clip; 5- Balance block; 6- pressure gauge; 7- sucker rod; 8- tubing; 9- centralizer; 1- dynamic liquid level; 11- screw pump; 12- casing; 13- Anti-rotation anchor; 14- sieve tube; 15- plug; 16- reservoir
(1) electric control part
The electric control box is the control part of the screw pump well, which controls the start and stop of the motor; Record the current and accumulated running time of the screw pump well during normal production; It has automatic protection function for overload and underload.
(II) Ground driving part
The ground driving device is the main ground equipment of the screw pump oil production system, and it is a mechanical device that transfers power to the rotor of the downhole pump to realize pumping crude oil. The driving device of mechanical transmission is mainly composed of reducer, motor, sealing box and square clamp.
(3) Underground screw pump
1. Structure of ground-driven single screw pump
It is mainly composed of stator, rotor and limit joint. The stator is made of high-quality steel shell filled with rubber, and the rubber sleeve has a double or multi-line spiral surface; The rotor is a single-headed or multi-headed spiral surface made of high-strength steel, and it is meshed with the inner surface of stator rubber after hard plating to form a sealed cavity. The stator goes down with the tubing and is anchored, and the rotor is connected with a sucker rod.
2. Working principle of ground-driven downhole single screw pump
The motor and driving device make the sucker rod rotate clockwise, and the sucker rod drives the rotor of the downhole screw pump to do planetary motion in the stator bushing; When the rotor moves, the oil-absorbing sealed cavity moves up from the oil-absorbing end in the axial direction, and a new sealed cavity is formed at the same time. The sucked liquid moves from the suction end to the discharge end with the upward movement of the sealed cavity. The continuous formation, upward movement and disappearance of the sealed cavity plays the role of a pump, lifting oil, sand, water and gas to the ground together.
(4) Supporting tools
(1) Special wellhead: it plays the role of protecting polished rod and sealing wellhead.
(2) polished rod: used for wellhead sealing.
(3) sucker rod centralizer: avoid or slow down the wear of sucker rod and oil well.
(4) tubing centralizer: it can reduce the vibration and wear of tubing string.
(5) Anti-reverse device of sucker rod: to prevent the sucker rod from reversing and backing off.
(6) tubing anti-drop device: anchor the pump and tubing to prevent tubing from falling off.
(7) Wax preventer: delay the deposition rate of paraffin and colloid in crude oil on the inner wall of tubing.
(8) anti-evacuation device: insufficient liquid supply in the formation will cause damage to the screw pump, and the installation of wellhead flow or pressure anti-evacuation device can effectively avoid this phenomenon.
(9) sieve tube: filter reservoir fluid.
II. Model and basic parameters of single screw pump
(I) Model representation method of single screw pump
Marking example:
GLB12-14 is a single barrel single screw oil pump with a nominal displacement of 12mL/r and a total stage of 14, and the sucker rod rotates.
(II) Basic parameters of single screw pump
See Table 2-1 for the basic parameters of single screw pump.
table 2-1 basic parameters of single screw pump
iii. characteristics of screw pump oil production system
screw pump is a positive displacement pump with few moving parts, no valve parts and complicated flow channels, small oil flow disturbance and even displacement. Because the cylinder rotor moves on the inner surface of the stator rubber bushing with rolling and sliding properties, the sand particles in the oil are not easy to deposit, and at the same time, the swabbing and pushing action caused by the uniform volume change between the rotor and the stator makes the oil-gas mixed transportation effect better, which has unique characteristics compared with other oil recovery methods in the production of crude oil with high viscosity, high sand content and high gas content.
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