Design and calculation of a preliminary design of a piston-type pumping unit Cai Shimin ' Niu Quanyu Yu Ziyu Yu Chunyan (Jilin Oilfield Company Oil Production Process Research Institute) Li Guang Sha Li Wang Yuchao (Jilin Oilfield Company No.3 Oil Production Plant) (Jilin Oilfield Company Xinbei Oil Production Plant) and due to oil layer The sanding caused serious pump damage and pump accidents. Inspired by the sealing structure of the piston of the automobile cylinder, a new piston type oil pump sealed by a piston ring group was preliminarily designed. This type of pump consists of a pump cylinder and a piston. However, the required length of the supporting pump can be greatly reduced. A piston groove is formed on the outer surface of the piston, and an elastic steel inner and outer piston ring group with a right-angled triangle section is fitted in the groove.

The outer piston ring has four bosses on the upper end face, and adopts a special opening structure, which can freely adjust its outer diameter while ensuring the sealing performance; both piston rings provide a liquid inlet passage in the lower stroke and seal in the upper stroke. effect. Compared with the traditional pumping system, the piston type pump has small fluid flow resistance and high efficiency, and is particularly suitable for heavy oil lifting.

Key words: piston pump structure design features At present, the plunger pump widely used in major oil fields at home and abroad often causes leakage due to severe wear of plungers, valves, etc., as well as sand production caused by the oil layer. Serious pump damage and card pump accidents. This not only increases the workload of downhole maintenance operations, but also affects the normal production of oil wells. Therefore, there is an urgent need to develop a new type of oil pump.

The piston W in an automobile engine is very similar to the working mode of a plunger in a plunger-type oil pump. In addition to the harsh working environment of a piston of a suction pump plunger, all other parameters are loose, and the piston ring seal of a current automobile engine is still The technology is quite mature. In order to adapt the pump to the three-phase coexistent working environment of gas, liquid and solid, the structure of the piston pump plunger was modified, and a piston-type oil pump sealed by a piston ring was preliminarily designed.

Structure and working principle Piston pump is composed of pump cylinder and piston. See the structure diagram. The outer side of the piston is provided with a rectangular groove, namely a piston groove, and an elastic steel inner and outer piston ring group with a right-angled triangular cross-section is arranged in the piston groove, and the bottom angle a of the cross section of the two piston rings is equal.

In the absence of force, the inner diameter of the inner ring is smaller than the diameter of the piston groove, and the outer diameter of the outer ring is greater than the inner diameter of the chestnut.

Piston type pump structure - piston; 2 - outer piston ring; 3 - inner piston ring; 4 - pump piston ring adopts open structure, this structure of the piston ring can guarantee the sealing at the same time, can freely adjust its outer diameter The interface at the interface is inclined, so that it can be easily discharged into the sand, so that the piston ring will not lose its contraction function. When assembling the piston ring assembly, the inner piston ring is first fit into the piston groove with an interference fit, and then the outer piston ring clearance fits outside the inner piston ring. The outer piston ring mainly has three faces: an upper face, an inner face and an outer face. There are four convex blocks on its upper end face, and a rectangular slot on the outer side, which is mainly used for sand control, can accommodate sand into the gap between the piston ring and the vegetable bowl, reducing sand scratching the pump cylinder and card pump, and prolonging the use of the pump. life. The two piston rings provide the intake passage on the down stroke and the seal on the up stroke to lift the oil flow to the wellhead. External piston ring shape see. At present, the piston-type pump is still in the structural design stage, the next step is to prepare the indoor structure simulation test, and then conduct field tests, and finally promote the application.

On the upward stroke during the up stroke, the outer piston ring is mainly affected by 4 forces (as shown): the upper end face is covered by the liquid pressure P, the inner side is supported by the inner piston ring 7V, and the outer side is supported by the pump cylinder. Extruding force F and friction force /. Because JVsina draws the depth of pump A hanging pump, m; S - outer piston ring upper end area, m2; a - piston ring bottom angle, (°); k - outside The friction coefficient between the piston ring and the chestnut.

When the piston moves upwards under the pulling force of the sucker rod, the outer piston ring is co-acted with the pressure P of the overlying fluid and the downward friction force/. In order to balance these two downward forces, the inner piston ring gives the outer piston ring a support for the force W, and this force disassembles a horizontal outward force (AT sincO makes the friction between the outer piston ring and the chestnut/ Further increase, so that the downward force (P + /) of the piston ring is increased. In turn, it increases the supporting force W, and at the same time, the horizontal force (iVsina) of the piston ring is further increased. Finally, a very tight seal between the piston and the piston ring is achieved to adapt to different types of wells, such as sand-prone wells, which can be mined with a pump equipped with a smaller piston ring group to extend pump use. life.

External piston ring upstroke stress analysis down stroke When the piston starts to shift to the down stroke after the end of the stroke, due to friction between the outer piston ring and the chestnut, the outer piston ring will remain instantaneously static. When the piston descends to the four protruding blocks on the upper surface of the outer piston ring, the outer piston ring moves downwards under the thrust of the piston. The fluid under the pump will follow the gap between the two piston rings, and the piston and the outer piston ring will protrude The space around the block enters the chestnut until the end of the down stroke, then it goes to the upper stroke and lifts the fluid up to the wellhead. The schematic diagram of the down stroke operation is shown. Because the piston type pump adopts the annular liquid inlet channel, the cross-sectional area of ​​the channel is large. When the radial dimension of the channel is 3mm, the minimum area can reach 282mm2, which is equivalent to the area of ​​a round hole with a radius of 9.5mm. Compared with the traditional pump, the pump has a low fluid flow resistance and high efficiency, and is particularly suitable for heavy oil lifting.

The body density is 95kg/m3, vegetable diameter 44mm, friction coefficient ft is 0.02, outer piston ring inner diameter is 30mm, outer piston ring upper end area is 8.13xlO-V2; on behalf of the person, when the pump leakage is severe and the pump inspection operation is required, only Need to replace the piston ring. Therefore, the use of a piston pump can save a lot of work and maintenance costs.

Low manufacturing cost The piston seal section of the piston pump has only the piston ring section, which is shorter than the original long piston. In the case of the same stroke, the length of the pump barrel can be shortened accordingly. In addition, the use of a skip valve eliminates the occurrence of undesirable phenomena such as gap leakage, valve opening delay, and the like, and simplifies the plunger structure, thereby significantly reducing production costs.

Applicable to high-gas, heavy oil and sand production oil and gas mining piston pump can enter the next stroke can enter the liquid, there is no hysteresis, but also to avoid the traditional oil pump air lock phenomenon.

The piston type pumping chestnut adopts an annular liquid inlet channel, which is larger than the conventional liquid inlet channel of the oil pump and has a low liquid inlet efficiency, and is particularly suitable for heavy oil extraction. The sealing section of the piston-type oil pump is much shorter than the conventional oil pump, and it has a sand control groove, which reduces the possibility of sand cards and can be safely used in sand production wells.

Piston ring seal combination can be serialized for different types of wells, and piston ring combination series with different bottom angles a can be used to achieve different sealing effects and meet production needs.

The low cost of retrofitting can be achieved by replacing the traditional pumping pump plunger with a low-cost piston-piston ring structure on the basis of the original pump cylinder, ie, transforming it into a piston-type pump.

In the process of pumping down, how to prevent the piston ring of the piston pump from falling off has not yet found a solution.

In order to achieve the cooperation with the existing pump cylinders, the selection of piston ring materials and the treatment of the mating surfaces, further experiments are needed.

In order to prevent the piston from oscillating around during operation, the sucker rod above the pump must be installed with a centralizer. The specific installation position and number of the centralizer need to be experimentally studied.

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