How to solve the problem of partial wear of the rod string in deep wells?

The exploration and development of deep-seated oil and gas resources is the main way to realize the strategic succession of oil and gas resources in oil fields. Vigorously developing deep and ultra-deep well drilling technology is the need for oil and gas exploration and development.

Relevant data show that China’s recoverable oil resources are estimated to be 15 billion tons, about 8.5 billion tons to be discovered and proven, accounting for 57% of the proven recoverable oil resources. This part of the to-be-proven oil resources are mainly distributed in the four basins of Tarim, Junggar, Qaidam, and Tuha, which are the main replacement areas for China’s oil production. At the same time, 73% of this resource is buried below 5000 meters. Realizing the development of deep-seated oil and gas is an important means to solve energy problems.

Sucker rod pumping systems are the oldest and most widely used type of artificial lifting system for oil wells. Sucker-rod pumping is the most widely used artificial lift method for onshore oil wells. Sucker-rod strings transfer the motion from the driving machine on the wellhead to the downhole oil pump.

Pump diagnoses are generally conducted through an interpretation of the pump dynamometer graph (pump card), which is a plot of the calculated loads at various positions of a pump stroke. In deviated wells, mechanical friction becomes nonnegligible since there is considerable contact between rods, rod guides, and tubing. Hence, the dynamic behavior of the rod string is different for deviated wells and vertical wells.

Conventional rod pump oil recovery is the most widely oil recovery method in our country. There are more than 90% wells are mechanical oil recovery wells in China, of which rod oil recovery accounts for more than 90% of the mechanical oil production wells. In rod oil production wells, especially deep wells or deviated wells, the sucker rod is easy to bend in the tubing, resulting in partial wear of the sucker rod. Therefore, it is necessary to lower the sucker rod centralizer to solve the problem.

There are many types of sucker rod centralizers, there are two main categories: rolling centralizers and nylon centralizers. Rolling centralizers: when going down the well, the sucker rod centralizer is connected to the sucker rod string. With the up and down movement of the sucker rod string, the roller is rotated to reduce the direct wear of the sucker rod and the tubing. The roller rolls on the inner wall of the tubing. The rolling material uses a metal material with a higher hardness.

When sand or other mechanical impurities are produced downhole, the roller is often “stuck” during work to cause the centering failure. As the hardness is high, the tubing is worn, which intensifies the tubing wear. The other type is nylon centralizer.

Because it is made of nylon or other wear-resistant and friction-reducing materials, it is molded on the thin neck of the central axis of the centralizer or sleeved on the central axis of the centralizer. When going down the well, the sucker rod centralizer is connected to the sucker rod string, and the nylon is in contact with tubing to prevent the partial wear of the sucker rod and tubing.

Due to the low abrasion resistance of nylon, the service life of nylon centralizer is relatively short. When nylon wears to a certain extent, the centralizer will fail. After failure, the centralizer will not protect the sucker rod.
In order to solve the problem of partial wear of oil wells, improve the use efficiency and service life of centralizers. San Jack has developed a new type of sucker rod centering device. The new sucker rod centralizing device is composed of a centralizing body, upper and lower joints, and a centralizing outer tube. Its structure is as follows:

1 Upper joints
2 Centralizing Body
3 Outer tube
4 Lower joints

The new centralizer has a centralizing outer tube matched with it. The centralizing pipe is connected with the tubing by threads, and the length of the centralizing outer pipe is consistent with the stroke length of the sucker rod. The centralizer has an upper joint and a lower joint and they are provided with a plurality of side holes communicating with the internal holes of the centralizer. The centralizer is connected to the sucker rod by upper and lower joints.

When is use, first connect the centering outer tube to the design position of the tubing string, and then run the tubing into the well section with serious partial wear. The centralizing body is connected in series in the rod string of the sucker rod, and is lowered into the tubing, thereby playing a centralizing role.

During the pumping process, the centralizing body moves up and down in the centralizing outer tube to keep the sucker rod centered in the tubing, thereby playing a centralizing role and preventing the sucker rod from being worn away. The well fluid in the lower tubing of the centralizing body enters the internal hole of the centralizing body through the side hole of the lower joint, and is discharged into the tubing of the upper body of the centralizing body through the side hole of the upper joint, so as to realize the normal flow of the upper and lower well fluids.

This new type of sucker rod centering device has a simple structure, good centering effect, wear resistance, is not affected by downhole sediment or other mechanical impurities, and can be used repeatedly.