Rod pump drive

Abstract

This utility model relates to drive units for plunger-type borehole pumping units. Improved operational reliability of the sucker-rod pump drive is achieved by comprising an electric motor, a lead screw mounted in a bearing and kinematically connected to the motor shaft, and a housing in which the lead screw is inserted. A nut mounted on the lead screw is fixed to vertical guides. The nut is connected to a hollow rod, in which the lead screw is located coaxially. The end of the hollow rod is configured to accept a pump rod. The lower end of the housing has a central hole. The lead screw and nut form a "screw-nut" transmission with trapezoidal threads. The drive is equipped with a locking device that prevents axial movement of the lead screw. The threaded surfaces of the lead screw and nut are nitrided.

Description

[0001] This utility model relates to oil production equipment, specifically to drive units for plunger-type downhole pumping units. It can be used in the operation of sucker rod pumps (SRPs), the drives of which are located at the wellhead.

[0002] An electromechanical drive for a sucker-rod pump for a production well is known under Russian patent for utility model RU 160381, F04B 47 / 02, 2016. The drive contains a working screw with a ball screw drive inside the rotor of an electric motor, mounted vertically on a welded steel frame. Recirculating balls in the drive convert the rotary motion of the electric motor rotor into vertical reciprocating motion of the sucker-rod pump. The upper end of the working screw is connected to the lower end of a guide roller, which moves inside a fixed bracket with locking balls, which is fixed to the welded steel frame. The locking balls allow the working screw to perform only an up-and-down reciprocating motion, without rotation around its geometric axis. The rotor with the built-in ball screw of the electric motor rotates in bearing supports.A ball screw nut is rigidly secured in the rotor's central bore. Recirculating balls are located between the ball screw nut and the rotor screw. These balls directly convert the rotor's rotation into vertical, linear motion, alternating up and down. The rotor moves up when the rotor rotates in one direction and down when it rotates in the opposite direction. This reciprocating motion is generated by electrical limit switches mounted at the upper and lower stop ends of the drive, periodically changing the rotor's direction of rotation. A disadvantage is the drive's complex design, which requires its placement above the wellhead with a long overhang. This results in its large dimensions and the need for welded frames, foundations, and supports. Furthermore, the drive's ball screw transmission has limited load capacity and is unreliable.Low reliability is explained by additional stress on the nut from the bending moment acting on the screw relative to the supporting surface of the nut.

[0003] A borehole pump drive is known under Russian patent RU 2680478, F04B 47 / 06, 2019. The drive comprises a housing and a submersible electric motor with hydraulic protection, the drive shaft of which is connected to a screw-and-nut rolling transmission. The nut of the screw-and-nut transmission is movably connected to the housing and connected to a piston rod sealed within the housing. The internal cavities of the housing are filled with oil and communicate with the borehole cavity through an elastic shell. The drive shaft of the electric motor is connected to the screw-and-nut rolling transmission via a reversible gearbox with a shift mechanism. The shift mechanism consists of a rod connected to the nut of the screw-and-nut rolling transmission and the reversible gearbox; the rod has an end-position lock. The torque from the electric motor shaft is transmitted through the hydraulic protection shaft and the reversible gearbox to the screw-nut transmission screw, which, when rotated, causes the nut to perform a reciprocating motion.The nut thus transmits movement through the hollow piston rod, centralizer, and piston rod to the plunger pump. When the nut reaches its extreme position, it moves the rod, which switches the direction of rotation of the reversing gearbox. To prevent the switching mechanism from "sticking" in the middle position, when torque from the electric motor is not transmitted to the screw, an end-position lock is used to adjust and lock the rod to its extreme position. The disadvantage is the complex design and limited reliability of the drive.

[0004] A ball-screw drive for a sucker-rod pump according to Russian patent for utility model RU219805, F04B 47 / 02, 2023, was selected as the closest analogue to the claimed technical solution. The ball-screw drive for a sucker-rod pump includes a housing, a vertical shaft, a nut, a tubular rod, and vertical guides. The vertical shaft consists of an upper mounting section and a lower screw section. The screw section of the shaft is located in the housing. The shaft is mounted so as to be able to rotate relative to the housing. Rotation is ensured by mounting the vertical shaft on a thrust rolling bearing. The upper end of the shaft is located outside the housing. The upper end is designed to provide a kinematic connection between the shaft and the drive motor shaft, for example, by means of a coupling connection. A nut is mounted on the screw section of the shaft by means of a set of balls. The nut, together with the screw section of the shaft, form a ball-screw pair.The nut is mounted on the shaft so that it cannot rotate around its axis. Nut rotation can be limited by any known method, such as mounting the nut on vertical guides using carriages. A tubular rod is secured to the nut. The rod and the nut are mounted so that they can move vertically. The lower part of the rod is located outside the housing. The lower part of the rod provides a kinematic connection between the rod and the submersible pump rod. A ball screw allows for motion conversion. When the nut reaches one of its extreme positions, the direction of shaft rotation is reversed. A disadvantage of using a ball screw is that, when mounted vertically, such a drive lacks a self-braking mechanism, is complex in design, and has a limited load capacity.Low reliability is due to the risk of corrosion and the possibility of mechanical impurities entering the transmission, which can lead to ball jamming. Furthermore, the need for special masts and fixtures to install the drive at the well also reduces reliability.

[0005] The technical result is to increase the reliability of the sucker rod pump drive.

[0006] The technical result is achieved due to the fact that in the drive of a sucker-rod pump, containing an electric motor, a lead screw mounted in a bearing and kinematically connected to the motor shaft, a housing into which the lead screw is inserted, a nut is placed on the lead screw, mounted on vertical guides without the possibility of rotation, the nut is connected to a hollow rod in which the lead screw is located coaxially to it, the end of the hollow rod is made with the possibility of attaching a pump rod to it, and the lower end of the housing is made with a central hole, according to the utility model, the lead screw and nut form a "screw-nut" transmission with a trapezoidal thread, the drive is provided with a lock that prevents axial movement of the lead screw, the threaded surfaces of the lead screw and nut are made with a nitrided layer.

[0007] The technical result is achieved by using a screw-and-nut sliding mechanical transmission to convert the rotary motion of the electric motor shaft into the reciprocating motion of the hollow piston rod and the pump rod. Unlike a ball screw transmission, the screw-and-nut transmission allows for the use of trapezoidal threads, which are self-locking. This increases the reliability of the sucker rod pump drive because the transmission nut is held under load by friction, and when the vertical lead screw stops rotating, the nut locks in place. This prevents the nut from disengaging from the lead screw thread when reaching its extreme position during reciprocating motion along the lead screw axis. Drive reliability is enhanced by ensuring the reliable operation of the screw-and-nut sliding mechanical transmission elements.With this type of transmission, the bearing surface of the nut is not subject to additional stresses from the bending moment to which the screw is subjected with other transmission types. A constant load acts on the bearing surface of the nut. The lead screw, with its trapezoidal thread, has a high load capacity, ensuring reliable operation when lifting the rod string of a sucker rod pump. The use of a "screw-nut" sliding transmission, in which the nut performs translational motion along vertical guides along the longitudinal axis of the lead screw, eliminates the need for space for the screw extension. The absence of screw extension above the nut allows the drive to be positioned both inside and outside the well without additional frames and supports, which also improves drive reliability by eliminating additional structures subject to loads during the lowering and raising of the rod string.Furthermore, the absence of spatially extended drive supports on the surface allows for the placement of a locking device in the upper section, preventing axial movement of the lead screw. A locking device, for example, in the form of a wellhead rod clamp, positioned between the electric motor and the lead screw housing, prevents the lead screw from moving downward. Upward movement of the lead screw is limited by a bearing. This ensures that the lead screw only rotates and increases the reliability of the screw-and-nut mechanical transmission, in which the lead screw only rotates in both directions, and the nut only reciprocates. The threaded surfaces of the lead screw and nut have a nitrided surface layer, preventing jamming of the motion conversion mechanism when exposed to mechanical impurities on its working surfaces, and protects the threaded engagement from wear, increasing the reliability of the sucker rod pump drive.

[0008] Fig. 1 shows a longitudinal section of the rod pump drive.

[0009] Fig. 2 shows a cross-section of the rod pump drive.

[0010] The sucker rod pump drive comprises an electric motor 1, the output shaft 2 of which is kinematically connected to a lead screw 3, the lead screw 3 being mounted by means of a bearing 4. The drive is equipped with a clamp 5 secured to the wellhead 6. The clamp 5 serves as a clamp for the wellhead rod. The lead screw 3 is coaxially mounted in the housing 7. A nut 8 of a screw-nut sliding mechanical transmission is located on the lead screw 3. The threads of the screw 3 and nut 8 are trapezoidal. The threaded surfaces of the screw 3 and nut 8 are nitrided. In the housing 7, vertical guides 9 are installed along its inner surface of the underground part. The guides 9 are made in the form of keys that enter into corresponding grooves on the outer surface of the nut 8. A hollow rod 10 is fixed on the lower end surface of the nut 8, into which a lead screw 3 is coaxially inserted. The stroke length of the nut 8 is equal to the length of the lead screw 3. The upper position of the nut 8 is at the top of the screw 3, the lower position is at the bottom of the screw 3.A central hole is made in the lower end of the hollow rod 10 for mounting the pump rod 11 of the submersible pump. A hole 12 is made in the lower end of the housing 7 for the rod 11.

[0011] The rod pump drive operates as follows.

[0012] When electric motor 1 is running, shaft 2 transmits rotation to lead screw 3 mounted with bearing 4 in housing 7. Lead screw 3 performs rotational motion. Lead screw 3 is limited from moving in the axial direction. Downward movement is limited by clamp 5, which is a lock preventing axial movement of lead screw 3. Upward movement of screw 3, for example, when pump rods 11 jam, is limited by bearing 4. When lead screw 3 rotates, nut 8, fixed from rotation by guide keys 9, moves along screw 3. At the same time, hollow rod 10 and rod 11 of the submersible deep-well pump fixed on it move linearly along the axis of screw 3 and housing 7. When nut 8 reaches its extreme position, the engine changes the direction of rotation, and nut 8 moves in the opposite direction, changing the direction of movement of rod 11. The direction of rotation of shaft 2 of engine 1 is controlled using a controller (relay).When nut 8 reaches its extreme positions, the controller commands motor 1 to reverse the direction of rotation of shaft 2. This periodic reversal of shaft 2 enables continuous cyclical reciprocating movements of hollow rod 10 and rod 11 of the submersible pump. A self-braking mechanism, implemented using a trapezoidal thread in the screw-nut engagement, allows for adjustable drive stroke length, enabling the use of a single drive with pumps of different stroke lengths. A nitrided coating of the threaded surfaces of screw 3 and nut 8 prevents abrasion and corrosion.

[0013] Thus, the claimed utility model allows to increase the reliability of the rod pump drive.

Claims

A rod pump drive comprising an electric motor, a lead screw mounted in a bearing and kinematically connected to the motor shaft, a housing into which the lead screw is inserted, a nut mounted on the lead screw is mounted on vertical guides without the possibility of rotation, the nut is connected to a hollow rod in which the lead screw is located coaxially to it, the end of the hollow rod is made with the possibility of connecting a pump rod to it, and the lower end of the housing is made with a central hole, characterized in that the lead screw and nut form a "screw-nut" transmission with a trapezoidal thread, the drive is provided with a lock that prevents axial movement of the lead screw, the threaded surfaces of the lead screw and nut are made with a nitrided layer.

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