VERTICAL DRIVE HEAD

Brief Introduction

Surface Drive and PC pump (Progressive Cavity Pump) is a new type of artificial lift system, which finds more and more applications in the oil fields. Surface drive suspends and rotates rod string and power is then transmitted downhole, which in turn drives the PC pump.
PC pump consists of two parts: rotor and stator. The high strength, chrome-plated rotor is the only moving part of the PC pump. The stator is a kind of tube with elastic synthetic rubber molded inside. A variety of elastomer is available for different applications. When rotor rotates in the stator, a series of sealed cavities are formed and these cavities move axially from the intake end to the displacement side. When one cavity disappears at the displacement side, a new cavity will form at the intake side. Trough continuous formation, motion and disappear of these cavities, fluid is then brought to the surface. Owing to their unique features, the surface drive and PC pump find wide applications in the oil fields, and they are strongly recommended for high viscous, sandy, gassy and water bearing oil.

Schematic drawing of surface drive and PC pump is shown in fig 1.

Fig.1 Surface Drive and PC Pump

Major Parts

Surface Drive

The surface drive is a specific facility to suspend and rotate the sucker rod, which in turn drives the PC pump. Then fluid can be brought to the surface by the continuous movement of rotor within stator. When the unit is stop, the surface drive head absorbs reversion torque and prevents thread off. It is mainly comprised of parts showing in fig 2.

Fig. 2 Surface Drivehead（Single Motor）

Fig. 3 Surface Drivehead（Dual Motor）

Motor

A Y serial three-phase asynchronous motor is screwed tight on the motor skid and by changing the location of the motor, V-belt tightness can be adjusted effectively. Technical specifications are shown in table 1.

Primary Specification

Explosion-proof motor, VF motor, VF Explosion-proof motor can also be provided. Protection grade is rated as IP55 for the conventional motor and explosion proof grade as dⅡBT₄ motor shows wide speed adjust range from 0 to 100Hz.

Main technical parameters of commonly used NEMA series motors

Generally, the countries that implement NEMA motor standards are mainly North America, South America and other regions, and the commonly used matched motor access power is generally 3 ~, 60Hz, 440 ~ 480V and so on. According to the custom of NEMA motor, different explosion-proof grades and NEMA series protection grades are matched.

series surface drive specification:

Detailed technical parameter description:

Wet centrifugal brake system

Braking System:The action of the backspin brake will result in controlled recoil speed until the energy is completely released.

The braking system utilizes a patented totally enclosed backspin control system that will automatically work whenever the normal forward rotational speed is interrupted and forces the system to rotate backwards.

The braking system uses centrifugal force during backspin to engage the large shoes against a stationary housing.

The braking system is immersed in synthetic oil that controls fluctuating temperatures while lubricating all the internal moving parts.

Stuffing Box

Stuffing box on the drive head is designed for the purpose of preventing oil leak occurred at the polished rod. By pressing packing in the stuffing box, oil leak can be eliminated. Owing to the two-stage sealing feature of the stuffing box, packing can be changed even when the wellhead still bears downhole pressure.

By pressing the packings tight against the polished rod, oil leakage can be prevented from the packing box. The packing box has a secondary sealing device, which makes packing change possible under well pressure. Various types of stuffing boxes are designed for different solutions, such as threaded stuffing box, clamped stuffing box, wellhead type stuffing box and rubber valve type stuffing box. The wellhead type stuffing box can directly connect the lower part of the surface drive to wellhead. The whole unit becomes more stable in unit structure and system running due to its lowered gravity center. Flow tees are available if necessary.

Fig 9    Stuffing Box Types

Notes: All stuffing boxes are applicable for polished rod in φ38、φ36、φ34、φ32、φ28(notice: conversion to British unit)diameters, but after selecting the stuffing box, polished rod size need to be stated as well in the order.

Features：

• Packing seal is adopted to withstand large pressure, showing reliability and safe performance；
• The sealing type is similar to heavy oil stuffing box, making maintenance easy and convenient;
• Various types of connections are available for different types BOP and wellheads；
• The secondary sealing feature of the stuffing box makes packing change possible under well pressure. No need to drain pipelines. Well site contamination caused by oil leakage can be avoided.

Packing Change Steps:

Usually, the packings do not need to be changed, even if mild leakage occurs. Screw tight the press cap downward with tool until no leakage is found at the stuffing box. If the press cap can not be screwed down, then packing change is needed.

Fig 10    Stuffing Box

1. Stop the unit according to requirements, with all necessary tools ready;
2. When the wellhead completely stops, close tight the master valve and open the sampling valve to drain tubing pressure;
3. When tubing pressure is zero, loose the press cap. Take out the burnt packings with specialty tools, replace new packings and screw tight press cap again.
4. Close the sampling valve and open the master valve. Start up the unit according to requirements.

Note：Make sure wellhead pressure is ZERO when changing the packings. This can be done by drain pressure trapped in the pipelines, screw tight the secondary seal or the tie-down bolts of rubber vale.

Electric Panel

The electric panel controls and protects normal operation of the unit. General electric panel and variable speed control panel are available for use.

Drive unit operation control system:

The main function of the control cabinet is PCP well driving and control, taking into account the display and control of oil well pressure, temperature, casing pressure, dynamic fluid level and other technical parameters, with the control system to form closed-loop control, automatic adjustment, can be set according to different well conditions; At the same time, it can form PID automatic adjustment control with the level of downhole dynamic fluid level, or other control methods (such as timing production, fixed displacement production, fixed speed production, etc.). This series of control cabinet has outdoor use requirements, IP54 protection level, adopts double door design, perfect sealing function, adapt to the local all-weather outdoor use conditions in Indonesia.

Main technical description：

Drivehead-Vertical motor Install

PCP Drivehead-（MG seriers）

PCP Drivehead -Double motor series

•Dual motor Drive Head

Generally, it is matched with super-large power (75HP*2,100HP*2) driving device, which is applied in South America (Venezuela, Peru) and so on to drive deep well large-displacement screw pump. The driving device is a wet centrifugal brake system.

PCP Drivehead- Centrifugal brake

When reversing(negative rotation), the lock wheel 5 is detached from the brake shoe 4 and separated. The lock wheel 5 reverses with the main shaft and drive the brake shoe 4 turns. The brake shoe 4 reversal generates centrifugal force and along the screw 2 axial expansion, oil resistant pad 1 at this time in contact with the housing inner wall, thus producing brake force, the faster the reverse speed, the bigger the centrifugal force, the greater the brake braking force.

PCP Drivehead- Permanent magnet direct drive motor

• Low noise (test noise around 60dB (A)), simple structure and easy maintenance;
• Low energy consumption, high efficiency and low temperature rise;
• 0-500rpm stepless variable speed, fully electrical control.
• Adopt no-oil seal design, no lubricating oil leakage, etc.
• High torque, high overload capacity, can withstand 2 times of torque short time overload.
• Soft start: through frequency conversion control, the speed of the system starts slowly and smoothly, so as to avoid the damage of the rod column of the screw pump by impact force and extend the service life.
• Soft brake: with advanced and reliable built-in brake unit and brake resistance, the brake force can be adjusted automatically according to the reverse speed, and the elastic potential energy of the pump can be gradually released.