BEAM PUMP (ROD PUMP)

 

Introduction                                                                                                   03

Parts and Components

Surface Equipments:

Prime Mover

Crank Shaft

Gear box

Beam Counter Weight

Hanger Assembly

Polished Rod Stuffing Box

Subsurface Components:

Down hole Pump

Tubing pump

Insert pump

Travelling and Standing Valve

Pump Barrel and Plunger

1.2       Beam Pump start-up operation                                                                   03

 1.3       Beam Pump Dynamometer                                                                          07           

1.4       Beam Pump Controlling and monitoring                                                                               09 

1.5       Beam Pump stopping operation                                                                  10 

1.6       Beam Pump trouble shooting

 

1. Basic System

 

Sucker rod pumping is the most widespread form of artificial lift used since the earliest days of the oil industry. The pumps are functionally the same as water-well pumps used as long as 1,500 years ago in China, Egypt, and Rome.

 

2. Basic Operation

 

In its simplest form the bottom-hole pump consists of a plunger working up and down in a closely fitted barrel.  The plunger contains a check valve that permits fluid flow upward but not downward.  Also called traveling valve, this check valve is usually of the ball-and-seat type in most modern pumps.

 

A second ball-type valve called the standing valve is located at the bottom of the barrel, and, like the check valve, allow fluid flow upward but not downward.

 

The ideal operating principles of the simple sucker rod pump can be demonstrated pictorially.  Initially, the plunger is stationary at the bottom of the stroke.  Both the traveling valve and the standing valve are closed at this point (Drawing No.1).  The fluid column imposes hydrostatic pressure in the tubing string above the travelling valve and in the pump barrel above the standing valve.

 

The load on the polished rod, that is, the top rod in the sucker rod string, and on the pumping unit is the weight of the rod string only.  As the plunger moves upward, the travelling valve remains closed, and the load of the fluid in the tubing is picked up by the rod string.

 

The load on the top rod and the pumping unit is now the combined weight of the rod string and that of the fluid column.  With minimal leakage between the plunger and the pump barrel, the pressure between the travelling valve and the standing valve is reduced, so the standing valve opens, allowing fluid to flow from the wellbore into the pump barrel. (Drawing No.2)

At the top of the stroke the plunger is stationary and both valves are again closed, so the fluid load is still being held by the plunger and the traveling valve (Drawing No.3).  Assuming that the pump barrel is now filled with fluid and that the fluid is incompressible, the traveling valve will open as the plunger starts downward.  The weight of the fluid column in the tubing will be transferred to the standing valve and the tubing, and the load on the polished rod and the pumping unit will again be only the weight of the rods.

 

 

Actual rod load diagrams used to evaluate pumping performance are called dynamometer cards.

 

 

3. Bottom-hole Pumps:

 

 

There are two basic types of bottom-hole pumps used for sucker rod pumping-Tubing pumps and Insert pumps.

 

The tubing pump is so named because the pump barrel is run on the tubing string.  The plunger is run into the well on the sucker rods.  The inside diameter of a tubing pump barrel is just slightly smaller than that of the tubing on which it is run, giving the highest pumping rate possible for a given installation.  Replacing the barrel of a tubing pump requires pulling the tubing.

 

The most common tubing and insert pump designs are controlled under API specifications.  Certain non-API pump designs- the casing pump and the multistage pump- have been shown to be effective under certain special well conditions.

4. Beam Pumping Unit:

 

The sucker rod pumping unit furnishes power in the form of reciprocating motion to the top of the sucker rod string.  The length of the stroke may vary from less than 1 foot to as much as 80 feet.

 

The relatively high rotating speed of the motor is first reduced by the belt drive and then by the gear reducer to rotation of the crank at the desired strokes/minute rate.  Rotation of the crank is converted through the crank arm, crank pin bearing, Pitman, equalizer, and equalizer bearing into reciprocating motion of the walking beam.  Walking beam motion is then converted to linear motion of the polished rod by the horse-head and hanger.

 

5. Surface Equipment:

 

 

Typical pumping well Christmas tree

The casing annulus should be equipped with a surface valve in addition to that on the casing gas vent line.  This valve may be used for fluid-level testing or the injection of defoamers, hot oil, or corrosion inhibitors.

 

Pumping Unit:

 

Although a number of different types of pumping units are used to furnish reciprocating vertical motion to the top of the sucker rods in a sucker rod pumping system, over 99% are beam pumping units.

 

The pumping unit structure includes the base and the Samson post.  In addition, the walking beam, equalizer, and Pit-man, which are parts of the operating mechanism, must be considered as structural members.

 

The base is a rigid structure supporting the loads of the prime mover, speed reducer, and Samson post and transmitting these loads uniformly to the unit foundation.  It must support these components and the operating mechanism while maintaining alignment for proper operation of the unit.

 

Actual foundation area and depth are dependent upon local soil conditions.  The foundation must distribute the unit loads to the soil so that there is no rocking of the unit during operation.  Drainage around the unit foundation should prevent rainfall or other water from soaking in around the foundation to weaken the soil support.

 

The Samson post is usually fabricated from three or four legs of rolled steel shapes.  It must support the walking beam, horse-head, equalizer, pit-man, and more than twice the peak polished rod load.  On top is the center bearing, or saddle bearing, which supports the walking beam.

 

The radius of curvature of the horse-head by design is the centerline of the center bearing.  The wire ropes forming the harness for the polished rod hanger form a tangent to the arc of the horse-head to provide linear motion from the oscillating motion of the walking beam.

Some conventional units have provisions for moving the walking beam relative to the saddle bearing.  This provision should be used only for adjusting alignment.  If used for changing stroke length, the center of curvature of the horse-head will not be the centerline of the center bearing, resulting in nonlinear motion of the polished rod.  Decreased polished rod life and decreased stuffing box packing life will result.

 

 Bearings

 

The center bearing and the equalizer bearing, or tail bearing, on the walking beam support oscillating loads, whereas the crank-pin bearing between the lower end of the Pit-man and the crank arm supports a rotational load.

 

 

 

Speed Reducer:

 

The purpose of the speed reducer is to convert the high-speed (300 to 1,200 rpm), low-torque output of the prime mover to the low speed (10 to 20 rpm), high torque required by the pumping system, a speed reduction of from 15:1 to 120:1.

This portion of the unit represents about 60% of the unit cost and, in operation, more than 75% of the unit failures.  It requires careful consideration in selection and in operation and maintenance.

 Prime Mover:

 

Counter Balance System:

 

The counterweight shown on the crank arm of the beam pumping unit is an important component of the system.  The counterbalance weight can also be placed on the walking beam, or an air cylinder can be used for the same purpose.  Pumping units can be described as beam-balanced, crank-balanced, or air-balanced.

 

The purpose of counterbalancing can be visualized by studying the motion of the rod string and the pumping unit in conjunction with the idealized pump operation illustrated previously.  In this simplified situation the load on the polished rod on the upstroke is the weight of the rods plus the  weight of the fluid.  On the down-stroke it is the weight of the rods only.

 

Without counterbalancing, the load on the gear reducer and prime mover during the upstroke goes in one direction.  On the down-stroke, the load is in the opposite direction.

This type of loading is highly undesirable, causing unnecessary wear and tear and power consumption.  In practice, a counterweight equivalent to the rod weight plus approximately one-half the fluid weight is used.  Proper counterbalancing results in the lowest loads possible on the gear box and prime mover, reduced failures and downtime, and reduced fuel or power requirements. Improper counterbalance results in unequal loading on the reducer and prime mover between upstroke and down-stroke, higher peak loads, and increased power requirements.

 

8. Controllers:

 

Since the optimum pumping installation design is matched to the inflow performance of the well to provide the desired rate of production, most sucker rod pumping systems will at times pump off and pound fluid.  The designer has included safety factors to ensure adequate capacity, almost always resulting in some over capacity in the pumping system when the system is in good working condition.

 

Time-cycle controllers or pump-off controllers are used to adjust the capacity of the pumping system to prevent fluid pounding while obtaining maximum production.  In practice, the time-cycle controller or pump-off controller is the final trim to optimize the outflow system design.

 

Time-cycle controllers: Time-cycling of the pumping unit was first accomplished by manually turning the pumping unit off and on. Selection of the duration of the on and off periods was by trial and error, frequently resulting in reduced production.  With increased use of electric power for pumping, automatic time-cycle controllers gained in popularity.

 

Earlier designs included a clock drive with pins set on a wheel to operate a control switch to turn the unit off and on.  This design was an improvement in control compared to manual control, but the accuracy of setting the duration of the off and on periods was limited.  Some sacrifice in production resulted.

 

 

Percentage timers:  Most modern pumping unit electric motor controllers are  equipped with a percentage timer to control the on-off cycle of the unit.

The duration of the total cycle is preset and fixed. The percentages of on and off times are then adjusted to give maximum production without fluid pounding.  For example, if the desired on period is 50%, the setting is 12 hours (out of a 24-hour day).  The unit will be on for 7½ minutes and off for 7½ minutes of the 15-minute preset cycle, resulting in a total on time of 12 hours each day.

 

 

Pump-off controllers.  The percentage timers will in most cases give the desired system capacity trim to provide optimum pumping system performance.  However, in some cases, as with a well that flows intermittently through tubing or casing (perhaps indicating an undersized pump), this type of control will still be inadequate, and occasional fluid pounding will occur.  In these cases, controllers that sense the pumped-off condition directly may be required.  Sensing of the pumped-off condition can be by various means: vibration, beam load change, motor load change, or polished rod load change.

 

Settings on this controller include set point, time off and minimum time on.  Set point is adjusted with the aid of a dynamometer recorder.  With this controller, any time the set point falls outside the load diagram, the unit will shut off.  Off time is set.  When the unit comes back on, it will pump for a set minimum time even if sensing a pumped-off condition.

 

“Pump-off  controllers”, however, are usually electronic devices with somewhat delicate sensors.  Operating and work-over personnel must be trained in proper care and handling to obtain good results with pump-off controllers.

 

Beam Pump operation:

 

Beam Pump start-up operation:

 

These types of pumps are driven by some sorts of surface pumping unit to furnish power to the sucker rods in the form of reciprocating motion. These surface units are mainly of two types. It could be an overhead electric motor driven, drive pulley and belts type or diesel or fuel gas driven engine type, which drives the generator for supply of electric power to the motor. Therefore, start-up sequence of the unit depends upon the type of power used to drive the beam pump. One of the main sources of surface pumping unit is electric power motor driven method. Hence here, we will discuss regarding the same:

 

A beam pumping unit transfers energy from the power unit to a sucker rod string.

The string of sucker rods transmits the energy from the beam pumping unit to the subsurface pump.

These rods are selected to be the lightest weight that can be used and still be strong enough to operate the pump efficiently.

The first sucker rod of the string is called the “Polished Rod”, and is usually very bright and shiny.

When the sucker rods move upward (upstroke) the trapped fluid is lifted to the surface through the tubing string.

 

Start Sequence:

 

Pre-start requirements are based upon, whether the start is after the initial well-completion, process alarm trip, and major shutdown/maintenance:

 

1. Initial start-up after Well-completion:

 

1. Get the new opening-up program from Area Programmer.
2. Confirm all the mechanical, electrical, Instrument jobs are completed and the area is clean and tidy.
3. Ensure that all discipline-crafts are available at site to assist start-up.
4. Conduct tool-box talks at site with co-workers as well as workers of other disciplines.

 

5. Carry-out the normal checking as per the commissioning check-list, if everything is normal, hand-over the well to the Production Supervisor.

 

 

1. b) After the process alarm trip:

 

1. i) check/identify the cause of the trip, if still ready to run signal is not obtained, re-check the pre-start requirement and rectify or report fault found until it is identified/normalized. Once ready to run signal obtained, Press Start Button.

 

1. If after a pre-set time limit the main motor started and tripped again, check further for electrical power supply and other safe-guarding system, like

vibration/high pressure switch(flow-line valve status).

 

• Further check for flow-line valves (may be valve closed, causes high pressure) or check due to high vibration.

 

1. If after the major shutdown maintenance:

 

Check for all normal   formalities,  like PTW, isolation/de-isolation, all well valves are lined-up as per requirements, electric power supply normalized, all control, protection and safe-guarding-systems are lined-up and are healthy. Once pre-start requirements are completed and if the ready to run obtained, Press Start Button.

 

Beam Pump Maintenance:

General

 

Production maintenance crews will carry out a half yearly preventive maintenance on all beam pumps as listed below:

 

1. Checks whilst the unit is running
   • Abnormal noise
   • Excessive vibration
   • Amperage down and needs balancing
   • Horse-head alignment and polished rod alignment

 

2. Maintenance Checks
   • Stop beam pump at 6 o’clock position.
   • Apply hand brake and insert brake latch (Lufkin).
   • Provide padlock on switch lever.
   • Remove gearbox inspection cover and check gears.
   • Check gear-box oil level, top up if necessary.
   • Check for evidence of oil leaks, and replace seals/gaskets as

necessary.

• Take oil sample, check of contamination if required by 2.4 above.
• Clean gear-box breather.
• Horse-head and polished rod alignment.
• V-belt tension and alignment.
• Check brake cables and balance, as well as brake shoe condition

and  replace/adjust as necessary.

• Balance unit if amperage is unstable.
• Grease all bearings
• Check hold down bolts.
• Check rotor foundation bolts.
• Check and tighten all other bolts.
• X-mass tree wing valve greasing and bolt tightness check.
• Check B.O.P.
• Stuffing box packing and victolic joint.
• Location valve/drain valve condition, check operation and grease.
• Pressure switch cut-off.
• Air compressor belt and guard (both units).
• Air cylinder and airline connection (both units).
• Diesel lube oil, fuel filter, radiator (both units).
• Apply lube oil on wire rope.
• Check general condition.
• Clear unit for start-up

Note: Most Preventive Maintenance checks on beam pumps are co-ordinates with maintenance Department (Instrument, Electrical and Mechanical).

 

Beam Pump Monitoring :

 

After start-up of a beam pump, the following parameters are to be monitored during the next couple of hours:

1. Check for any leaks in the unit, sucker rod traveling stuffing box, flow-line etc.
2. Check number of strokes per minutes.
3. Flow-line and casing wellhead pressure.
4. Motor current amperage reading.
5. If the pump is running on timer, check timings.
6. Motor winding and bearing temperature.

 

 

Typical Daily Checks:

1. Check for leaks, flow-line pressure.
2. Electrical power supply amperage reading of the drive motor.
3. Lube oil crank-case level check.
4. Battery charger and batteries.
5. Observe and listen for any unusual noise or vibration.
6. Record a full set of readings.
7. Compare the readings taken, with known normal operating conditions.
8. Record all known problems and report to the concerned department for corrective action.

 

 

Beam Pump stop sequence:

 

As it is motor driven beam pump unit, stopping the unit for operation and maintenance, there are very few points to be considered. If it is programmed for minor maintenance, proper isolation(electrically as well as mechanically) are to be done. If it is major maintenance or work-over repairs of the well, then the isolation procedure should be accordingly, like isolation (electrically as well as mechanically by spading or positive isolation by spool removal and blinding), then drive motor is stopped.

 

Basic problems and trouble-shooting in such well operations:

 

This section outlines a recommendation for identification and solution of typical Beam Pump Well Operations problems. The only way a failure can be analyzed and its cause determined is by data collection. When a problem occurs you simply cannot have too much information.

 

Information that should be routinely compiled on each such well includes production data (such as water, oil, and gas), run life, unit starts and stops, dynamic and static fluid level, and pump setting and perforation depth. Information also should be obtained on sub-surface equipment like, dynamometer readings/cards, visual observations of equipment and Bottom Hole Temperature.

 

When a Beam Pump Well is first put on production, data should be collected daily for the first week, weekly for the first month, and a minimum of monthly after the first month. Production data during the first month are very important because they will indicate whether the pump is performing as designed. If a down hole pressure instrument is installed, operating Bottom Hole Pressure is equally important.