Essential Information for Operating and Servicing Pumping Units in Oil & Gas Production
It may come as a surprise, many of the lively oil wells in the world are only slightly producing wells converted to artificial lift systems. In fact, the portion of wells using mechanical lifts is so high, most (if not all) wells on multiple leases utilize pumping units. Why? Because mechanical lifts are both reliable and straightforward to run.
Therefore, the majority of lease pumpers favor this method over all other types of artificial lift systems. To understand more about the maintenance and services required for these dependable devices, operators should understand these basic pumping unit fundamentals.
Electric Prime Motor Mechanical Lifts
Wells using electric prime motor mechanical lifts are both easy to learn how to operate, and to program to full automation. Generally, in electrical control setups (see Figure 1) the power line will carry the electrical energy to an area close to the site, but away from the guy line location.
Usually an underground power line with a mounted fuse panel (in most cases this is at the rear of the pumping unit). Many locations also utilize a second electrical panel, which is typically equipped with an on/off switch, automatic control box, and is placed on a post. Lease pumpers should be able to comprehend the mechanics and how to run each of the components, as well as how to identify any issues that could occur.
Natural Gas Engine Mechanical Lifts
Natural gas engine mechanical lifts are fairly dissimilar from electrical prime motor units. This is particularly true for wells using the gas from the well for its fuel supply. With these conditions, lease pumpers need to vent the gas within the well not being utilized for fuel in order to try and sustain the formation backpressure. The goal is to be as close to zero as possible.
In most cases, lease pumpers are on site each day for 8 hours or less. Therefore, in situations where workers utilize manual controls (ex. starting or stopping the controls manually), only a limited amount of schedules are available for the pumping unit. While a pumping unit can operate 24/7, it does not mean it will result in a higher oil production.
Another option for lease pumpers is to turn on the pumping unit right before they leave, while shutting it down once they arrive the following day. This results in roughly 16 hours of operations, and can also cause lower overall oil production.
The last option is to run the unit throughout normal business hours. During this timeframe, the lease pumper can utilize multiple scheduling options. This includes 8 hour on/off cycles, running continuously, or other scheduling options. However, the most capable approach is for the lease pumper to utilize an engine controlled approach. This approach permits the engine to operate automatically without anyone having to be present (including starting and shutting down).
Engines provide options not available for electric motors. For instance, by setting the controls, the pumping unit can be positioned to tag the bottom within as close as 1 inch. However, if the pump is unable to pump oil, raising the engine RPM will cause the rod to stretch and the device to tag the bottom. After the pump has re-established operations, the worker can fine-tune the RPM to avert issues with tapping the bottom.
In order for the best possible operation reliability, the pumping unit engine must be modified accurately. When workers do not use a proper maintenance schedule, it can (and will) end in a production loss, as well as add additional responsibilities to the worker’s already hectic schedule.
Rotation Direction
It is very common for companies to change the rotation direction of conventional gear-driven, walking beam pumping units either every six months or annually. This prevents the wear and tear to the gears by changing the forces that cause the wear to these parts, and applying it to the opposite sides of the gear teeth. This is typically accomplished by reversing the connection of any two three-phase motor wires. Note that this option is not available for natural gas pumping units.
Many pumping units (like the Mark series) utilize weights that must rise toward the wellhead during operations. Generally, chain drive gearboxes will usually require unit counterweights in order to move in a specific direction and to properly lubricate the gearbox.
Lease pumpers should also record the rotation direction for each pumping unit in the field manual to ensure the pumper can alert the person replacing the motor of the unit’s rotation direction prior to the issue.
Timing Controls
There are two main categories of pump operation timing controls:
- 24-hour clocks can be utilized for operating the pump within a given time frame, and
- percentage timers which can typically be found in many of the newer automatic control box options
24 hour clocks come in several different styles. For example, some can be controlled to cycles of 15 minutes on and 15 minutes off; while other timing controls can be set for smaller intervals (time frames less than 5 minutes). These types of clocks are great for setting pumps to operate with irregular pumping cycles or for operating at specific times of the day.
Percentage timers are available to use for cycles consisting of 15 minutes or more. They have one control dial granting the lease pumper the ability to set the timer to operate for a specific percentage of the cycle. For instance, if the percentage timer is set for 15 minutes at 50 percent runtime; the pumping unit will operate for 7 ½ minutes, then shut off for 7 ½ minutes during each 15-minute cycle period. With 96 15-minute intervals in a day, the pumping unit will run for 7 ½ minutes for each of the 96 cycles throughout the day. The same goes for other percentage timers.
For example, a 2-hour timer set for 25 percent runtime will continually operate for 30 minutes, and shut off for 90 minutes during each cycle. This repeats 12 times per day resulting in a total runtime of 6 hours (or 25 percent).
Pumping Schedules
In order to figure out the most suitable schedule and exactly how long a pump should run in a 24-hour period can be tough. For instance, if a well is producing both water and oil, and requires a 12-hour pumping day for the highest oil production; the worker can utilize several different schedule options to reach this goal. These schedule options can include:
- Around the Clock Cycles of 15 minutes operating and 15 minutes without operations
- Around the Clock Cycles of 30 minutes operating and 30 minutes without operations
- 12 Cycles of 1 hour operating and 1 hour without operations
- 6 Cycles of 2 hours operating and 2 hours without operations
- 2 Cycles of 6 hours operating and 6 hours without operations
- 1 Cycle consisting of 12 hours operating and 12 hours without operations
During periods when the well is not operating, the liquid level builds up in the casing at the hole’s base. As the levels increase, the column weight increases causing a buildup of the backpressure; as the backpressure rises, the rate of oil production will decrease until the backpressure is equivalent to the hydrostatic pressure (which will stop all operations).
Therefore, there is specific timeframe to allow the fluid to collect, any amount of time beyond that does not create an increase in oil production. Hence, whether you operate for 20 minutes an hour or 12 hours per day, the overall results can create the same outcome only requiring 8 hours of production time. Therefore, if the unit is able to pump the entire oil accumulation to the surface utilizing only 30 minutes of operation, then there is no reason to operate the pump for longer than one hour or more for each cycle.
Then again, if the lease pumper operates the pump without permitting the fluid to accumulate completely, it can decrease the backpressure, allowing a more stable hydrocarbon flow.
For instance, if the formation flow rate drops each hour by half the oil flow, until the flow ceases around 18 hours. Afterwards the well typically takes around 6 hours of operations to eliminate the fluid buildup. In these instances, a typical pumping schedule may consist of operating the pump for 6 consecutive hours per day.
Nonetheless, operating the pump more often will help keep the back pressure from accumulating, and helps maintain a greater formation flow rate. An example of this would be having the pump operate for 15 minutes (or more) every hour, equaling a total of 6 operational hours per day. This in turn helps to prevent the formation flow from stopping and results in a better possibility for higher overall production. That said, it is important for the lease pumper to remember there are multiple financial factors to consider prior to creating the ideal pumping schedule.
Pumping Unit Maintenance
To properly maintain a pumping unit, one of the first things the lease pumper should do is create a proper maintenance schedule (including daily, weekly, and monthly inspections) and to stick to it. This information should also be recorded into the GreaseBook app to help the lease pumper make certain the proper procedures are performed.
For example, many supplies store offer a wide variety of lubricants. They can have different additives, weights, even the container types used. During each on-site application, there are typically only a small amount of lubricant options appropriate for use; and often times, only one is really suitable for the task.
It is unrealistic to expect lease pumpers to recall every type of required, and/or the exact location each lubricant should be used. To help ensure the proper lubricants are used, accurate and complete record records should be maintained. This can help assure the correct quantity and lubricant type is applied, as well as when the lubricant should be changed out. Furthermore, it can prevent mixing non-compatible lubricants with one another.
Daily Inspections
One of the positives of oil field equipment is its reliability, and with the proper maintenance can function for years before experiencing any serious issues. However, in order to prolong the unit’s life expectancy, daily inspections should be performed to locate any issues prior to occurring damage.
When making inspections, lease pumpers should ensure the radio volume in the vehicle is completely down (or shut off). By listening carefully, you can determine a great deal about the pumping unit’s condition. Lease pumpers should also include checks for: leaks (ex. lubricating oil) or loose objects (ex. nuts, bolts, washers, etc.) in their daily inspections.
Weekly Inspections
Weekly checks should include the following:
- Perform Daily Inspection Steps
- Observe the Pumping Unit (make sure to completely walk around the unit)
- Stop at Proper Observation Points and Watch Each Component for One Entire Rotation (The lease pumper should be looking for any signs of unusual motion, uncommon noises, or vibrations.)
- Examine the white safety line to ensure the pitman arm safety pins are correctly aligned. (For more information see Gearbox and Pitman Arm Issues below.)
Monthly Inspections
Monthly inspections should include:
- Completing the weekly check duties
- Examining the gearbox fluid levels (helps to determine if any leaks are present)
- Lubricating any worn components such as the pitman arm bearings, saddle, or tail.
Quarter and Semi-Annual Inspections
Quarter and semi-annual inspections are essential. This is especially true for many new units, as many of these devices require semi-annual lubrication procedures (as shown in Figure 4).
As the pumping unit gains wear over time, it will require the interval to gradually change first to five months, then four, and eventually every three months. However, some units may require monthly lubrication, as well as additional special maintenance requirements in between lubrications. A portion of these examinations are performed during operations, while others require the unit to be completely shutdown and to set the brake lever.
Gearbox and Pitman Arm Issues
There are a variety of harmful pumping unit situations, but the two typically causing the most damage include when the pitman arm comes loose, and when the gearbox gear teeth are stripped. Therefore, it is essential to provide extreme care when changing the stroke length (see Figure 5).
This includes accurately cleaning, keying, lubricating, and tightening the crank pin bearing wrist pin. If for some reason the nut were to loosen and fall off; it will damage the hole in the crack, triggering the walking beam to twist and breaking the wrist pin.
The lease pumper should have a white safety line painted across one nut face. It should be placed stretching from counterweight to the safety pin, as well as on the crank for several inches. This allows the workers to recognize any alignment alterations of the components — both during operations and downtime.
As daily inspections are performed, pumpers should make not of even the slightest changes that could indicate a nut (or other components) is coming loose. After a stroke length change, workers should inspect nuts and other components on a daily basis for movement starting the very first week.
Lease pumpers should always pay close attention when examining the gearbox oil level, making sure to check the oil for metal shavings. You can obtain small samples from the plug or lower petcock.
Typically, you can detect metal shavings by placing a small amount of oil onto a clean, dry cloth. If the pumper discovers any metal shavings, the worker should remove the cover, flush and clean out the gearbox, and add new oil.
Occasionally, workers should remove the gearbox cover (typically at least once annually) and closely examine the gearbox interior using a flashlight (see Figure 6), particularly when it comes to chain-driven units.
Lease pumpers should always look at the lubrication troughs. This helps to ensure the appropriate oil levels so every bearing receives the proper quantity of oil needed to engage all the necessary components (ex. gears, oil dippers, etc.). Periodically workers should change the oil out, clean the filter, and remove any water or sludge that has accumulated.
Oil in the Gearbox
Pumping units have a variety of sizes, styles, gearboxes, and types of gearbox oil. This can include: chain drives, double-gear drives, and single-gear drives. In addition, each of these gears contain dippers, and with each rotation the dipper will pick up the oil, carry it, and empty it into a lubrication trough (allowing for the four shaft bearings to be lubricated). However, poor maintenance can cause a variety of problems. This includes:
- Accumulating Sludge — typically caused by aged oil, incorrect additives, or mixing oil
- Difficulty Starting — typically caused by low oil or overly viscous oil, especially in cold weather
- Foam — typically caused by an overfilled gearbox
- Gear Wear — typically caused by contaminants (ex. bits of dirt, metal, etc.) in the oil
- Poor Lubrication — typically caused by low oil levels
- Rust — typically caused by water in the oil
- Poor Gear Surface Coverage — typically caused by overheating the oil, or too thin of oil
In most cases, these issues can be corrected by properly flushing the gearbox and completing an oil change.
Understand, not only is it vital for operators to recognize the various problematic pumping unit indications, but also how to fix these issues!
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