Well Operation and Automatic Controls
You may choose to operate your well continuously, or only run the submersible pump for part of the day. The well capacity and the amount of fluid you need to produce in a day will determine which is best for your operation.
In the past, pump controls were fairly simple and standardized. Computer controls have become much more popular, and allow for greater automation. New versions and control designs are common, however, it’s important to understand how your specific setup works.
Fig. 1: The wellhead of an electrical submersible pump. It includes a check valve, pressure gauge, union, ball valve, and a hose for monitoring production.
One of the more important parts of the wellhead is the check valve, which must hold when the electrical submersible pump is in operation. If the check valve leaks, the liquid can drain back into the formation. This can cause the pump to freewheel and turn counterclockwise while the well is shut in. If the power is turned on while the pump is spinning in reverse, the sudden torque can cause shaft failure. In order to repair the pump after that sort of failure, you’d need to pull the entire pump. To prevent problems keep an eye on the wellhead gauge, which will usually indicate if a problem is developing.
Well Installation and Controls
Deeper wells and wells that have higher production volumes will have more elaborate controls, as well more complex equipment. In Figure 1, you can see an electrical submersible pump that’s about as simple as it can be. It has everything such a well needs to operate, but on a marginally producing well, it would have a minor impact on the lease income in the event of problems. With a higher producing well, it’s usually worth it to invest in more complex systems. The more information you have, the easier it will be to recognize and analyze production problems and reduce downtime.
Running a Pump Full Time
To monitor a well’s production, you’ll want to install a chart at the wellhead. When the pump is operating continuously, the chart will have two steady lines on it. One indicates the casing pressure while the pump is running, and the other indicates the tube pressure in the flow line. You’ll want to keep an eye on the chart even when the well is operating normally. You’ll then have a set of baselines you can use to diagnose problems. Without the record that a chart provides, analyzing performance to identify problems is more difficult.
Figure 2. This chart shows a typical record of a pump in continuous operation. (courtesy of Reda Pump Company)
Running a Pump Part Time
There are some particular things to look out for if you’re only going to be running your submersible pump part of the time. When the pump isn’t in operation, the casing pressure will increase and the tubing pressure will be lower. When the pump is on, the reverse will be true, with the casing pressure dropping as the liquid level in the casing falls. Likewise, the line pressure in the tub will increase when the pump is operating. There are sets of diagrams that demonstrate what the chart will show if the pump is not operating normally.
Figure 3. A chart showing a typical chart record of a pump running only part time.(courtesy of Reda Pump Company)
When you do run into problems with a submersible pump, you’ll most likely need some special equipment. It’s also a good idea to have an experienced technician on site who can offer advice and weigh in on decisions.
When you pull the tubing, the cable clamps and bands should be removed, and the electrical line should be spooled onto a special trailer that has been brought to the lease for the workover. After servicing, the electrical line can be re-clamped to the outside of the tubing as it’s run back into the hole.
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