September 24, 2015
Determining plunger velocity is an important part of plunger detection and can help protect your plunger lift system from dangerous high velocity impacts. One of the problems with current optimization and safety features in plunger lift programs is that they rely on the arrival time of a plunger to estimate the velocity of the plunger. These algorithms use the well depth along with the arrival time to calculate the velocity. This is not a very accurate measurement because two major assumptions are being made. Firstly, there is no certainty that the plunger is at the bottom of the well, and secondly, an assumption is made that the plunger is traveling at a consistent speed throughout the entire time it travels up the well.
The better way to safely and optimally operate a plunger well is to use surface velocity. The speed at which the plunger enters the lubricator determines the amount of impact on the anvil and spring. This is what should be monitored because this is where fast plungers can do the most damage. There is a new breed of sensors emerging that will tell you not only when the plunger arrives, but the velocity the plunger is travelling at. But how do we know if this is accurate?
At ETC, we have run many different plunger types at many different speeds. Collectively, this adds up to tens of thousands of plunger runs that have been monitored and recorded by the Cyclops plunger arrival sensor and Sasquatch plunger velocity sensor.
The plunger is pulled through a short run of tubing into a lubricator using an electric motor. The speed of the motor can be varied to move the plunger at a faster or slower velocity. The approximate speed of the plunger can be calculated based on the speed of the motor.
To further validate the velocity that the Sasquatch is reporting, independent measurements are taken using photo sensors. Multiple sets of holes are drilled along the tubing and photo sensors are inserted. These sensors are made up of two parts, a light emitter and receiver. This creates a beam of light across the tubing that is broken when the plunger passes by. We then take the timing between each set of sensors tripping to get the actual velocity as the plunger passes by. This can only be done in a controlled testing environment as holes cannot be drilled into tubing in the field, but it further validates the speed at which the plunger is travelling at the surface of the well.