Case Study: Optimizing Plunger Lift with an Electric Actuator
The primary motivation for the implementation of the electric actuator was operational efficiency. With the current conventional plunger set ups, the field relies entirely on pneumatics: using supply gas to actuate a multitude of valves. Stainless steel tubing (usually 3/8”) is used to pull gas off of a scrubber bottle upstream of a regulator. This gas is used to run the Kimray actuator and the solenoid valve. The solenoid valve receives the signal from the ABB (i.e., plunger logic) box and motherboard, telling it to send supply gas to the actuator.
The actuator itself is the valve that controls flow from the well; it continually opens and closes to stop or start a plunger cycle (the actual settings used to optimize these plungers will be discussed in subsequent sections of this document). The figure to the right shows the components of a typical plunger set up.
The main problem with this current set up is the fact that it relies on a steady supply of dry gas to run the pneumatics. Considering the fact that the plunger is (hopefully!) bringing liquid to surface, there is always the chance that the supply gas stream is not as dry as needed. When the regulator or the valve are running off a potentially wet gas stream, operational issues are encountered.
For example, condensate in the gas stream can cause o-rings in a valve to swell up around the piston that regulates flow. When this occurs, the piston is no longer able to move along its axis, and thus the valve is no longer functional. Operators can sand the o-ring to fix it temporarily, but this is a Band-Aid solution and does not address the root of the problem.
A wet gas stream can also cause the diaphragm to blow. When this happens, the valve cannot hold pressure to keep it shut, and thus it cannot properly regulate the actuator to cycle the plunger. Operators diagnose this problem by hearing gas constantly vent out of the valve.
Solenoid valves are prevalent across the field, with approximately one third of the wells in the field on plunger or intermitter as their form of artificial lift. By utilizing battery power instead of pneumatics, the electric actuator (in theory) would have significantly fewer operational issues by eliminating the use of solenoid valves to regulate flow. The end goal is to have operators spend more time optimizing plunger cycles and less time fixing faulty surface equipment.
THE ELECTRIC ACTUATOR
To address the issues that come with using pneumatics, operations trialed an electric actuator: the the R2L, offered and supported by Kimray, Inc. The timing of these installations will be covered in the next section. They sound great in theory, but how do they work?
The photos below show the R2L in the office with the actuator casing off so you can see the internal components, including the card, gears, and backup battery. The R2L uses the same valve body as the conventional pneumatic actuator and has a universal power input (24/115/230AC & 12/24DC). It has a battery backup and can be manually overridden.
The table below shows key characteristics of the actuator.
At the end of 2015, Kimray approached operations about trialing the electric actuator, citing sustained success other operators have had using them in New Mexico. Due to the lack of historical data for plungers on area wells, the decision was made to outfit the well with conventional plunger equipment from the onset. Doing so allowed operations to make sure the well would indeed respond well to a plunger before trying new equipment. Once the cycles started looking promising, Kimray allowed the client to trial the R2L with the option to purchase. Since it was installed in late February of 2016 (and purchased in May), there have only been a few minor hiccups to report. The results have been exciting and display the potential these actuators have for future implementation on a larger scale.
RESULTS & BENEFITS
The R2L electric actuator has proven to be a success. There are three main benefits to using the electric actuator over conventional pneumatic equipment:
1. As discussed, the primary motivation is to increase efficiency by reducing the amount of time operators have to spend fixing faulty solenoid valves and replacing top works on the actuator. This has been proven true.
2. Second, there is a significant cost savings opportunity. On average, operations is replacing two solenoids per well per year and one actuator top works per well per year because of wet supply gas (Note: this is an estimated average. In reality, some solenoids are operational for a longer period of time while others are replaced more frequently). With solenoids costing ~$300 and the actuator top works costing ~$600, operations is spending $1200 per year on replacement parts on average. While the electric actuator is more expensive upfront than its pneumatic counterpart, not having to continually buy replacement kits or new solenoids altogether presents an opportunity to save ~$1200 per year.
3. Another thing to note is the battery voltage. The ‘jail battery’, which is the primary source for the R2L electric actuator for this well, consistently stays between 12.7 and 14 volts. Even in periods of consistent rain recently, the battery has been able to keep up with the actuator since it has been in operation. The battery charges during the day and gets down to about 12.7 volts at night. Even though the R2L has the battery backup, if conditions continue to be as they have been for the last month, we should never have to use it.
In summary, the operations team received a recommendation from the vendor for improving operating costs and driving some efficiencies as these wells are moved towards artificial lift setups. Despite some initial hiccups that tend to accompany any new piece of equipment, two different options were tested and have ultimately been successful thus far, with substantial gains made in reliability. While not the least expensive piece of equipment, going forward the company will see prescient benefits in terms of OPEX, efficiency goals and an enhanced social license to operate via reduced fugitive emissions.