Plunger velocity is the key to safe and optimized plunger lift operation. Historically, plunger lift control systems have recorded the time it takes the plunger to travel from the bottomhole bumper spring to the lubricator, where a plunger arrival sensor is installed. Using this time and the well’s depth, the average velocity is calculated. This velocity is used to shut in the well on one or more high-speed impacts to protect the lubricator from damage. Extremely high-velocity impacts can compromise the spring and lead to potential lubricator breaches.
Many operators use the average velocity to reactively adjust for fast- or slow-moving plungers. Sales time or shut-in buildup times are adjusted to modify the amount of fluid brought to surface in each trip to maximize production. Using average velocity has become an accepted practice based on the technology available. However, the available technology means a lack of visibility when it comes to plunger lift operation. Historically, there has been no way of detecting when or if the plunger reached bottom, how much the velocity changed as it ascended, and its velocity when it impacted the spring inside the lubricator.
Instances where the plunger rapidly accelerates at surface can be ignored by the control system because average velocity over the entire depth of the well is used. If the plunger’s surface velocity is much faster, it puts undue wear on the surface equipment. This leads to lubricator springs and plungers being prematurely replaced, resulting in increased operating costs.
Conversely, if the surface velocity is much lower than the average velocity, the control system may have unnecessarily shut in the well. Extended shut-ins reduce overall production and create volatility in the production profile. This cost can be amplified because of remote location access restrictions, multiple plunger lifts going into the same line, distance to the compressor or facility restrictions. One well’s inconsistent production profile can cause increased pressure fluctuations, which in turn destabilize entire fields. This single issue can cause lost revenue and production for hours, days, weeks or even months in remote areas.
Plunger Velocity Sensor
The most recent advancement in plunger lift technology is the introduction of the plunger velocity sensor. This new type of sensor not only detects the plunger’s arrival, but also its velocity as it passes by the sensor. It allows operators to finally see the plunger’s velocity at the surface as it impacts the lubricator spring, leading to increased safety, lower maintenance costs and increased production.
With the release of the SasquatchTM Plunger Velocity Sensor operators can finally see the surface velocity without having to make assumptions. So, what has been seen so far? The data confirms that the plunger rapidly accelerates at surface due to gas expansion in many cases. We also found cases where the surface velocity was well above or below the anticipated velocity. In these cases, the operator believed the plunger lift system was running safely and consistently because they were monitoring the average velocity.
In our third case, a well in Canada appeared to be operating properly. When the Sasquatch was first installed, the plunger did not appear to be detected consistently. In reality the plunger was not making it to surface in time and was not being detected by the existing sensor. The controller would shut the well in longer in an attempt to build pressure. The result was an exceptionally fast plunger at surface the next cycle. Once again, the controller was seeing a slower average velocity and the operator was not aware of the problem.
The conclusion is that the surface velocity does not always track the average velocity and operators have to be careful what assumptions are being made. By monitoring surface velocity, we can learn how the system is performing and what impacts the spring at the top is actually taking. Using this information, we can start to see ways to optimize production and improve safety, whether manually adjusting system parameters or adopting an algorithm that uses the surface velocity to smooth out the cycles and automatically adjusts to maximize performance.
INNOVATIVE
Sasquatch is the next stage in the evolution of plunger detection. As the first ever plunger velocity sensor, not only will Sasquatch signal that a plunger has arrived, actual velocity of the plunger will be calculated at surface. Repetitive fast plungers are a common problem in plunger lift causing production downtime and costly damage to equipment. A lubricator breach can lead to incident reports, spills and injuries. Sasquatch gives you the power to prevent these occurrences by enabling detection of fast plungers long before they cause problems.
The unique design of Sasquatch is based on the proven technology behind the Cyclops plunger arrival sensor. ETC’s innovative line of plunger sensors provide advantages that no other plunger sensors offer, such as the ability to adjust sensitivity and upgrade or troubleshoot problematic wells right at the well head.
RELIABLE
Sasquatch is built to sustain extreme cold and hot temperatures, operating reliably from -40oC to +70oC (-40°F to +160oF). Sensitivity is adjustable to accommodate a wide range of plungers and lubricators, eliminating missed arrivals. An embedded micro-processor filters out environmental noise caused by nearby equipment or electrical storms, minimizing false detections. A rugged watertight aluminum enclosure protects Sasquatch from the elements, and built-in mounting provides snug and secure installation on a lubricator.
VERSATILE
Sasquatch features a ½” NPT port to connect either a Teck connector and armored cable, or a standard cable gland and instrumentation cable. Sasquatch operates over a wide range of input voltages, simplifying inventory management.
OPERATION
Sasquatch is based on the trusted technology of the Cyclops plunger arrival sensor, which uses a modern magnetic sensor for detection, as opposed to a traditional coil. An intuitive patent-pending algorithm allows the sensor to quickly and accurately calculate actual velocity of a plunger as it travels by Sasquatch. Up to 120 arrivals with date, time and velocity information are available to download right from the unit on-site. Sasquatch can also be connected to your SCADA system for real-time remote access.
COMMUNICATION
Sasquatch speaks Modbus! An integrated communications port provides access to current and historical information regarding plunger arrivals and velocity readings. This port also allows for communication with Vision Device Management software for testing & troubleshooting.
CASE #1
In one instance, we worked with a major producer in the San Juan Basin to install the Sasquatch on a well that they believed was operating optimally. On this well, the controller was optimizing to a target average velocity of 750 ft/min. Using the Sasquatch, the automation system recorded surface velocities greater than 1200 ft/min, 60% higher than the average velocity.
Once the faster surface velocity was identified on this well, it allowed the operator to adjust the control parameters to ensure that the surface velocity was safe given the equipment specification. Also, identifying that the surface velocity could change dramatically on some cycles showed that more fluid was being produced on these cycles. This is an opportunity to increase production and reduce maintenance by spreading the fluid load evenly across all cycles.
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