Oil separators perform a crucial task in upstream petroleum operations, but process control instability can cause product losses and downstream equipment fouling. One facility in Canada faced serious reliability issues with its oil separator, significantly reducing uptime and curtailing throughput.
In our article in the November issue of World Oil, titled “Production technology: How a minor instrument upgrade led to major oil separator savings,” Michael Cowan of Spartan Controls and I discuss simple instrumentation upgrades that not only resolved these reliability problems, but also significantly increased production.
Oil separator interface level
Three-phase separators are relatively simple devices consisting of a series of baffles and weirs that separate the mixed-phase feed stream into gas, oil, and water.
Figure 1. Oil separators at remote sites exploit the difference in specific gravity to separate incoming well fluids into gas, oil and water. A separation failure can cause lost product and limit site production.
One of the most critical measurements for an oil separator is the oil/water interface level on the left side of the tank. If the interface drops too low, oil will leave with water and likely be lost. If the interface level rises too high, water will flow over the weir and go to oil processing equipment, which is not designed to handle water.
In normal operation, the interface controller maintains a consistent interface level.
Interface controller issues
A remote well site in Alberta, Canada, was struggling with an increasingly unreliable pneumatic interface controller. Even after decreasing throughput to reduce separator loading and minimize process upsets, the controller still required frequent service calls, as many as 23 in a single year.
With help from Spartan Controls, an Emerson Impact Partner, site personnel decided to replace the problematic controller with an electronic model, the Fisher™ FIELDVUE™ L2t Liquid Level Controller. The new controller uses displacer technology to measure level, and it can regulate operation using traditional on/off or continuous control to provide a steady flow to downstream operations.
Figure 2. The recently introduced Fisher™ FIELDVUE™ L2t Liquid Level Controller from Emerson is a cost-effective replacement option for existing pneumatic controllers. It can be installed through a 2-in. hole in the side of a horizontal oil separator vessel, or through the top of a vertical vessel.
One advantage of the new controller was that its installation required no modifications to the vessel. Spartan Controls application experts also determined that the interface level control valve was a significant operations bottleneck, so plant personnel replaced it with a higher capacity valve and a digital positioner.
Figure 3. Replacing the existing control valve with a newer model dramatically increased separator throughput.
Dramatic improvements
The new equipment was installed and commissioned in short order, and the site immediately noticed significant operational benefits.
Performance and maintenance issues related to the interface reading went from 23 incidents a year to zero, and separator uptime immediately jumped to 99-plus percent. Separator control improved dramatically, allowing the site to take full advantage of the higher capacity valve, while increasing production significantly. These improvements resulted in a very quick return on investment.
Cutting-edge control
For well sites struggling with oilfield separator issues or interface measurement reliability, it may be time to consider an upgrade. As this case study shows, simple and inexpensive upgrades can have outsized impacts on uptime and production volume. Modern digital controllers offer many new control options, along with reliability improvements and remote data monitoring, to dramatically increase profitability.
Explore the features of the Fisher™ FIELDVUE™ L2t Liquid Level Controller with the virtual demo.
