Troubleshooting the separators.

An underperforming separator is a common problem in the upstream processing plants. Several different types of separators can be met in the oil and gas fields. Typically, they are gas/liquid type or liquid/liquid type separators. When a separator starts to underperform, it requires troubleshooting. First, the effect of poor performance is observed. Then the cause for it should be identified. Possible solutions have to be evaluated based on the collected data.  

Effects:

Separator performance negatively affects the downstream process equipment when the effluent streams are out of spec, such as:

• Too much liquid in the separated gas.
• Gas blow-by to the liquid outlet.
• Too much oil in water/ too high content of BS&W in oil.

  The need to troubleshooting comes up when either the one or more of the mentioned conditions occur due to degraded performance over time, or when the operating conditions are no longer within the original design envelope. Changes in the operating conditions may be due to introduction of subsea tieback. Alteration of production stream composition due to waterflooding front break-through to the production wells is among other conditions.

Causes:

Separators may underperform at given operating conditions due to various reasons. Most common are:

• Wrong type of equipment was chosen in a first place.

Right type of equipment was chosen, but sized incorrectly.

• Operating conditions changed outside of the working envelope of the equipment.

  Separator troubleshooting always begins with assessment of the process as a whole, collecting the data, such as vessel design specifications, operational data, maintenance program, and the vessel performance. The quality of the data are critical for the understanding the causes of the issues, and developing the possible steps addressing these issues. To provide a good baseline, collection of consistent data over a period of time is essential.

Evaluation of the separator performance regarding various effects may include following:

• Sampling the fluids from inlet and outlet streams. Measurements of sediment content, presence of emulsion, and droplet size distribution are helpful in identification of the performance issues.
• Mapping of the fluids interface, presence of a “rag” layer and its thickness, if there are suitable means of doing it, e.g. sample nozzles.
• Sampling of the solid phase and identification of its composition to determine its origin.

  Good understanding of the separating process with appropriate utilization of various diagnostic techniques will provide clear picture of the separator operation and will reveal the cause of the poor performance.

Possible solutions:

Individual assessment is required to proposes a specific solution based on the findings. Some solutions, though, are often preferable due to their relative ease of implementation:

• Retrofit of the separator internals.
• Modification of inlet pipe geometry and the type of fittings/valves used upstream the separator.
• Evaluate recycle streams. “Bad oil” streams may deteriorate separator performance significantly.
• Mesh demisting designs and plate packs are susceptible to fouling. Evaluate if this is the case.
• Review the operating liquid levels. Review the measurement instruments, their calibration. 

Usually there are multiple ways to improve the separator performance in each specific case. Evaluation of economic and technical parameters should be taken into consideration in order to choose the most viable option.