Flow Measurement within a Gas Lift System

Flow Measurement within a Gas Lift System

A free flowing oil well has to have enough downhole pressure to maintain an acceptable production flow. If this downhole / formation pressure is too low, the well must be artificially lifted. Gas (besides water) injection can be used to maintain the formation pressure.

The gas injection / lift technology is also employed in oil fields near Brunei. An accurate and reliable flow measurement is vital in optimising the injection rates. Too little gas injection and the oil production is reduced - too much gas injection nevertheless also impedes production. At the same time, the excess gas can’t be exported for sales.

At the given customer, differential pressure flow meters have been employed since more than 30 years for this measurement task, though these meters are drifting over time. While the pressure transmitter can be calibrated, the primary element (orifice plate) cannot. There is also no means to verify the accuracy. The impulse lines can also be blocked with entrained liquids which leads to incorrect flow readings.

Due to the unreliable flow readings from the installed differential pressure meters, the responsible engineers weren't able to properly balance the injection volume of natural gas within the gas lift system. The required frequent maintenance or meter exchange wasn't an option, as being a vital process in production, the gas lift system cannot be shut down during daily production.

FLEXIM demonstrated the capability and accuracy of its FLUXUS ultrasonic clamp-on flow meters in various field evaluation trials. With the good results garnered, the field operators engaged FLEXIM for a flow survey exercise covering the complete gas lift system.

A list of more than 60 measurement points was drawn up. Two sets of portable FLUXUS flowmeters were utilized to enable simultaneous measurements. From the results of the survey, it was obvious that some differential pressure flow meters have drifted significantely over time. Wrong flow data also lead to wrong process settings. The plant operatores had been over-injecting gas all the while.

With the new data collected from the flow survey, the operator is now able to better balance the gas lift system and carry out precise process optimisation. Now, the right dose of natural gas for the optimal gas lift can be injected, while excess gas can be exported for sales. Savings of about 400.000 US $ are already realised over a 3 month period.

Based on the big success of the flow meter survey, the operator now equipes the measurement points, previously served with differential pressure meters, with permanent FLUXUS clamp-on ultrasonic flow meters.

Advantages

  • No measurement drift, no flase readings - highly accurate and reliable measurement data
  • No process interruption for installation
  • Virtually maintenance free measurement solution
  • No pressure losses in the system as when employing differential pressure meters

 

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