Lease Automatic Custody Transfer (LACT) Working Principle

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LACT schematic
LACT schematic

As we can see on the schematic, the first stage of┬áLease Automatic Custody Transfer (LACT) system is a strainer/gas eliminator. The strainer is needed to remove the gas from crude so it wouldn’t damage the meter. The crude then will flows through BS&W (basic sediment and water) vertical mount sensor probe. If the BS&W reading exceeds the sales requirement it might trigger the diverter valve or sound the alarm. The diverter valve will flow the crude back to the processing unit while the alarm will allow operators to manually take corrective action.

After flowing through the diverter, the sampler takes a calibrated sample. The sample size is proportional to flow as the meter send signal to sampler to control the sampling process. The sampler stores crude sample to a container which has a mixing pump to mix the liquid. The mixer will make sure that the liquid became homogeneous before it uses as a sample liquid. This small sample will be used to calibrate the meter for BS&W and gravity.

The last stage is the positive displacement meter. This device must be proven a least once a month. The prover can be installed permanent as shown in figure or using mobile calibrated prover.

References:
1. Surface Production Operations, Ken Arnold and Maurice Stewart

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