LACT Unit Base Volume versus Base Prover Volume

Update: I should have also mentioned that Rossella will be conducting an October 15 webinar, Optimizing Wellpad Custody Transfer of Liquid Hydrocarbons. If you’re in the onshore oil & gas industry, you’ll want to register and bring your custody transfer questions.

The custody transfer process exchanging oil & gas production between business entities is a critical part of the overall production process. I received this question to an earlier post, How to Prove Your LACT Meter:

I was wondering if you could explain the difference between Base Volume and Base Prover Volume when proving meters.

In that post, Emerson’s Rossella Mimmi shared how provers were used to compare a known volume against the Lease Automatic Custody Transfer (LACT) unit’s flow meter output, where the ratio between the prover reference volume and the meter reading is the meter factor, which is used to correct the meter reading.

I shared this question with Rossella and asked her if she could help me explain the difference. She explained:

Rossella Mimmi  Pipeline Oil & Gas Industry Manager Flow Solutions Group

Rossella Mimmi
Pipeline Oil & Gas Industry Manager
Flow Solutions Group

I think the question refers to how the meter factor is calculated, dividing the prover reference volume by the base volume. Basically two quantities are compared, one is the volume actually measured by the flow meter, the other one is a reference known volume that is the prover’s one.

This is a prover’s operating principle:

Daniel-48in-Pipe-ProverThe prover consists of a length of pipe whose internal volume has been very accurately determined; the displacer is forced to travel at the same velocity as the liquid in the pipe. During meter calibration the meter and the prover are connected in series so that the volume swept out by the piston or sphere can be compared with the volume registered by the meter whilst liquid is flowing steadily from one to the other. As the displacer enters the calibrated pipe section it trips a detector, thereby initiating a count of pulses from the meter under calibration.

A second detector is tripped when the displacer reaches the end of the calibrated pipe section, thus stopping the meter pulse count. This volume is compared to the volume indicated by the meter, to determine a meter factor. This operation is carried out without interrupting the flow of liquid through the meter. Automatic valves, external or internal to the prover, control or divert the flow to cause travel of the displacer during the proving run. Proving should be performed under the same conditions as it is normally expected to operate. The meter prover must have a capacity large enough to provide proving runs of adequate duration.

The question and answer were too good to leave buried in an email exchange, so I wanted to share it with you.

You can connect and interact with other flow and oil & gas professionals in the Flow and Oil & Gas tracks of the Emerson Exchange 365 community.


Leave a Reply