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Petrobras chooses in-rack flow computers for Brazilian natural gas operation

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Oilfield Technology,

In the heart of this Brazilian rainforest, in the Urucu province, 38 flow streams of natural gas are transferred to an oil treatment plant owned by Petrobras. The Urucu province is the second largest natural gas reserve in Brazil with an average daily production of over 5 million m3/d.

Because of recent regulations published by the National Oil Agency requiring a better measurement of accuracy for oil volume transfer, Petrobras needed to review its existing installations and specify equipment compliant with these new regulations.

Choosing a new flow computer

“If we had chosen the classic model of dedicated flow computers (EMED), the costs and the engineering for the presentation of results would be very high, since for the implementation of 68 EMEDs we had an average cost of US$ 40 per unit, where the units would vary from 4 – 10 in. and pressure class varying between 300# and 2500# (19 units),” said Francisco Carlos Campana Aragon, Senior Equipment Engineer for Petrobras.

Because of this high cost, this was clearly not an option for Petrobras. Aragon then discovered ProSoft Technology’s in-rack flow computers for Allen-Bradley PLC and SLC platforms.

Four 2100-AGA modules were installed in an 8-slot Allen-Bradley chassis (PLC 5/80) to calculate the volume for the 38 flow streams transferred through the oil treatment plant. These modules continuously transfer calculation results to the PLC, providing total compliance with the API 21.1 standard.

The gas then leaves the oil treatment plant and is transferred 12 km to the oil extraction plant where 16 flow computers (MVI46-AFC) calculate the flowrates and gas volumes. The MVI46-AFC modules communicate through the backplane with an SLC 5/03 for each extraction plant.

“Thanks to the interaction between ProSoft’s MVI46-AFC in-chassis flow computer module and the SLC processor, we could implement an automated system for calculation and presentation of results totally compatible with the level of automation used in our plant,” said Aragon. “The cost would have been much higher using the classic dedicated flow computers (EMEDs) than those obtained through the in-chassis flow computer module.”

Computing the flow

The flow computer’s computation is divided into two stages. First, the oil is measured with the gas ‘in solution.’ Then, three 2100-AGA modules transfer the results to the PLC data memory where the gas amount is subtracted from the oil volume which is supplied by the module. This is accomplished by using a correlation involving the gas density (also supplied by the module), oil density, pressure and temperature.

“The test system for each extraction plant was only possible totally automatically without volume loss because of the ProSoft flow computers and the PLC and SLC processors,” said Aragon. “If we had chosen the old solutions using EMEDs (dedicated flow computers) the costs would have been much greater. The ProSoft modules are a success story for us. The integration between the MVI46-AFC and the 2100-AGA flow computers along with the flexibility of the SLC and PLC processors were the decisive factor in that success.”

Pipelines in the Urucu field

Natural gas from the Urucu field is shipped via pipeline 280 km to Coari on the Solimoes River. A second natural gas pipeline is also under construction running some 500 km from Urucu to Porto Velho in Roraima State, shipping natural gas for consumption by thermo-power plants in this region.

These projects, scheduled for completion within the next two years, are paving the way for economic and industrial development, generating jobs and reducing the price of electricity by approximately 50% lower than the current rates in the region.

Written by Danetta Bramhall
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Adapted from press release by Elizabeth Corner

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