Use of Two Excess Gas Flowlines at Åsgard

Equinor is considering cutting CO2 emssions by reducing compressor work for excess gas on Åsgard A, by simultaneous use of the two excess gas flowlines between Åsgard A and Åsgard B. Petrell was contracted to perform blowdown calculations and to assess leakage detection.

The blowdown of excess gas flowlines between Åsgard A and Åsgard B in the case there is a fire at Åsgard B involving these flowlines, is by means of the HP flare at Åsgard A. The scope of work included to establish export conditions based on requirements to export temperature at Åsgard A and receiving pressure at Åsgard B for a set flow rates. The simulation model was calibrated with operational data. Blowdown simulations were then performed in order to see whether requirements to minimum temperature in pipes and flexibles were met, whether flare capacity and flow rate (momentum) were met, as well as requirement to maximum release rate from a leak at the flexible risers/pipework at Åsgard B.

Various configurations with multiple blowdown valves and with varying FO diameters were considered, also looking at different valve opening times and opening delay. Simulations were also performed to determine whether it would be possible to detect at Åsgard A which of the lines that was leaking.

The simulations were performed using VessFire 2.