Use underground pipeline as gas storage tank: how could I simulate the supply time?

[pipingren]

Hi guys:
Now we have one 40km underground gas pipeline which is not in service, and we want to use this gas pipeline as gas storage tank and supply gas to gas turbine. Total length is 40km, initial pressure is 5.5MPag, and GTG gas supply pressure is 3.5MPag, so we need to know how much time (10h, 8h,,,,?) this pipeline can supply gas to GTG.
what software can I use to simulate this senario?

[gtaa]

Just do the calculations by hand. You shouldn't use software if you do not know how to do the problem yourself - it is bad practice.

Determine the quantity of gas within the pipeline at both the start and end conditions, then divide by the gas consumption rate. Be sure to use the same units in all your calculations. My spreadsheet to do this uses standard volumes (Sm³ or MMScfd) as you don't have to mess around with density changes. However, you can use mass if you calculate the density at start and end conditions first using P(MW)/zRT.