Old Vent Question

I have a 1950's military house located in Utah and it has been updated with new furnace and ducting, which is not the issue. I am more concerned or curious about a length of ducting approximately 24in by 12in going from the attic to the crawlspace. Nothing is on either end it is just open metal ducting that you can either look down (attic) or look up (crawlspace). There is however a length of gas piping inside of the ducting but I cannot find its source or reason for being in the attic.

Should this be plugged for insulation purposes or does it actually vent the crawlspace for some reason?

Any light on this topic is great.

Thanks