If an array of vent points were opened along a line that is roughly perpendicular to your location, the sound could have been very loud.
To have gone on as long as you describe, a lot of $$$ worth of gas would have been lost, the contents of many miles of pipeline. Perhaps they got a report of a leak somewhere and vented a whole section of pipeline in order to avoid an explosion in a populated area.
Yep. It’s roughly perpendicular to me.