There may not be a ready answer, but I thought I’d give it a shot anyway.
The US government is accusing Iran of either providing the drones that carried out the recent attracks on Saudi refineries, or of carrying out the attacks themselves. I’m curious what type or types of Iranian UAVs might have the required capability, which seems to be a) at least 500km range; 2) ability to launch offensive weapons either autonomously or via remote command; 3) a history of having been used by the Yemeni Houthis, who have claimed responsibility. Wikipedia has a list of known Iranian UAVs, but I looked at the individual linked pages and nothing really jumped out as likely. Anyone have any light they could shed?
Lots of cites in both for further reading. Most of the drones listed look like Predator/Reaper knockoffs, IMHO. Per both papers, China’s sold a bunch to all of the entities in the region. (Maybe not the Houthis or Daesh, officially.)
A lot of the analysis is focused on multi-use capability, which generally requires ground control, which limits the range listed for the drones in both papers. If the entity accepts losing the drone to complete the mission, then really it’s more in the category of a (slow) surface-to-surface missile. A drone the size of Predator is needed if it needs 40 hours of endurance while carrying a bunch of cameras, radios, and a few missiles/GPS guided munitions. Cut the required endurance to an hour or three (300 km / 100- 150 km/hr), make the entire drone the warhead, and I’d think you can make the platform quite a bit smaller. Give it GPS guidance—oil production machinery doesn’t move—and who needs ground guidance? Alternatively, use a UAV the size of an Iranian -129, and stuff explosive where fuel used to go.
Anyway, the papers won’t answer your question that I can tell, but some of the info and cites within them might help.
Could it be modified kit drones that use a servo to drop and prime incendiaries to ignite the oil reservoirs? Would need deployment in close proximity though as the range of those are likely extremely limited. I am just speculating though. It’s just a bit fishy that a drone deployed by Iran, launched from Iraq would not be detected by radar and other means of surveillance and assuredly dodge at least Russian S200-S400 or Patriot missile batteries, Especially in a region where Royals live and their primary source of wealth and export is located. More speculation: Iran didn’t do this or authorize this, Houthi rebels that have been given arms by Iran did. That doesn’t exactly make them responsible. Pompeo is jumping the gun and trying to start a war? Wouldn’t a drone large enough to be able to fly that mileage be able to be detected with ease?
The large refineries that were attacked, so far as I know, do not have any uncovered oil storage, so incendiaries would not do much. More likely they used high explosive charges of some sort, although simply crashing the drones into storage tanks or piping could potentially do significant damage
This attack does suggest some serious deficiencies exist in the Saudi air defense system.