Just to give an idea (if that link I put up is correct) and Al Qaeda have retaken Azzan that's just more headaches for the Saudi coalition.
Below is a Google image showing the location of Azzan and the port of Al Mukalla that the article says that Al Qaeda control and an image from the Washington Post showing the oil producing area of Marib (and pipeline) and the areas of Houthi control in mid 2014 before taking control of the capital in Sept 2014.
https://en.wikipedia.org/wiki/Houthi_takeover_in_Yemen
According to ExxonMobil's website they own interests in the Marib and Jannah blocks which produce on average 195,000 b/d and "the fields produce to a central oil production unit, then through a pipeline to Salif on the Red Sea, where a 3MB FSO holds it for export. Loading is from Ras Isa Marine Terminal, operated by Yemen Hunt Oil Company."
http://www.exxonmobil.com/crudeoil/about_crudes_marib.aspx
Yemen is very messy for the Saudis, the UK and the US as you can see. Trying to defend Marib and Salif will ultimately prove futile in my opinion whilst the Russians remain in Syria backstopping Iranian power and creating power vacuums for groups like Al Qaeda and ISIS. Well that's the way I read it at least.
Eshmun
