That article is very poorly written - or purposely biased. Better to just go to the source.
The budget deal in 2017 enabled the sale of $2B in oil to help fund among other things modernization of the SPR - whatever that is given its a cave in the ground. It also allows them to stop if its harmful to the strategic directive.
The SPR is 714M barrels - so at $80 a barrel at current prices it would be $57B, so $2B is about 4%. There were however other times they agreed to sell oil to pay for things. The government provides a list - link below.
So in general - there was no plan to sell 50% of the SPR in 18 months. This was decided purely by one branch on their own accord.
Sec. 404. up to $2 billion of oil from the SPR and for deposit of the proceeds of the sale in the Modernization Fund. It also prohibits sales under this authority if such sales would limit the ability of the SPR to meet its strategic purpose of preventing and reducing the adverse impacts of severe domestic energy supply interruptions. S
The law:
https://docs.house.gov/meetings/RU/RU00/CPRT-114-RU00-D001.pdf?Source=GovD
The DOE outlays all sales for the SPR here:
https://www.energy.gov/ceser/histor...ection 403 of the,FYs, commencing in FY 2018.