It's not that they don't know how to produce oil. It's that the oil company has been so heavily mismanaged and used for political purposes that it has become extremely inefficient.
http://www.economist.com/news/americas/21607824-venezuelas-l...
> IN 2003 Venezuela’s then president, Hugo Chávez, fired more than 18,000 employees, almost half the workforce, of the state-run oil corporation, Petróleos de Venezuela (PDVSA). Their offence was to have taken part in a strike (pictured) called in protest at the politicisation of the company. Their punishment was to be barred from jobs not only in PDVSA itself but also in any company doing business with the oil firm. The axe fell heavily on managers and technicians: around 80% of the staff at Intevep, PDVSA’s research arm, are thought to have joined the strike. At the stroke of a pen, Venezuela lost its oil intelligentsia.
Obviously, this wouldn't have happened in a free market. But even other state-run oil companies haven't made this kind of blunder.