A broken oil platform in the lake. Photo: Fabiola Ferrero for The Wall Street Journal Corruption, political purges and collapsing investment at state oil company Petróleos de Venezuela SA, known as PdVSA, have slashed output across this nation to levels last seen in the 1980s. Venezuela still holds the world’s largest reserves of crude oil, according to BP PLC. But a close look at its decaying oil industry shows it will struggle to get those reserves out of the ground anytime soon, deepening...