Venezuela’s state oil firm PDVSA has started reducing oil production and has asked its joint ventures, including those with Chevron, to also cut output, as storage space is running out amid the U.S. naval blockade and oil export embargo. PDVSA has asked Petrolera Sinovensa, its joint venture with China National Petroleum Corporation (CNPC), as well as its joint ventures with Chevron – Petropiar and Petroboscan, to reduce production via shutting off some wells and clusters, sources with knowledge of the operations have told…