Venezuela’s beleaguered oil export system is narrowing rapidly around Chevron as shipments to its largest traditional customer in China remain stalled amid an intensified U.S. oil embargo and mounting geopolitical upheaval. Shipping data as of January 6 shows crude loading for Chinese buyers at Venezuelan ports has been on hold for the fifth straight day—but Chevron’s vessels continue to load and export crude to the United States. PDVSA’s attempts to serve its Asia contracts have been disrupted by the U.S. naval blockade…