With at least some partners likely to balk at the request, PDVSA [PDVSA.UL] could face even bigger obstacles to import diluents and, in consequence, to keep barrels flowing from the Orinoco belt, its main producing region. PDVSA is responsible for providing the naphtha, or light crude, needed to dilute the extra heavy oil produced at the Orinoco Belt, according to contracts signed with foreign partners including Chevron (CVX.N), Repsol (REP.MC) and ONGC.