There's nothing crude about changes taking place in the global oil industry. Saudi Arabia, Venezuela, Nigeria, Indonesia, and the former Soviet Union are gaining experience in operating state-owned oil companies--and that means a diminished role for such private enterprises as Exxon Corp. and the Royal Dutch/Shell Group, according to A.T. Kearney Inc., Chicago. Government-run oil companies will increasingly take over investment functions as well as refining and distribution, leaving private companies to handle customer relations, billing, and infrastructure.