HAS SAUDI ARABIA stopped believing in a bright future for petroleum? That is the question that in recent weeks has hung over Saudi Aramco. The desert kingdom’s national oil goliath has a central position in the world’s oil markets. Its market value of $2trn, five times that of the second-biggest oil firm, ExxonMobil, and its rich valuation relative to profits are predicated in large part on its bountiful reserves of crude and its peerless…