By Arathy Somasekhar HOUSTON (Reuters) -Oil prices settled marginally lower on Monday as concerns of an oversupply outweighed geopolitical tensions in Russia and the Middle East. Brent crude oil futures settled 11 cents, or 0.2%, lower at $66.57 a barrel. The global benchmark has traded between$65.50 and $69 since early August. U.S. West Texas Intermediate crude (WTI)contract for October, expiring on Monday, closed down at$62.64 a barrel, down 4 cents, or 0.1%. The more actively traded second-month co ...