Collapsing crude prices are confronting scores of smaller U.S. oil producers with the grim choice of either shutting older high-cost wells or burning through cash in the hope of riding out the downturn. As oil prices fell by more than half over the last six months from more than $100 per barrel, the U.S. oil industry responded by slowing its blistering growth and dialing back expansion plans. Now, with U.S. crude around $46 a barrel, operators are already closing some small old wells, known as strippers, and tens of thousands of similar wells are on the verge of losing money.