Rising U.S. oil production, coupled with the Permian pipeline capacity constraints, are set to lead to a build-up in Cushing, Oklahoma, inventories that will put further pressure on the benchmark U.S. oil price, widening its discount to Brent Crude to as much as $15 a barrel—which would be the widest WTI discount to the international benchmark since December 2013, according to Citigroup. “As U.S. production grows, the likelihood is overwhelming that a lot of the valves to get into the Gulf Coast are going to close,” Ed Morse,…