Sunoco Logistics Partners ( SXL.N ) said on Wednesday it is forming a joint venture with Exxon Mobil ( XOM.N ), giving the midstream company strategic assets near the Dakota Access line while expanding its West Texas footprint for the second time in less than two months. The joint venture, called Permian Express Partners, will consist of assets owned by both companies, according to a statement. Sunoco Logistics will take a stake of 85 percent, while Exxon will control the remaining 15 percent.