In a pressing quest to secure the best possible crude, U.S. refiners are increasingly going straight to the source.     Firms such as Marathon Petroleum Corp and Delek U.S. Holdings are buying up tanker trucks and extending local pipeline networks in order to get more oil directly from the wellhead, seeking to cut back on blended crude cocktails they say can leave a foul aftertaste. While the business of hauling crude from individual oil wells to bulk storage depots or pipeline hubs has become a lucrative niche in recent years thanks to the shale oil revolution, refiners are getting into the “first mile” game for a different reason: taking control of their supply chains to secure a more predictable, consistent stream of crude.     Phillips 66, the nation’s fourth-largest refiner, has added trucks and offloading equipment at several of its refineries to help reduce its reliance […]