A recent drought in oil company mergers and acquisitions could be coming to an end over a new Texas range war: U.S. shale producers are building miles-long horizontal wells that are running into their rivals’ land holdings. This week, U.S. shale producer Concho Resources Inc (CXO.N) said longer horizontal wells are among the factors spurring its $8 billion deal for rival RSP Permian Inc (RSPP.N), with well spacing and sharing infrastructure needs also playing roles. RSP Permian controlled the land adjacent to its own in many cases.  The average length of U.S. shale wells has grown by roughly 1,500 feet, or 25 percent, in the past three years to 7,213 feet, according to RS Energy Group, an energy investment data provider. Producers are drilling longer shale wells – some exceed three miles – to extract more crude from each well.