The U.S. tight-oil boom is here to stay despite low crude prices as technological breakthroughs will allow steep reductions in costs, the head of U.S. firm ConocoPhillips (COP.N) told a seminar organised by oil-producing group OPEC. Tight oil reservoirs can remain viable today, breakeven costs are already down by 15 to 30 percent,” said Ryan Lance, chairman and CEO of Conoco. Oil prices crashed over the past year after OPEC decided against cutting production to tackle a global glut that arose from a U.S. shale oil boom.