OPEC and lower global oil prices delivered a one-two punch to the drillers in North Dakota and Texas who brought the U.S. one of the biggest booms in the history of the global oil industry. Companies are leaning on new techniques and technology to get more oil out of every well they drill, and furiously cutting costs in an effort to keep U.S. oil competitive with much lower-cost oil flowing out of the Middle East, Russia and elsewhere.