BP Plc was struggling to seal cracks in its Macondo well as far back as February, more than two months before an explosion killed 11 and spewed oil into the Gulf of Mexico. It took 10 days to plug the first cracks, according to reports BP filed with the Minerals Management Service that were later delivered to congressional investigators. Cracks in the surrounding rock continued to complicate the drilling operation during the ensuing weeks. Left unsealed, they can allow explosive natural gas to rush up the shaft. “Once they realized they had oil down there, all the decisions they made...