Prior to the BP oil well explosion on April 20, 2010, BP hired Halliburton (the cementing contractor) to plug the well and temporarily abandon it, a standard practice in the industry.
Still, by mid-April, the well seemed a qualified success. BP was convinced it had found a lot of oil. Until engineers in Houston could make plans to start pumping it out, the workers on the nearly complete well, in a standard practice, would plug it and temporarily abandon it.
One of the final tasks was to cement in place the steel pipe that ran into the oil reservoir. The cement would fill the space between the outside of the pipe and the rock, preventing any gas from flowing up the sides.