WASHINGTON — BP announced this morning that its engineers will soon begin pumping cement into the Deepwater Horizon oil well in the Gulf of Mexico through a relief well and will have completed sealing it by Saturday, killing for good a deep-sea well whose explosion 150 days ago killed 11 offshore drilling rig workers and sparked an economic and environmental catastrophe whose size is still being calculated.

In a statement, BP said that because engineers had determined that no oil or gas was in the original well when the relief well intercepted it on Thursday afternoon, technicians would move immediately to the cementing process. Had oil and gas been found there — something that had not been expected — BP would first have dumped heavy drilling mud into the well.

"It is expected that the MC252 well will be completely sealed on Saturday," BP said in its statement, using the abbreviation of the well's official geographic designation in the Gulf's Mississippi Canyon.

BP has said that the well would be abandoned and that no effort would be made to produce from it in the future.

The final sealing of the well, which exploded April 20, was an anticlimax to the drama that had enveloped the Deepwater Horizon site for much of the spring and summer. As many as 60 ships at a time, including drilling rigs, crowded the area 48 miles off the Lousiana coast during the summer as BP sought to shut down the gusher. Television broadcast live video feeds of crude oil boiling into the water from the crippled well. Flames roared in the air above as two drilling vessels flared natural gas collected from the well. Thick crude oil blanketed the ocean's surface.

That scene began to change when technicians succeeded in closing off the well with a containment cap on July 15, and then used heavy drilling mud and cement pumped in from the top to seal the well in early August. Retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the spill, said last week that the well posed no further threat to the Gulf.

Completing the relief well, which BP had begun drilling May 2, was considered a final safety measure, however. Allen had said that government scientists remained concerned about the possibility that the August cement job had not sealed the well's annulus — the space between the wall of the wellbore and the drilling pipe — and that oil and gas could still flow from the rock reservoir into the well and to the seafloor.

But BP said that technicians aboard the Development Driller III platform found no evidence of hydrocarbons in the annulus after they determined that the relief well had hit its intended target on Thursday.

Even with the well sealed, work will continue at the site. BP said another offshore drilling rig, the Development Driller II, will continue to search for the drilling pipe that was originally in the well when it exploded, but has since vanished. Officials had expected to find the pipe when they lifted the well's failed blowout preventer from the seafloor last week. No pipe, however, was found to be holding the blowout preventer in place.

The blowout preventer, which was designed to clamp onto the drill pipe and seal it in the event of an explosion, is now on the mainland, where investigators are trying to determine why it didn't work.