(AP) -- The government's point man on the Gulf oil spill says BP has resumed drilling a relief well meant to intersect the blown-out well and seal it for good.
Retired Coast Guard Adm. Thad Allen said Monday that cement forced down from the top of the crippled well last week has hardened enough that workers could begin drilling the final 100 feet of the relief well.
Engineers were drilling 20 or 30 feet at a time, then pausing to make sure they were still on the correct course to hit the broken well. It could be the end of the week before the wells intersect.
The relief well will be used to pump more cement and mud into the busted well to permanently seal the source of the oil that spilled into the Gulf for nearly three months.
Federal officials have long said the relief well is the final step to ending the oil leak, which spewed an estimated 207 million gallons of crude into the Gulf of Mexico since the Deepwater Horizon oil rig exploded and sank in late April.
Work on the well, which is 18,000 feet below the surface of the ocean, started less than two weeks after the rig sank.
Crews will need to dig about 100 feet down and about 4 feet to the side to intersect the capped well, and the work will be done carefully and in stages.
Once the wells have met, crews will pump more mud and cement into the crippled well as part of a "bottom kill" meant to permanently seal the well.
Experts warn getting two shafts to intersect at the same point so far below ground is tough, and BP said it may take more than one attempt to make the wells meet.
Explore further: 'Shocking' underground water loss in US drought