BP was working to ready the first of two relief wells to bore into its blown-out Gulf of Mexico well about 3.9 km under the seabed and permanently plug and seal the leak.

Along the way, the company aims to begin the kill process with a "static kill," which involves pumping heavy drilling mud and cement in the well from the top.

The well remains capped, having shut in all oil flow since July 15.

Here is an explanation of BP's next steps, according to retired Coast Guard Admiral Thad Allen, the top official overseeing the spill response, and Kent Wells, BP's senior vice president of exploration and production:

The Relief Wells
• On July 25 a rig that had been drilling the first of two relief wells was reconnecting its riser and drillpipe after shutting down operations to move out of the path of bad weather.

• Once reconnected, a plug that had been placed in the well to keep it stable will be removed, and the well will be cleaned.

• BP will then insert and cement in place the last piece of pipe, called casing, at the bottom of the relief well prior to boring into the Macondo well.

• After the casing is in place but before drilling resumes, BP aims to begin a static kill.

• The relief well has drilled 3,921 meters beneath the seabed and remains on target to intercept and kill the leak in August. The weather-related shutdown has likely pushed the finish date to the second half of August from the middle of the month.

• The finish date depends on how well the static kill works, how deep the relief well must bore into the stricken well, and how many times BP must pump in heavy drilling fluid and cement.

• The second relief well, a backup to the first, bored 3,341 meters beneath the seabed by July 12, when drilling was suspended to avoid disturbing the first relief well's use of sensors to find its right intercept target.

The Static Kill
• The static kill resembles BP's failed "top kill" in May, except that the well is capped and sealed.

• The top kill failed because heavy mud shot out the top of the leak along with crude and couldn't smother the leak.

• As with the top kill, heavy mud will be pumped into the well from surface vessels through pipes and hoses connected to a failed blowout preventer at the seabed.

• Because oil no longer has an escape route, the mud is expected to push it back down to the reservoir.

• Cement can then be pumped into the well to plug and kill the leak at the bottom.

• The first relief well will then drill into the space between the well's pipe and the strata, called the annulus. If oil is flowing there, more mud and cement will be pumped in through the relief well.

• Once that cement dries, the relief well will bore into the well pipe to ensure that the static kill plugged it. If not, more mud and cement will be pumped in at the bottom to finish the job.

• The static kill could accelerate the entire kill process if it works as intended.

Well Pressure
• BP has monitored pressure in the well since it was sealed shut on July 15 for signs of leaks or problems.

• Pressure has slowly risen from 6,700 pounds per square inch on July 16 to 6,904 psi on July 25.

• Rising pressure indicates the pipe and cement in the well remain intact after the April 20 blowout. Lower or falling pressure would be a sign the well is damaged, allowing oil to leak out the sides and possibly breach the seafloor.

• Pressure above 7,500 psi would show the well is intact, while pressure that falls or fails to rise above 6,000 psi would indicate a problem. The slowly rising pressure could be a sign that the reservoir is largely depleted from the leak.

Backup Oil-Capture Vessels
• BP still aims to assemble a surface oil-capture system of four vessels that can siphon up to 80,000 barrels a day from the wellhead.

• That system will include a rig, the Helix Producer; a well-testing ship, the Toisa Pisces; and two Transocean drillships: the Discoverer Enterprise and the Discoverer Clear Leader.

• Each would be connected to wellhead equipment via hoses and pipes that allow for a quick disconnect if a hurricane approaches.

• The system remains on tap as a backup if any problems arise with the static kill and the first relief well.