As the first of the Deepwater relief wells sinks to within a few hundred meters of intersecting the leaking Macondo oil well deep below the Gulf of Mexico's seafloor, BP's moment of truth is coming. Unfortunately, so is tropical storm Alex and its 95 kilometer-per-hour winds. The National Weather Service's National Hurricane Center forecasts that Alex could become a hurricane on Tuesday, possibly delaying the drilling of relief wells generally seen as the best and last hope to plug the 9.5 million liters of crude gushing into the Gulf daily.

The first relief well, which BP started drilling on May 2, is about 5,100 meters below the Gulf's surface and has another 275 meters to go before it can be lined up to intersect the main Macondo well. As the relief well has gotten closer to the Macondo well, BP has twice removed the drill bit and replaced it with a wire line tool that sends current into the surrounding rock formation. That ranging signal is returned by the original well's casing, allowing workers to pinpoint Macondo's exact location. The process of replacing the drill bit with the wire line tool can take up to two days, a delay BP is willing to endure to improve the accuracy of their drilling.

When BP gets close enough, it will drill right into the Macondo well and pump heavy drilling mud down the relief well with the help of four pumps, each with 2,200-horsepower engines. Kent Wells, BP's senior vice president of exploration and development, says that the relief wells should require less pressure to install the drilling mud than the earlier failed attempt to force mud from ships on the Gulf's surface straight down into the Macondo well 1,500 meters below (a procedure known as a "top kill"). In a video posted to BP's Web site describing the relief well work, Wells says he has a "tremendous confidence" in his company's relief well operation. By injecting the drilling mud at an angle near the bottom of the well, the mud will meet less resistance, Wells says of the "bottom kill" procedure. Both wells are still estimated to take about three months to complete, which means neither would be ready before the beginning of August.

Alex is expected to make landfall between Brownsville, Texas, and Ciudad Madero in Mexico at mid-week. This would spare BP's oil collection south of Louisiana from a direct hit but might still disrupt these efforts as well as relief well drilling. BP is planning to install a floating riser system that would allow more rapid disconnection and reconnection of its oil-collection system. The company is also developing plans for additional leak containment capacity and flexibility for mid-July, including a second floating riser system and additional capacity through a new cap on the Macondo well's broken blowout preventer.

Image of the Transocean semi-submersible rig Development Driller III (drilling the first relief well) courtesy of BP p.l.c.