The latest news about the BP gulf oil spill situation is that during the current testing of the new cap on the Macondo well, oil has been detected seeping up through the ground from the attached reservoir. This could be a minor issue, or it could presage a catastrophe.
When the well is completely shut in, the pressure in the well and the near part of the reservoir has no relief so it hits its maximum level and just stays there, pushing out on all sides looking for some weak link through which to escape. An open pipeline is the weakest link and the pressure normally forces the oil into the pipeline. When the pipe is completely sealed, however, there is no other ready outlet.
Minor ground oil seepage might be no big deal
If the ground above the reservoir is very stable and solid then nothing will really happen. A very minor seepage of oil from the ground might be just a normal condition for the area. It might have even existed before the BP gulf oil spill occurred, or indeed, even before the Macondo well was dug in the first place. Or maybe not.
Another blow out is worst case
If the increase in pressure resulting from sealing the well has caused a structural failure in the geology above the oil reservoir, then it could be the first sign of a worst-case scenario. If the seep develops into a major rupture and starts spewing large amounts of oil out through the ground, there would be no proven way to reseal the reservoir. The best immediate alternative would be to draw as much oil as possible out through the existing pipeline to reduce the pressure as much as possible and, hopefully, slow the oil leaking through the ruptured ocean floor. It would be a minor aid at best.
Meanwhile, the oil would continue spewing from the ocean floor in large quantities for the foreseeable future. Increasing the pressure in the reservoir by keeping the well head sealed off may create a risk of opening up these ground vents elsewhere above the reservoir. Close monitoring of the pressure levels are required to make sure that at the first sign of this happening on a significant level, the well is opened to relieve the pressure.
Macondo well pressure changes explained
Ordinarily, under the best case, the pressure at the well head would rise when the well is shut in until it reached its predicted maximum level and stayed there. Any sudden drop in pressure would indicate a blowout somewhere else. That would be bad, potentially very, very bad. Pressure that doesn’t rise or doesn’t rise to the predicted level indicates that the oil already has another point or points of egress and is already leaking into the ocean from somewhere else besides the sawed-off remnant of the Deepwater Horizon’s pipeline.
Current state of BP gulf oil spill testing
At present, BP says that the pressure is continuing to rise slowly. Since the period of testing was extended, it seems that the rate of the rise did not match predictions. The original testing deadline would have allowed for time for the pressure to reach its maximum without a time extension. This could mean slow leaks elsewhere in the system slowing the rate of pressure increase, or bad predictions. With the discovery of ground seepage, the former would seem to the case. Without in depth knowledge of the nature of the geology surrounding the reservoir, it’s impossible to determine the risk level. Presumably, Admiral Allen, the National Incident Commander, and the engineers at BP have that detailed information and have determined the risk of a significant blowout to be minor for now.
If the seal holds and the test concludes successfully, BP could either leave it sealed until the relief well is finished allowing the well to be permanently sealed with cement, or they could use the valves on the containment cap system to draw oil to the surface ships without releasing any into the ocean waters.
Update on Gulf of Mexico Oil Spill – 19 July. BP. July 19. Retrieved from www.bp.com/genericarticle.do?categoryId=2012968&contentId=7063829 on July 19, 2010.