Monday, July 5, 2010

Deepwater Oil Spill - Not everything is clearly successful

Yesterday I noted that the report from the Unified Command had the well at 17, 400 ft. And I was corrected to note that this is measured depth (MD). Well today the depth has increased a further 300 ft to 17,700 ft , an additional gain of 300 ft, and bringing the well to within 60 ft of the point where, earlier, they said they would run the final casing. And at that drilling speed, they should be perhaps there by now, in fact this number would suggest that they might have reached it. There then still remains the delay while they run that casing, which could be some significant additional time, depending on conditions. (The second relief well is at 13,900 ft). The two wells will then be connected, and the bottom kill attempt started.

The complexities of life seem to be influencing other aspects of the spill and situation today. The voyage of the “A Whale” to sweep up large quantities of oil has so far been inconclusive and, despite the large fleet of vessels employed for the process, only an average of 900 barrels a day is reported as having been skimmed and recovered, initially by the two companies BP relied on
BP said it would reach the stated goal largely by deploying two companies that have the necessary expertise, trained staff and equipment: the nonprofit Marine Spill Response Corp. and the for-profit National Response Corp.
Part of the problem of accurately assessing performance comes in the definition of what is being counted as recovered, the oil, or the initial oil & water volume before the oil is recovered. (Of which latter volume some 31.3 million gallons has been recovered). The same sort of questions, in other words, applied to the overall oil recovery as are now being asked of the “A Whale” performance.

More questions are also being asked of other aspects of the spill response. There is an article, for example in the Times Picayune that critically reviews the move to dredge and create sand islands between the Louisiana coast and the oil spill site. The article notes some of the major concerns, for this series of 6-ft tall berms that will be created over an 80-mile stretch. These include that by changing the seabed geometry the dredging might reduce the energy-adsorption of the coast as storms approach.

This ties in to the changes in the natural flow patterns of the area, with some areas seeing increased fluid flow that will accelerate erosion, while other areas will lose the ebb and flow of seawater, critical to the health of the protected areas.

The berms created have already been proven to be fragile, with some protective barriers that were emplaced by the National Guard off Holly Beach having been eroded away by the actions of Hurricane Alex. However this was partly due to their location, and to be effective the berms, made with Hesco baskets, need to be further from the water.

The new floating riser system is now anticipated (after the storm delay) to be in place and working by the end of the week. This will capture additional oil through the kill lines, hopefully allowing the vents on the top of the cap to be closed, although the will still be some spill around the base to prevent hydrate formation. (And if the new cap is in place will also help with the height of mud column that can be generated when the two wells are connected and the kill begins).

Incidentally the report on waste collection that BP released today does show that some of the boom is being pressure washed to remove, and collect the oil that it captured.

The current numbers are:
For the first 12 hours on July 5 (midnight to noon), approximately 8,340 barrels of oil were collected and approximately 4,095 barrels of oil and 28.8 million cubic feet of natural gas were flared.

On July 4, total oil recovered was approx. 24,955 barrels:
• approx. 16,920 barrels of oil were collected,
• approx. 8,035 barrels of oil were flared,
• and approx. 56.9 million cubic feet of natural gas were flared.

1 comment:

  1. Assuming a depth of 17,000 ft - 5000 ft of sea water, the depth of the well below the bottom is 12,000 ft.

    I've read somewhere that the mud has a density of roughly 1 psi / ft. So a 12,000 ft column of drilling mud pushes down by 12,000 psi. But that replaces oil, which has a density of 1 psi / 3 ft or 4000 psi currently.

    So drilling mud will increase the pressure at the bottom of the well by 8,000 psi. I think I read that the oil pressure at the base of the BOP is 10,000 psi. So filling the well with drilling mud won't be enough to stop the flow. The drill mud will have to extend up the riser above the BOP.

    Assuming all this stuff is true - which I just made up - its not a fix with 100% certainty. And that doesn't even take into account the possibility of leaks elsewhere in the well which are spilling into the seabed elsewhere.