http://www.theoildrum.com/node/6501* Somewhere in the comments they discussed Monkeyfister's observations last night I think
Part of the ABC story deals with a drop in the production volumes that are being picked up by the riser insertion tube (RIT) that is taking oil from the leak to storage tanks on the surface.
BP spokesman John Curry told The Associated Press on Sunday that a mile-long tube inserted into the leaking well siphoned some 57,120 gallons of oil (1,360 barrels a day) within the past 24 hours, a sharp drop from the 92,400 gallons of oil a day (2,200 bd) (and 15 million cf of natural gas) that the device was sucking up on Friday. However, the company has said the amount of oil siphoned will vary widely from day to day.
Both of those numbers are significantly short of the 5,000 bd that the system was anticipated to remove from the riser, thereby significantly lowering the amount that is piped to the surface. At the same time there is an Op-Ed piece that has just run in the NYT which suggests, based in part on the measurements at Purdue from the oil venting video, that the real flow rate is around 40 – 100,000 barrels a day. BP have not released some of the information that would allow ball-park calculations of the actual flow, despite their claim to be open and transparent (I included the Unified Command in that decision initially but they don’t have that ability and I recognize the error). But there are some some factors that should perhaps be considered in evaluating the possible accuracy of these estimates (recognizing that there may never be a way of making an accurate assessment, though there now is a group, including the folk from Purdue, that will provide a final analysis that will be peer-reviewed and released to the public).
In an earlier post, BP had noted that the pressures that they were recording at the top of the well, and across the BOP were lower than they had anticipated, and that they were falling. They need to have this information before they inject the mud into the bottom end of the riser to do the top kill later this week. The Op-Ed piece suggested that this will only limit the leak, but if the kill works it will actually stop the leak and allow a cement plug to be placed at the top of the well, sealing it from leaking. However the mud must be injected at a pressure greater than that within the well itself, and in sufficient volume that it will flow down the well, rather than through the BOP and out the broken riser. This is achieved by raising the flow level to such a value (in this case 1,680 gal/min of mud) that there is too much resistance for this to flow through the gap in the BOP and the flow therefore pushes back down the well, filling it with mud with sufficient density that it will overcome the pressure at the bottom of the well.
Now the pressure along the passage that oil and gas makes as it goes from the reservoir, up through the initial well, through the BOP, down the riser, and then either into the RIT or out into the ocean, undergoes several pressure drops. With each drop the gas content will preferentially expand more and take up a greater volume of the total flow space.