OGJ Senior Staff Writer
HOUSTON, May 27 -- US Geological Survey Director Marcia McNutt said a team of scientists and government officials reviewing the oil spill in the Gulf of Mexico came up with flow rate estimates of 12,000-25,000 b/d, depending on the methodology used.
McNutt reported initial findings of the Flow Rate Technical Group (FRTG) during a news conference from Washington, DC, on May 27. US Coast Guard Comm. Adm. Thad W. Allen assembled the group after the initial flow rate estimate came into question. BP PLC was not part of the group, but it provided information to the group.
Early in the spill response, USCG and BP estimated the spill flow rate at 5,000 b/d based on what McNutt called limited data.
“These numbers are still preliminary,” McNutt said of the FRTG numbers, adding different teams used different methods for initial estimates. Another team will release an estimate “in a few weeks,” she said.
A mass-balance team made its estimate based upon the volume of oil seen on the surface of the water, saying that it believed 130,000-270,000 bbl of oil was on the surface on May 17. Using that estimate along with calculations of oil already burned, skimmed, dispersed, or evaporated, the team calculated a flow rate estimate of 12,000-19,000 b/d.
McNutt noted that a plane can only fly over part of the spill in a single day so the team extrapolated for the entire spill area.
The plume modeling team observed video of oil and gas coming from a bend in the damaged riser or from the end of the riser. Its initial estimate was 12,000-25,000 b/d.
McNutt said estimates were difficult to make because an estimated 75% of the flow was natural gas. She also noted that the flow can vary in its GOR. She did not talk about pressure in any of the estimates.
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Scientists estimate a higher oil spill flow rate in gulf