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USGS Updates Macondo Well Flow Estimates

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Deepwater Horizon Gulf of Mexico Oil Spill

A sub-team of scientists and engineers working for the U.S. Geological Survey (USGS) now estimate that the level of oil flowing from the Macondo well prior to June 3, when BP cut the riser pipe, could range between 20,000 b/d and 40,000 b/d of oil.

On May 27, the Plume Modeling Team initially estimated that between 12,000 b/d to 25,000 b/d of oil was flowing from Macondo, based on observation of video of the oil/gas mixture escaping from the well, using particle image velocimetry analysis to estimate fluid velocity and flow volume.

Members of this team used additional video that BP was directed to provide to calculate updated lower and upper bound range estimates for the period of time before the Riser Insertion Tube Tool (RITT) was inserted and before the riser was cut. Most of the experts concluded that, given the limited data available and the small amount of time to process that data, the best estimate for the average flow rate for the leakage prior to the insertion of the RITT is between 25,000 b/d to 30,000 b/d.

The Plume Modeling Team is one of several sub-teams formed under the FRTG to pursue independent approaches using numerous methodologies to estimating the oil flow rate from the damaged well. Two other teams that are part of the FRTG also have released updated estimates for the Macondo oil well flow. The FRTG will soon have an assessment of how much oil has been flowing from BP's well since the riser was cut on June 3.

"Developing accurate and scientifically grounded oil flow rate information is vital, both in regards to the continued response and recovery, as well as the important role this information may play in the final investigation of the failure of the blowout preventer and the resulting spill," said Admiral Thad Allen, the National Incident Commander.

Another sub-team working on the well flow estimate, the Mass Balance Team, now estimates that the average flow rate for the well is between 12,600 b/d to 21,500 b/d of oil, up slightly from the team's initial estimate range of 12,000 b/d to 19,000 b/d.

This team is using remote sensing data from deployment of the Airborne Visible InfraRed Imaging Spectrometer (AVIRIS) and satellite imagery to calculate the amount of oil on the ocean surface on a certain day. The team is correcting the value for oil evaporated, skimmed, burned, and dispersed up to that day and divided by time to produce an average rate.

The Woods Hole Analysis, led by Woods Hole Oceanographic Institution (WHOI) and assisted by researchers from Johns Hopkins University, University of Georgia and the Massachusetts Institute of Technology, initially estimated the total flow rate at .12m3/s to .23m3/s from before the riser was cut is a preliminary bulk flow estimate. This team used acoustic technologies to measure flow rates after the top-kill attempt ended and before the riser was cut. Using a remotely operated vehicle, flow estimates have been derived from three different view angles above the riser pipe and three different view angles above the blowout preventer.

Two additional teams are working in independent estimates that are expected to be completed later this month. The Reservoir Modeling Team will describe the geologic formations as well as composition and pressures of the oil, natural gas, and other compounds that are being released. Using open-hole logs; pressure; volume, and temperature data; core samples; and analog well or reservoir data, the team will populate computer models and determine flow rate from targeted sands in the well as a function of bottomhole pressure.

The second team, the Nodal Analysis Team, will use input from reservoir modeling (including pressure, temperature, fluid composition and properties over time) and pressure and temperature conditions at the leak points on the sea floor, along with details of the geometries of the well, blowout preventer, and riser to calculate fluid compositions, properties, and fluxes from both before and after riser removal.

A team of federal scientists led by Energy Secretary Steven Chu is analyzing pressure readings from the blowout preventer stack and the riser to assess flow rates and how flow rates may have changed as a result of the riser being cut. The Department of the Interior and the Department of Energy have directed BP to provide precise differential pressure measurements inside and outside the top hat to allow federal scientists to develop another independent estimate of how much oil is flowing from BP's well.

"Each of the methodologies that the scientific teams is using has its advantages and shortcomings, which is why it is so important that we take several scientific approaches to solving the problem, that the teams continue working to refine their analysis and assessments, and that those many data points inform the updated best estimate that we are developing," said USGS Director Dr. Marcia McNutt.

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