Worst Case Discharge (WCD) is a calculation used by the Bureau of Ocean Energy Management, Regulation and Enforcement to determine the maximum

flow rate Flow rate may refer to: * Flow measurement, a quantification of bulk fluid movement * Mass flow rate, the mass of a substance which passes per unit of time * Volumetric flow rate, the volume of fluid which passes per unit time ** Discharge (hydrol ...

for an offshore oil well in the event of an

oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into ...

. WCD first came to prominence in the aftermath of the

Deepwater Horizon Oil Spill The ''Deepwater Horizon'' oil spill (also referred to as the "BP oil spill") was an industrial disaster that began on 20 April 2010 off of the coast of the United States in the Gulf of Mexico on the BP-operated Macondo Prospect, considered ...

to determine potential liability if another oil spill were to occur.

History

The now defunct Minerals Management Service planned to implement Worst Case Discharge studies before the

though the first actual was performed in August 2010 to model the Deepwater Horizon spill. In January 2011, several major oil and gas companies were allowed to resume deepwater drilling while Worst Case Discharge studies were being completed. In March 2011, the Worst Case Discharge study on the Deepwater Horizon Oil Spill was released to the public in the Flow Rate Technical Group final report.

Calculation methods

Analytical equations

Analytical equations are the simplest method for calculating WCD. However analytical equations cannot account for the rapid change in pressure and saturation near the well bore and have been replaced by simulation modeling.

Reservoir simulation

Reservoir simulation Reservoir simulation is an area of reservoir engineering in which computer models are used to predict the flow of fluids (typically, oil, water, and gas) through porous media. The creation of models of oil fields and the implementation of calc ...

is the method used by the BOEMRE to calculate WCD as simulation can accurately model the rapid changes near well bore that occur in an uncontrolled blow out event. The BOEMRE currently uses the Merlin

finite difference A finite difference is a mathematical expression of the form . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for t ...

simulator and nodal analysis package to perform all WCD studies since using the software to determine the official flow rate for the

. Engineers typically use radial modeling to calculate WCD as a radial model can employ sufficiently small grid cell sizes around the well bore that increase in volume as cells extend into the

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteri ...

. Full field modeling is generally only needed if a geologic barrier like a fault or pinch out is close enough to the well being studied there is pressure interference. Engineers also need to calculate the highest rate in each combination of geologic layers as the well is drilled. The WCD rate can be higher in certain cases if specific layers blowout rather than the entire reservoir as different combinations of aquifers, gas layers, and oil layers can limit or enhance flow.

References

External links

BOEMRE Worst Case Discharge
{{DEFAULTSORT:Deepwater Horizon Oil Spill Deepwater Horizon oil spill