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overpressure

 
Dictionary: o·ver·pres·sure   (ō'vər-prĕsh'ər) pronunciation
n.
A transient air pressure, such as the shock wave from an explosion, that is greater than the surrounding atmospheric pressure.

tr.v., -sured, -sur·ing, -sures.
To cause or subject to overpressure.

overpressurization o'ver·pres'sur·i·za'tion (-ĭ-zā'shən) n.

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Military Dictionary: overpressure
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(DOD, NATO) The pressure resulting from the blast wave of an explosion. It is referred to as "positive" when it exceeds atmospheric pressure and "negative" during the passage of the wave when resulting pressures are less than atmospheric pressure.

Wikipedia: Overpressure
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Contents

The term Overpressure (Δp) is applied to a pressure difference, relative to a "normal" or "ambient" pressure, in two different circumstances:

Geologic overpressure

Geological overpressure in stratigraphic layers is fundamentally caused by the inability of connate pore fluids to escape as the surrounding mineral matrix compacts under the lithostatic pressure caused by overlying layers. Fluid escape may be impeded by sealing of the compacting rock by surrounding impermeable layers (such as evaporites, chalk and cemented sandstones). Alternatively, the rate of burial of the stratigraphic layer may be so great that the efflux of fluid is not sufficiently rapid to maintain hydrostatic pressure.

Common situations where overpressure may occur: in a buried river channel filled with coarse sand that is sealed on all sides by impermeable shales, or when there is an explosion within a confined space.

Implications

It is extremely important to be able to diagnose overpressured units when drilling through them, as the drilling mud weight (density) must be adjusted to compensate. If it is not, there is a risk that the pressure difference down-well will cause a dramatic decompression of the overpressured layer and result in a blowout at the well-head with possibly disastrous consequences.

Because overpressured sediments tend to exhibit better porosity than would be predicted from their depth, they often make attractive hydrocarbon reservoirs and are therefore of important economic interest.

Overpressure calculation (explosive)

Overpressure is determined using "Wiebull's formula" where: ∆р = 2410(w/v)^0.72

  • 2410 is a constant based on 1 bar or 100 kPa = 14.51 psi
  • Note: 0.72 is an exponent
  • W = explosive weight
  • v = volume of given area (primarily used to determine volume within an enclosed space)

Effects of overpressure

Compound Pressure Effects[1]
RDX/C4 10 psi (0.69 bar) *Reinforced concrete buildings severely damaged
  • Severe heart and lung damage
  • Limbs can be blown off
ANFO psi (0.28 bar) *Most buildings collapse except concrete buildings
  • Injuries universal
  • Fatalities occur
KClO3 psi (0.14 bar) *Residential structures collapse
  • Brick walls destroyed
  • Injuries common
  • Fatalities may occur

See also

References


 
 

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Military Dictionary. US Department of Defense Dictionary of Military and Associated Words, 2003.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Overpressure" Read more