overpressure n : a transient air pressure greater than the surrounding atmospheric pressure; "the overpressure of the blast kills by lethal concussion"
- excess or markedly
elevated pressure, especially a transient high pressure due to
- 1904, trans. unknown, Wilhelm von Leube, Julius L. Salinger
(ed.), Medical Diagnosis,
- ... or whether the bronchiectatic cavity is due principally to a yielding of the bronchial walls to the inspiratory and expiratory pressure, to the overpressure of the engorging secretion, ...
- 1997, Task Committee on Blast Resistant Design, Design of Blast
Resistant Buildings in Petrochemical Facilities,
ASCE, page 3-14
- The walls facing the explosion will experience a reflected overpressure.
- 2004, Peter Smith & R.W. Zappe, Valve Selection Handbook
5th ed, Elsevier, p191
- Figure 5-19 shows a breather valve that carries separately a direct-loaded vacuum relief value and an overpressure relief valve.
- 1904, trans. unknown, Wilhelm von Leube, Julius L. Salinger (ed.), Medical Diagnosis, page 101
excess or markedly elevated pressure
- German: Überdruck
- Italian: sovrappressione
- Norwegian: overtrykk
- To subject to a high pressure
Overpressure can mean:
- In geology: the pressure regime in a stratigraphic unit that exhibits higher-than-hydrostatic pressure in its pore structure. This phenomenon is the primary cause of "oil gushers". This is described below.
- In military terminology, the pressure caused by an explosion over and above normal atmospheric pressure, especially when measuring the effects of nuclear weapons or thermobaric bombs.
Causes of overpressureOverpressure 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.
A common type of situation where overpressure may occur is in a buried river channel filled with coarse sand that is sealed on all sides by impermeable shales.
ImplicationsIt 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.