Overburden pressure

{{short description|Stress imposed on soil or rock by overlying material}}

Pressure is force magnitude applied over an area. Overburden pressure is a geology term that denotes the pressure caused by the weight of the overlying layers of material at a specific depth under the earth's surface.{{Cite book|last=Baker|first=Richard O.|url=https://www.worldcat.org/oclc/908335687|title=Practical reservoir engineering and characterization|date=2015|others=Harvey W Yarranton, Jerry Jensen|isbn=978-0-12-801823-1|location=Amsterdam|oclc=908335687}} Overburden pressure is also called lithostatic pressure, or vertical stress.{{Cite book|last=Khan|first=M. Ibrahim|url=https://www.worldcat.org/oclc/261122682|title=The petroleum engineering handbook : sustainable operations|date=2007|publisher=Gulf Pub|others=Rafiqul Islam|isbn=978-1-60119-627-9|location=Houston, TX|oclc=261122682}}

In a stratigraphic layer that is in hydrostatic equilibrium; the overburden pressure at a depth z, assuming the magnitude of the gravity acceleration is approximately constant, is given by:

$P(z)\; =\; P\_0\; +\; g\; \backslash int\_\{0\}^\{z\}\; \backslash rho(z)\; \backslash ,\; dz$

where:

• $z$ is the depth in meters.
• $P(z)$ is the overburden pressure at depth $z$.
• $P\_0$ is the pressure at the surface.
• $\backslash rho(z)$ is the density of the material above the depth $z$.
• $g$ is the gravity acceleration in $m/s^2$.

In deep-earth geophysics/geodynamics, gravitational acceleration varies significantly over depth and $g$ should not be assumed to be constant, and should be inside the integral.

Some sections of stratigraphic layers can be sealed or isolated. These changes create areas where there is not static equilibrium. A location in the layer is said to be in under pressure when the local pressure is less than the hydrostatic pressure, and in overpressure when the local pressure is greater than the hydrostatic pressure.