Disclaimer: Not to be confused with Compressibility factor .
A measure of relative change in density or molar volume under a unit pressure variation:
\beta = \frac{1}{\rho} \left( \frac{\partial \rho}{\partial p} \right) = - \frac{1}{V_m} \left( \frac{\partial V_m}{\partial p} \right) |
Symbol | Dimension | SI units | Oil metric units | Oil field units |
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or | M-1 L1 T2 | Pa-1 | kPa-1 | psi-1 |
Compressibility measures resistance of Continuum body to compression/decompression and is inverse to Bulk modulus :
c = \frac{1}{K} |
Compressibility depends on the thermodynamic conditions at which it is measured and as such is not a material property.
The two major medium compression/decompression processes are isothermal and isentropic which result in different values of compressibility:
Isothermal Compressibility | Isentropic Compressibility | ||
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Both and are not dependent on the amount of chemical substance and defined under specific conditions of thermodynamic process and as such are the material properties and properly tabulated for the vast majority of materials.
In engineering practise, when the term Compressibility is used as material property it normally means Isothermal Compressibility: .
Compressibility is related to Z-factor and Formation Volume Factor (FVF) as:
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On the other hand Petroleum Industry is traditionally using symbol to denote compressibility which often lead to confusion with heat capacity. |
See also
Physics / Mechanics / Continuum mechanics / Continuum body
[ Isothermal Compressibility ][ Isentropic Compressibility ]
[Fluid compressibility] [Pore compressibility] [Total compressibility]