Synonym: Pressure diffusivity = Hydraulic diffusivity

Ability of reservoir to translate fluid pressure throughout the pore volume:

(1)	$\begin{array}{l}\displaystyle \chi = \bigg< \frac{k}{\mu} \bigg> \ \frac{1}{c_t \, \phi} = \frac{M}{\beta}\end{array}$

where

$\begin{array}{l}\displaystyle M = \left< \frac{k}{\mu} \right>\end{array}$	multiphase fluid mobility
$\begin{array}{l}{c_t}\end{array}$	total compressibility
$\begin{array}{l}{\phi}\end{array}$	effective porosity
$\begin{array}{l}\beta = c_t \, \phi\end{array}$	storativity

In case of single-phase reservoir flow:

(2)	$\begin{array}{l}\displaystyle \chi = \frac{k}{\mu \cdot c_t \cdot \phi}\end{array}$

where

$\begin{array}{l}k\end{array}$	formation permeability
$\begin{array}{l}\mu\end{array}$	dynamic fluid viscosity

Typical values for 1 md aquifer is $\begin{array}{l}\chi \sim 10^{-2} \, { \rm m^2/s}\end{array}$ (or $\begin{array}{l}\small \sim 10^7 \, { \rm md \cdot kPa/cp}\end{array}$ or $\begin{array}{l}\small \sim 10^6 \, { \rm md \cdot psi/cp}\end{array}$ ) and grows proportionally to permeability and declines proportionally to viscosity.

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See also