The most accurate way to simulate Aquifer Expansion (or shrinkage) is full-field 3D Dynamic Flow Model where Aquifer Expansion is treated as one of the fluid phases and accounts of geological heterogeneities, gas fluid properties, relperm properties and heat exchange with surrounding rocks.

Unfortunately, in many practical cases the detailed information on the aquifer is not available which does not allow a proper modelling of aquifer expansion using a geological framework.

Besides many practical applications require only knowledge of cumulative water influx from aquifer under pressure depletion.

This allows building an Aquifer Drive Models using analytical methods.

Below is the list of the most popular models:

Transient			Pseudo Steady State	Steady State
Edge-water drive		Bottom-water drive	Fetkovich	Schilthuis
Radial	Linear	Allard-Chen
Radial VEH	Linear VEH
Carter-Tracy
Hurst (IARF)

All models have a form:

(1)	$\begin{array}{l}\displaystyle Q^{\downarrow}_{AQ}(t)= F_{[m_1... m_N ]}(t, p(t))\end{array}$

where $\begin{array}{l}[m_1... m_N ]\end{array}$ is a set of aquifer drive model parameters.

The model parameters may include aquifer area and volume (for finite aquifer) and aquifer mobility.

In Material Balance Analysis the aquifer model is used to

calculate cumulative water influx from aquifer $\begin{array}{l}Q^{\downarrow}_{AQ}(t)\end{array}$ based on historical records of formation pressure $\begin{array}{l}p(t)\end{array}$

and then to:

match the results to the formation pressure prediction from MatBal.

Moving through these iterations will lead to calibrating the aquifer properties.

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See Also