The actual petroleum reservoir is always constrained in volume (usually by seal and a cap rock).

But in some practical applications the observation time is too short to see the effects of the reservoir boundaries.

In this case a reservoir flow can be analytically modeled with infinite boundary reservoir:

Linear Flow	Radial Flow

Numerical model always performs calculations with finite boundary.

There are hybrid models which perform numerical calculations in finite volume composite and infinite boundary analytical model outside the composite.

A typical example is 3D flow simulations with infinite aquifer.

See Also