# Extrapolated Pressure (p*)

Extrapolated pressure is the predicted pressure that a buildup will stabilize back to at infinite shut-in time. For a semi-log or radial analysis (shown in the plot below), it is obtained from the intersection of the semi-log straight line at infinite shut-in time, which is the limit of 1 hr for Horner or superposition radial time.

For a model, it is obtained from the continuation of the model line using the specified shut-in time (tshut-in).

It is important to note that p* is not the actual final average reservoir pressure at infinite shut-in time. To determine the final average reservoir pressure, an appropriate reservoir model needs to be developed that applies proper material balance techniques.