Wellbore sandface pressure after a given well is shut-in for hours

p_e = p_{wf}(t_e) \bigg|_{q = 0}

This definition is based on the practical observation of wellbore pressure in shut-in wells for well intervention purposes.

It is the simplest and the most popular definition of formation pressure and is widely used in all upstream industry applications.

The definition of shut-in time is specific to each field or sometimes field area depending on the rock properties and the past well intervention experience.

Some conventions are to pick at the end of the radial flow, as the most common number from the past pressure tests, which makes this definition close (but still not equal) to the