Time to stabilization (tstab) is defined as the time it takes for the radius of investigation to reach all of the reservoir boundaries.
Stabilization originated as a practical consideration and reflected the point at which pressure no longer changed significantly with time: that is, it had stabilized. With high-permeability reservoirs, this point was not difficult to observe. However, in tight formations, it takes a very long time for pressure to stabilize — often months, or even years. Moreover, except where there is a pressure maintenance mechanism acting on the pool, a true steady state is never achieved and pressure never becomes constant.