The Allowable APB Tab

Allowable Annular Pressure Buildup (APB) is the maximum allowable additional pressure (which is introduced due to a temperature change) that can be allowed in an annulus without causing a rupture of the constituting strings and can be sustained by itself (i.e. with no help from its neighboring annuli). Therefore, the allowable APB is the minimum of the following two:

1. APB for Inner String Collapse
2. APB for Outer String Burst

Usually, the inner string is weaker in collapse than the burst of the outer string. Besides the above two, there are two more consequences of APB in any annulus:

1. Fracturing of the formation at the outside string shoe that is open
2. Overpressure of the surface equipment or in the wellhead