Stuck Pipe Part#2: Differential Stuck

A condition whereby the drillstring cannot be moved (rotated or reciprocated) along the axis of the wellbore. Differential sticking typically occurs when high-contact forces caused by low reservoir pressures, high wellbore pressures, or both, are exerted over a sufficiently large area of the drillstring. Differential sticking is, for most drilling organizations, the greatest drilling problem worldwide in terms of time and financial cost. It is important to note that the sticking force is a product of the differential pressure between the wellbore and the reservoir and the area that the differential pressure is acting upon. This means that a relatively low differential pressure (delta p) applied over a large working area can be just as effective in sticking the pipe as can a high differential pressure applied over a small area.
https://glossary.slb.com/en/terms/d/d...