Definition
Differential Sticking — Differential sticking is a form of stuck pipe in which the drill string is pressed against a permeable formation and held there by the pressure difference between the overbalanced mud column and the lower formation pressure, embedding the pipe in the filter cake.
Also known as: differential sticking, differential pipe sticking, wall sticking
What causes differential sticking
Differential sticking happens when part of the drill string lies motionless against the wall of a permeable formation while the mud column is overbalanced — its hydrostatic pressure exceeds the formation pressure. The pressure difference pushes the pipe into the soft filter cake and holds it there over the contact area. The larger the contact area and pressure difference, and the longer the pipe is stationary, the greater the sticking force. Circulation is usually unaffected, which helps distinguish it from pack-off.
Prevention and remedy
Prevention centers on keeping the string moving, minimizing overbalance and wall contact, using good mud with a thin, low-permeability filter cake, and adding stabilizers or spiral drill collars to reduce contact area. Once stuck, remedies include reducing mud weight where safe, spotting an oil- or surfactant-based freeing pill across the stuck zone, and jarring. If these fail, the operator finds the free point and backs off to fish the stuck portion.
Why it matters for rentals
Spiral collars and stabilizers that reduce contact area help prevent sticking, and fishing tools are needed if it occurs.
Rent spiral drill collars to reduce sticking risk, and keep fishing tools ready — contact us to plan your BHA.