Casing Patch

What a Casing Patch Is

A casing patch is a short section of expandable pipe, run on a work string and positioned across a damaged interval of casing — a split, a corrosion hole, an unintended perforation, or a leaking connection. Once in position, an internal expander (mechanical or hydraulic) forces the patch radially outward until it contacts and seals against the original casing ID, with seals at each end of the patch providing the pressure barrier across the repaired interval.

The result is a repair made from the inside, without pulling the damaged casing string — valuable because pulling and replacing a casing string is one of the most expensive and time-consuming interventions a well can undergo.

When and Why a Casing Patch Is Run

• Corrosion or mechanical damage that has breached casing integrity at a specific, identifiable depth, where the rest of the string remains sound.
• Unintended perforations or communication between zones that shouldn't be in contact, where sealing the specific breach restores proper zonal isolation.
• Leaking connections or collapsed sections that threaten well integrity but don't justify a full workover pulling the string.

How Expansion Works

The patch is run in at a reduced outside diameter, small enough to pass through the existing casing without catching. Once positioned across the damaged interval, an expander cone or hydraulic expansion tool is drawn or pumped through the patch's bore, plastically deforming it outward until it contacts the casing ID along its full length. Elastomer seals at each end of the patch, also expanded against the casing wall, provide the actual pressure barrier; the expanded pipe body itself restores mechanical support across the damaged section.

Reduced Inside Diameter

Because the patch sits inside the existing casing rather than replacing it, the resulting ID through the patched interval is smaller than the original casing ID — by roughly the patch's wall thickness after expansion. Any tool, packer, or completion hardware planned to pass through that interval afterward has to be checked against the reduced ID, which can constrain future options in that section of the well.

Common Failure Modes

• Incomplete expansion leaving gaps between the patch and the casing ID, often from scale, debris, or an out-of-round casing section preventing full contact.
• Misplaced depth, setting the patch so part of the actual damaged interval falls outside its coverage.
• Expander or setting tool malfunction during the run, leaving the patch partially expanded or stuck mid-expansion.

Casing Patch vs. Cement Squeeze

Both repair a compromised interval, but by very different mechanisms. A cement squeeze, set up with a cement retainer, forces cement through the leak path itself and into the annulus or formation behind it, sealing from the outside as the cement cures. A casing patch installs a new mechanical liner on the inside of the casing, sealing directly against the casing ID rather than relying on cement reaching and sealing an external leak path. Where the leak path is accessible and well-defined, a patch is often the more predictable fix; where cement needs to reach behind the pipe itself, a squeeze is the only option.

Frequently Asked Questions