Repairing Casing Leaks

Once a leak has been detected, the optimal repair solution must be determined. Repairs can be mechanical, with packers, bridge plugs or patches, or chemical, with cement or permeability modifying chemicals. Two methods were highlighted, the first the most established, the cement squeeze job, the second a relatively new technology, the casing patch.

HOMECO Internal Steel Casing Patch

The internal steel casing patch is a thin wall steel liner that is run in a corrugated configuration (before setting) with a fiberglass mat, covered with epoxy, on the outside. It can be used to seal leaks in tubing or casing including perforations, collar or thread leaks and splits as well as reinforcing worn or corroded intervals. It is run on drill pipe or tubing using a drilling or workover rig. It is set (expanded) using a hydraulic pulling tool and expanding assembly. The advantages include speed (trip time plus 45 - 60 minutes), minimum reduction of the inside diameter (an unexpanded patch can be run through an expanded patch), multiple patches can be set and it works where squeezes have failed. The chief disadvantage is price: to set a 20 ft. patch is $10,000, plus rig time, pump rental, travel and supervision. The standard patch is a low carbon steel with a temperature rating of 325 °F. A high temperature patch is available for temperatures up to 600 °F and a corrosion resistant patch is available for use with stainless casing.

The information required to begin a job includes casing size and weight, hole deviation, differential pressure requirements, well fluid, weight, and level (the process works in all fluids except diesel), depth and description of damage, downhole temperature and the height and pulling capacity of the rig. The patch comes in 20 ft sections and 10 foot multiples. A double rig can set up to a 60 foot section, which can be prepared in the shop; otherwise they can be welded on site. It is recommended that when the patch is used for patching perforations or splits that it cover the entire region plus six to eight feet overlap above and below to avoid casing damage. The wellbore must be scraped and milled if needed for clearance, then circulated to clean it out. No sand at or above the damage can be tolerated.

Petroleum Technology Transfer Council, 16010 Barkers Point Lane, Ste 220, Houston, TX 77079
toll-free 1-888-THE-PTTC; fax 281-921-1723; Email hq@pttc.org; web www.pttc.org