Casing in an oil or gas well can be damaged during the drilling or servicing of a well or can deteriorate during the life of a well. In either case, casing repair is required.
When a well is drilled there are multiple strings of casing of various sizes that are installed in the well starting from the largest to the smallest diameter--one being installed and cemented inside another. Occasionally during the process of drilling or completing the well, casing can be damaged which results in a decrease in the expected performance and life of the casing.
To repair the "bad spot" in the casing, a casing patch can be installed. One style of casing patch utilizes a packer equipped with seals which anchors the patch. A packer is a device that can be set at a particular depth and is conveyed by wireline, coiled tubing or drill pipe.
The state-of-the-art casing patch is an expandable patch requiring no packer to place and hold the patch on depth. It is a combination of a steel pipe and sealing elements which can be expanded across the damaged casing with a tool called an expander mandrel, usually conveyed by drill pipe.