Casing Backoff

For both vertical and horizontal wells, the casing backoff tool facilitates backoff of uncemented casing stumps at a selected coupling location downhole after a section has been cut and retrieved. It is capable of generating up to 60,000 ft.lbm of torque and maintains the original casing strength and integrity. The casing backoff tool eliminates

• reduced casing drift diameter resulting from internal casing patches
• left-hand drillpipe
• the need for overtorquing connections in a left-hand workstring on a blind backoff from surface.

Anchors and torque generator

The tool has nine subassemblies, featuring two hydraulic anchors and a torque generator. The two hydraulic anchors allow the tool to be used in horizontal wells because drill collar weight is not required to hold them open. After the backoff tool is cycled, the anchors work in tandem with the torque generator—using only hydraulic pressure—to break out and unscrew the casing-threaded connectors with approximately a half turn per cycle. When connection torque is sufficiently lowered, the backoff tool is pulled out of the hole, and a casing spear is run to complete the unscrewing and recovery of the casing stump. A threaded connection remains downhole for the new casing string to be stabbed into and made up.

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