North Sea slot recovery requires extended cutting durability and cutting coordination 

Undertaking a slot recovery from a well in the North Sea involving the removal of 1,300 m of 9 5/8-in casing presented Statoil with several challenges. Pull resistance levels in the well varied due to inconsistent cement and settled barite in the annulus between the 9 5/8-in and 13 3/8-in casing.

Conventional cut-and-pull BHA assemblies require a trip to surface for each cutting depth because the cutting tool must be redressed with a fresh set of knives before each cut. Trips to surface can add several days to the overall operation, depending on the number of cuts required, cutting depth, and hole conditions. In addition, most conventional cutting tools do not provide surface indication that the casing cutting has been completed.

Three sets of knives enable more cuts in fewer trips

To increase slot recovery efficiency for Statoil, Schlumberger recommended running an 8 1/4-in CutMaster X3 MCPC to make multiple cuts and using a releasing spear with a downhole pulling tool to recover the cut casing sections. The CutMaster X3 MCPC, which is activated remotely and has three sets of blades that can make up to 12 cuts in a single trip, could complete multiple cuts of 9 5/8-in casing in fewer trips. Its indexing piston enables it to switch to a different set of cutting blades with each flow cycle.

Upon completion of each cut, the Flo-Tel downhole mechanical position indicator provided surface indication to confirm that the casing string had been successfully cut.

Efficient slot recovery saves USD 200,000

In only two trips, 1,300 m of 9 5/8-in casing was cut into 11 sections. All cuts were made in 6 to 14 minutes each. The ability of the CutMaster X3 MCPC to make multiple cuts eliminated 6 trips, saving Statoil approximately 1.5 days of rig time and USD 200,000.