Schlumberger

Case Study: First 30-in Casing Exit Enables Slot Recovery in Gulf of Suez for Dana Petroleum

TrackMaster CH whipstock and Millmaster bi-mill complete 17 1/2-in casing exit and 20-ft rathole in 11 hours

Challenge: Mill at least a 16-in exit through 309.7 lbm/ft, 30-in conductor casing, and drill a rathole for sidetracking, although there are no known whipstock systems large enough to anchor in 30-in casing.

Solution: Set a 16-in OD TrackMaster CH cased hole whipstock system with an anchor expandable to 20 in, and a Millmaster carbide-insert bi-mill inside a 94 lbm/ft, 20-in joint of casing and manually cut a window in it. With the whipstock inside the 20-in casing, run it into the well, cement in place, and through the 20-in casing’s precut window, access and mill an exit through the 30-in conductor casing.

Result: Milled a 17.5-in exit through the 30-in casing and drilled a 20-ft rathole in one trip that totaled 11h, saving the well for production and marking the first successful exit through 30-in casing.

Sidetracking from 30-in casing without a 30-in whipstock anchor

Well A23 in the Gulf of Suez’s east Zeit field had a single 30-in casing string. Due to platform constraints, Dana Petroleum wanted to recover the slot. Attempts to mill through collapsed conductor casing at 600 ft had been unsuccessful. And, because the collapse occurred below the window, it was not possible to recover the conductor and sidetrack. A whipstock system was required that could anchor in the 30-in casing, enabling a full-gauge window to be milled for sidetracking. However, there are no whipstocks made with anchors large enough set in 30-in casing.

Whipstock preset in 20-in casing to run inside 30-in casing

Dana Petroleum Drilling Team and Schlumberger reasoned that for this unique challenge called for an original solution: They started by setting a 16-in OD Trackmaster CH cased hole whipstock system with an anchor expandable to 20 in, and a Millmaster carbide-insert bi-mill inside a 94 lbm/ ft, 20-in joint of casing and manually cutting a window in it. WhipSim whipstock simulation software was used to model the window in the 20-in casing to reduce the risk of what would be a never-performed dual casing exit.

The anchored whipstock inside the 20-in casing would be run into the well and cemented in place. And through the 20-in casing’s precut window, the 30-in conductor casing would be accessed and milled to complete the exit.

Window milled in 30-in casing accessed through 20-in string

In one trip, the 16-in OD TrackMaster CH whipstock lead and follow mills completed a 17.5-in, 22-ft long exit in the 30-in casing. The exit was milled and dressed in 11 h, during which 2,000 lbm of steel accumulated at the ditch magnets.

The minimum window gauge was 16 3/4 in, and the bottom of both windows was at 584 ft. This effort marked the first time an exit was completed through 30-in casing. The whipstock assembly also drilled a 20-ft rathole, enabling the 16-in directional BHA to pass through the casing exit and drill ahead without delays.


Download: First 30-in Casing Exit Enables Slot Recovery in Gulf of Suez for Dana Petroleum (0.70 MB PDF)

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