Schlumberger

Technical Paper: First 30-in Casing Exit Enables Slot Recovery in Gulf of Suez’s East Zeit Field

Society: SPE
Paper Number: 167940
Presentation Date: 2014
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Abstract 

To increase production in East Zeit field, the operator wanted to recover a slot occupied by a well with collapsed 30-in conductor. Because of platform constraints, driving new pipe was not an option. Attempts to mill through an obstruction at 600ft were unsuccessful. And because the collapse occurred below the window, it was not possible to recover the damaged conductor and sidetrack. A whipstock system was required that could anchor in the 30-in casing, enabling a full-gauge 16-in window to be milled for sidetracking. However, there are no whipstocks made with anchors large enough to set in 30-in casing. 

To solve the problem, the service provider proposed running 600ft of 20-in casing inside the 30-in conductor. However, no case histories for dual casing exits at these large sizes were available. Potential problems included ability to mill the 20-in (0.5-in) and 30-in (1.0-in) casing wall thickness; potential mill tracking between the 20-in and 30-in casings; and the availability large milling bits. A unique solution was proposed: set two joints of 20-in casing in slips before running the whipstock; set a 16-in cased-hole WS using an expandable anchor just below the rotary table inside the 20-in casing; pull the entire assembly and hand-cut the window in the 20-in casing; run in hole with the whipstock inside the 20-in casing and cement in place; access and mill an exit through the 30-in conductor through the 20-in casing’s precut window. A software program was utilized to ensure the correct alignment of the whipstock face to mitigate the risk of mill tracking. 

In one trip, the whipstock system was safely run and successfully milled a window in the 30-in casing accessed through the exiting porthole in the 20-in string. The 16-in OD cased-hole whipstock lead and follow mills completed a 22ft long 17 1/2-in exit in the 30-in casing. The exit was milled and dressed in just 11hrs during which 2000 lbs of steel accumulated at the ditch magnets. The minimum window gauge was 16 3/4-in, and the bottom of both windows was at 584ft. This effort marked the first time an exit was completed through 30-in casing. The whipstock assembly also drilled a 20ft rathole allowing the 16-in directional BHA to pass through the casing exit and drill ahead without issues or delay.

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