Gaining new access to old wells

y Jimmy Land, David Moran

January 15, 2014

In an age of increasingly hard-to-tap resources and high demand, operators are continually searching for reliable, cost-effective ways to extend production and improve recovery in mature or damaged wells. A cased hole whipstock system that uses dynamic modeling software to engineer a wellbore exit design, is providing new access to old wells that might otherwise be abandoned.

A North Sea operator used the whipstock system to successfully sidetrack an aging, abandoned well and perform a slot recovery that created access to a new wellbore. The system set a mechanically anchored whipstock in the existing casing, milled a full-gauge 18 ½-inch window and set the world’s largest tight-tolerance liner in the 20-inch casing, saving the operator five days of rig time.

The Schlumberger TrackMaster CH cased hole whipstock system is designed to mill clean, full-gauge windows for access to wells with high-grade steel and chrome casings, and in formations with unconfined compressive strengths of more than 40,000 psi. The technology, which can be configured to provide fast, high-quality windows and sidetracks for any application, is enhanced with the use of sophisticated casing exit simulation software that helps ensure subsequent drilling and completions strings are not impacted by the dogleg across the whipstock. A drillstring analysis program models the sidetrack and provides real-time analysis of the modeled parameters.

In the North Sea project, Schlumberger selected the whipstock technology for a customer wanting to perform an efficient, cost-effective slot recovery operation on a well that had been drilled in 1974 and recently plugged and abandoned because of damage to the existing completion and casings. Such an endeavor is typically costly and requires several days of rig time.

The objective was to set the whipstock in the original 20-in. casing, mill a clean, full-gauge 18 ½-in. window to provide access for the new wellbore and then run a large, 17-in. liner through a casing exit with the dogleg optimized for the comple- tion string. Pre-job analysis, modeling and planning were integral to optimizing the design of an operation that would deliver a successful outcome.

Planning the Installation During the planning stage, simulations provided realistic predictions of how each bottomhole assembly (BHA) would perform, while calculations were made to indicate the stresses of all the components as they passed through the window. The WhipSim whipstock simulation software was used to ensure the tight-tolerance liner could be installed with the large-size whipstock assembly and window.

This was accomplished by modeling the milling operation and the geometry of the milled window, and by testing the pass-through assemblies for the completed window. An advanced mill design platform validated the milling string design and operating procedures. The Runner drillstring analysis program modeled shear setting operations, jar placement, dogleg severity (DLS) and full-well contact force profiles for the subsequent strings.

The operation involved running the whipstock system in the hole and anchoring it at the planned depth and orientation. Parameter recommendations from the pre-job modeling were used to complete milling of the window. The milling operation left a 15-ft rathole to accommodate the BHA. After a trip to change out the BHA, the sidetracked well was drilled to section total depth.

The 17-in. liner with a maximum outer diameter of 17.2-in. was then assembled and installed; the largest ever run through 20-in. casing, setting a world record. The shoe track passed over the whipstock and through the window within the Runner program’s predicted drag, which was monitored as the liner was being installed. The DLS predicted by the Runner program and the actual DLS matched, as confirmed by gyro survey data.

By isolating the damaged 20-in. pipe, mechanically anchoring the whipstock in the original 20-in. casing, and milling the full-gauge 18 ½-in. window with the dogleg optimized for the completion string, the customer was able to eliminate five days of rig time and significantly reduce costs in revitalizing this aging well. As a result of the success of the project, the operator plans to deploy the whipstock system with dynamic model- ing on all future workovers where a new intermediate barrier casing and liner string are necessary.OE

Jimmy Land is the Global Business Manager for the Drilling Tools & Remedial segment at Schlumberger. He has been in the role since March of 2010. Jimmy joined the SERVCO division of Smith International in 1979 and has since held a variety of senior operations positions in Louisiana and Texas. He has a BA in Political Science with a minor in Business from McMurry College, Abilene, TX.

David Moran is the SETC Advisor for Bit Selection and Real Time Optimization at Schlumberger. He has been in the role since 2010. David began working in the oil and gas industry in 1980, and joined Smith International in 1991. He has a BS in Geology from Skidmore College, Saratoga Springs, New York.