Technical Paper: Lessons Learned From Combined Whipstock Operation: Set Whipstock/Mill Out/Cement Squeeze/Drill Out in One Trip

Society: SPE
Paper Number: 98120
Presentation Date: 2006
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ConocoPhillips pre-drilled wells for the Magnolia tension leg platform (TLP) development in 2003 using a dynamically positioned semi-submersible drilling vessel1. The Magnolia field is located in 4,674 ft of water at Garden Banks (GB) block 783 in the Gulf of Mexico. During the pre-drilling phase, two wells were successfully sidetracked out of 13.625 in. casing in one trip using an extended gage, one trip whipstock system.

The first whipstock operation was through cemented pipe and the second was through uncemented pipe, which had communication to a shallower, weak formation. This paper focuses on whipstock operations through uncemented pipe and describes the planning and execution of the first successful attempt at setting a whipstock, milling the window, squeeze cementing the window, and drilling out cement and rathole – all on one trip while using synthetic base mud (SBM).

Due to the high spread rate cost of deepwater drilling, every effort is made to reduce critical path time while managing risk and safety. Typical whipstock operations through uncemented casing can require three or more round trips to prepare a window for drilling ahead. On the GB 783 A-4 BP1 well, window milling/cementing operations through uncemented casing were conducted in a single trip. The whipstock was oriented and set at 11,080 ft measured depth (MD) in a 54° angle hole. The window was milled, the assembly pulled above the window, and the openhole squeeze cemented. After waiting on cement to set, the cement was drilled out and a successful formation test achieved. An additional 130 ft of rathole was then drilled with the mills to place the stabilizers on the next drilling assembly below the whipstock. Operations from the start of running the whipstock until the mills were laid down took 2.6 days. A total of 1,861 lbm of metal shavings was safely recovered.

This paper highlights 1) whipstock installation and window cutting operations, 2) safety and operational best practices for removing, handling, and monitoring metal cuttings that, if not removed from the hole, can be problematic for subsea blowout preventer (BOP) systems, 3) equipment modification made to mitigate risk for cementing through a milling assembly, and 4) design considerations for achieving a successful squeeze.