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. Introduction The Magnolia TLP development wells were drilled from a dynamically positioned semi-submersible rig, which required using a subsea BOP stack and subsea wellhead equipment. The typical casing program for the wells was 36 in. × 20 in. × 13.625 in. casing strings run to the mudline. The 13.625 in. casing weighs 88.2 lbm/ft and is HCQ-125 grade pipe. A 10.75 in. drilling liner is run to obtain high enough fracture gradient to drill to total depth (TD). An 8.062 in. production liner was then run and hung off in the 10.75 in. drilling liner that also functions as production casing. Both the 10.75 in. drilling liner and the 8.062 in. production liner for the GB 783 A4 well stuck off bottom while being run. Numerous attempts to fish the 8.062 in. liner out of the hole were unsuccessful. In order to have 8.062 in. casing set across the producing zone of the original geologic targets, it was necessary to set a whipstock above the 10.75 in. liner and sidetrack the well. The 13.625 in. casing in the area above the 10.75 in. drilling liner was uncemented in order to prevent potential annular collapse issues. One of the previous wells in the pre-drill program, GB 783 A2 ST3, had sidetracked out of 13.625 in. casing by setting a whipstock. The whipstock was set across a length of casing that had cement in the casing by openhole annulus. A number of "Lessons Learned" were obtained during whipstock operations on the A2 ST3 well. These lessons learned and others from previous deepwater whipstock operations were used to help evaluate the risk and optimize the procedures on the A-4 well.
A long, tight clearance liner was recently installed through a whipstock-milled window in a deepwater well. The length and weight of the liner, coupled with the tight clearances, pushed the limits of current technology. The liner was successfully run through a deep whipstock milled window and cemented at a depth below 24,000'. This paper describes the planning and execution involved in this critical well construction operation. Introduction Installing a long, tight clearance liner through a milled window is a critical operation that presents many technical and operational challenges. Recently in the U.S. Gulf of Mexico, ConocoPhillips Gulf Region Deepwater Exploration milled a window in 13–5/8" casing and subsequently ran 9551' of 11–3/4" liner through a 12–1/4" window to a depth of 24,382' MD. Planning, equipment selection and proper execution were the keys to success. The first critical success factors were to construct a window with adequate clearance and minimal dogleg severity and then to provide a quality borehole below the window. A one-trip whipstock was selected to construct the window and provide rat hole below the window for drilling ahead. Various bottom hole assemblies were run to directionally drill and open the borehole to an interval depth of 24,382'. Prior to running the 11–3/4" liner, a borehole imaging survey was run to confirm suitable hole geometry and adequate clearance in the open hole interval. Considerable effort was made to select the proper equipment to run and cement the 11–3/4" liner. Finite element analysis was applied to select casing connections that would provide maximum clearance while maintaining integrity to support high tensile loads combined with severe bending across the window. In addition, extra attention was given to selecting auxiliary casing equipment needed to ensure that the liner would be successfully run to bottom and cemented. This paper illustrates the level of planning and detail required to successfully install a long, tight clearance liner. A case history of the planning and execution demonstrates the effort needed to successfully implement such a challenging operation. Planning Milling the Window Method and Equipment Selection After reviewing other sidetracking options including milling and casing recovery, a cased hole sidetrack utilizing a whipstock was selected as the most cost effective option with the lowest operational risk. A technically advanced whipstock system capable of producing a clean, full-length, full gauge usable window followed by sufficient rat hole to accommodate a rotary steerable drilling assembly in one trip was desired. Two types of whipstock systems were considered for the cased hole sidetrack, 1) conventional and 2) extended gauge multi-ramp design. The conventional whipstock usually has a 1–1/2 to 3 degree single ramp and a cylindrical shaped mill head dressed with crushed carbide. Inherent problems with the conventional design are, 1) inconsistency in the shape and location of the window, 2) the mill progresses slowly at the center point of the casing, and 3) formation imposed mill limitations. The extended gauge multi-ramp whipstock system features a specially designed whipstock face with multiple ramps, each with its own taper, and a milling tool with a conical shaped mill that can be dressed to accommodate different formation properties. This type of whipstock provides additional footage to the vertical face of the whipstock. The additional footage lengthens the usable portion of the window and reduces the dogleg through the window. By lengthening the vertical face of the whipstock, the departure angle of the milling tool is not sacrificed.
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