Development, Testing and Field History of a True One Trip Casing Exit System
Authors: Nazzal Greg , Rehbock Hans , Miller Troy 
Published: December 2007

A method is described by which a casing exit may be made with greatly improved efficiency compared with traditional multiple run whipstock methods. Economic advantages of a single trip system are self-evident. The described system contains state-of-the-art technologies, including anti-whirl window mill technology, Metal MuncherTM carbide inserts, a Finite Element Analysis (FEA) milling BHA and enhanced whipstock recovery methods.

Original design concepts are reviewed, as well as early prototype testing. Innovative modifications were made to conventional mill cutting structures. Integrated engineering efforts across three divisional companies and five product lines — fishing, packers, liner hangers, bits and directional drilling — were required to design a premier casing exit system. Recent testing as well as three commercial successes are summarized

Introduction

Current market trends and operator cost-reduction initiatives encourage operators and service companies to work more closely together to develop innovative and economical solutions. Financial benefits are also being viewed as less product-cost specific, and more as part of the total project economics. In other words, products that have higher cost, as long as they provide operator value or reduced operational cost has gained acceptance.

Development of the one-trip window cutting was undertaken to satisfy this objective. First, by reducing the number of BHA trips required to cut a window for casing exit, the system enhances the economics of re-entry applications. In addition, its modular design makes it suitable for use in a variety of applications. Finally, flexibility regarding growing sophistication of completion technologies was considered paramount toward further expandIng the range of potential casing exit applications.

Background

Current casing exit technology "evolved" from early whipstock systems designed for directional drilling applications. These tools were later found to have application in casing exits, and modifications to improve efficiencies have been underway ever since. The one-trip system described herein is one result of extensive design refinement of early technology.

Limitations of Conventional Techniques. In conventional whipstock window cutting operations, there are two methods of anchoring the whipstock: a packer/anchor assembly and a mechanical bottom-trip anchor. As with any whipstock job, proper pre-well planning and wellbore preparation is the key to success. Chart 1 addresses some of the critical issues to be considered while pre-planning a casing exit.

The mechanical bottom-trip anchor is held in the open position during run-in by brass shear screws and a low force spring. Since the setting of the anchor is initiated by applying set-down weight to the top sub, a bridge plug or other false bottom must be in place at setting depth before the whipstock is run (Figures 1 & 8). After orientating, a set-down weight is applied to the anchor, shear screws are sheared allowing the anchor to be activated. As more set-down weight is applied to the anchor, the 3 slip design moves up over the tapered cone and wedges between the cone, which is torsionally locked to the anchor body and the ID of the casing. A 5-1/2" anchor was tested to 17000 Ft-lbs of torque and artificially vibrated to simulate drilling conditions with no observed movement. The anchor was then rated to 10000 Ft-lbs.

A whipstock packer is first set in casing and usually a gyro is run to give the lug orientation. Then, the whipstock is oriented in the required direction by means of an adjustable splined anchor, which is attached to the bottom of the whipstock (Figure 2). P. 135