Sidetracking Technology for Coiled Tubing Drilling
- L.J. Leising (Schlumberger Dowell) | D.D. Hearn (Arco Alaska Inc.) | E.A. Rike (Schlumberger Dowell) | D.M. Doremus (Schlumberger Dowell) | P.R. Paslay (Techaid Corporation)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 1996
- Document Type
- Journal Paper
- 414 - 421
- 1996. Society of Petroleum Engineers
- 1.6.1 Drilling Operation Management, 1.6.2 Technical Limit Drilling, 2 Well Completion, 1.5 Drill Bits, 1.6.8 Through Tubing Rotary Drilling, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.4.6 Thermal Methods, 1.11.4 Solids Control, 1.10 Drilling Equipment, 1.6 Drilling Operations, 1.14 Casing and Cementing
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Coiled tubing (CT) drilling is a rapidly growing new technology that hasbeen used for shallow new wells and reentry applications. Averaged over thelast 4 years, the number of wells directionally drilled with CT has doubledeach year from 3 wells in 1991 to over 50 in 1995 (Fig. 1).
A new market has evolved as being a major application for CT drilling. Thismarket is through-tubing drilling. The motivation driving through-tubingdrilling is low cost rigless reentry when overbalanced and safe drilling withChristmas tree and tubing in place when underbalanced (for reduced formationdamage). The lower cost of mobilization of a coiled tubing unit (CTU) to anoffshore platform or Arctic wellsite vs. a rotary rig provides additionaleconomic incentive. In addition, the ease of drilling 4-3/4-in. and smallerboreholes with CT is an advantage in a region which does not have anestablished practice of slimhole drilling.
The remaining key enabling technology for viable through-tubing drilling isthe ability to sidetrack in casing below the tubing tail. The threetechnologies (cement sidetracking, whipstock in cement, and through-tubingwhipstock) that have been developed for sidetracking are described in thispaper.
A mathematical model of forces, penetration rates, and torques for windowmilling with the cement sidetracking technique is presented. Window milling hasbeen a "seat of the pants" operation in the past. to the authors'knowledge. this is the first published work on the mechanics of window milling.The analysis has shed much light on the interaction between motor bendingstiffness, motor bend angle. and allowable advance rates for "timedrilling."
The results from several yard tests are presented, and indicate some of theproblems associated with sidetracking. The photographs of the sectionedhole/window illustrate the ledges caused downhole from minor" bottomholeassembly (BHA) changes.
The cement sidetrack technique has been successfully applied many times inthe field, and the results of one of these field applications is presented.
When faced with a production problem in the past, an operator had nodrilling options unless the tubing was pulled and a conventional reentry wellwas drilled through production casing. While this is done at a reasonable coston most land operations, the rig mobilization costs offshore (and under Arcticconditions) dictate that only the wells with the highest potential can justifythis type of expensive reentry. In areas of high rig mobilization costs, arigless through-tubing reentry can save 50% or more over the cost of aconventional reentry.
With the advent of CT drilling. the option of through-tubing drilling hasbecome a reality. Now, when faced with a production problem. an operator hasthe following through-tubing sidetracking options:
- cement sidetracking (CS)
- whipstock in cement (WIC)
- through-tubing whipstock (TTW).
Each of these techniques is discussed individually.
Cement Sidetracking (CS). This technique is the most straightforward.
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