State-of-the-Art Coiled-Tubing Operations at Prudhoe Bay, Alaska
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 11533, "Stateof- the-Art Coiled-Tubing Operations at Prudhoe Bay, Alaska," by J.Y. Julian, SPE, T.L. West, SPE, K.E. Yeager, R.L. Mielke, J.N. Allely, SPE, and C.N. Jenkins, SPE, BP plc; P.D. Perius, R.L. Bucher, and C.I. Foinquinos, Schlumberger; K.C. Forcade, SPE, J.A. Fagnant, and D.B. Montgomery, Orbis Engineering; J.G. McInnis, ASRC Energy; and J.K. Sack, SPE, Petrotechnical Resources of Alaska, prepared for the 2007 International Petroleum Technology Conference, Dubai, UAE, 4-6 December. The paper has not been peer reviewed.
The full-length paper details a field trial of coiled tubing (CT) with an installed fiber-optic line. More than 150 fiber-optic CT (FOCT) operations have been performed successfully at Prudhoe Bay and Kuparuk, Alaska. Cementing, perforating, fishing, milling, and other operations were conducted successfully during the 2-year field trial.

Introduction
Prudhoe Bay, with its long history of innovative CT intervention, continues to push the limits of CT technology as its wells become increasingly complex. Daily operations with three 24-hour/day CT units allow a quick pace for technology development. Multilateral and ultraextended-reach well-intervention capability is the primary push for developing new CT technology. Wells are being drilled that are deeper, farther, and harder to work on than at any other time. Although many of these are designed to be "interventionless," history suggests that at some point in the life of the well, intervention will be required.

FOCT
One of the most exciting technology developments in recent years is intelligent CT with fiber optics. The fiber-optic line is encapsulated inside a 0.071-in.-outside-diameter (OD) inconel tube that is pumped through a standard CT reel.
The FOCT and a downhole sensor package convey real-time depth, temperature, and pressure at the downhole end of the CT. These measurements can be used to make informed decisions with actual data, rather than inferring downhole conditions on the basis of surface data such as CT pump pressure and wellhead pressure. The system consists of surface electronics, modular tool strings, and software.
The system provides real-time accurate depth correlation using a casing-collar locator (CCL) and downhole temperature and pressure monitoring (both inside and outside the CT). Distributed temperature sensing (DTS) also can be obtained, allowing temperature readings at 3-ft intervals along the entire length of the CT.
Data are transmitted from the tool string up the fiber-optic line to an electronics package that converts the fiber-optic signal to a wireless signal, allowing communication to the control cab. The data are displayed by a command-and-acquisition software program and can be viewed remotely.

FOCT Tool String.
The FOCT tool string obtains CCL data and measures CT downhole pressure, downhole production-tubing pressure, and down-hole temperature. The fiber-optic connection can be blanked off during CT operations that do not require its use.
The tool string is 2 1/8-in. OD with a 0.688-in. minimum restriction. Field data show that the restriction has no effect at typical CT pump rates. Ball-operated tools can be run below the tool string, which can pass a ball as large as 5/8 in.