commercially viable:
• new wells to about 3,000 ft [914 m] • safety-sensitive operations • through-tubing reentry • underbalanced drilling.
CT drilling is ideally suited for underbalanced drilling. In depleted zones, drilling under- balanced minimizes formation damage and differential BHA sticking.15 Schlumberger drills and completes more than 100 wells per year with coiled tubing. The majority of vertical CT drilling activity occurs in Venezuela where 30 to 60 surface-hole sections are drilled and cased each year. A self-contained CT drilling barge, designed specifically to minimize the impact of encountering shallow gas zones in Lake Maracaibo, was commissioned in 1995. Typically, this barge drills a 121
⁄ 4 3 ⁄ 8 -in. hole 1,000
to 1,800 ft [300 to 550 m] deep. Specialized equipment runs 95
-in. casing, executes cement-
ing operations and conducts wireline logging. Schlumberger has constructed more than 275 vertical wells in Lake Maracaibo, each requiring an average of four days to complete. Operations on the North Slope of Alaska,
6 1 2 5 4 7
> Coiled tubing drilling on the Alaskan North Slope. A typical CT drilling reentry at Prudhoe Bay, Alaska, USA, consists of running an expandable whipstock through existing 41
2 4
including the Prudhoe Bay fi eld, represent one of the most successful CT drilling applications of the past decade, clearly demonstrating CT effi- ciencies and economics. Two fit-for-purpose hybrid CT drilling units operate continuously on the North Slope, each capable of drilling and completing three wells per month. A typical North Slope CT drilling well involves a direc- tional through-tubing reentry to access bypassed oil (left). To date, more than 400 North Slope wells have been reentered using CT drilling technology.16
-in. tubing and setting it at the kickoff depth in
7-in. casing (1), squeezing existing perforations by running CT to the top of the whipstock and pumping cement (2), milling out pro le nipples at the end of the tubing and cutting a 3.8-in. casing-exit window (3), drilling a 33 hole (4), deploying a 23 8
-in. sidetrack -in. liner on CT without a hanger in the lower tailpipe
(5), cementing the liner to 200 ft [60 m] above the casing-exit window (6), and perforating the liner using hydraulically activated guns run on CT (7).
14. Boumali A and Wilson S: “ Treating the Tough Ones,” Hart’ s E&P 76, no. 12 (December 2003): 57– 59.
15. Ackers M, Doremus D and Newman K: “ An Early Look at Coiled-Tubing Drilling,” Oil eld Rev iew 4, no. 3 (July 1992): 45– 51.
Byrom TG: “ Coiled-Tubing Drilling in Perspective,” Jou rnal of Petroleu m Technology 51, no. 6 (June 1999): 57– 61.
16. Gantt LL, Oba EM, Leising L, Stagg T, Stanley M, Walker E and Walker R: “ Coiled Tubing Drilling on the Alaskan North Slope,” Oil eld Rev iew 10, no. 2 (Summer 1998): 20– 35.
increase in oil production from 238 B/D [37.9m3
/d] to 776 B/D [123.4 m3 /d]. Inherent advantages— fast trip times and
continuous circulation without pipe connections, live well intervention with improved pressure control and a smaller footprint for reduced envi- ronmental impact— that make CT attractive for remedial wellbore and reservoir applications are also advantages for coiled tubing drilling.
Reentry and Underbalanced Drilling Since 1991, coiled tubing has been used to con- struct thousands of vertical and directional wells. CT drilling applications include deepening, side- tracking and drilling new wells, especially for shallow gas reservoirs and gas-storage projects and environmentally sensitive locations. After a decade of profi table operations, four CT drilling applications have proved technically and
McCarty TM, Stanley MJ and Gantt LL: “ Coiled Tubing Drilling: Continued Performance Improvement in Alaska,” paper SPE 67824, presented at the SPE/IADC Drilling Conference, Amsterdam, The Netherlands, February 27– March 1, 2001.
Luht R and Tinkham S: “ Selection Crucial to CT Drilling Success,” The American Oil & Gas Reporter 46, no. 3 (March 2003): 116– 123.
Spring 2004
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