Coiled Tubing Takes Center Stage
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Coiled Tubing Takes Center Stage David Bigio nCoiled tubing drilling on Lake Maracaibo, Venezuela. With the well control equip- Andy Rike ment of the CT unit, wells are drilled into suspected pockets of shallow gas. The gas is Anchorage, Alaska, USA drained to prevent it from becoming a hazard to conventional drilling. When it comes to coiled tubing, there can be few doubters left. What Axel Christensen Mærsk Olie og Gas was once a fringe service has moved to center stage in the oilfield the- Copenhagen, Denmark ater of operations. Jim Collins Doug Hardman For many years, coiled tubing (CT) opera- have combined to dramatically expand the Calgary, Alberta, Canada tions occupied the twilight zone of a fringe uses of coiled tubing (above). service offering niche solutions to special- Today for example, coiled tubing drills Denis Doremus ized problems. However, over the past five slimhole wells, deploys reeled completions, Patrick Tracy years, technological developments, logs high-angle boreholes and delivers Sugar Land, Texas, USA improved service reliability, gradually sophisticated treatment fluids downhole. This increasing tubing diameter and an ever- article will look at the technical challenges Glen Glass growing need to drive down industry costs presented by these services and discuss how Suncor Inc. they have been overcome in the field.1 Calgary, Alberta, Canada Niels Bo Joergensen For help in preparation of this article, thanks to Von 1. This article is an elaboration of a speech given by Cawvey and Lamar Gantt, ARCO Alaska Inc., Anchor- Roberto Monti, President, Schlumberger Dowell: Mærsk Olie og Gas age, Alaska, USA; Dave Ackert, Dowell, Montrouge, “Cost-Effective Technology Levers to Improve Explo- Esbjerg, Denmark France; Larry Leising, Dowell, Rosharon, Texas, USA; ration and Production Efficiency” presented at the Bart Thomeer, Dowell, Sugar Land, Texas; David Baillie, Offshore Northern Seas Conference, Stavanger, Nor- Schlumberger Wireline & Testing, Montrouge, France; way, August 23-26, 1994. Douglas Stephens Mark Andreychuk, Wayne Murphy and Doug Pipchuk, Esbjerg, Denmark Dowell, Red Deer, Alberta, Canada. In this article, SLIM 1, DLL (Dual Laterolog Resistivity), Litho-Density, SRFT (Slimhole Repeat Formation Tester), RST (Reservoir Saturation Tool), Pivot Gun, Power Pak and FoamMAT are marks of Schlumberger. SPOOLABLE is a mark of Camco International Inc. October 1994 9 Drilling Slimhole Wells Injection and shallow tion extended using underbalanced CT Slimhole wells—generally those with a final 160 gas wells 71% drilling, resulted in production three times Through-tubing reentry diameter of 5 inches or less—have the wells 13% greater than predicted rates (see “Prudhoe potential to deliver cost-effective solutions Conventional reentry and Bay CT Drilling Reentry Well” next page). to many financial and environmental prob- 140 deepened wells 12% Wells in Prudhoe Bay are drilled in clus- lems, cutting the amount of consumables Exploration wells 4% ters from pads—the same way that they are needed to complete a well and producing drilled from platforms offshore. The logistics less waste.2 Other benefits depend on what 120 of supplying and servicing an extreme loca- kind of rig drills the well. Compared to con- tion are also similar to those encountered in ventional rigs, purpose-designed smaller the North Sea. However, with about 1200 rotary rigs can deliver slimhole wells using 100 wells—of which ARCO operates half— fewer people on a much smaller drillsite, Prudhoe Bay benefits from potential which cuts the cost of site preparation and economies of scale. significantly reduces the environmental As with any mature operation, there is a impact of onshore drilling.3 80 need to extend field life and gain incremen- Coiled tubing drilling combines the virtues tal reserves at a cost that reflects today’s oil of a small rig with some unique operational price. While the primary aim is to devise a advantages, including the capability to run 60 strategy for low-cost well redevelopment, a the slim coiled tubing drillstring through secondary aim is to improve the productiv- existing completions to drill new sections ity of horizontal wells by reducing forma- CT drilling job count below. There is also the opportunity to har- 40 tion damage associated with conventional ness a coiled tubing unit’s built-in well con- overbalanced drilling. trol equipment to improve safety when In line with these objectives, candidate drilling potential high-pressure gas zones. wells for CT drilling are divided into two 20 This allows safe underbalanced drilling— classes: when the well may flow during drilling.4 •the replacement of waterflood wellbores Although there were attempts at CT that have corroded because of the high drilling in the mid-1970s, technological 0 carbon dioxide content of the water 1991 1992 1993 1994 advances were needed to make it viable. Estimate •horizontal sidetracks to replace conven- These include the development of larger tional gravity drain wells, tapping new diameter, high-strength, reliable tubing, and nThe rapid increase in CT drilling. This zones and improving recovery. the introduction of smaller diameter positive estimate of the number of jobs performed Four years ago, ARCO began sidetracking displacement downhole motors, orienting does not include many informal and the existing wells using conventional Arctic unreported reentries and drilling attempts tools, surveying systems and fixed cutter bits. that have been carried out over the rigs. The corroded tubing was pulled and Furthermore, currently available coiled tub- years—particularly in Canada. new well sections drilled. ARCO realized ing engineering software enables important that this was going to be a necessary proce- parameters to be predicted, such as lock without pulling the production string is a dure for the future, but that conventional up—when tubing buckling halts drilling cost-effective way of sidetracking or deep- technology was going to incur considerable progress—available weight on bit, expected ening existing wells. costs. Using a traditional Arctic rig to enter a pump pressure, wellbore hydraulics and The development of through-tubing, reen- Prudhoe Bay well, drill the sidetrack and wellbore cleaning capability.5 try underbalanced drilling is of great interest run a completion costs over $1 million—as It was not until 1991 that the first positive in the Prudhoe Bay field on the North Slope many as 800 sidetracks may be needed in results of CT drilling were seen with the of Alaska, USA, where operator ARCO ARCO’s Prudhoe Bay unit. deepening of a vertical well in France by Alaska Inc. has an alliance with Dowell to The goal of the Arco-Dowell alliance is to Schlumberger Dowell and Elf Aquitaine, develop coiled tubing technology.8 The develop a lower cost alternative to conven- and the drilling of two horizontal reentry alliance has already scored a number of tional rig sidetracks. To date, promising results wells in West Texas, operated by Oryx technical and commercial successes. For show that CT sidetracks can ultimately be Energy Co.6 Today, experience has been example, a 600-ft [180-m] horizontal sec- performed at half the cost of rig operations. built up, technology development continues (continued on page 14) and the number of wells drilled worldwide 7 is set to increase rapidly (above, right). 2. Randolph S, Bosio J and Boyington B: “Slimhole 5. Simmons J and Adams B: “Evolution of Coiled Tubing More than two thirds of 1994’s expected Drilling: The Story So Far...” Oilfield Review 3, no. 3 Drilling Technology Accelerates,” Petroleum Engineer 150 CT-drilled wells will be injection or (July 1991): 46-54. International 65, no. 9 (September 1993): 26-34. shallow gas wells—including steam injec- 3. “Questioning the Way We Drill,” Oilfield Review 6, 6. Ackers M, Doremus D and Newman K: “An Early no. 3 (July 1994): 4-9. Look at Coiled-Tubing Drilling,” Oilfield Review 4, tion wells in California and pilot wells to Faure AM, Zijlker VA, van Elst H and van Melsen RJ: no. 3 (July 1992): 45-51. relieve pockets of shallow gas in Lake Mara- “Horizontal Drilling With Coiled Tubing: A Look at 7. Leising LJ and Rike EA: “Coiled-Tubing Case Histo- caibo, Venezuela. However, these wells Potential Application to North Sea Mature Fields in ries,” paper SPE/IADC 27433, presented at the Light of Experience Onshore The Netherlands,” paper SPE/IADC Drilling Conference, Dallas, Texas, USA, tend to be no deeper than 1640 ft [500 m] SPE 26715, presented at Offshore Europe Conference, February 15-18, 1994. and take only one day to drill. Aberdeen, Scotland, September 7-8, 1993. 8. “New Life for an Old Slope,” Journal of Petroleum Through-tubing reentry in underbalanced 4. Leising LJ and Rike EA: “Underbalanced Drilling With Technology 46, no. 5 (May 1994): 388-390. Coiled Tubing and Well Productivity,” paper SPE conditions is a category of CT drilling that 28870, presented at the SPE European Petroleum may grow significantly. Reentering wells Conference, London, England, October 25-27, 1994. 10 Oilfield Review Prudhoe Bay CT Drilling Reentry Well Drilled 3 3/4-in. openhold underbalanced through 4 1/2-in. tubing into two target sands. Rig operations CT drilling operations Gas-lift hardware 3 7 3 /4-in. open hole 8 3 2 / -in. predrilled line subsequently underreamed to 4 /4-in. (2 holes / ft plugged with aluminum) 1 4 /2-in. production string 1 7-in. liner 4 /2-in. tubing Shale Sadler Rochit sandstone Lower Romeo interval 586 ft Drilled in 1980, Well 2-16 had been worked over hydrostatic pressure of the mud in the annulus nWell 2-16 after sidetracking and with the ultimate com- a number of times but despite two matrix stimu- and therefore the bottomhole pressure during pletion including the 2 7/8-in. predrilled liner plugged with aluminum. During drilling, gas was injected inside the 4 lation treatments had become a poor producer.