AN EFFECTIVE DOWNHOLE ALTERNATIVE— COILED TUBING TECHNOLOGY

Based on a workshop sponsored by PTTC’s Appalachian Region on August 20, 1998, in Morgantown, WV.

BOTTOM LINE

Coiled tubing has been well accepted as a cost-effective alternative for performing a number of downhole operations. It also can perform a variety of tasks on live wells without creating overbalanced conditions that risk formation damage, which is a significant advantage over conventional technologies.

PROBLEM ADDRESSED

Improving the economic efficiency of fluid transport in a wide variety of petroleum applications can increase profits. Coiled tubing, an emerging technology not widely used in the Appalachian region, has great potential to increase profitability in drilling, production, completion, stimulation, and managing water production of both oil and gas wells throughout the region. It also can minimize formation damage attributable to overbalanced borehole conditions.

KEY WORDS:

Coiled Tubing, Underbalanced Drilling, Formation Damage, Natural Gas Storage, Horizontal Drilling

SPEAKERS

Tom Suhy
BJ Caltech

Kevin Stiles
CNG Transmission

TECHNOLOGY OVERVIEW

Several advancements in coiled tubing design have made it a more attractive option:

• Better metallurgy has resulted in higher tensile strengths and resistance to buckling, better properties for welding, and stronger resistance to corrosion (coatings also are available).
• Improved manufacturing methods and quality control have led to better products at a lower price.
• The availability of more size options (3/4 in to 4 1/2 in) and lengths (up to 3,500 ft) have opened up a wider variety of applications.

Coiled-tubing drilling can be done safely and effectively with conventional rigs in vertical, deviated, and horizontal wells. The development of large diameter (larger than 2 in) tubing provides strength to resist buckling and higher capacity to transport the mud volume required for drilling motors. Tubing with installed electric lines is used for steering downhole drilling.

As compared to conventional drilling, the advantages of coiled tubing include: a greatly reduced risk of formation damage by fluid leakoff and fines migration by allowing underbalanced drilling. Coiled tubing also reduces time tripping in and out of the hole. Also, real-time, full-time readout of subsurface conditions allows better well control.

Coiled tubing production strings can be installed under pressure (i. e., without killing the well), thus minimizing opportunities for formation damage. Other advantages include quicker installation and retrieval of strings (no connections to make or break) and easier downhole service access.

Coiled-tubing completions, stimulations, and workovers also have distinct advantages over conventional methods. Small-and intermediate-diameter coiled tubing in multifunction strings with electric lines have applications in well logging, well testing, and other tool conveyance, especially in horizontal wells. Stimulation with coiled tubing can be performed underbalanced (e. g., removing scale mechanically followed by solvent cleanup) or under highly overbalanced conditions for perforating existing skin damage.

Workovers and repairs performed with coiled tubing on both vertical and non-vertical wells are feasible under no-kill conditions when operating underbalanced. Further advantages include the ability to: easily and accurately place well treatments, set hydraulic packers, and perform straddle-packer treatments. It is easier to perform well-head replacements, set/retrieve plugs, test casing pressure, address vertical extensions, and do cleanouts.

Coiled tubing usage in pipelines, flowlines, and highpressure injection lines also can be economic. Design life and flow characteristics are good. Long lengths with fewer welds mean fewer X-ray inspection steps and faster installation. With less equipment, the overall environmental impact is reduced. Coiled tubing is pre-hydro-tested and inspected for corrosion.

Windows-based software is available to help design successful applications of coiled tubing. This software addresses:

• The prediction of flow characteristics in wells and tubing, including flow rates and pressure losses,
• Tubing force and stress analysis for run-in and runout and for a number of in-situ operations, and
• Cleanout analysis for predicting circulation of particulate matter to the surface.

LESSONS LEARNED

1. Operators using coiled tubing technologies in the Appalachian region are realizing economic benefits. It is not just a tool for cleanouts any more. The development and proving of coiled tubing technologies elsewhere means that lower cost, lower risk applications are available for the Appalachian region.
2. A prime advantage of using coiled tubing technologies is the ability to avoid unnecessary formation damage.
3. The limits of coiled tubing technology applications have not yet been reached.

FIELD RESULTS

Gas storage case studies reviewed by a regional operator demonstrated the economic and technical viability of coiled tubing operations. Formation stimulation with a coiled tubing scale cleanout using bits and mills, followed by an underbalanced (no well-kill) solvent cleanup, significantly boosted well deliverability. This was proven at the Woodhull Field storage facility (Oriskany) in Steuben County, New York, and at the Oakford Field storage facility (fifth sand formation) in Westmoreland County, Pennsylvania. Typical treatments took one to two days and cost $20,000 to $25,000 per well.

At the Oakford storage facility, a highly overbalanced coiled tubing perforating procedure using nitrogen (N2) at twice the reservoir pressure penetrated through skin damage and microfractured the formation. Two wells were successfully treated. The operator believes this treatment will work in wells not suited for conventional frac treatments.

The operator also recommended coiled tubing technology for wellhead replacement, setting or retrieving plugs, conducting casing pressure tests, running fishing and milling tools, underbalanced drilling, whipstock setting, and drilling short radius horizontal wells from existing wellbores.

CONNECTIONS:

Coiled Tubing Technology:
Tom Suhy
BJServices/ Caltech
Route 2, Box 506
Clarksburg, WV 26301
Phone 304-624-9802

Gas Storage Case Studies:
Kevin Stiles
CNG Transmission
445 West Main St. Clarksburg, WV 26302-2450 Phone 304-623-8403

For information on PTTC’s Appalachian Region and its activities contact:
Douglas Patchen, Program Director, Appalachian Oil & Natural Gas Research Consortium
West Virginia University, NRCCE-Evansdale Dr., PO Box 6064
Morgantown, WV 26506-6064
Phone 304-293-2867 x-5443, Fax 304-293-7822, E-mail dpatch@wvunrcce.nrcce.wvu.edu

Disclaimer: No specific application of products or services is endorsed by PTTC. Reasonable steps are taken to ensure the reliability of sources for information that PTTC disseminates; individuals and institutions are solely responsible for the consequences of its use.

The not-for-profit Petroleum Technology Transfer Council is funded primarily by the US Department of Energy’s Office of Fossil Energy, with additional funding from universities, state geological surveys, several state governments, and industry donations.

Petroleum Technology Transfer Council, 2916 West T. C. Jester, Suite 103, Houston, TX 77018
Toll-free 1-888-THE-PTTC; Fax 713-688-0935; E-mail hq@pttc.org; web www.pttc.org