The evolution of coiled tubing (CT) and hydraulic workover (HWO) equipment has changed various concepts concerning drilling operations. A new system that combines these two proven technologies can now perform slimhole drilling operations without the use of a conventional derrick-based drilling rig; hydraulic workover equipment provides the capabilities to handle and set the casing program, and by using a continuous drill string, the coiled tubing equipment does the drilling.

This combination provides a viable alternative to normal drilling-rig operations, and in addition, increases the number of options available to the operator for solution of drilling and completion problems. Use of the system can enhance cost efficiency, alleviate equipment availability delays, and reduce environmental impact.

The system is designed to work under pressure, which facilitates drilling while under balanced and subsequently provides formation protection. Additional advantages of rigless drilling over conventional derrick-based drilling include:

  • Increased system portability

  • Decreased system size

  • Enhanced pressure handling options.

This paper describes the components of the system, including the required hydraulic workover equipment, the coiled tubing components, and other necessary elements such as fluid handling equipment. Procedures are presented for drilling and completing a well without the use of a conventional, derrick based drilling rig. The components that make up the bottom hole assembly are also discussed for both normal and horizontal drilling scenarios.

Current need, application, and advantages of the system

The availability of alternative methods for performing an operation is invaluable to an operator in providing job-planning flexibility. In drilling, for example, particular concerns involve equipment availability, environmental impact of moving and operating the rig, and cost consideration in general. In addition, in normal drilling operations, there must be a sound surface or structure upon which to erect the derrick that is capable of supporting the cumbersome size of the derrick as well as the pipe weight. These concerns are successfully managed with this new method for drilling since use of a large derrick is not required.

HWO Development

Because of their small size, the first hydraulic workover units were used primarily for moving pipe within the production string or for moving small production strings.1 Today's hydraulic workover units have grown in capability far beyond the units introduced into service in the 1960's. Maximum downward forces ("snubbing") that this equipment can exert have increased from 30,000 pounds to 300,000 pounds. Maximum pulling forces have increased from 60,000 pounds to the current 600,000 pounds, and bore sizes have increased from 4-1/16 inches to the current 11 inches. Pipe handling capability of the larger units now includes 9-5/8-inch casing.2 These capabilities (Table 1) along with a newly-developed series of related surface equipment, such as 1l-inch slip bowls that have been pull tested to 900,000 pounds, allow for the running and setting of many casing programs as well as production strings.

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