UNIQUE "THROUGH TUBING" COMPLETION MAXIMIZES PRODUCTION AND FLEXIBILITY

Low cost reservoir access is a key component to sustaining production from maturing fields. Coiled tubing drilling (CTD) and through tubing rotary drilling (TTRD) can achieve significant cost savings by sidetracking through existing production tubing. However, the critical completion phase of these sidetracks is challenged by small clearances and equipment. During the course of completing over 450 CTD sidetracks through 4 B=" and 3 B=" production tubing in Alaska, a number of innovative completion designs have been developed to achieve zonal isolation, maximize production, allow for selective multilateral production, and preserve the parent wellbore for additional sidetrack opportunities.

This paper will detail specialized liner cementing equipment and techniques and provide design and operational guidelines for several proven through tubing completion options: Tapered 3 3/16" x 2 7/8" fully cemented liners. Placement of larger 3 3/16" liner in the upper build section permits future sidetracks (with 2.75" bit) to other trapped oil deposits. Insertion of a specialized sub in the liner provides flexibility for low cost selective multilateral production or low cost patch isolation of upper oil lense perforations. Hollow whipstocks permit production from previously isolated parent wellbores immediately or in the future. Combined cemented and slotted liner completions save TCP perforating costs. Check valves in inflatable bridge plugs or in whipstock anchor packers provide protection to existing perforations while drilling and allow production to be reestablished.

Work is progressing with expandable screens and solid liners to address unconsolidated sands and wellbore instability.

Continuous innovation and close collaboration with the service industry has yielded successful solutions for challenging through tubing completions. These proven techniques have positioned CTD as the preferred method for reentry sidetracks on the North Slope and maximized reserves recovery. The completion options discussed in this paper may make low cost through tubing sidetracks more feasible for other mature fields.