Unique "Through Tubing" Completions Maximize Production and Flexibility

Abstract

The challenge with through tubing sidetrack completions has been dealing with small clearances and the lack of ready-made equipment. Over the last 10 years and 450 coiled tubing drilling sidetracks on Alaska's North Slope a number of unique completion designs have been developed to maximize production and achieve vertical/zonal isolation. These completion techniques are now proven, and may make lower cost through tubing sidetracks more feasible for other mature fields. Introduction 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 custom equipment. During the course of completing over 450 CTD sidetracks through 4 1/2-in. and 3 1/2-in. production tubing in Alaska, a number of innovative completion designs have been developed to maximize production, achieve zonal isolation, 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-in. × 2 7/8-in. fully cemented liners. Placement of larger 3 3/16-in. liner in the upper build section permits future sidetracks (with 2 3/4-in. bit) to other undrained 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.Combined cemented and slotted liner "bonzai" completions save tubing conveyed perforating costs.Preserving parent wellbore production - Standing valves in inflatable bridge plugs or in whipstock anchor packers provide protection to existing perforations while drilling and allow production to be re-established. When the lateral liner has to be cemented, hollow whipstocks can be used to re-establish production from the parent wellbore.Aluminum kickoff billet at top of liner provides 100% lining of wishbone multi-laterals.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 re-entry sidetracks on Alaska's North Slope (figure 1). The completion options discussed in this paper may make low cost through tubing sidetracks more feasible for other mature fields.

Microhole arrays for improved heat mining from enhanced geothermal systems

“…While the depth, azimuth and inclination at the kick off point in the main large-diameter borehole can be well controlled (Johnson and Hyatt, 2005), microhole drilling has limited capabilities for real-time adjustment of azimuth and inclination due to the small pipe diameters, which cannot accommodate large directional measurement tools. Nevertheless, the controllable microhole orientation at the kick-off point and the known effects of gravity, pipe strength (or allowable bend angle) and ROP allow for some directional drilling capabilities, sufficient to generate an array of a specific layout.…”