Abstract
On the Norwegian continental shelf, well interventions often use wireline's relatively small equipment footprint and weight. However, some operations still require fluid conveyance to specific depths, for which coiled tubing (CT) remains the only possible, economic option. Challenges related to reach and to achieving high annular velocity require the use of large-diameter CT. However, with crane capacity ranging from 30 to 48 t, lifting such strings is not possible. The alternative is joining CT pipes offshore.
The conventional way of joining two strings offshore is by creating a butt weld, which connects parts that are nearly parallel and do not overlap. This welding technique, if done onsite, has been long known to decrease CT life by 50% at the weld location. In addition, welding activity offshore raises significant safety issues. Another method of splicing two CT strings consists in using a spoolable dimple connector. Recent engineering advances have addressed several operational challenges related to those connectors, such as fatigue caused by cycling and pressure, ballooning around the dimple area, pressure sealing, and material corrosion.
The spoolable dimple connector was used in two CT intervention campaigns to achieve operation objectives in terms of reach and pumping rate. Those operations put forward considerations that must be accounted for during the planning phase. The connector placement was determined by carefully simulating weight distribution to minimize axial load on the dimple area. Several best practices were captured when the equipment was assembled and during interventions to increase integrity of the connector. Detailed measurements allowing for the connector wear and performance monitoring were taken under various work scopes, including cement squeeze and milling, plug setting, perforations, proppant cleanout, and sliding sleeve shifting. Significant improvements in performance with regards to the number of bending cycles and running meters were achieved with this new connector design. For instance, the operations under consideration saw a single connector clocking up to 33,600 running meters in chrome completions.
Using a large-diameter CT can now be included as an option for various well intervention work scopes in places where crane lifting capacity is limited. The use of a redesigned spoolable connector allows for more extended reach wells to be drilled and a wider selection of completion size to be installed. It also paves the way for well startup operations that require fluid conveyance, such as proppant fracturing because post-fracturing cleanout can now be performed using CT.
