A North Sea gas well was drilled and completed in 2000. Soon after the well was put in production, sand was also produced and became a major problem. Since the process system on the satellite platform was not capable of handling the sand, sand screens were installed in the well to prevent any further sand production. During the following years the sand screens became completely blocked and production ceased. The well was shut in for the next 10 years until a thru-tubing recompletion program was executed: milling out the permanent packer, fishing and retrieving the existing sand-screens and installing 130 m of new screens in a live well, all with 2 3/8–in. intelligent coiled tubing (CT). Intelligent CT interventions are operations in which rea-time downhole data is used to improve operational efficiencies. The realtime downhole data that can be obtained during CT operations include accurate depth correlation, pressures, differential pressures and temperatures. In combination with a realtime downhole camera, the high quality of data proved to be very valuable during the decision-making process, since the actual downhole situation can be assessed while many uncertainties are being eliminated. The visuals obtained by the camera played an important role in the choice of fishing tools and in discovering the exact position of fish and packer elements. This paper describes the challenges, the operational execution and the lessons learned from the recompletion project. It also explains in detail the operational aspects of the intelligent CT and how it was beneficial to the successful execution of the intervention program. Following the successful operation, the well was produced through the well test package on board the support jack-up, and production figures exceeded expectations. After this initial well, interventions in several more wells followed, whereby thru-tubing sand screens were installed with use of intelligent CT.
In the Southern North Sea, many fields are suffering from declining gas production due to depletion of the reservoir and associated liquid loading. At some time during the operating life of offshore production facilities, the ability for these facilities to keep operating economically at a further decline in gas production, will need to be evaluated. To avoid early abandonment of these offshore assets, well deliquification or liquid unloading techniques, like Velocity String (VS) installations, are considered for extending the operating life of these mature fields.Large diameter (2 3/8 and 2 7/8-in.) chrome coiled tubing (CT) strings are being installed in deep gas wells in the Southern North Sea, as part of a large-scale installation project, including some 20 wells over a period of two years. A self-propelled jackup work vessel is used to house all the coiled tubing, well test and associated equipment needed to enable well interventions on the small production platforms and NUI's (Normally Unmanned Installations). Critical to the success of the project was the cross-discipline approach to preparing, selecting and testing appropriate coiled tubing hardware and tools, hazard analyses and logistical coordination.In this paper the preparation of the project, the operational details and lessons learned are presented. Candidate well-selection criteria and the choice for the selected coiled tubing material and size are discussed as well. Due to the size of the project, which is a worldwide first of this magnitude and set-up, both in terms of investment and quantity of offshore installations, good case histories for large diameter offshore chrome velocity string installations are provided.At time of writing not all the velocity strings have been installed. The velocity strings installed thus far have yielded incremental gas production of the order of 50,000-150,000 sm 3 /d (1.7 -5.3 Mscf/day) per well, which is in line with expectations. Based on the initial production results and production expectations for the remainder of the wells, the production life of these assets is expected to extend with many years.
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