The installation of the first single-trip Technology Advancement for Multilaterals (TAML) Level 4 multilateral (ML) junction system was completed in a subsea, gas-injection well. It was drilled to support oil production from the Tilje and Ile formations in the Smørbukk Sør field in the Norwegian Sea, approximately 193 km offshore in 300 m water depth.After injecting for ten years, the well will be converted to a gas producer from the same formations. Because of the Norwegian Sea's environment, the multilateral system had to be low risk and simple to install, with the capacity to minimize pipe trips and withstand the heaving seas. The casing exit had to be long enough to accommodate running a rotary steerable system through the window to drill the lateral to TD. This window had to be milled in a single trip in 13%Cr 110 casing followed by milling into the Garn 4 hard-impermeable sandstone with possible quartz stringers.Hollow-whipstock technology has been employed for more than ten years in the North Sea, but a new system, designed to be installed in a single trip--a savings of two pipe trips--was selected for this project. The hollow whipstock was perforated through after the liner was installed in the lateral to regain hydraulic access to the main bore below the junction. The hollow whipstock was used for the milling and production/injection phases and was not retrieved, saving an additional pipe trip. The well completion used several cementing and completion products and services, including liners with screens and swell packers. Stage cementing was performed to isolate permeable formations between the junction and the reservoir.The well was successfully completed and gas injection began with increases in production being noted from the adjacent producing wells. Although it was unusual to use a multilateral well for gas injection, the technology proved that it can be applicable to any multilateral well requiring a Level 4 junction.
A major operator in the Norwegian continental shelf recently implemented an improvement program focused on increasing standardization and efficiency on subsea well operations. By including a Vertical Christmas Tree (VXT) rather than a Horizontal Christmas Tree (HXT) in their subsea completion design, several wells can be batch completed with a rig. VXT Installation can then be completed with an Installation, Maintenance, and Repair (IMR) vessel, eliminating the need for a Rig or Light Weight Intervention (LWI) vessel. In order to use an IMR vessel for VXT installation, a new method needed to be developed for the establishment/removal of a temporary second barrier between the well and subsea completion. The goal was to achieve a barrier valve solution that would be installed as part of the completion string. Furthermore, without requiring intervention via wireline or an LWI, it would accomplish three positional phases: open, closed, and then open again. The tool would be installed in the open position, allowing for all standard completion operations to be conducted. For example, lighter fluid could be pumped into the tubing prior to setting a packer, allowing for bull heading in a well control situation. By incorporating the valve into the completion string and ensuring the well design and operation is planned accordingly, wireline intervention can be entirely avoided The more common methods for suspension and initiation of subsea wells during BOP removal and VXT installation include installing shallow set bridge plugs in the tubing and/or a tubing hanger plug. The intervention plugs would then be removed using a riserless LWI vessel. This method is often associated with high cost and enhanced operational risk. A technology group was assembled in order to close the technical gaps inhibiting a fully intervention-free operation for completion installation. Technology personnel from both the operator and service company worked together closely to develop a glass plug solution that met all the necessary requirements needed to overcome this challenge while still minimizing associated risk. The proposed solution is a barrier valve to be integrated as part of the completion string; using glass plug technology, it will accomplish three positions: open, closed and then open again. The glass plug will first be installed with the bypass ports in open position, allowing for standard completion activities to be conducted. For example, an operator would still be able to accomplish bull heading in the event of a well control situation. The bypass is shifted to the closed position after a predefined number of tubing pressure cycles have acted on the glass plug system. Once the bypass is closed a ISO14310 V0Q1 well barrier is established. The glass plug barrier is only shattered after the tubing above the glass has been subjected to a predefined number of pressure cycles while applying a specific overbalance. After, the barrier element has shattered the valve it activates its final open state, resulting in full bore ID through the valve. This was developed and qualified according to ISO 14310 V0Q1 / ISO 28781 V1Q1 and installed in less than a year. By utilizing this glass plug the drilling rig can batch complete subsea wells and at a later stage batch install the VXT with an IMR vessel. The product can also be installed as part of conventional completion string were shallow barrier is required, eliminating the need of intervention. By implementing this technology, the operator saves time and cost addition to reduced HSE exposure associated with well intervention.
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