From Completion to Production without Intervention in a VXT Subsea Completed Well
Authors: Ommundsen Susanne Loen , Schiefloe Berit Sara , Balstad Olle , Haukelid Eskil , Solland Åsmund 
Published: April 2020

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.