Use of Pressure-Activated Sealants to Repair Leaking Subsea Horizontal Tree Connectors (Unlatch HXT)

Abstract A large, Australian operator was in the process of a subsea abandonment campaign of 12 wells, 9 of which were completed with Horizontal Trees (HXT) installed, when they initially noted hydraulic system failure from multiple HXT H4 connectors during their attempts to hydraulically unlock and remove the trees. Planned contingency unlock methods were employed but proved to be successful for only 2 of the 9 HXT's. As the operator progressed through the campaign, all 9 of the HXT connectors of the same make and design were confirmed to be affected. To proceed with abandonment operations as planned, and avoid the extensive costs associated with a significant scope change, the operator identified the need to restore hydraulic integrity as the only practical means of generating sufficient force to unlock the connectors and remove the HXT's. The operator made contact with an engineered sealing solutions provider and discussed the issue at hand. Through analysis and discussion with the operator, a repair procedure was developed to utilize a subsea accumulator skid to inject a custom blended sealant via HFL's through a RWOCS plate and into the HXT Tree Connector Unlock System. This sealant would then be injected to completely fill the unlock chamber temporarily restoring integrity of the damaged elastomeric seals and enabling the connector to be unlocked conventionally Following the development of the necessary approach and sealant blend, the first two HXT connectors were repaired and successfully disconnected using a retrofit RWOCs panel skid with affixed accumulators. Prior to performing the third repair, the operator designed and manufactured a purpose-built accumulator skid with all associated tooling to streamline the operation. The next two HXT connectors were then successfully repaired and disconnected using this enhanced equipment spread and methodology. Currently, operations have proceeded using this methodology with 100% success rate to unlock connectors on all the remaining wells. Whilst the root cause of the failed seal elements within the connector has not yet been determined, the repair procedure has proven to be successful and has evolved over time to meet the bespoke requirements of each connector, including sealant repair of the Tree Connector Lock chamber, thereby enabling cycling of the connector to break friction and encourage movement of the locking dogs prior to TCU repairs. This approach, along with modified overpull techniques, has proven successful in enabling the HXT's to be removed.