Case Study

Unique, one-stop-shop hydrate remediation solution enables client to efficiently access and unblock flowline.


Oil and Gas





In October 2020, a major operator contracted Oceaneering to remediate hydrates blocking their flowline in multiple locations.


The hydrate obstructed flow from the subsea asset to the topside platform and prevented the operator from flushing the flowline and decommissioning subsea infrastructure. Oceaneering successfully developed an innovative solution to establish flowline access points at desired locations. The access points allowed Oceaneering to use its Hydrate Remediation Skid (HRS) and Flowline Remediation System (FRS) to remove the blockage and re-establish communication from the subsea asset to the platform.


The operator wanted to decommission an exhausted subsea flowline located in the U.S. Gulf of Mexico at a depth of approximately 6,300 fsw.

Prior to decommissioning, the flowline needed to be flushed and flooded with seawater. However, during an unsuccessful flushing operation completed by the operator, communication could not be made between the topside platform and subsea flowline manifold termination (FLMT). After further investigation, hydrate blockages were identified at five separate locations along the flowline. With no access points available for hydrate remediation, Oceaneering was tasked with creating tap points where internal pressures of up to 3,000 psig were present. The access points were required to provide a seal, enable depressurization of the flowline, and support hydrate remediation operations.

Our Solution

Oceaneering proposed an innovative hot tapping approach to develop a system capable of sealing on the outer diameter (OD) of the flowline and tapping into the bore without removing the flowline’s three-layer polypropylene (TLPP) coating.

Hot tapping is the controlled process of introducing access to the flowline’s inner diameter (ID) by drilling a hole through the OD while internal pressure might be present.

For this project, Oceaneering designed, developed, fabricated, tested, and installed an entirely unique engineered system. This included customized subsea clamps, sealing saddles, and all auxiliary equipment. Oceaneering also executed the offshore operation using its fleet of remotely operated vehicles (ROVs) to install four complete systems along the approximately 60 miles of flowline. A proprietary FRS was used in conjunction with our HRS to remediate all suspected hydrates and ensured communication was established between the topside platform and subsea FLMT.

Execution Plan

The project was conducted in three phases.

Phase one included approximately three months of front-end engineering and design (FEED) study to establish and define technical requirements, applicable standards, and project guidelines, including scope, schedule, and cost. Phase two lasted seven months and included the detailed design, development, fabrication, and testing of the system. Phase three was approximately one month and included vessel mobilization and the offshore installation and operation of system and remediation of the flowline. To execute the offshore scope, the Oceaneering team followed the general operational sequence detailed below.

  • The custom subsea clamp was lowered and secured onto the flowline.
  • The Oceaneering pressure annulus relief (PAR) tool was set and latched onto the clamp.
  • Once a spot face seal prep was created on the flowline OD, the tool was removed and replaced by the sealing saddle.
  • The saddle sealed against the spot face and allowed the hot tap drill tool to operate, creating access holes to the ID of the flowline while containing the internal pressures and preventing any environmental hazards.
  • After drilling operations were completed, the saddle enabled the flowline to be sealed in and the drilling tool was removed and replaced with a high flow manifold to support any additional intervention operations.

Project Highlights

  • Exceeding the client's expectations while meeting schedule and budget constraints
  • Engineering a reliable system while minimizing downtime
  • Enabling the rapid mobilization of tooling spread
  • Executing a successful campaign using complex systems and complete solutions
  • Increasing efficiency by eliminating the requirement to remove flowline coating or complete any subsea dredging
  • Completing the work scope in challenging conditions and high sea current at approximately two knots
  • Using expertise in ROV operations to perform delicate tasks including system installation and operation of complex systems
  • Validating products through extensive system integration testing

Oceaneering provided the client with a one-stop-shop for the entire scope of the project, including development and fabrication of a unique solution, vessel mobilization, ROVs, and offshore execution phase of the project.

This enabled the client to streamline communication, project management, and expedite the complete project within the desired timeline.

Out of five subsea clamps manufactured and delivered to the client, four of the systems were installed. All were successfully operated without any failure or downtime. The custom clamp system held exceptionally well without needing to remove any TLPP coating from the flowline nor dredge the half-buried flowline.

Oceaneering succeeded in removing all hydrate blockages in the flowline and establishing communication from topside platform to subsea asset to perform flushing operations.

The project was completed without incident, on time, and to budget, demonstrating Oceaneering’s ability to use best practices in identifying solutions to challenges.

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