The Magazine for Underwater Professionals

Jul/Aug 2019


Smart new skid eliminates hydrate in GoM pipeline system

Newly developed hydrate remediation skid incorporates smart, real-time software to address and prevent the potentially harmful build-up of hydrate in small volume subsea pipeline systems, writes Gram Hall, regional products manager at i-Tech 7

Figure 1: Skid being lowered into place using certified lifting points designed for safe, even lifts

Incorporating intelligent, real-time software, the next generation hydrate remediation skid (HRS) has successfully completed its maiden mission in the Gulf of Mexico (GoM).

Unlike any other skid of its kind, the latest innovation has been developed by i-Tech 7, Subsea 7’s Life of Field business unit, to efficiently remediate and prevent the potentially harmful build-up of hydrate in a subsea production facility.

As part of the company’s hydrate remediation service, the innovative techniques are based on a combination of pressure reduction and chemical injection technology to accurately dislodge and disassociate blockages in small volume pipeline systems.

Over a 12-day period, i-Tech 7 was contracted by an independent oil and gas operator in the GoM to carry out hydrate remediation work on a Xmas Tree hub. The project also included remediation of several chemical and hydrate blockages within the umbilicals before they were cut, abandoned and plugged. Pressure testing was fully automated.


Operating in water depths up to 1524 metres (5000 feet), the HRS was deployed from Subsea 7’s Jones Act compliant IRM, survey and light construction vessel the Harvey Intervention, capable of operating in depths up to 3000 metres.


As the operation could not be performed internally via the subsea infrastructure or from the platform, the HRS was selected due to its advanced instrumentation and controls and simplicity of use. This allowed accurate and efficient remediation of blockage issues and quickly restored production to the customer’s facility. Thereby, minimising the impact of an unplanned shutdown and any risks associated with downtime.

As an ancillary piece of equipment, which is complimentary to the hydrate skid, the subsea reservoir system is an 8.5- x 20-foot (2.6- x six-metre) frame that holds four 400-gallon (1500-litre) bladders. This allowed the operator to take the skid subsea with ‘clean’ fluids for injecting, while the system simultaneously returned ‘dirty’ fluids. The HRS then disposed the effluent into a sealed container for recovery of both small and large amounts of hydrocarbons.

This system is completely configurable and is deployed by crane and positioned on the seabed near the access point to the subsea asset (see figure 1).


Once on the seabed, the ROV retrieved one end of a hydraulic flying lead which was inserted into the hot stab manifold on the subsea reservoir system. The ROV then took the other side of the flying lead and plugged it into the manifold mounted on the ROV that connects to the effluent line on the hydrate skid. The skid then drew the fluid from the reservoir through the skid and into the affected line.

The operation was successfully completed on time, within budget and without incident. Since the initial project, it has been used on three further hydrate remediation projects with the same operator.

Built in the GoM during 2018, the HRS is suitable for deepwater operations in maximum operating depths of 3000 metres (10,000 feet). It is designed to interface with work-class and heavy work-class ROVs, independent of the ROV contractor, operating on multi-service vessels or drilling rigs. It can be integrated with any ROV in the market regardless if it is a top hat or cage system (see figure 2).

  • Figure 2: Each skid is built with a set of interchangeable ROV interface adapters which allow for easy mounting to all ROV models commonly used offshore

While the flow rate performance (configured with redundant pumps) is typical of conventional ROV-mounted pumps (2gpm/7.5lpm), it can operate at 6000 psi (415 bar) in atmospheres with more than 3000 metres hydrostatic pressure. At maximum operating depth, hydrostatic pressure is approximately 4500 psi (310 bar). The system can reduce the hydrostatic pressure down to 15 to 30 psi Absolute (one to two bar).

Weighing 726 kilograms (1600 pounds) in the air and neutrally buoyant in seawater, it features enhanced automated controls, which can depressurise jumpers, wellheads, umbilicals, and chemical injection lines with small volume production piping infrastructure.

Unlike other conventional skids, the power supply is built into the unit. This allows the distribution of power across to the skid to be completely isolated from the ROV power.


The HRS is designed to maintain as close to 100% uptime as possible. If maintenance is required, components can be easily and quickly interchanged. It needs only one electrical line and two hydraulic lines to connect to the ROV. Communications are processed through the ROV umbilical and into the control room where the hydrate remediation technician operates the software from a laptop whilst liaising directly with the ROV pilot and co-pilot.

To mitigate risk, the skid has several safety features built into it:

  • If communications are lost during operations all valves will auto-function to the closed position.
  • Should all power be lost to the skid and pressure to the line is higher than ambient, the check valves, which are built into the pumps, will not allow the inventory of the line to escape through the system.
  • Software has built-in failsafe measures to minimise human error during operations.

An external rental tool can be added to the skid to allow a rapid fly-by external inspection of the pipeline using a non-intrusive sensor. This helps to assess wall thickness and provide early identification, in real-time, of hydrate and wax anomalies. Pressurised hydrate inhibitors are then routed through the production piping in either direction to inhibit the flowline and prevent hydrate reformation.
The HRS system employs new digital technology which utilises electrically actuated process valving for the management, monitoring and distribution of hydraulic process circuits (see figure 3).

  • Figure 3: Electronically actuated valves with position feedback offer a significant advantage in reliability, automation and resolution control

Advanced automated control allows the user to have greater system flexibility to monitor the interaction and behaviour of the hydrocarbon contents of the operator’s pipeline. With comprehensive topside software control, the operator thereby has more precise capabilities to accurately monitor pressures and flows.

HRS skids have high accuracy instruments fitted that allow for high fidelity measurements of pressure versus volume recordings, which can aid in determining the approximate locations of blockages.

To concisely disassociate hydrates from the natural gas, the skid can also accurately mix and inject the inhibiting (antifreeze) chemicals into the process line to treat de-inventoried production hydrocarbons to prevent the reformation of hydrates during recovery. This will then precisely measure and utilise trends to monitor the hydrate removal rate. Better diagnostics will allow more efficient and accurate decision making, which allows the company to deploy well stimulation solutions earlier and more effectively.

Prior to the inaugural hydrate remediation project with the independent operator in the GoM, the HRS underwent two extensive sea trials in water depths of 1493 metres (4900 feet) to qualify the new hardware system.


The HRS skid was fitted to the ROV and was configured to perform tests while ROV operations were off the critical path. The company worked with flow assurance engineers to gain access to the affected line blockage to ensure best means of access and cooperated with the operator to inject chemicals for treating the production stream and mitigating the formation of blockages.

The skid carried out its first deployment, successfully without any technical difficulties. This allowed for function testing of all systems in deepwater conditions. Any adjustments to system parameters were able to be performed with onshore support in real-time. The trial successfully concluded with 100% of the hydrate being removed and remediated.

Without the need for any further reconfiguration to the system, the HRS can be used to inject fluid, through a metering valve, of very precise amounts of dosing chemicals into the subsea asset. It can also be used for many applications such as ROV workover control, hydrotesting, back seal testing, and other various fluid injection activities.

Looking to the future, there are plans to upgrade the system further to enhance its ground fault detecting capabilities within the system.





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