With the advances in subsea tools and equipment, more subsea well intervention operations are being performed by remotely operated vehicles (ROVs), said Knut Eriksen, senior vice president, subsea products, Oceaneering, at OTC 2012 in Houston on April 30 in a presentation on “Exciting Developments In Subsea Well Intervention.”

“What is well intervention?” he asked. “It includes completing planned and incident-based operations. Planned interventions include workover and completion, flow issues, well control and inspection.

“As we see more and more future hardware going on the seafloor in deeper and deeper water, it will require more capabilities and interventions. It is a very challenging future for us and others with the intersection between tools, products, and services,” he continued.

Using ROVs enables operations to use alternative vessels that are smaller and less costly, he explained. For working on control systems, for example, operations can be done without returning to the surface for reconfiguration.

The system can also be adapted to test pressure integrity of flowlines before a platform is deployed in a field development. The ROV can test the unconnected ends of production umbilicals.

ROVs are also used for hydrate remediation. The system allows the ROV to pump down the pressure in the line and equipment or inject chemicals, Eriksen said. Most frequently, ROVs are used for emergencies due to hydrate formation.
“For hydrate remediation, it is a lot simpler if you plan for interventions in the design phase,” he noted.

“We can eliminate considerable operating expense for small hydrate volumes in trees, manifolds, and jumpers,” he said.

There is also a flowline hydrate remediation system designed for larger volumes. These can be operated by the ROV subsea or can depressure the line and be connected to the surface through dual, coiled tubing.

Well stimulation systems can be installed on the tree or manifold hub. Fluids can be delivered to the well through a dual, coiled-tubing unit from the vessel. These units can be deployed, controlled, operated, and retrieved from a vessel of opportunity.

Another area where ROVs are getting more attention is in well control and containment systems, especially for deepwater wells. Companies throughout the world are working on systems to control deepwater wells, Eriksen emphasized.

“A substantial amount of intervention is required. New rigs have led to development of BOPs during drilling,” he noted. “There are now ROV BOP testing and override skids that can test BOPs after deployment. It uses clean hydraulic fluids and has sufficient fluid capacity to override the rams. It can be supplemented by sea water if necessary.”

An auxiliary BOP override system can either be stationed on the vessel or pre-installed on the BOP. The system provides high-pressure fluid to close the rams. The ROV can connect large flowlines to the accumulators and BOP stacks.

A new system is under development with 5,000 psi to 7,500 psi operating pressure to handle shear forces for larger and heavier tubulars, he said.

Until recently, there was a lack of interface communication between various equipment and insufficient flow capacities on BOPs. There is now an intervention stab plate designed to plug into existing stacks. These removable stab plates are designed to reroute hydraulic fluid as required or to bypass leaking functions.

An emerging technology involves using the ROV for subsea replacement of regulators. Previously, the BOP and riser had to be recovered to the surface to replace the regulators.

Other functions being performed by ROVs include subsea dredging, tree release during well abandonment operations, subsea pipeline, flowline and riser inspection, powering all-electric subsea trees, and using smaller, satellite ROVs to access areas on equipment that the larger ROVs can’t reach.

Contact the author, Scott Weeden, at sweeden@hartenergy.com.

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