Future ROV requirements in deepwater

Dec. 1, 1999
Looking back while looking forward is often a way to approach the solving of complex problems.

Looking back while looking forward is often a way to approach the solving of complex problems. As the offshore energy industry inexorably moves into deeper water in its search for energy resources, the means to support these efforts becomes more complex, more expensive, and more demanding of innovation. How did we get to where we are today? How will we move forward to address the new opportunities presented by deep water?

Until now, we have addressed the requirements of finding, developing, producing, and transporting energy from the ocean floor by utilizing surface-based technology. We explore, drill, complete, produce and transport products by reaching the seafloor from the surface through ingenious devices, which depend upon the surface of the sea for their support and operation.

When the industry was young, we thought that the practical limits of deepwater operations were set by the mooring ability of the drill ships, the depth of manned intervention, the length of platforms legs, and the size and depth capabilities of the pipelay vessels.

As time went on, the industry developed innovative solutions, such as dynamically positioned drillships and construction barges. Additionally, elegant production platforms reached from the seafloor to the surface on rigid or tension legs and remotely operated intervention systems became more commonplace. At about 3,000 meters, the industry stands at a turning point. Have we finally reached the end of the extension of surface-based support or will another burst of inspiration, ingenuity and innovation move us once again past this point?

Recently, a major operator announced that work had commenced on the design of a seafloor drilling platform. Although the concept still utilizes power from the surface, it also marks a major departure from the heretofore-traditional approach.

Seafloor drilling based on remotely operated and controlled hydraulic ram drilling operations including pipe handling appears to be a viable cost- effective alternative to the expensive surface-supported deep water drilling operations.

Deepwater intervention has moved from manned saturation diving to today's many varieties of heavy work class underwater tool carrying robotic systems known as remotely operated vehicles (ROV). As water depths increased, the design of these systems evolved to balance requirements between the size and weight of the systems and the tooling and power required for their work tasks.

Some of the more recent innovations have been in the area of higher voltage systems to reduce the size and weight of the armored power and communication/control umbilical and electric motors and the use of new lighter weight flotation.

Since intervention is at the heart of any subsea development, we should consider some innovative suggestions which have been put forward.

  • Semi-autonomous ROV: One concept involves a semi-autonomous ROV (SAROV), which can be launched with enough power to fly to an underwater docking station where it will plug into a light-flying umbilical or tether and conduct its tasks. The docking station would be a part of the subsea completion and would have its own permanent umbilical to control wellhead functions, while additionally providing power and control functions to the SAROV. Alternatively, a docking station could be lowered to the seafloor and the SAROV would fly to this station and plug in to the docking station. Unfortunately, this is not quite as elegant a solution as the former as it entails a heavy armored umbilical and an underwater tether winch, as well as a large surface spread to handle the equipment.
  • Onboard power ROV: Another approach utilizes onboard power for the ROV and still maintains a connection to the surface with a smaller diameter lightly armored fiber optic umbilical. The specific function of the umbilical would be to support launch and recovery and real time control and communication with the ROV. The power source is the key to this concept. Remarkable progress has been made in the field of self-contained power and the concept must be considered further.

In fact, a prototype system for light work tasks utilizing rechargeable batteries is being designed and built. An alternative approach would be to incorporate a small diameter power cable in the fiber optic umbilical and a rechargeable power source on the ROV. The ROV could recharge its power source while on the bottom between work tasks.

  • Autonomous ROV: A few forward-thinking survey companies have taken the road toward completely breaking the tie with the surface. They have ordered autonomous underwater vehicles (AUV) powered by advanced design fuel cells. When pre-programmed, the AUVs can perform their missions of survey and information gathering without any ties to the surface. They are launched over the survey site, descend to the sea bottom, fly the survey routes and gather information. Upon completing the mission, they return to the surface for the recovery and information management phases. Estimated cost savings exceed 1/3 of conventional methods costs, and in fact, the precise survey routes of the AUV's will provide higher quality data than existing "conventional" methods. Innovation and advancements in technology by the manufacturers and support by both the survey companies and their customers made this possible.

New requirements force development of new and innovative solutions. In turn, innovation may also entail a threat to the traditional approach. Once implemented and developed, these solutions become a part of a "springback" phenomenon.

If systems forced upon us by deepwater requirements work effectively in 3,000 meters can they not be used cost effectively in lesser depths? This has been repeated time after time in this industry as new concepts are forced upon us in order to meet new requirements.

In order to objectively look at the future and address the new requirements that will be generated, we must not continue to provide "comfortable" solutions, just because they are extensions of our current methods.

Rather, we must truly be objective as well as innovative and work to offer solutions that will challenge our creativity and test our resolve. Otherwise, saddled with the burdens of the past, we will be unable to move forward into the future.

Bruce C. Gillman, P.E.
President and Chief Executive Officer
Sonsub International, Inc.
Houston, Texas