Executing subsea tasks in in today’s offshore environment, in large part requires a three prong approach, consisting of: divers; Observational Remotely Operated Vehicles (ROVs); and Work Class ROVs (WROV). Though each of the aforementioned approaches has inherited advantages over the other, they equally have drawbacks when comparatively analyzed. For this reason, we have carefully selected the following videos that visually illustrate the aforementioned.
Observational ROV Performing in a Work Class Environment
Subsea manifolds are key in routing, isolating and manipulating the content of subsea wells: this, of course, requires that the manifolds be fully operational. However, in the real world, this is not always the case, as highlighted by manifolds which were installed in the North Sea, which proved to be defective once operations ensued on the sea floor. This was due to the fact the manifolds were missing hydraulic caps, preventing the linked wells from producing. This was compounded by the fact that accessing the area where the hydraulic caps were missing were utterly inaccessible by a WROV.
As a result, the operator had to decide whether to recover the manifolds to install the missing caps, a cost prohibitive solution, or find a subsea solution. In the end, the operator opted for the latter, resulting in an OROV being outfitted with a torque tool to install the missing caps. The use of an OROV in an arena that is dominated by WROVs proved to be a unconventional and very forward thinking solution, that allowed the wells linked to the manifold to successfully produce.
WROV Installing Flying Leads
This video gives an excellent example of a WROV handling and installing flying leads at the Neptune Canada Cabled Ocean Observatory: a task that an OROV is not suited for. This is due to the fact that the weight of a flying leads can easily exceed the buoyancy capabilities of an OROV (Click here for more detail on flying lead handling). In addition, connecting wet-mateable subsea connectors requires the use of a WROV's manipulators to provide the sufficient force to mate and unmate a connector—as shown in the above video. This video also shows the advantages a WROV's front porch offers, allowing for storing and housing additional components, at depth, such as the wet-mateable debris caps by way of a crate positioned on said porch.
As the video progresses, it illustrates how easily the mudline is stirred via an ROV's manipulators. It is important to note that in a setting where both an ROV’s manipulators and thrusters are simultaneously employed, this can cause severe visibility issues when conducting underwater tasks. This video, however, does not capture such severe scenario, but does shows in great detail the manner by which operations are carried out on the sea floor.
A Diver and Swift Motions
This video which is very high paced does a great job of highlighting the advantages of using a diver, as well as the dangers that a diver must contend with. The first item to notice once the video starts is the orange airbag which is removed from the section of the pipeline, such airbags are key for diving projects as they provide additional buoyancy when landing weight intensive objects, such as the pipeline section. In spite of this, air bags also pose a threat to a diver’s well-being. This is exemplified by the rupturing of an airbag, causing the weight intensive item to abruptly travel downward, and trap a diver at depth after it has settled. Conversely, ROVs remove the human equation from the risks of subsea operations.
As the video progresses, the advantages of using a diver over an ROV become highly apparent; as exemplified by the diver’s rapid hand movements as he tightens the nuts on the pipeline’s studs while using an impact wrench: removing of the pipeline’s cover further demonstrates the diver’s dexterity. Conversely, employing a work class ROV to connect pipeline sections together, or remove a blind flange at depth, requires specialized tooling and intervention equipment, resulting in a cost and time intensive operations.
Editor's Note: All copyrights lie with the user accounts to which the videos are linked to, which is provided via the information button on each video. The videos illustrated herein strictly adhere to the United States' Fair Use Doctrine. As such, they are used for educational purposes, and to review existing offshore technologies, while giving a transformative commentary in the manner by which the technologies in said videos interact with their environment. Reaching Ultra and the proprietors of said videos have no business association, relationship, or interest.