New underwater installation and inspection system for jackup rigs
Building on experience gained from using its Crane Boom, MultiCAM and CamScan camera systems, UWG has developed Spudcam, a new system for monitoring the installation of jackup rigs without needing an ROV.
Mobile jackup rigs are widely used to support drilling or production facilities and increasingly in temporary production and maintenance work. Typically, three or four extendable legs support these rigs; each has a foundation footing known as a spud can. Generally conical in section, these spud cans can be over 15 m in diameter and may need to penetrate the seabed by two to three times their diameter to achieve equilibrium.
When installing a jackup rig, it is critical to watch each spud can landing on the seabed as the leg is extended. This practice ensures that the spud can does not land on a seabed structure (such as a pipeline), very uneven ground or
the edge of the footprint left by a previously sited jackup rig – an increasing risk, as rigs are frequently moved in and out of a location. If a jackup’s leg does slip into a depression, the resultant lateral movement of a single leg can result in poor rig positioning, damage to the rig or platform, lost drilling days or, in the worse case, injury to personnel or collapse of the rig.
Spud cans are traditionally landed with the help of camera systems mounted on ROVs. This combination is used to survey the seabed at the proposed installation site and provide a real-time view to operators on the surface as each leg is extended. The same ROV–camera combination is used during regular maintenance of rigs or platforms to inspect the rig legs for corrosion. As the maintenance cycle may be as short as two weeks, frequent access to ROVs is essential for some rigs.
However, being dependent on ROVs has its drawbacks: they are relatively costly and their mechanical and electronic complexities mean that they require careful maintenance and, typically, a four-person operating team to ensure trouble-free use. In addition, ROVs can only be used in calm conditions, which may mean expensive delays while waiting for suitable weather.
UWG’s Spudcam system eliminates the need for ROVs by using a camera assembly (subsea video camera, white LED light sources, actuator and extendable arm) attached to a track secured to the side of each of the rig’s legs. The tracks are fixed to the leg when the jackup rig is in dock and remain there permanently.
In operation, the rotational pivot at one end of the camera assembly is attached to a carriage, which rides along the track. Controlled from the surface, the camera assembly is lowered, under its own weight, to a position near the base of the leg just before it is fully extended. The pivot enables the arm to move ±90° from the horizontal. The articulated joints allow full freedom of movement for the camera so that the seafloor all around and beneath the spud can is viewable.
High-quality images are received throughout the operation and are digitally recorded at the surface. If required, a slave monitor can relay the information to teams in different locations on the jackup rig. Using these images as a guide, it is possible to locate the spud can on a fresh area of seabed, or in the exact centre of an existing spud can depression.
Once the site is confirmed as clear and safe, the camera arm is folded against the track. The whole assembly is then pulled away from the base of the leg using a surface winch attached to a steel rope, which forms part of the cable bundle. This cable bundle also includes hydraulic and electric lines to supply the camera system.
Typically, the camera system will be lifted from one leg to the next to repeat the operation. However, to speed up the installation procedure, individual Spudcam systems can be fitted to each leg of the jackup and run in parallel – another advantage over the use of an ROV for the operation.
Owing to the relative low-cost of the system, Gary Omer, projects engineer (electronic products), UWG, envisages a rig having one or two camera systems permanently available to send down the tracks and inspect the jackup structure on a regular basis. He says, “Very high resolution colour camera systems, with excellent very low light characteristics, are now much more widely available. Such systems offer considerably enhanced performance, which can be readily applied to a wide variety of new applications that could not previously be viewed in real time, and/or without using ROVs. Reducing dependency on ROVs has major weather window availability benefits and is a very cost-effective alternative.”