Cyril Poissonnet reports on working safely around offshore installations by using a capable MiniROV
Remotely operated vehicles (ROVs) have long proved their worth in the offshore oil and gas sector and today are more essential than ever. The players in this market have an ongoing dedication to innovation – via both new solutions and adapting existing ones – and technical excellence.
Teledyne SeaBotix is one of these players. Its vectored Little Benthic Vehicle (vLBV) is a man-portable MiniROV offering power and communication for a multitude of sensors and tools in a choice of depth ratings starting from 300m, all the way to 4,000m.
Offshore installations offer more challenging conditions for an ROV than those encountered in pools, tanks, lakes or even nearshore. Offshore winds generate waves and currents that make deployment and operation more difficult than in still waters.
The vLBV is a vectored thruster vehicle. Horizontal motion whether forward/reverse, left/right or rotation clockwise/counterclockwise is achieved by intelligently combining the propulsion of four thrusters simultaneously. Not only is the vehicle quicker to respond, it also offers much more power and speed than a single thruster especially for lateral motions. As a result, the vectored thrust vLBV is ideal for handling up to 1 to 2 kcurrents often found in shallow water around offshore installations.
Rent or own
Several small and large offshore service companies own multiple vLBVs that are used for inspections around offshore installations. One of Teledyne SeaBotix’ customers uses a vLBV950 in 600m (1,800ft) depth for environmental surveys on behalf of oil majors. HD video and high-resolution digital stills of the seabed are collected to evaluate the impact of a potential drill site on the environment. Another service provider uses a vLBV300 outfitted with a high-resolution, narrow field-of-view, Sound Metrics Aris Sonar to check for alignment of two underwater structures in zero visibility conditions in Alaska. In these examples the end customers are oil majors that have infrequent use of the vehicles. It is more cost effective for them to rent the equipment and expertise of a trained pilot for a particular job rather than invest in the purchase of an ROV system that would seldom be used.
But sometimes inspections have to be performed weekly or monthly. The US Environmental Protection Agency’s (EPA) Code of Federal Regulations (CFR) 40 requires mandatory weekly or monthly inspections of sea chest water-cooling intakes on all offshore installations built after 2008. In this case, it is more cost effective for the oil major to purchase equipment and training and to perform the routine inspections with their own personnel rather than hire a service provider. This is the solution Chevron chose for sea chest inspection aboard Jack St Malo.
WROV Versus MiniROV
Work Class ROVs (WROV) have historically been the underwater workhorse around offshore installations. MiniROVs are no match for the lifting power and tooling WROV can support. However, when it comes to inspections, a vectored MiniROV such as the vLBV offers very similar flight performance due to similar power to drag and power to weight ratios. MiniROVs can fit in spaces where an WROV cannot, such as inside subsea tree installations. MiniROVs can perform inspections in challenging conditions and close to expensive pieces of equipment without risking damage to the installation.
300m MiniROV systems are only a fraction of the cost of a WROV, however, when deep water deployments are required (1,000 to 4,000m), even a MiniROV needs a launch and recovery system (LARS), tether management system (TMS), and a control room. Although there are cost savings in the purchase of the MiniROV, the more important saving is the reduced cost of commissioning and smaller deck space requirement.
Typically, a WROV is deployed on a dynamic positioning (DP) vessel with a large, permanently installed A-frame for the launch and recovery system (LARS) plus control van and workshop. The rate for a vessel of this type is approximately US$120k/day. Comparatively, a MiniROV system can fit in a single 20ft containerised delivery system (CDS) with control room, LARS and TMS all in one portable package. The CDS can be deployed on a vessel of opportunity for US$15k/day.
The commissioning for the MiniROV is one order of magnitude less expensive than the WROV. If the WROV is only going to be used for deep water visual inspections or carrying basic sensors that could fit on a MiniROV, then the CDS becomes a logical and very cost effective approach for inspections. The CDS also provides an ideal mobile solution for platform/rig or floating production storage and offloading vessel (FPSO) riser inspections.
For more information at www.engineerlive.com/iog
Cyril Poissonnet is with Teledyne SeaBotix.