Abstract The ROVDrill Mk.2 is a state-of-the-art seabed push sampling, rotary coring andin situ testing system designed for working in 2500m water depth and obtaininggeotechnical data to a depth of 120m below seabed. The system has beendeveloped as a geotechnical upgrade to two ROVDrill subsea robotic drillingsystems previously utilised in rotary coring mode in deep-water for the seabedmining industry.
The paper considers the key design features of the current generation of subseadrill rigs and contrasts some of the key conceptual design differences betweenthem. A brief case study looking at the evolution of the ROVDrill Mk.2 rig ispresented including discussion of some of the technical upgrades and an outlineof its principal specifications.
A number of benefits of seabed drilling are highlighted, with particular regardto working in deep water and harsh environments. With the elimination of humanexposure to pipe and tool handling risks, improved operational efficiency andsample quality and increased borehole depth accuracy, the development of seabedpush sampling, rotary coring and in situ testing systems are attractive to theoffshore site investigation market and a real alternative to traditional drillships.
A Brief History of Subsea Drilling Technology Subsea drilling equipment began to appear in commercial use in the 1970's. Theearliest examples of these units were diver operated, marinized terrestrialsingle-shot rotary diamond core drilling rigs used for shallow rock coring forsurvey purposes. They also found application installing the small diameterpiles which are used to restrain and stabilize oil and gas pipelines in shallowwater zones with rocky seabeds, such as those found in the Persian Gulf and NWAustralia coastal oilfields.
During the last 25 years or so, in step with the marine industry move to deeperwater beyond diver depths and taking advantage of increasingly standardized andsophisticated ROV control technology, subsea drill rigs have become remotelyoperated. Early examples remained as single-shot rotary coring systems, butmore capable rigs were developed initially for the deep-water scientific rockcoring research community. As the technology matured more sophisticated drillrig functionality was developed such as subsea pipe storage racks, iron-roughnecks/foot-clamps for pipe make/break, drill/grout mud pumps andcomplete monitoring and surveillance systems.
Since 1996 a number of heavier duty subsea drill rigs have been built for usein the both geological research and commercial subsea geotechnical market. These units are of higher power (up to 150HP) and are capable of drillinglarger diameter bores (typically in the range 50mm to 75mm core diametercapability) and to greater depth (from 20m to over about 100m) than previousrigs. Systems targeting the geotechnical market additionally feature as aminimum push sampling (i.e. sampling of uncemented soils) and cone penetrationtesting (CPT) capabilities.