Subsea Ice Risk Assessment and Mitigation
Recent experience from field developments on the Newfoundland Grand Banks, off Canada’s East Coast, highlighted the cost and schedule risk associated with protecting seabed infrastructure from gouging icebergs. The conventional approach has been to dredge the seabed, creating Excavated Drill Centres (EDCs) into which the wellhead equipment is set, with the top of the Xmas trees safely below the extreme iceberg keel floating or gouge depths. Development of innovative alternative systems has been identified by industry as a key driver in allowing the more marginal projects anticipated for the future to proceed.
SIRAM focused primarily on the East Coast of Canada, specifically the Grand Banks and the Labrador Shelf, whence field data and operational experience is increasingly available and multiple well-drilling centres will be needed to develop marginal and satellite fields. Tie-backs from future wells to existing production facilities is being considered for the Grand Banks, while development of offshore Labrador gas may involve full subsea production and export, eliminating surface facilities altogether. Just as surface facilities require assessment of ice and iceberg contact risk, subsea facilities require assessment of risk from iceberg-keel interaction. C-CORE responded to this need with the SIRAM program, aimed at quantifying site-specific risk and developing broadly applicable solutions, including mitigation techniques and structures, for protecting subsea infrastructure from interaction with ice and iceberg keels.
In pursuit of these objectives, SIRAM developed improved models for estimating iceberg keel contact frequency and loads, as well as identified and evaluated novel protection concepts as alternatives to conventional EDCs.
The objective was not to necessarily eliminate EDCs entirely, but rather to explore alternatives for field developments where the cost of dredging an EDC (perhaps in variable seabed conditions, ranging from dense gravel seeded with boulders to hard pan or bedrock) would undermine project economics, given the smaller hydrocarbon asset in place and the reduced number of producing wells. An ISO19906 basis for establishing target reliability or annual exceedence probabilities for safe and environmentally responsible systems were provided based on the probability of an event and the consequence should an event occur.
While the region of interest and basis for environmental conditions is the East Coast of Canada, specifically the Grand Banks and Labrador Shelf, the results of the program, however, are applicable to other ice-prone regions where iceberg and ridge keels may interact with subsea infrastructure. Focused R&D for ridge interaction with subsea infrastructure may be a natural extension of this present work and could form, in part, a basis for future activity.