Ice gouging of the seabed is a significant consideration for offshore pipelines in the arctic. A methodology is presented for using GIS (Geographical Information System) software for analyzing pipeline burial depth requirements for protection against ice gouging. This approach allows users to perform development concept evaluations, estimate pipeline burial depth requirements, test and optimize various routes and configurations, and generate estimates for pipe and trenching costs once the required input parameters are generated for a specific region, site or development. The framework and algorithms are described and ice gouge data from the public domain are used for demonstration purposes. The use of the LCP (Least Cost Path) algorithm (included in most GIS software) for pipeline route optimization is demonstrated. This subject is of relevance for any offshore development that requires trenching of pipelines in an ice-gouged seabed.
A substantial portion of the world's petroleum reserves are believed to be in arctic offshore regions and other offshore ice- frequented environments. As the world's energy demand continues to increase, oil and gas developments in these environments will also increase accordingly. Consequently, more subsea pipelines will be constructed in these environments. Some of these pipelines (i.e. flowlines, subsea tiebacks and export pipelines) will be constructed in regions where the seabed is subjected to gouging by ice, requiring the evaluation of the magnitude of the risk, risk mitigation requirements and associated costs.
The assessment of pipeline burial depth requirements for protection against ice gouging of the seabed is generally performed by specialists for a limited number of pipeline route options. However, the evaluation of offshore development options can involve the assessment of a number of field configurations and pipeline routing alternatives. The ability to determine pipeline burial requirements and costs, without reverting to specialists during iterations of the field development planning process, potentially represents a significant advantage in terms of time and cost savings. GIS (Geographical Information System) software is useful in the offshore design process, since various relevant data sets (i.e. bathymetry, sediment types, hazards, etc.) can be incorporated into the same platform. GIS software is being used fairly extensively in assessing pipeline routing and hazard assessment for applications on land, but similar offshore applications are not common.
The procedure outlined here can be adapted to various regions, provided the required parameters are available. The analysis requires rasters defining ice gouge crossing rates and gouge depth parameters (as well as other parameters such as pipe response, failure criteria, etc.) to calculate the pipeline cover depth required to meet the target reliability, as well as cost values or functions to produce the associated cost rasters used as the basis for the LCP (Least Cost Path) analysis, which can assist in the selection of the optimum pipeline layout. While generating these rasters and incorporating the required algorithms would require the services of a specialist, the GIS tool can be readily employed by others who need to consider pipeline protection in the context of the overall development scenario(s). The final design would still be evaluated or checked by a specialist.