Iceberg Impact Research Articles

Technical And Economic Evaluation Of Ship-Shaped Floating Production And Storage Systems For The Canadian East Coast Offshore

Abstract This paper discusses the evaluation and technical feasibility of Ship-shaped oil production systems for the Nova Scotia, Grand Banks and Central Labrador areas. A general analysis of vessel dynamic response to wind wave action, current and ice is presented, on the basis of which two preferred designs are outlined: a fully dynamically-positioned ship, and a single point-moored vessel with a counterweight and a turret. The production downtimes due to the shuffle lanker oil export system are also studied using a wave hindcast computer model. An estimate of the economic threshold values for resources and well productivity is presented. The potential for early production systems and reservoir testing is highlighted. Introduction There are many systems available to the operator for development of offshore oilfields. These include floating production systems, fixed structures (concrete and steel), compliant structures, surface wellheads, subsea wellheads, subsea manifolds, glory holes to avoid iceberg scour, flowlines, pipelines, tankers, trenches, storage, offshore offloading systems and any combination of these. All have advantages and disadvantages. In shallow waters (less than 300 m water depth) and in ice-free environments, the fixed structure systems with export by pipelines appear the most popular and economic for elatively large fields. Where the size of the field is not large enough to support long pipelines and large production structures, floating production facilities with shuttle tanker export systems, together with subsea production systems, must be considered. A vast area of the Canadian east coast has ice-infestedaters. Large fixed structures, designed to withstand the impact of ice and icebergs are probably too expensive for the size of the majority of oil fields to be discovered. Floating facilities, on the other hand can be moved away if ice conditions are too severe. Consequently, based on existingworld-wide technology, this paper discusses ship-shaped floating production, storage and offloading systems (FPSO). The ship-shape system has a number of attractions compared with a semi-submersible floating production vessel; namely:The motion characteristics of a large ship are as good as a semi-submersible as shown in Figure 1.The ship can be more heavily ice-strengthened than a semi-submersible. Also, if a large bergy bit does puncture the ship (see Fig. 2), a ship can, in general, withstand a greater degree of structural damage and flooding.The ship can store up to 150 000 tonnes of oil which will reduce downtime for shuttle tanker loading during bad weather.The ship provides a large deck area for production equipment compared with the restrictions placed on semi-submersibles.For dynamically-positioned and internal-turret moored systems the ship will protect risers and moorings from pack ice and bergy bits. The turret area is large enough to install equipment to overcome problems of high-pressure swivels.Due to its relatively low costs, the FPSO could also be used as one step in the over-all development of a large oil field as well as for marginal field developments.

Geotechnical Sampling of the Sea Floor

Abstract Introduction A part of exploration for petroleum resources is the development of a regional geological model of a prospect area. Such a model requires ground truthing of geophysical data through sampling of bedrock sequences. This ground truthing is provided by borehole drilling and, in areas where the bedrock closely approaches the seafloor, can be achieved cheaply and effectively with remotely operated seafloor drilling systems. Development of offshore petroleum plays requires a knowledge of the engineering properties of the seafloor sediments at the location of the potential development. Offshore Canada, the need for detailed geotechnical knowledge of the seafloor sediments is increased by the requirement to provide protection for pipelines and production systems from impact of ice and icebergs. Information is required for foundation studies, excavation/trenching criteria and the more general consideration of effective loading on buried systems resulting from iceberg impact on the overlying seabed. Generally, geotechnical information of this kind has been obtained from borehole drilling and associated in-situ geotechnical measurements. In the offshore, this is expensive if carried out from a surface drilling vessel, particularly in water depths greater than 150 m, where the use of a dynamically positioned drill vessel becomes almost essential. As a result, increased emphasis has recently been placed on the refinement of geophysical tools and the development of remotely operated portable seafloor- mounted sampling and measurement systems for cost-effective preliminary assessment of extended areas. Acoustic "Sampling" Considerable work has been carried out on the relationship between acoustic velocity and impedance and other physical properties of marine sediments (e.g., Laughton, 1954; Hamilton et al., 1956; Hamilton, 1970; Sutton et al., 1957; Morris et al., 1978). This work was originally aimed at accurately predicting sound velocity in seafloor sediments from a knowledge of average grain size and sediment type. In recent years, the emphasis has' been on the remote measurement of acoustic properties for the estimation of the physical properties of the sediments (e.g., Li and Taylor Smith, 1969; Lee et al., 1977; Maclssac and Dunsiger, 1979). (figure in full paper) acoustic impedance mismatches resulting from changes in the physical properties of the sediment within a sedimentary sequence to map stratigraphic boundaries. Measurement of the reflected energy enables the acoustic impedance of the sedimentary interface to be calculated and thus changes in the physical properties of the sediments to be predicted. Advances in the design and manufacture of high-resolution marine seismic systems have led to the development of systems with well-defined and repeatable broadband output pulses. Sound sources such as the Huntec Deep Two Seismic System have enabled quantitative measurements of acoustic reflectivity and online graphic display of reflectivity indices to be included as part of the standard survey data acquisition (Parrott el al., 1979, 1980). The reflectivity data, coupled with the acoustic character of the seismic record has proved effective in defining sediments type and mapping the boundaries of geological units on the seafloor.

Monte Carlo simulation of iceberg impact probabilities

This paper presents a formulation for determining the uncertainties in the prediction of iceberg impacts with offshore structures at a particular location using a Monte Carlo simulation. Empirical Bayesian estimates of the probabilities of the TOP event (defined as the impact of an iceberg with an offshore structure) are made using a fault tree analysis. An available computer code, based on fault tree analysis, has been adapted for calculation of the iceberg impact probabilities. The procedure indicated for obtaining the uncertainties of prediction of iceberg impact with offshore structure can be used also when cut sets of current, wind, wave, and storm data are available instead of the drift angles.