寒冷海域での油流出に関する研究

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Cold-water oil spill countermeasures may be very complicated by low temperature, presence of ice, short period of daylight and lack of support facilities in northern areas. Japan has had no offshore operating experience in such cold environments. Considering of the recent development of oil and gas resources at the Sakhalin shelf, it seems very critical that Japan should develop, strategically and technically, a level of preparedness to prevent and respond against accidental oil spills from tankers or offshore oil production facilities in the Sea of Okhotsk. The main objectives of this study are 1) to identify a set of vital requirements and conditions needed to develop a national contingency system for preventing and responding to a big oil spill in ice-infested water, and 2) to develop fundamental understanding on the fate and behavior of spilled oil in ice-infested waters and to identify key technologies and techniques to recover spilled oil in drift ice. With the abovementioned objectives in mind, the following themes have been studied. (See Fig.1) 1) Study on total oil spill response system for cold oceans: A general survey was made on existing maritime laws and regulations for the prevention of shipping accidents and pollution of marine environment, Japan's current contingency response system, environmental sensitivity index maps, and related information and database systems. Besides, sea ice and other meteorological and environmental conditions of the Sea of Okhotsk were reviewed and risks of oil spills were investigated. Six recommendations were raised as the conclusions of this study: (1) To establish a cooperative relationship with Russia and other nations concerned, (2) To establish a regional cooperative network among governmental and local institutions and experts, (3) To prepare maps of environmental sensitivity index of the northern coasts, (4) To develop reliable technology for mechanical oil recovery in drift ice, (5) To develop a method for estimating the spreading and drifting of oil slick in drift ice and method for identifying the oil slick covered by snow and ice, (6) To develop a real-time information system for assisting the oil spill response operations In addition to the above, an Internet-accessible sea ice database system for the Southern Sea of Okhotsk was established based on the data from three governmental institutes. 2) Review and assessment of the capability of existing oil-recovery equipments in cold icy ocean: Existing different oil recovery systems have been evaluated when in use in icy waters and their defects were identified. Based on this review, an experimental effort was made to develop a "net-belt type" oil recovery system especially designed for collecting highly viscous oil. In addition, the leaking behavior of highly viscous oil captured in front of oil booms have been studied experimentally. Different gelling powders were examined of its gelling efficiency on different oils. And a trial was made on how to apply the gelling powder from underwater to oil slick staying under the ice. 3) Study on the change of oil properties in icy waters: Laboratory studies were made on changes of oil properties such as viscosity and interfacial tension when the oils were cooled down from normal temperature and brought to freezing temperature. The process of oil encapsulation in ice and release from ice were laboratory-studied. The adhesion strength of oil slick to ice was investigated and the removal of oil slick from ice was successful by flushing with sea water. 4) Study of oil spreading in ice-infested waters: A theoretical analysis was made to predict the extent of oil slick spreading underneath the ice in the initial stage(short time after the release). A numerical simulation program for the same case has been developed, based on a level-set method describing the time-based change of oil slick profile. The numerical model seemed more adaptive to non-homogeneous cases than analitical method where ice has uneven underwater surface. The migration of the oil slick by sea current have been studied in the ice tank of SRI.[figure]
独立行政法人海上技術安全研究所の論文
2000-09-13

寒冷海域での油流出に関する研究

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