Research On Key Technologies Of Pollution-free Underwater Oil Storage And Oil Spill Emergency Recovery

Today in China most of the ascertained offshore oil and gas resources are locatedin coastal waters, among which many marginal oil fields are yet to be developed. Itwould cost a lot if equipments like gathering pipelines, fixed storage tank platforms orberthed ships are used to develop marginal oil fields. Therefore, a new productionmode of underwater oil storage was proposed, which means the extracted crude oilwould be directly stored in the underwater storage tanks, waiting to be transported byoil tankers. Gravity platform underwater oil storage and oil-water replacementunderwater oil storage are the two main ways of underwater oil storage. But the hugebuoyancy need to be overcome. The gravity platform is not quite suitable for marginaloil fields because it costs too much due to its large scale, and the load carried by thefoundation varies as the amount of oil changes. Though the oil and water replacementunderwater oil storage is a proper way for marine oil exploration, the marine pollutionrestricts the application of this technology. Then the oil-water separationpollution-free underwater tank is proposed.The pollution-free underwater oil storage model is firstly put forward in thisresearch on the basis of pollution-free underwater oil storage technology. A newunderwater oil spill emergency recovery and storage equipment is then proposedaiming at oil leakage that may occur during the process of offshore oil drilling and oilstorage. Related theoretical experiments and sea tests are carried out. The main workof this paper is as follows. Three new types of pollution-free underwater oil storagemodes are presented including the mode of shallow water fixed platform with oil tank,the mode of shallow water mat underwater oil storage platform mode, and the modeof underwater oil storage with floating dock in deepwater. A series of physical modeltests are carried out, including the process test and heat preservation property test.Materials of diesel, liquid petrolatum, and diesel with water are successively used tocarry out the oil and water replacement process test which shows that the oil-waterseparation technology can avoid the oil-water pollution, demonstrating the feasibilityof the oil-water separation and replacement technology. Plastic-coated fiberglass clothis used as the material of heat preservation inner tank and soft sensing based on neural-network is used to measure and figure out the temperature of crude oil. Then aqualitative and quantitative research on heat preservation properties is conducted. Theresearch shows that high pour point crude oil still has good fluidity during a certainperiod of time because of small temperature change.The exploitation of offshore oil has always been accompanied by accidents andrisks. Oil spill accidents may occur in the process of oil and gas production because ofpipeline breaking, platform damage and careless operation. The consequence will beserious in the environment and ecology. A new underwater oil spill emergencyrecovery and storage equipment is proposed to avild oil leakage that may occur duringthe process of offshore oil drilling and oil storage. And related theoretical experimentsare conducted to simulate the main processes of underwater oil spill recovery andstorage. The problems encountering in the experiment and the force on mooring linesunder wave-current condition are analyzed. Results show that the underwater oil spillemergency recovery and storage technology is feasible in practice.The CIP numerical calculation model has been established for the interactionbetween waves and oil collecting bag. The force and response of collecting bags havebeen simulated for different model forms, sizes and their locations in the water depth.The simulated results show collecting bags with smooth surfaces, shorter share andsubmerged in the water will lead to smaller wave forces. Frequency-domain analysisis conducted on the simulated result, showing that the force of soft bags is smallerthan that of rigid ones with the same size. That is to say, it would be relatively safetaking rigid bags instead of soft bags during engineering design. In addition, howwave force affects the underwater diaphragm is simulated. Study results show that theinfluence of wave force on the diaphragm is small. The consistency of numericalsimulation results and experimental results proves that the developed mathematicmodel in this paper is applicative for these problems.At last, the example project design and sea tests are introduced based on thepollution-free underwater oil storage technology, underwater oil recovery and storagetechnology. A1200m3shallow underwater oil storage platform is designedconsidering conditions of Shengli oil fields including oil deposit, geology andgathering and transportation. The calculation shows that both strength and stabilitymeet the requirements. Related schemes are compared and better ones are selected forevery single procedure through the above design. The sea tests validate the whole process and verify the feasibility of pollution-free underwater oil storage technologyand the key technology of heat preservation. Corresponding problems are found andsolved in the sea test. This experiment has a significant reference value for theapplication and promotion of pollution-free underwater oil storage technology,underwater oil recovery and storage technology.