| At present, the water cut of many reservoirs in our country that were treated with water injection at their earlier recovery stage went up rapidly. These reservoirs have gone into their middle- and high-water-cut recovery stages at which many blocks were under development with low recovery rate and economic benefit, and in great need of recovery method alternation. For example, in SaBei transmission zone of DaQing, ShengLi HuDong, DaGuang YangSan-mu and the six blocks of Xinjiang, etc., the ratio of total oil produced to OOIP is only 15% after more than twenty-year's water injection development and the water content ratio is up to about 80% in these reservoirs. How to effectively improve the development efficiency and enhance the recovery rate of such reservoirs has been paid great attention to by many petroleum workers of our country. Theoretic and practical achievements of recent years have proved that thermal process by steam injection is a prospective technology for enhanced recovery of watered reservoirs. Therefore, the study of thermal recovery mechanism by steam injection and the correspondent reservoir engineering study of watered reservoirs have both important theoretic value and applicable value.On the basis of deep research into the internal and external works about steam injection thermal recovery of watered reservoirs, directing at the characteristics of watered reservoirs and their recovery characteristics, and applying laboratory experiment method, laboratory tests, screening standards and reservoir engineering analysis on steam injection transmission after water flooding were deeply and systematically studied with combination of reservoir engineering, numerical simulation, mathematical statistics, economics and marginal analysis theory, etc. The study process has great difficulty and depth, and belongs to the front line of this discipline. Acknowledgements from the study process are as follows. First, from the study of laboratory tests on the recovery mechanisms, it can be concluded that:(1) Steam flooding of watered reservoirs is a significantly prospective EOR technology.(2) When the recovery method is altered into hot-water flooding in watered reservoirs, influence on the ultimate developing efficiency is not obvious because of thermal expansion and the limitation of viscosity reduction. And the residual oil saturation will still be up to about 22%.(3) When the recovery method is altered into steam flooding in watered reservoirs, the oil-water (steam) phase permeability under high temperature keeps constant with that before water flooding.(4) The amount of water storage in the formation has no great influence on the ultimate residual oil saturation of steam flooding development, while different amounts of water storage significantly affects the economic benefit of steam flooding.Secondly, from the study of the development efficiency by steam injection, it can be concludedthat:(1) For the heavy oil reservoirs that have shallow burial depth, low formation pressure, favorable physic character and low primary recovery ratio of total oil produced to OOIP, steam injection development can result in better recovery efficiency.(2) Whether cyclic steam injection is implemented has no significant effect on the ultimate recovery factor of steam injection development; whether cyclic steam injection is implemented in oil wells has no significant effect on the ultimate recovery efficiency of steam injection development, therefore, for those well with bad conditions and have not been completed according to thermal recovery requirements, cyclic steam injection may not be carried out.(3) The recovery efficiency of steam injection is sensitive to oil saturation and core intersection. For those regions that have oil saturation less than 0.45 or core intersection less than 10m, steam injection development should not be applied.Thirdly, from the study on the influence of formation water storage on the heat loss of the steam injection development, it can be resulted that:(1) The increment of t...
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