Abstract: Steam assisted gravity drainage is an advanced technique to develop extra heavy oil.Nowadays,there are two methods to start up SAGD process.One is cyclic steam stimulation and the other is circulation steam.Relative to cyclic steam stimulation,steam injected cycle preheating is more uniform and more stable to start up SAGD process.However,the completion string structure to apply circulating steam is complicated.It is difficult to attain optimizing parameters of startup Phase.In terms of a fully coupled discretized wellbore model,circulating phase′s parameters are optimized during three phases of initial circulation phases,pressure differential phase and converted full SAGD phase.Reasonable parameters about steam rate,steam quality,steam pressure and chance and magnitude of pressure differential are attained.

Key words: SAGD, preheat startup, cyclic gas injection rate, convection, heavy oil development