Study On Thermal Chemical Cyclic Steam Stimulation After Multicycles Of Steam Stimulation

Cyclic steam stimulation has been widely used at home and abroad as a common production method for thermal recovery of heavy oil.However,with the increment of huff and puff cycles,problems such as ineffective steam stimulation,serious inter-well steam channeling,high water cut and low operation degrees have become prominent.Further measures should be taken to enhance oil recovery.Taking Shan 56 Block,Shengli Oilfield as an example,the actual production model was established by the STARS module of CMG software.According to the distribution of oil saturation and temperature,the distribution of remaining oil was determined and the appropriate operating method was selected.The research of mechanisms of thermal chemical cyclic steam stimulation was conducted,including the effects of steam,CO₂,N₂ and viscosity reducer.A homogeneous numerical simulation model was established based on average geological parameters and orthogonal tests were designed to evaluate the influencing factors of thermal chemical cyclic steam stimulation.After analyzing the shortcomings of visual analysis and analysis of variance,the gray correlation analysis was selected to rank the influencing factors of thermal chemical cyclic steam stimulation.The main influencing factors were formation pressure,steam quality,thickness of oil layer and steam injection temperature.Based on the previously established model,the optimization of injection method,injection amount and injection timing of CO₂ and viscosity reducer was conducted.Viscosity reducer should be sequentially injected with steam and CO₂ should be co-injected with steam.The injection amount of mass concentration of 0.5%wt of viscosity reducer and CO₂ should be 50t.And the viscosity reducer should be injected at the initial stage of production and CO₂ should be injected during the middle of production.The effects of reservoir static parameters of thermal chemical cyclic steam stimulation were analyzed to find the suitable reservoirs for thermal chemical cyclic steam stimulation.Under different oil prices,two factors were considered to draw composite charts to provide development plans and economic evaluation for similar reservoirs.