基于CO2驱技术采收率的注采井距设计理论方法OA

The reservoir engineering theory for CO2 flooding development remains imperfect.The existing design methods for the injection-production well spacing fail to meet the demands of CO2 flooding development design.There is an urgent need for a highly targeted design method for the injection-production well spacing of CO2 flooding.Therefore,based on the development characteristics and action mechanism of the CO2 flooding technology,this study screened the main influencing factors of the development effect of CO2 flooding and conducted a correlation analysis.Subsequently,the correction functions of the gas injection ratio and the gas injection intervention timing were introduced.On this basis,the existing technical oil recovery model for CO2 flooding is extended and refined to establish an evaluation model for the technical oil recovery of the multi-factor synergy of CO2 flooding.On this basis,by integrating factors such as technical elements,economic benefits,and field production capacity,a reservoir engineering theory approach for designing the technologically and economically reasonable well spacing of CO2 flooding,which synergized multiple objective functions,was developed.The research findings indicate that factors exerting a substantial influence on the development performance of CO2 flooding encompass the heterogeneity coefficient,injection-production well spacing,effective reservoir thickness,formation pressure,average reservoir permeability,and crude oil viscosity.Although the gas injection rate has a relatively negligible impact on the oil recovery in reservoir numerical simulations,it is closely associated with the gas channeling index during development practices.Therefore,it cannot be overlooked.The evaluation model of the technical oil recovery for the multi-factor synergy of CO2 flooding is derived by expanding and modifying the time span and boundary conditions on the basis of the existing model.It is more consistent with the actual development characteristics of CO2 flooding in the water-alternating-gas(WAG)process.The theoretical method for the design of reasonable injection-production well spacing in CO2 flooding,which is established based on this model,can intuitively and rapidly obtain multiple design indices of injection-production well spacing by plotting the design chart of technologically and economically reasonable well spacing for CO2 flooding.Taking the design process of injection-production well spacing for CO2 flooding in Reservoir M of a low-permeability oilfield in China as an example,by applying this method,the economically optimal well spacing of Reservoir M is determined to be 360 m;the economically limiting well spacing is 75 m,and the technologically and economically reasonable well spacing is 153 m.