The Scheme Optimization Of Gas Injection Parameters And Adaptability Analysis Of CO₂ Flooding In Offshore Low Permeability Thick Reservoirs

At present,for low permeability reservoirs,CO2 flooding has become one of the most important technology to improve oil recovery.Especially for offshore oil fields,gas drive should be vigorously developed due to the particularity development of them.Although gas displacement technology has preferable effect of EOR,it also has some deficiency.Gas channeling is one of the most significant problems of gas displacement technology.Gas channeling is more significant in thick reservoirs.It will affect the sweep efficiency,which reduces the capacity.Therefore,it is necessary to analyze the adaptability of CO2flooding,to optimize the gas injection parameter and to improve gas drive development effect in thick reservoirs.In this paper,the injected gas source of the target reservoir is analyzed.The reservoir and fluid reservoir conditions of the target reservoir is analogized with the implemented CO2 flooding reservoirs.The minimum miscible pressure was calculated through a variety of theoretical calculation method.For the target reservoir has low permeability and thick oil horizons,the mechanism model of the target reservoir is established using ECLIPSE numerical simulation software.The effects of the pressure,temperature,crude oil composition,injected gas composition,structure angle and permeability heterogeneity are analyzed.The CO2 injection parameters such as injected gas composition,gas injection site,gas injection timing and gas injection speed are optimized.On this basis,a comprehensive optimization design is accomplished in the practical target reservoir numerical model.The results prove that the target reservoir has the injected gas source.The reservoir and fluid conditions are adaptive for CO2 drive.The minimum miscible pressure is27.18MPa,which is lower than the reservoir pressure,so the target reservoir can implement CO2 miscible flooding.Based on the research result of the effect factors of CO2 flooding,the prioritization scheme of CO2 injection parameters is:adding 5%C5 and5%C6 in CO2,top injection and bottom production,injection in advance,injection rate of60×10~4m~3/d and avoiding perforation of high permeability layers.As the result of optimization is applied to the numerical model of the target reservoir,recovery percentage is increased by 11.39%,so the development effect of CO2 flooding is improved effectively.This paper initially formed gas drive adaptability analysis method and gas injection parameters optimization technology of gas drive of thick reservoirs,and can provide a reference for offshore thick gas drive reservoirs development.