Study On Reducing Minimum Miscibility Pressure Of CO₂ And Crude Oil By Esters

CO₂ flooding is a technology to enhance oil recovery efficiency and is an important technology for CO₂ utilization and storage.It has been widely used at home and abroad.In the process of using CO₂ for oil recovery,CO₂ miscible flooding has a greater application advantage due to its higher oil recovery effect.For some deep or heavy oil reservoirs,the minimum miscible pressure of CO₂ flooding is higher and usually higher than the formation fracture pressure,so that only the CO₂ immiscible flooding can be used for crude oil recovery.If the minimum miscibility pressure of CO₂ and crude oil can be effectively reduced,such a reservoir can be driven by CO₂ miscible flooding,which will be of great significance for the application of CO₂ in enhancing oil recovery.In order to explore and solve the problem of high minimum miscibility pressure between CO₂ and crude oil mentioned above,this paper proposes a method for increasing the solubility of CO₂ in crude oil and the volume expansion coefficient of crude oil,and reducing the minimum miscible pressure of CO₂ and crude oil by esters.In this paper,the solubility of CO₂ in different carbon chain lengths and different functional group ester liquids and the volume expansion coefficient of the corresponding system were determined under different pressure and temperature conditions.At the same time,the infrared absorption spectra of CO₂-different chain lengths and functional group ester liquids were determined by in-situ infrared technique.The dispersion characteristics of CO₂ in ester liquids were studied.The results show that the dissolution of CO₂ in ester liquids and the volume expansion of the system are closely related to temperature,pressure,chain length and functional groups.The chain length and functional groups also have significant influence on the infrared spectra of CO₂-ester liquids.It was also found that a variety of low-stability interactions can be formed between ester liquid molecules.At the same time,CO₂ molecules can interact with ester molecules in various forms,and with the increase of pressure,it can disintegrate the molecular structure of ester liquid,thus enabling CO₂ to exist in ester liquids in a special dispersion form.By measuring the solubility of CO₂ in polar organic liquids and the volume expansion coefficient of the system after adding different carbonyl liquids and different ester liquids,it is clear that the ester carbonyl group has superior solubilization and swelling effect compared with ketone carbonyl and aldehyde carbonyl.At the same time,the experimental results also show that the more ester groups in ester liquids,the better the solubilization and expansion effect.The more polar organic liquids,the better the solubilization and expansion effect of ester liquids.The solubility and volume expansion coefficient of CO₂ in simulated oil and crude oil after adding ester liquids were measured.The interfacial tension between CO₂ and crude oil before and after adding ester liquids was also measured.On this basis,the minimum miscibility pressure was obtained by extrapolation.The results show that the ester liquid can significantly enhance the solubilization and swelling of the CO₂-simulated oil/crude oil system,and the minimum miscibility pressure of CO₂ and crude oil is significantly reduced.The ester molecules can not only interact with CO₂ molecules,but also enter the crude oil to play a role between crude oil molecules,so that the force between the crude oil molecules is reduced,under this dual action,the minimum miscible pressure of CO₂ and crude oil is significantly reduced by adding ester liquid.