The Interfacial Agents For Enhancing Oil-scCO₂ Interaction

As a green solvent,scCO2 is used extensively in enhanced oil recovery,extraction,cleaning,and synthesizion,etc.However,its applications are limited due to the low solubility.Thus,in order to improve the performances of scCO2,scCO2-solube additives were used.Similar to the surfactants used in water/oil system,in the oil/scCO2 system an amphiphilic compound with scCO2-philic and oil-philic porperty might improve the interaction between oil and scCO2,which has practical significance to the study of low-permeability reservoir recovery by CO2-EOR.Three kinds of interfacial agents which are long chain alcohol polyoxyethylene ethers(Cn+2(m);GC2n+4(m);TX),silicon contained polyoxyethylene ethers((PEG)n-TS)and aliphatic esters(C(n+2)-(m+1))were designed and synthesized.Their solubility was got through dissolving pressure tests at different temperatures.According to the experimental results,there were three factors to affect the solubility which are temperature,pressure,and density of scCO2.The increase of pressure and density of scCO2 both had a positive effect on the solubility,while the increase of temperature reduced the solubility.Moreover,the structural effect on solubility was analysized which shows that a longer molecular chain or a larger molecular volume will result in a lower solubility in scCO2.Then the interfacial agents(additives)were added to the octacosane/scCO2 and oil/scCO2 mixture systems to study their effects on the dissolving pressures of the system.The experimental data showed that the dissolving pressures were reduced by the additives.It was found that,the performances on reducing the dissolving pressure are related to their solubility in scCO2 and the match degree between the additive and the oil.Additive with a better solubility in scCO2 and a similar chain length with the oil molecule performs better.In order to investigate the effect of interfacial agents on material exchange between crude oil and scCO2,extraction tests,volume change rate tests and slim-tube tests were carried out.Firstly,by adding the interfacial agent into scCO2,the extraction rates of scCO2 from oil were found to be improved.Secondly,the volume change rates of the oil drop were improved by the long chain alcohol polyoxyethylene ethers and C(n+2)-(m+1),which indicates scCO2 could extract more oil with the additives.While the volume change rates of the oil drop were reduced by the(PEG)n-TS,which shows that(PEG)n-TS trend to enhance the process of scCO2 entering into the oil drop.Lastly,the analysizing results of the oil recovered by scCO2 with additives shows that there are more light hydrocarbons in the oil recovered.In the end,the IFTs between crude oil and scCO2,heavy oil and scCO2 and octacosane and scCO2 were tested.The interfacial agents could reduce the IFT between the crude oil and scCO2,interfacial agent with a better solubility in scCO2 could reduce the IFT to a lower extent.The long chain alcohol polyoxyethylene ethers and C(n+2)-(m+l)mainly effect on the light hydrocarbons in the crude oil,their effects on the heavy oil/CO2 and octacosane/CO2 systems were not so good.But,(PEG)n-TS showed the best ability on reduce the IFTs,they could reduce the IFTs between scCO2 and heavy oil and scCO2 and octacosane.The studied amphiphilic compounds showed better ability to reduce the IFT than the published ones.