Solubility Of Nonionic Surfactants Used In CO₂Miscible Flooding

Due to low permeability, natural energy shortage, fast recession of oil production and low level of development, it becomes more and more difficult to recover for low permeability reservoirs. CO2flooding enhanced recovery technology, which meets the needs of oilfield development and increases production of oil and gas, solves the problem of CO2sequestration and cuts CO2emissions to protect the atmospheric environment. Howerver, for many reservoirs mixed phase can not be achieved under permitted pressure, namely CO2minimum miscible pressure is higher than permitted injection pressure. This paper investigates the surfactant solubility in SCCO2in order to decrease the interfacial tension between oil and CO2and reduce the minimum miscibility pressure.Firstly, this thesis studied surface and interface performance of three series of nonionic surfactants. Compared to the straight chain fatty alcohol ethoxylates (A series) and double long chains fatty alcohol ethoxylates (B series), C series of nonionic surfactants which possess with highly methyl-branched tails performed the best surface and interface properties. Wherein the alkane-water dynamic interfacial tension of C3could be reduced to ultra-low value (magnitude10-3mN/m). In the same series of nonionic surfactants, γcmc also increased as EO number increased.Secondly, this article also designed and set up a high-pressure flow device using for measuring solubility of surfactants in scCO2, of which the maximum working pressure and maximum working temperature could reach to30MPa and150℃respectively. Then we focused on solubility of the three series of nonionic surfactant, and the results showed that nonionic surfactants with a high degree of methylation tails were preferably soluble and micelle-micelle interactions showed a large effect on the solubility. The increasing of EO number and chain length reduced the solubility of surfactants. Temperature, pressure and density all influenced the solubility of surfactants. However, γcmc had no effect on surfactant solubility. Further investigation showed the additon of alcohols other than decanol improved the solubility of C1, and the alcohol (n-hexanol) bearing with hydrophobic chain length similar to C1effectively reduced the cloud point pressure of C1. The bigger amount of alcohol had better effect.Finally, this thesis synthesized three series of nonionic surfactants ethers (amount to14) containing polyoxyethylene chain, of which epoxy equivalent weight was measured, the yields were all above50%. The structure of products were confirmed by ESI/MS. Compared with nonionic surfactants, glycidyl ethers showed inferior solubility.