Research On Stabilization Mechanism And Flow Characteristics Of CO₂ Foam On The Basis Of Gas-soluble Surfactant

As a kind of oil displacement agent for oil field,Carbon dioxide can both implement to decline the emission and enhance the oil recovery.Thus,it is one of the best ways for carbon dioxide to be used and stored efficiently.However,due to the characteristics of carbon dioxide such as low density,low viscosity and the formation heterogeneity,it will lead to the phenomenon of carbon dioxide breakthrough,gravity segregation and gas channeling.Therefore,it makes the mobility control of carbon dioxide as a key point for whether it can be used efficiently.As a kind of green solvent,supercritical carbon dioxide can dissolve some special surfactants and be injected into the reservoir as the form of gas slug.It is called carbon dioxide foam mobility control technology based on the gas solubility surfactant.It has the advantages of both the strong ability of foam regeneration and good effect on gravity segregation control,which contribute to widen carbon dioxide foam's application.Therefore,it can provide critical guiding significance for CCUS technique in petroleum industry.In this paper,through the Waring Blender method,some kinds of normal gas surfactants'performance for carbon dioxide foam are evaluated.The interfacial tension between gas surfactant and carbon dioxide and the stability of carbon dioxide foam have been analyzed to optimize the best one.Then the phase characteristics of the whole system have been studied through the visible PVT analyzer.In the meanwhile,the function between supercritical carbon dioxide molecule and surfactant and the fundamental of the surfactant adjustment have been studied by the method of molecular dynamics simulation.Based on the property of SiO₂ nano particle and gas surfactant system,the nano particles'synergistic action on the surfactant has been revealed.Through the core simulation of foam seepage experiments,the generation feasibility of the carbon dioxide foam based on the gas surfactant has been analyzed.The results show the plugging capacities under different injection mode and diffluence effect at different permeability ration.The results indicate that the optimized surfactant which can both be dissolved in the supercritical carbon dioxide quickly and can generate carbon dioxide foam with a steady quality is AOT.The stability of foam which is used AOT is the best one.At the certain pressure,the surfactant concentration increased with the agent.The surfactant content which is dissolved in the supercritical carbon dioxide increased with system's balance pressure when the agent concentration is certain.Among the three agents,the F pentanol has the best property of solubilizing power,then the pentanol and alcohol.It is because when length of carbon chain is increasing,the affinity between alcohol and AOT is enhanced.Then the polarity of the system is enlarged so that this kind of agent has good effect of hydrotropy.The affinity between carbon dioxide and alcohol is increasing when the carbon hydrogen bonds turn into the carbon fluorine bonds by fluorination.The F pentanol molecule and the tail chain of AOT impede the reunion between AOT molecules.Thus,the solubility of AOT is enhanced.The results of molecular dynamics simulation show that the Van der Waals force and hydrogen bond interaction between the agent molecules and carbon dioxide molecules is helpful to form the supercritical carbon dioxide/agent disperse system.Therefore,the density and polarity of carbon dioxide have been increased so that the solubility is enhanced.The hydrophobic effect between AOT and SiO₂ can form the stable disperse system.Meanwhile,when the value of concentration ratio between AOT and SiO₂ is at 0.2,based on the surface wettability change of SiO₂,the SiO₂ has the best adsorption state at the liquid-gas interface.It enhanced the film strength and the space grid structure has been formed to impede the film drainage and foam gathering in order to have the synergistic stability effect for carbon dioxide foam.Based on the supercritical carbon dioxide which carries the gas surfactant into the core,the foam generated by carbon dioxide has high resistance factor and long stable time.The resistance factor is increasing with the permeability.The residual resistance factor is increasing with the increasing permeability but has a low growing rate.And it has efficient profile control ability when the heterogeneous core's permeability ratio is below 10.