Study On Preparation And Performance Of CO₂ Intelligent Response Foam With Temperature And Salt Resistance

Nowadays,foam is widely used in foam drainage and gas recovery.However,due to the harsh environment of the underground,such as high temperature and high salinity conditions,the generated foam cannot exist in the underground stably,so it ruptures when it cannot reach the ground,and the effect of drainage and gas recovery cannot be achieved.On the other hand,if the foam produced by the foaming agent is too stable,it will not be able to defoam naturally after reaching the ground.It is necessary to add a defoamer to defoam,which requires certain filling equipment,and there may be slow,incomplete,emulsified defoaming,etc.problem.Against this background,it is particularly important to prepare a responsive foam system that still has better performance in harsh environments.In this paper,a combination of experiment and molecular dynamics simulation was used to synthesize three responsive tertiary amines 11-DUSNa,10-DUSNa,and 9-DUSNa and compounded11-DUSNa with dodecyl hydroxy sulfobetaine（CHSB）2:1 to obtain a responsive temperature and salt tolerant foam system,the foam properties and CO₂ response performance of the compound system were studied,and the temperature and salt resistance and response mechanism were revealed.The experimental study of foam performance found that the three synthetic tertiary amines 11-DUSNa,10-DUSNa,and 9-DUSNa all have certain response and foam performance,and the foam performance increases with the increase of the carbon chain length.Since CHSB contains hydroxyl and hydrophilic groups and its own amphoteric structure,it has good temperature and salt resistance.When CHSB is at a concentration of 0.02 mol/L,it has the best foam stability and liquid carrying capacity.11-DUSNa and CHSB have the best response performance and foam stability when the compound ratio is 2:1,the response performance can be repeated by N₂ bubbling,CO₂ protonation and defoaming,and dropwise addition of Na OH solution to deprotonation and return to the original state,and the response can be repeated more than four times,and the foam performance of the compounded system is better than that of two separate surfactants.Through foam half-life,surface tension test,foam morphology observation and other tests,it is found that the compound system has better resistance to divalent salt ions Ca²⁺and Mg²⁺,the monovalent salt ions Na⁺and K⁺have a bad bubble effect on the foam,and the compound system has good high temperature resistance.The simulation study of foam performance found that:the response mechanism of 11-H⁺DUSNa/CHSB compound system is that 11-H⁺DUSNa will interact with itself and the head group of CHSB electrostatically,which weakens the diffusion ability of surfactant in water,which makes surfactant molecules form micelles in the liquid phase,can not reach the interface to stabilize the foam,so the foam bursts quickly after response.Low concentrations of Mg²⁺and Ca²⁺will stably combine with the surfactant head group to make the surfactant enter the gas-liquid interface to stabilize the foam,however,Na⁺and K⁺will dissociate from the surfactant molecules faster and affect the surfactant molecules to enter the gas-liquid interface,and the foam will be damaged.Na⁺and K⁺have basically no effect on the response performance of the model,Ca²⁺and Mg²⁺affect the electrostatic combination of11-DUSNa head group with itself and with CHSB to a certain extent,which prolongs the defoaming time.Temperature has little effect on the model of the compound system.The high temperature accelerates the diffusion speed of surfactant molecules,which is beneficial to the diffusion of surfactant molecules to the gas-liquid interface to stabilize the foam,so that the compound system has better temperature resistance.