Experimental Study And Application Of Improving The Stability Of CO₂ Foam By Using SiO₂ Nanoparticles

The surfactant-stabilized CO₂ foams can effectively control the mobility of CO₂,strengthening the advantages of CO₂.However,the surfactant has a large retention loss in reservoir rock and do not have a good stability under high-temperature and high-salinity reservoir conditions.Nanoparticles can be used as stabilizer to improve the foam sta bility,and are able to cause synergistic effect under certain conditions.Nonetheless,the gas of the foam is not distinguished,besides very few study report on its application.Therefore,it is necessary to study the synergistic effect and application of CO₂ foam stabilized by nanoparticles and surfactants.The synergistic effect rules,mechanisms and their influence factors of SiO₂ nanoparticles and SDS are firstly investigated through static evaluation and analysis methodology.The research results show that the synergistic effect will not appear until the contact angle between SiO₂ nanoparticles and water is higher than 79.83°.And the synergistic effect exits only in a SDS/SiO₂ concentration ratio range,the effect is strengthened firstly and then weakened as the concentration ratio rises from 0.10 to 0.40,achieving its best effect at 0.17.The mechanisms of the synergistic effect include modulating the nanoparticles' absorbing position on the interface,weakening the disproportionation effect,improving the properties of foam film,slowing down foam drainage and increasing the mechanical strength of foam.Temperature,pressure and inorganic salt ions are found to be the important factors influencing the synergistic effect.Then the seepage law and oil displacement mechanisms of CO₂ foam stabilized by SDS/SiO₂ are studied through micro experiment.The results show that the foam generated by SDS/SiO₂,with more mechanical strength,have stronger “wipe” effect on the oil adhere to the rock than SDS solution,in that enhancing oil recovery.Moreover,the “wipe” effect,combined with fast reciprocating motion of foam in porous media,plays an important role in enhancing oil recovery.At last,the profile controlling and oil displacing capacity and the retention of nanoparticles are investigated through sandpack experiments.The results show that the SiO₂ nanoparticles are able to improve the plugging and oil displacing capacity of CO₂ foam.And the core damage is not obvious when the nanoparticles' concentration is lower than 1.5wt%.