Investigation Of Interfacial Film Thickness And Dielectric Properties Of Oil-gas-water Multiphase System

The interface problem of materials was one of the important scientific problems affecting petroleum exploration and development.In order to improve oil recovery,surfactant molecules,salt ions,and nanoparticles were usually introduced into the oil/water interface to reduce interfacial tension,improve interfacial viscoelasticity,and adjust reservoir rock wettability,thereby improving reservoir development efficiency.So,in the oil-gas-water multiphase system,the interaction between the interface molecules was a basic scientific problem for constructing the drilling and production theory and improving the recovery efficiency.The research was focus on the interaction between the hydrogen bond network structure at the interface and the interface potential.Macroscopically,it was the relationship between the thickness of the interface layer and the dielectric properties.In this thesis,using the advantage of oblique-incidence reflectivity difference(OIRD)technology that was sensitive to the thickness and dielectric properties of the interface layer,the OIRD technology was applied to investigate the interfacial film thickness and dielectric properties of the oil-gas-water multiphase system,revealed the OIRD response characteristics of the interfacial film layer thickness and dielectric properties,establish the medium model which was suitable for oil-gas-water multiphase system,prove the law of interaction between the interfacial film thickness and the dielectric properties,elucidate the synergistic change mechanism of interfacial film thickness and dielectric properties.The mechanism was used to the study of molecular adsorption behavior at the interface of oil-gas-water multiphase system.The main research results were as follows:(1)The OIRD response characteristics of the interfacial thickness and dielectric constant were revealed.The thickness of the interface layer and the dielectric constant usually changed synchronously.In this thesis,by designing a single-variable experimental sample,it was clear that those two parameters were positively correlated with the imaginary part of the OIRD signal.Meanwhile,it was confirmed that the dielectric distribution characteristics of the sample surface depended on factors such as the type,density and arrangement of surface molecules.(2)The variation law of the interfacial film thickness under stimulation has been proved.The thickness of the static air/water interface layer(water film layer)was stable,about 1 nm,while the detection of dynamic water film thickness was more universal.In this thesis,the thickness of the perturbed water film layer was detected,and it was confirmed that the thickness of water film varied with the wave amplitude,and was the thickest at the node and the thinnest at the antinode.(3)A three-layer medium model which was suitable for the oil-gas-water multiphase system was established,and the interaction relationship and mechanism of the interfacial layer thickness and dielectric constant were further clarified based on the model.When using OIRD technology to solve the interface problem,firstly,a threelayer dielectric model which was suitable for the sample system should be established as: the upper cladding layer-the interface layer-the base layer.Among them,the material composition of the interface layer was usually complex and difficult to determine.For the oil-gas-water multiphase system in this thesis,when the oleic acid film thickness d’ < 5 nm,the three-layer medium model was: air-oleic acid film and water film-bulk water.The thickness of the interfacial layer was dominated by the oleic acid film and gradually increased,and the dielectric properties of the interfacial layer were dominated by the water film and gradually decreased.During the thickening process of the oleic acid film(5 nm < d’ < 130 nm),the three-layer medium model was:air-part of the oleic acid film-bulk water.The thickness of the interface layer does not change synchronously with the dielectric constant,and the dielectric constant decreases.The reason was that the pressure of the overlying layer gradually increased,which inhibited the movement of molecules in the interface layer.During the process of oleic acid transforming from the film state to the bulk state(d’ > 130 nm),the thickness of the interface layer and the dielectric constant showed an upward trend until the oleic acid film transformed into the bulk state,the thickness and dielectric constant of the interface layer remain stable.(4)The adsorption state of the interface molecules was verified,the dynamic process of each adsorption state transition was monitored in real time,and the interaction mechanism of the interface molecules was revealed.The free singlemolecule state,pre-micelle state and spherical micelle state of the interface molecules can be intuitively characterized from the OIRD data.By analyzing the OIRD data,the mechanism of the dynamic process of each adsorption state transition can be known:first,the micelles undergo hydrolysis under the attraction of bulk water molecules and dissociate into a single-molecule state;then,the single molecule diffused from bulk water to the subsurface layer,and the diffusion process conformed to Fick’s second law;finally,a large number of single molecules were adsorbed into the surface layer,and the adsorption effect at this stage can be described by the Arrhenius formula.