## 3 Mechanism of Molecular Deposition Film Technology
### Mechanism of Molecular Deposition Film Technology  
The mechanism of molecular deposition film oil recovery technology differs from those of traditional chemical recovery methods such as polymer flooding, surfactant flooding, alkali flooding, and composite flooding. This technology utilizes a water solution as the transmission medium, and the molecular deposition film agent relies on electrostatic interactions to form a thin film that effectively deposits on the negatively charged rock surface to create a nanometer-thin film, altering the interaction state between the reservoir surface and crude oil. This facilitates the removal of crude oil by injected fluids during pore washing, thereby achieving enhanced oil recovery. After over a year of research, it was found that this technology primarily contributes to altering wetting properties, enhancing spontaneous imbibition ability, increasing diffusion effects, and reducing oil-water interfacial tension in oil reservoirs. (1) Altering the wetting properties of the reservoir water/oil system  
Under the influence of interfacial tension, stable contact angles are formed at oil-water, oil-solid, and water-solid interfaces. A contact angle less than 90\({}^{\circ}\) indicates hydrophilicity of the solid surface; a contact angle of 90\({}^{\circ}\) suggests amphipathic properties; and a contact angle greater than 90\({}^{\circ}\) signifies hydrophobicity (i.e., water repulsion) of the solid surface. According to the Laplace equation (where the curved liquid surface is spherical), the pressure difference between the non-wetting phase and wetting phase on both sides of the capillary tube in the reservoir represents capillary pressure. \[p_{c}=2\sigma\cos\theta/r \tag{1}\]  
where \(p_{c}\) is the capillary pressure (MPa), \(\sigma\) is the interfacial tension (MPa), \(\theta\) is the contact angle (\({}^{\circ}\)), and \(r\) is the pore radius (m). The wetting properties of sandstone and quartz slabs were assessed using the contact angle experiment method, with kerosene (12 h soaking) and a molecular film solution (24 h soaking) as the test substances. In this experiment, the circumference (C) and height (h) of the water droplet in contact with the rock surface were initially measured to calculate the contact angle (\(\theta\)). The experimental findings revealed that following treatment with kerosene, although there was an increase in the contact angle of water droplets with sandstone and quartz slabs, their wetting properties remained unchanged (Table 2). However, after immersion in a molecular film solution, both types of slabs exhibited a transition from strong hydrophilicity to strong hydrophobicity. This suggests that adsorption of the molecular film onto the core slab surface led to its manifestation of strong hydrophobic characteristics. Molecular deposition film oil displacement agents have the capability to mitigate the strong water-wetting clogging phenomenon. They induce a transition of strongly oil-attracting surfaces to non-wetting or weakly water-wetting states, thereby achieving optimal efficiency in oil displacement (Figure 3). Similarly, these agents can also transform strongly water-attracting surfaces into non-wetting or weakly water-wetting conditions, leading to the most effective oil-displacing outcomes. \begin{table}
\begin{tabular}{c c c c} \hline
**Lithology Types Tested for** & **Clean Thin Film** & **Soaking with Kerosene (12 h)** &
\begin{tabular}{c} **Soaking with Molecular** \\ **Deposition Film Solution (12 h)** \\ \end{tabular} \\ \hline Sandstone (\({}^{\circ}\)) & 38 & 72 & \(151\) \\ Quartz (\({}^{\circ}\)) & 32 & 65 & 144 \\ \hline \end{tabular}
\end{table} 
Table 2: Wetting angle test results of different rock types under different experimental conditions. Changing the distribution of oil and water in reservoir pores  
The MD film can reduce the adhesion and dispersion of quartzite surfaces. Adhesion includes intermolecular forces, capillary forces, and electrostatic forces, indicating a highly complex adhesion mechanism.