Volume 23: Sustainable Energy Solutions for a Post-COVID Recovery towards a Better Future: Part VI

Effect of Nano Polymer Microspheres Adsorption on Negatively Charged SiO2 Surface: Molecular Dynamics Simulation and Experimental Study Wenjing Zhao, Jing Wang, Shun Wang, Huiqing Liu,Xu Zhang, Haien Yang, Ping Yi



As a major profile control method for low permeability reservoirs, nano polymer microspheres (NPM) are used for thousands of wells in Changqing Oilfield every year, and have achieved excellent effect of EOR. Different from the profile control particles optimized based on the theory of matching between particle and pore throat size, the main mechanism of NPM is to increase the flowing resistance after adsorption on the pore throat surface.
However, there is a lack of quantitative research on the adsorption law of NPM, and the double-layer HPAM molecular model, without considering electrical properties, used by scholars cannot reflect the real formation charge properties and the expansion characteristics of NPM, and cannot reveal the adsorption law of NPM, which seriously affects the efficient application in the field.
In this paper, the dynamic adsorption capacity of NPM in sandstone reservoir is studied by QCM-D. Then, a customized SiO2 coupon is used to simulate the cumulative static adsorption capacity of NPM at a certain position of the reservoir. At the same time, above two experimental methods were used to study the effects of different expansion time, different expansion ratio NPM combination and salinity on dynamic and static adsorption capacity. Finally, by changing the mass fraction of H2O and HPAM to simulate NPM with different expansion time, a three-layer molecular model of “NPM + mineralized water + negatively charged SiO2” was constructed to verify the experimental results and reveal the adsorption mechanism of NPM from the molecular scale.
The results show that the maximum static and dynamic adsorption capacities of NPM are 9.26 μg·cm-2 and 0.18 μg·cm-2 respectively. The aggregates in NPM solution will adsorb the monomer on the surface of SiO2 coupon, so there are both adsorption and desorption happened. The maximum cumulative static adsorption capacity reached 150 μg·cm-2 after 3 days of expansion. The combination of different expansion time and new NPM has synergistic effect, which can double the adsorption capacity of expanded NMP. The adsorption capacity of NPM increases with the increase of salinity, and NPM can reduce the mineral adsorption capacity of pore surface.
The research results of this paper quantitatively characterize the adsorption capacity of NPM under different conditions, which lays a foundation for the establishment of adsorption characteristic model in the numerical simulation study of NPM profile control. It also can guide significance for the determination of NPM combination type and the judgment of NPM adsorption position, i.e. flow diversion position, in the field application.

Keywords nano polymer microspheres,absorption, molecular dynamics simulation,experimental study,negatively charged sio2 surface

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