Implications of Wettability and Pore Size Superposition on Nanoconfinement Effects for Unconventional Oil and Gas Development Using Mesoporous Zeolites

The nanoconfinement effect is crucial in unconventional oil and gas development, yet the regulatory mechanism of wettability on it remains unclear. In this study, three SBA type molecular sieves with different pore sizes were used as model materials. Isothermal adsorption experiments were conducted using a BET analyzer, and pore size distributions were determined using the BET method and the DFT method, to systematically investigate the influence of wettability on the nanoconfinement effect. The results show that SBA molecular sieves with different pore sizes exhibit significantly different propane adsorption behaviors. SBA-15-4.2 with smaller pore sizes undergo capillary condensation at lower pressures, while SBA-15 and SBA-15-18 with larger pore sizes require higher pressures. The pore size distribution of the mixed SBA molecular sieve system exhibits a weighted superposition characteristic of the individual material pore size distributions, with each material contributing differently in different pore size ranges. Wettability significantly affects gas adsorption, diffusion, and condensation processes: unmodified SBA molecular sieves are highly hydrophilic and unfavorable for propane adsorption; shale pore surfaces have complex wettability and exhibit unique adsorption preferences for propane. After hydrophobic modification, the isothermal adsorption curve of the oil-wet SBA composite system is closer to that of shale, and the shale isothermal adsorption curve can be well fitted by adjusting the proportion of SBA molecular sieves in the mixture. This study provides a theoretical basis and experimental means for understanding the production mechanisms of unconventional reservoirs and optimizing production technologies.