Impacts of Polar Molecules of Crude Oil on Spontaneous Imbibition in Calcite Nanoslit: A Molecular Dynamics Simulation Study
S Wang and J Wang and HQ Liu and FN Liu, ENERGY & FUELS, 35, 13671-13686 (2021).
Spontaneous imbibition is a crucial method for developing tight reservoirs. The interactions between fluid and solid are key to imbibition behavior. In this work, the molecular simulation method was used to study the occurrence state of polar molecules in calcite nanoslit and the mechanisms of their impacts on spontaneous imbibition. The results showed that both adsorption energy and molecular orientation were key parameters for characterization of the occurrence state of polar molecules. The temperature and average area controlled by each polar molecule affected the adsorption energy by changing the molecular orientation, and the quantitative relationship was established by the regression analysis method. During spontaneous imbibition, polar molecules affect imbibition by delaying the advance of water molecules in the first hydration layer, and the degree of delay depends on the synergistic effect of the adsorption energy and the molecular orientation. By coupling the adsorption energy and order parameters, a concept of a steric hindrance factor was proposed. The spontaneous imbibition process in calcite nanoslit can be divided into two periods, a linear period and a plateau period, but it experiences a short elastic period before spontaneous imbibition. The recovery degree of octane in the elastic period is only related to temperature and that in the linear period is related to the temperature and steric hindrance factors. Temperature promotes the diffusion of water molecules to the deep pore and reduces the steric hindrance factor, which further reduces the inhibiting effect on water molecules. Finally, a prediction model for the recovery degree of octane in calcite nanoslit with polar molecules is proposed, which provides theoretical guidance for improving the spontaneous imbibition recovery of tight carbonate reservoirs.
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