Mechanism of Pressure Difference Variations on Heavy Oil Start-Up and Percolation Effects.

To investigate the influence of pressure difference changes on the micro start-up and percolation of heavy oil, a micro visualization displacement device was used to characterize the start-up time and oil-water percolation state of heavy oil. The mechanism of different pressure differences, as well as the frequency and amplitude of pressure difference changes, on the start-up and percolation balance of heavy oil was clarified. The results indicate that high-pressure difference and pressure difference changes can reduce the start-up time of heavy oil. A reasonable frequency of pressure difference changes effectively promotes the balance between positive and negative pressure shear and fluid-solid response. Large pressure difference changes can effectively break the viscous and adsorption resistance during heavy oil start-up; reasonable pressure difference can exert the synergistic effect of pressure difference and infiltration, achieving a balance between the water wave and the initial water film thickening process as well as the continuous percolation process of wire drawing, oil droplets, and oil columns during the medium-to-high water content period; a reasonable frequency of pressure difference variation during the high water content period can promote the superposition of inertia effects at the oil-water interface and break the balance of the oil-water interface. A large amplitude of pressure difference variation is beneficial for the strong deformation of the oil-water interface and the shear dislocation peeling of the oil-solid interface. Therefore, a relatively high amplitude of pressure difference variation and a reasonable frequency of pressure difference variation, as well as the synergistic effect of pressure difference and infiltration, are the keys to effectively start heavy oil and improving oil recovery during the ultrahigh water-cut period.