Sealing characteristics and discrete element fluid dynamics analysis of nanofiber in nanoscale shale pores: Modeling and prediction

The nanoscale pores in shale oil and gas are often filled with external nanomaterials to enhance wellbore stability and improve energy production. And there has been considerable research on discrete element blocking models and simulation about nanoparticles. However, nanomaterials are not just nanoparticles and there are few re-searches on fiber-based discrete element dynamics sealing calculations. Moreover, nanofibers have better sealing efficiency relative to nanoparticles. In this paper, a fiber-based discrete element fluid-solid coupling sealing model was established to clarify the dynamic migration and sealing process of nanofibers in shale pores. The innovative nanofiber model guarantees real-time force deformation and bendability during nanofiber flow process. The factors influencing sealing efficiency on shale pores with fiber concentration, aspect ratio, diameter, density, stiffness, rotation and Poisson's ratio have been conducted. Furthermore, the simulation results with and without fiber were certified by theoretical and experimental results which increased the credibility and appli-cability. Results indicate that the sealing efficiency increases by 69.40%, 139.12%, and 254.89%, respectively, as the fiber concentration increases from 0.5% to 1%, 1.5% and 2%. The increase in sealing efficiency is not linear for fiber concentration. The sealing efficiency is almost the highest as the ratio of aspect ratio is 1:15 in the initial stage of sealing. And fiber diameter with 1/15 of the pore outlet diameter is a reasonable choice if economical applicability is considered based on the sealing process. Furthermore, practice has proved that the sealing effect of bendable fibers is increased by 14.50% compared with non-bendable fibers. The bending of the fiber can improve the efficiency of shale pore sealing. And the research can provide theoretical and technical support for the nanofiber optimization of sealing nanopores of shale oil and gas.