A new insight into failure mechanism of granular plugging zone for wellbore strengthening in deep fractured reservoirs based on force chains energy dissipation

Abstract

The structural integrity of a granular plugging zone is critical for its ability to withstand pressure in geological formations, directly impacting the success of drilling operations in oil, gas, and geothermal reservoirs. Mesoscopic force chains, formed by the contact between granules, are essential for pressure support in these zones. This study sheds light on the pressure stability of the granular plugging zone's structure in deep wellbore conditions, especially in response to pressure fluctuations. Adopting a fresh perspective on energy dissipation in strong force chains, we conducted a photoelastic experiment to accurately observe how energy dissipation evolves in these chains under simulated pressure fluctuations in deep wellbore environments. The results show that particle shape, type, size, fluid environment, and porosity significantly impact energy dissipation. Triangular and strip-shaped particles reduced the force chain energy dissipation by over 65 %, with rates dropping from 0.0200 %/s to 0.0060 %/s. Mixed-size particles showed a dissipation decrease of 58 % to 84 % compared to single-size ones. Oil-based drilling fluids increased dissipation to 0.0083 %/s, whereas a 1 % porosity reduction decreased dissipation by 13 %. The evolution of force chain energy is driven by external loads and internal dissipation from granular interactions. Displacement and structural damage disrupt the mechanical equilibrium of particles transferring the strong contact force, triggering energy surface changes that consequently lead to macroscopic failure. Optimizing particle shape, incorporating elastic materials, and increasing plugging zone density can enhance energy dissipation efficiency, thereby improving structural strength and stability.