Shear stability enhancement in fracture plugging zones: Unveiling failure mechanisms and adhesive benefits through photoelastic analysis

Addressing lost circulation during drilling operations typically involves the utilization of lost circulation materials (LCMs) to create a fracture plugging zone (FPZ), which effectively decouples the wellbore fluid column pressure ( P w ) from the formation pressure ( P f ). This FPZ, comprised of aggregated granular LCM particles, frequently succumbs to shear stress, with shear failure being the predominant mode of structural failure, leading to ongoing fluid losses. To illuminate the failure mechanisms of the FPZ under conditions of escalating drilling differential pressure ( P w - P f ), we utilized photoelastic experiments to capture and visualize the evolving mesoscopic mechanical structure of the FPZ. Photoelastic images were analyzed using the modified ten-step phase-shift method to calculate the shear stress distribution within the FPZ. Results indicated that shear failure is characterized by recurrent bidirectional shearing interactions between the FPZ and the fracture surface, accompanied by a significant increase in stress concentration at the initiation of shear failure. To augment the shear stability of the FPZ, a methodology inspired by the composite nature of concrete—comprising sand, stone, and cementitious materials—was adopted. The integration of adhesive particles within the FPZ resulted in a marked reduction in internal shear stress and an enhancement of its load-bearing capacity. These findings substantiate that the incorporation of adhesives effectively bolsters the mechanical stability of the FPZ across both mesoscopic and macroscopic scales. • Shear stress extraction of FPZ by photoelastic experiment. • Mechanism of mesoscopic mechanical structure failure of the FPZ. • Adhesive strengthening the shear stability of the FPZ.