Simulation Study of Wellbore Collapse in Fractured Rock-Like Samples Based on 3D Printing

To study the wellbore collapse patterns in inclined sections of wells within fractured formations, methods such as 3D printing and CT scanning were used to obtain rough fracture surfaces of deep shale. Layered casting was employed to prepare rock-like samples with varying fracture inclinations and rough surfaces. Triaxial experiments were conducted to explore the impact of different drilling methods on wellbore collapse in these sections. The experimental results showed: (1) Fractured rock-like samples prepared using 3D printing and layered casting can substitute deep shale for studying wellbore collapse patterns in inclined sections. (2) When simulating horizontal drilling along the maximum horizontal principal stress, the wellbore remained relatively stable. In contrast, drilling along the minimum horizontal principal stress led to severe wellbore collapse, especially shear slip collapse along bedding fractures at a 60° dip angle. (3) Taking into account the wellbore trajectory, the mechanical weakness of bedding fractures, and their spatial distribution, it is recommended to drill horizontal wells along the direction of maximum horizontal principal stress. The critical collapse density was also predicted. These findings provide a basis for the preparation of fractured rock-like samples and offer a valuable reference for understanding wellbore collapse mechanisms in fractured formations.