Simulating Perforation Damage With a Flat-Jointed Bonded-Particle Material

We explore the feasibility of using a bonded-particle model (BPM) to simulate the rock disaggregation process occurring near a wellbore perforation in sandstone by addressing the simpler question: Can we construct a 2D BPM that produces surface fragments when subjected to boundary conditions similar to those around a wellbore perforation in dry sandstone? The answer to this question is yes. We can construct a 2D flat-jointed material to represent Castlegate sandstone. Our synthetic material matches much of the macroscopic response (including the direct-tension and unconfined-compressive strengths) and many of the mechanisms that occur during direct-tension and compression tests as well as the trends in the macroscopic response and the primary mechanism that occurs during thick-walled cylinder (TWC) tests to produce a breakout failure type. The primary mechanism is termed “buckling-assisted fragmentation,” in which a buckling and spalling process produces thin fragments of rock similar to onion skins, and thereby produces a breakout failure type. The perforation-collapse behavior of our synthetic material is related to the hole resolution (defined as the number of grains across the borehole diameter), with TWC strength decreasing as hole resolution increases. This observation suggests that perforation strength in a given material will decrease with increasing perforation size.