Challenges in Modeling Jointing in Sedimentary Rocks

Recent research conducted by Edoardo Pezzulli, Patrick Zulian, Alena Kopaničáková, Rolf Krause, and Thomas Driesner examines the effectiveness of standard phase-field models in simulating jointing within sedimentary rock layers. The study highlights both the advantages and limitations of these models, particularly focusing on the volumetric-deviatoric split and the AT1 and AT2 phase-field formulations.

The authors found that while these formulations can qualitatively reproduce joint saturation and demonstrate a negative correlation between joint spacing and sedimentary layer height, they also exhibit significant shortcomings. Specifically, the phase-field method tends to overestimate joint spacings by a factor of two when compared to alternative numerical methods and real-world observations. Additionally, the AT1 model produces unrealistic compressive fractures, and the AT2 model shows premature shearing at layer interfaces.

The research identifies that these issues stem from the intrinsic properties of the phase-field lengthscale and an unsuitable strength envelope resulting from the volumetric-deviatoric split. The authors argue that the distortion of the stress field around dilating fractures leads to premature joint saturation, halting the formation of new fractures and resulting in larger joint spacings than those observed in nature.

The study concludes that there is a need for the development of more suitable constitutive phase-field models for geological applications, emphasizing the importance of benchmarking these models against geological observations to enhance their reliability. This research could have significant implications for the understanding of rock fracture mechanics and the modeling of geological processes.

For further details, the full paper can be accessed at arXiv:2408.14449.