Fracture propagation mechanisms of supercritical CO2 fracturing in bedded rocks: a novel brittleness prediction approach for bedded rocks

Abstract Regarding the unclear mechanism of fracture propagation in bedded rocks during supercritical CO 2 (SC-CO 2 ) fracturing, this study proposed a method for fabricating artificial bedded rock specimens using modeling materials. Based on these specimens, true triaxial SC-CO 2 fracturing experiments were conducted to systematically investigate the effects of bedding structure and rock matrix brittleness on fracture propagation behavior and initiation pressure. A spatial development index was introduced to quantitatively characterize the extent and complexity of fracture growth in 3D space. The findings indicate that among bedding angle, bedding spacing, and rock matrix brittleness, bedding angle has the greatest influence on fracture initiation pressure. Compared with matrix brittleness, the bedding structure exerts a more significant impact on fracture spatial configuration. To overcome the limitations of conventional brittleness evaluation methods when applied to bedded rocks, two theoretical models were developed to predict Poisson’s ratio and elastic modulus across various bedding angles. Based on these models, a novel brittleness prediction approach—integrating mineral composition, mechanical parameters, and bedding angle—was proposed, enabling a more accurate characterization of the overall brittleness of bedded rocks. Notably, while previous studies have indicated an inverse relationship between rock brittleness and initiation pressure, this study demonstrates that this inverse relationship holds only under constant bedding angles. When bedding angles vary, the relationship shifts to a positive one. This study not only provides an effective method for scientific evaluating brittleness in bedded rock but also offers theoretical support for designing and optimizing SC-CO 2 fracturing strategies in bedded reservoirs.