Fracturing behavior of shale reservoirs in water, N2 and SC-CO2 fracturing process

This paper proposes a numerical simulation model to comparatively investigate the fracturing behavior of shale reservoirs in water, N₂ and CO₂ fracturing process. This numerical model considers the heterogeneity of shale, the mechanical properties of bedding plane and different damage modes through a mechanical-seepage-damage coupling analysis. This model is verified by shale fracturing experiment and used to explore the combined impacts of stress ratio and bedding angle in water, N₂ and CO₂ fracturing process, respectively. The results show that the fracturing behavior varies with the type of fracturing fluids, bedding angle and stress ratio. During the initiation and propagation of fracturing cracks, tensile damage is dominant and permeability increases significantly. Without considering the impact of bedding angle, the damage initiation pressure, breakdown pressure and fracturing effectiveness reach the maximum when stress ratio is 1. CO₂ fracturing may be a better option than nitrogen fracturing due to more fracturing cracks, more complex fracturing network and larger damage number.