###### Abstract  
The initiation and propagation behavior of fractures induced by supercritical carbon dioxide (SC-CO\({}_{2}\)) jet fracturing is significant to evaluate stimulated reservoir volume (SRV). However, the propagation characteristics of fractures induced by SC-CO\({}_{2}\) jet in layered rocks with layers having different mechanical properties have not yet been studied. In this study, four groups of artificial sandstones were used to conduct SC-CO\({}_{2}\) jet fracturing experiments and investigate the fracture initiation and propagation behavior in hard and soft layered rocks. A strain collection device was employed to monitor the strain changes of the specimens during the experiments, and after the experiments, a three-dimensional scanner was used to obtain the morphologies of the main fractures. Experimental results showed that the SC-CO\({}_{2}\) jet fracturing can be divided into the pressurization of the perforation pressure stage and fracture propagation stage, and the fractures initiation and propagation is intermittent. Three types of main fractures have been found--longitudinal fracture, transverse fracture and oblique fracture--and the formation mechanism of the main fractures has been elaborated. The rock strength can affect the number and complexity of fractures created and the fracturing rate, and the Young's modulus of rock has an effect on fracture propagation length. The fractures mainly develop near the perforation and are difficult to propagate to another layer with different mechanical properties. The result in our study is conducive to the application of SC-CO\({}_{2}\) jet fracturing technology in the field. fracture propagation; SC-CO\({}_{2}\) jet fracturing; hard and soft layered rock; strain monitoring; three-dimensional scanning +
Footnote †: journal: Applied Sciences  
fracturing has been proposed in recent years [10,11], gaining great attention due to its particular properties and encouraging results [12, 13, 14, 15]. The SC-CO\({}_{2}\) has unique properties, including a low viscosity similar to the gas state, a large density similar to the liquid state, a low surface tension, and a high diffusivity [11, 13, 16, 17, 18]. As a fracturing fluid, SC-CO\({}_{2}\) has many potential advantages, such as avoiding the problem caused by swelling of clays [19], enhancing desorption of CH\({}_{4}\) due to its greater adsorption capacity than that of CH\({}_{4}\)[20], reducing water usage and minimize environmental pollution [21]. To combine the advantages of hydra-jet fracturing and SC-CO\({}_{2}\) fracturing, the SC-CO\({}_{2}\) jet fracturing has been proposed [12, 21]. To investigate the feasibility of applying SC-CO\({}_{2}\) jet fracturing to unconventional resources, researchers have done many numerical simulations and experimental studies. [PERSON] et al. [21] found that SC-CO\({}_{2}\) jet fracturing could achieve a better pressurization effect than the pressurization effect of water jet fracturing under conventional formation and operating conditions by using numerical simulation and laboratory experiments. [PERSON] et al. [12] investigated the influence of the factors, including jet pressure, jet distance, nozzle diameter, perforation length and perforation diameter, on the effect of SC-CO\({}_{2}\) jet fracturing by conducting experiments on organic glasses, and found the optimal jet distance and nozzle diameter were 10 mm and 2 mm, respectively. [PERSON] et al. [19] and [PERSON] et al. [22] investigated the perforation ability of SC-CO\({}_{2}\) jet by laboratory experiments, and provided a theoretical foundation and experimental proven for field application of SC-CO\({}_{2}\) jet perforation technology, which was beneficial to the integration of perforation and fracturing by SC-CO\({}_{2}\) jet. [PERSON] et al. [23] found that the pressurization effect of SC-CO\({}_{2}\) could easily lead to fractures initiation and propagation at three locations (the root, the middle, and the tip of perforation) by numerical simulation.