Supercritical CO2 is a kind of fluid

which is in a special state between gas and liquid

with unique properties such as low viscosity

high diffusivity

and zero surface tension. Thus

supercritical CO2 can be used as fracturing liquid to assist crack initiation and propagation without leading to the damage of reservoir zones. In this study

the mechanisms of supercritical CO2 fracturing were obtained by studying and analysing the characteristics of rock breaking and fracturing with supercritical CO2. The results indicate that

owing to its lower viscosity

supercritical CO2 can easily penetrate into micro-pores and micro-cracks and build fluid pressure systems with varied magnitudes in rocks

which results in tensile and shear failure. In conventional hydraulic fracturing

the initiation pressure is high

and the fractures are single or multiple straight cracks. Most fractures penetrate through mineral grains with high strength along the same direction

and the fracture sections are smooth and flat. However

the initiation pressure of supercritical CO2 fracturing is lower than that of conventional fluid fracturing methods; the fracture network is complex

and fractures are connected with each other. Generally

the induced fracture majorly initiates along the lower-strength grain boundaries

but seldom penetrates the mineral grains. Moreover

the fracture planes are rough. This study provides theoretical support for implementation of supercritical CO2 fracturing technology.