Energized fracturing with CO₂: a numerical simulation of the effects of thermodynamic properties of CO₂

Energized fracturing with CO2 is considered as an alternative method to conventional water-based hydraulic fracturing, which brings advantages in water conservation and environment protection as well as in hot enhanced geothermal systems (EGS). However, the varying thermodynamic and transport properties of CO2 could be problematic in energized fracturing. To investigate the effects of CO2 pressure-temperature-dependant properties on fracture propagation, an extensive numerical simulation is performed using a robust fracturing simulator developed on Complex Systems Modelling Platform (CSMP-HF). Based on the Span-Wagner equation of state, the thermodynamic and transport properties of CO2 in varied in-situ conditions (i.e., pressure and temperature) during energized fracturing process are calculated. The simulation results show that in-situ stress conditions affect the fracture growth speed under constant CO2 mass rate. The additional storage volume brought by injection system contribute significantly to the hydraulic fracturing speed. Higher propagation speed may result in dynamic fracture propagation and thus resulting in branching, a subject for further research.