Nucleation of remote hydraulic fractures

Hydraulic fracturing is widely recognized as the most effective method for creating Enhanced Geothermal Systems (EGS). However, its application has been associated with induced seismicity, leading to the shutdown of several projects. As an alternative, low-viscosity fluids, such as CO2, may be used because they tend to generate complex fracture networks by inducing numerous small, isolated (remote) fractures without requiring high-pressure injection. Despite this potential, however, the mechanisms and conditions that govern the formation of such patterns remain poorly understood. This study identifies two critical factors through poroelastic analysis: (1) prolonged pressure diffusion facilitated by the low viscosity of the fluid, and (2) heterogeneity in Biot’s coefficient. To validate these findings, hydraulic fracturing experiments were performed on two types of marble: fine-grained marble, representing a homogeneous sample, and coarse-grained marble, representing a heterogeneous sample. Both water and CO2 were used as injection fluids. The results demonstrate that remote fractures only form in heterogeneous rocks when CO2 is used as injection fluid. These findings suggest the potential to develop a safe and innovative reservoir stimulation technique that effectively stimulates large surface areas by strategically alternating the viscosity of the injection fluid while maintaining low injection pressures.