A State-of-the-Art Review of Hydraulic Fracturing in Geothermal Systems

As a renewable and green energy source, geothermal energy holds tremendous developmental value. Hydraulic fracturing plays a significant role in enhancing geothermal energy extraction by improving reservoir permeability and creating pathways for fluid flow. Previous reviews have primarily focused on specific aspects of hydraulic fracturing, such as fracturing processes, cyclic hydraulic fracturing, and sustainability metrics, without comprehensively addressing the gaps in experimental and modeling approaches under real geothermal conditions. This work aims to bridge these gaps by summarizing the current studies on hydraulic fracturing methods, examining critical factors such as loading scheme, injection fluid, and rate, identifying limitations, and proposing potential solutions. Key findings reveal that rock temperature, sample size, and confining pressure significantly influence fracture propagation. However, laboratory experiments often fail to replicate field-scale conditions, particularly for temperatures exceeding 200 °C and for large rock samples. Numerical and theoretical models, although insightful, require further validation through experimental data. To address these limitations, this study suggests potential approaches suitable for hydraulic fracturing under real-world conditions, such as ultra-high-temperature, high-stress environments, and large-scale experiments, which are critical for advancing geothermal systems. This work can serve as a foundation for enhancing the efficiency and sustainability of geothermal energy extraction through hydraulic fracturing.