Novel thermochemical fracturing: A breakthrough in sustainable and efficient enhanced geothermal systems (EGS)

Enhanced geothermal systems (EGS) are crucial for accessing earth's vast geothermal potential, particularly in low-permeability formations. However, conventional EGS stimulation via hydraulic fracturing often entails high operational costs, substantial water consumption, potential environmental impacts, and risks of induced seismicity. This study presents a novel thermochemical fracturing approach to enhance EGS performance and sustainability while addressing these limitations. The in-situ exothermic reaction of sodium nitrite (NaNO₂) and ammonium chloride (NH₄Cl) was applied to a 12-inch carbonate rock sample. A specialized core flooding apparatus enabled real-time evaluation of temperature profiles, permeability, and heat transfer enhancements. The thermochemical stimulation increased permeability by 109% (from 19.01 to 39.70 mD) and enhanced heat transfer by 530%. These improvements stem from an extensive micro-fracture network generated by high-pressure nitrogen gas pulses, contrasting with larger planar fractures from hydraulic fracturing. Notably, this was achieved with only a 3.3% increase in porosity, indicating preserved rock integrity. The exothermic reaction prevented core cooling during ambient-temperature stimulation fluid injection, avoiding thermal shock. The thermochemical stimulation primarily generates nitrogen gas (N₂) and a brine solution as byproducts. The generated N₂ offers the additional benefit of providing well lifting energy, simplifying flowback operations. The novel application of thermochemical stimulation in EGS represents a promising, eco-friendly, and operationally efficient alternative to conventional EGS stimulation techniques.