Sustainability of Fractured Rock Permeability under Varying Pressure: Fid-Bau Portal

Sustainability of Fractured Rock Permeability under Varying Pressure

Kluge, C. / Blöcher, G. / Milsch, H. / Hofmann, H. / Nicolas, A. / Li, Z. / Fortin, J.

Sustainable energy production is key for today’s energy and heat demand and relies on the successful stimulation of low-permeable oil, gas or geothermal reservoirs. Fracture permeability is a substantial topic in recent laboratory and numerical studies. Our aim is to study the sustainability of fracture permeability at varying effective stress with a focus on the fracture mechanism involved. We aim to further characterize the permeability evolution for different modes, mode I tensile fractures, saw-cut fractures, mode I tensile fractures with shear displacement and mode II shear fractures, in the laboratory, covering all fracture modes commonly observed in EGS. The hydraulic experiments are carried out in a triaxial compression cell. To simulate production and injection procedures in a geothermal reservoir, the effective pressure is varied and permeability is continuously measured. The permeability development of different fracture types at high effective stresses has been investigated and a general decrease of permeability at already low effective stress was observed in all tests. Shearing does not lead to a sustainable permeability increase for the tested sandstone. Conclusively, any reduction in pore pressure after stimulation will damage the fracture permeability irrecoverably.