Study on Foam Fracturing of Granite for the Development of Enhanced Geothermal Systems

Abstract

Foam fracturing has been considered as a potential approach to address water utilization concerns with hydraulic stimulation in the development of enhanced geothermal systems (EGS). This paper reports the recent progress of a project sponsored by the U.S. DOE’s Geothermal Technologies Office (GTO) Waterless Stimulation Initiative. The objective of project is to assess the feasibility of foam fracturing as an alternative approach to hydraulic fracturing. This paper describes the development of a foam fracturing test system at Oak Ridge National Laboratory (ORNL), which can be used to perform hydraulic fracturing of rock-like materials with both water and foamed liquids under pressure to 6,000 psi (41.4 MPa). The system, which consists of two sections: one for foam generation and the other for foam injection, has the capability of testing materials under pressure control in both monotonic and cyclic (up to 50 Hz) injection modes. Experimental results of foam fracturing on Charcoal Black granite are reported for cylindrical specimens with a blind hole studied using water and nitrogen-gas-in-water foam as the fracturing fluids. The effects of fracturing fluids and injection modes on the breakdown pressure and failure responses of the material were examined. The observations from the experimental work and the implications to EGS application are presented and discussed.