Rhyolite Magma Drilled in Iceland Could Power the World's Hottest Enhanced Geothermal System

Abstract

When molten rhyolite unexpectedly flowed into an exploratory geothermal borehole at ~2100 m depth in the Krafla central basaltic volcano, in Iceland, it created the prospect of producing geothermal energy of extremely high-enthalpy. The temperature of the intrusion most likely exceeded 900 oC and had a pressure of 40 MPa, a pressure greater than hydrostatic for its depth. The low hydrogen and oxygen isotopic ratios of the glass indicate that this rhyolite magma formed by partial melting of hydrothermally altered basalts rather than by differentiation of mantle-derived basaltic magma. In August 2010, after being cooled for many months by injection of cold water, the borehole was completed as a production well and allowed to heat. By January 2010, the rate of heating indicated that the deepest part of the well would thermally equilibrate at ~ 500 oC by October. The results of long-term flow tests, that began in mid-May and will continue for some months, will be reported at the GRC annual meeting. Today many EGS projects under development contemplate drilling production and injection wells as deep as 5 km to reach 200 oC. At Krafla we are discussing creating the world’s hottest enhanced geothermal system producing from geothermal system at 500 oC at only 2 km depth. If successful, power outputs from the Krafla well would be orders of magnitude greater than those currently envisaged for EGS wells elsewhere.