| Abstract |
A rock database has been established at Orkustofnun, Iceland, representing formations in active low- and high-enthalpy geothermal systems in the country. More than 500 rock samples have been collected spanning basaltic to rhyolitic composition and including lavas, hyaloclastites, intrusions, and a few sedimentary rocks of volcanic origin. The hydrothermal alteration of the samples varies from literally fresh rocks to true greenschist facies rocks. Petrological and mineralogical studies as well as chemical analysis are completed on more than half of those samples. The majority of the samples has been measured with respect to gas permeability, porosity, and grain density. A portion of the samples has undergone more specialized measurements such as acoustic velocity, thermal conductivity, resistivity and mercury injection. The results show among other things very little difference between effective and total porosities. Liquid permeability is considerably lower than gas permeability, but relationship based on physical parameters can be shown to exist between those properties. Matrix permeability is shown to predominately relate to capillary tube model behavior with weak dependency on porosity. There are indications for significant reduction in permeability for a small degree of alteration, while the opposite is indicated for higher degree of alteration. The physical parameters show little dependency on confining pressure. |