Petrophysical Parameters of Rocks Saturated with Liquid Water at High Temperature Geothermal Reservoir Conditions

Abstract

A laboratory system for the investigation of water saturated rocks at temperatures up to 250 ?C and controlled confining and pore pressures up to 50 MPa was developed and successfully applied for investigations on rock samples from Icelandic high temperature geothermal fields. The samples were selected from a core-collection of deep boreholes at Iceland GeoSurvey.
The samples came from depths where the ambient temperature is in the range 150-230?C and both from the smectite and the chlorite alteration zones.
Four-electrode resistivity, compressional and shear wave velocity were measured at equilibrated temperatures ranging from 25?C to 230?C and at estimated in-situ pore and confining pressure. The samples were exposed to these conditions for periods up to some days to investigate their stability.
Three out of six samples were successfully measured over 200?C. Two of them are from the chlorite alteration zone and one from the smectite zone. All the three samples show much stronger temperature dependence of the conductivity than expected from pore fluid conduction. This indicates that surface conduction is the dominant conduction mechanism. The temperature dependence of the compressional wave velocity above 100?C is similar to what could be expected from the temperature dependence of the velocity in pure water.