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Abstract

An analysis of two rock samples, hyaloclastites and basalts, at in-situ reservoir conditions has been done to identify the role of temperature on the seismic velocity and attenuation. The goal is to establish a temperature-dependent fluid substitution analysis of geothermal rocks using Gassmann equation within the framework of Biot's poroelasticity. The analysis of temperature-dependent wave attenuation is shown for hyaloclastites. The results show that the general decreasing trend of seismic velocity towards temperature may be related to the thermophysical characteristics of fluid. Using Gassmann equation it has been shown that the presence of steam bubbles can reduce the effective elastic property of rocks which indirectly demonstrates the role of temperature to the seismic velocity. The Q factor, i.e., inverse of attenuation, behaves surprisingly almost in the same way as the seismic velocity with temperature, except in the lower temperature range. The Q factor increase with the temperature is supposed to be a quick viscosity decrease. The later decrease of Q factor may indicate the presence of steam bubbles due to the further temperature increase. This finding demonstrates that the application of temperature-dependent fluid substitution modelling using Gassmann equation can be applied for the characterization of geothermal reservoir systems. Copyright © (2008) by the Society of Exploration Geophysicists All rights reserved.