Seismic Signatures of Temperature-dependent Geothermal Rocks at In-situ Reservoir Conditions

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 present the result of using Gassmann equation within the framework of Biot’s poroelasticity for a fluid substitution analysis of geothermal rocks. The analysis of temperature-dependent wave attenuation is shown for hyaloclastites. The results show that P wave velocities decrease with the temperature rise in a systematic way. The general decreasing trend of seismic velocity towards temperature may be related to the fluid characteristics with the temperature. Using Gassmann equation it has been shown that the presence of steam bubbles can reduce the effective elastic property of rocks. The Q factor 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 Gassmann fluid substitution modelling may be used for the characterization of geothermal reservoir systems.