| Abstract |
In the evaluation of a geothermal resource it is critical to know the reservoir geometry, temperature, saturation, state of saturants, pore pressure, porosity and permeability. These are the parameters which will determine the production feasibility and cost effectivness of a geothermal prospect. The increasing sophistication of seismic wave data collection and processing and recent exerimental work on factors governing wave propagation in rocks has stimulated increased interest in the use of active seismic techniques to determine the -- in situ physical state of crustal rocks for engineering applications. In this paper we review experimental work showing how wave velocities in rocksaresensitive to parameters of interest to geothermal exploration; effective pressure, the degree of water saturation of the pores, and the bulk modulus of the pore phase. Seismic attenuation is even more sensitive to the degree of saturation and the microgeometry of the pores. Both velocity and attenuation are strongly temperature dependent and reflect thermal fracturing of the rocks at elevated temperatures. By combining data on attenuation and velocity of compressional and shear waves considerably greater constraints may be placed on the environmental state of the rocks than on the basis of P velocities alone. |