INFLUENCE OF FLUIDS ON THE ELASTIC PROPERTIES OF SANDSTONE AT HIGH-PRESSURE AND TEMPERATURE

Recent geophysical investigations revealed the existence of zones in t he Earth's crust with anomalous low seismic velocities. The nature of these zones is still under debate, although there are some indications that they might be correlated with changes of porosity and hydraulic permeability as well as with the presence of fluids. To test this hypo thesis an experimental study of the influence of fluids on the elastic properties of sandstone as a model rock system for crustal conditions was performed. The investigations were conducted at a hydrostatic pre ssure of 300 MPa and temperature up to 850 degrees C. They revealed th e strong influence of different fluids (neutral, acid, alkaline) on th e elastic properties of sandstone as a result of mineral reactions, ph ase transition and of changes of the rock microstructure. To evaluate the phase changes the computer modeling was performed. Together with i nvestigations of the role of volatiles in geochemical processes includ ing the influence of mineralized fluids on mineral reactions these stu dies will contribute to the petrophysical and geochemical interpretati on of geophysical measurements.