P and S reflection seismic profiling and well logging in the travale geothermal field

Abstract

Two high resolution seismic reflection profiles, obtained with vibrators as sources of P and of horizontally polarized SH waves, were recorded and elaborated. In the well CH-3, 2704 m deep and located close to the profiles, several geophysical logs were carried out: temperature, SP and induction, density, natural radioactivity, and sonic logs with P and S wave velocity measurements. These data enabled the calculation of the elasticity moduli and of the mechanical properties of the rocks affected. The sonic log results were subsequently calibrated by means of a vertical seismic profile which permitted the computation of synthetic seismograms and a VSP log for comparison with the seismic sections and correlation between S and P seismic reflectors. The structural maps obtained from data interpretation describe with sufficient detail the fracture trend of the Travale field. By comparing V s and V p velocities for the different geological units, as defined by the interpretation, the change in the α = V p /V s ratio and in the Poisson coefficient has been tentatively utilized to correlate the seismic data with material properties. The influence of lithology on the elastic constants is discussed, as well as the influence of the saturating fluids and of the degree of saturation. The different attenuation of the P and S waves, depending on the above-mentioned characteristics, demonstrates the possibilities offered by seismic methods in the evaluation of the potential of geothermal reservoirs.