Steam zone

Table 2 indicates that the steam zone is characterized by a pore pressure increase of about 150 psia, a temperature increase of about 250 $^{\circ}$F, and a gas saturation value of about 90%, compared to ambient conditions. The pore pressure increase results in a V_p decrease of about 5%. The temperature increase and replacement of water with steam vapor causes a net decrease of about 35-40%, from Figure Vptemp. The combined effect of heat, pressure and steam vapor suggests that the steam zone should be associated with a total V_p decrease of 40-45%! Since the gas saturation increases to 90%, the density of rocks in the steam zone should decrease by about 15%. The magnitude of these combined velocity and density changes is very dramatic and should be easily visible in time-lapse seismic data as large time delays and bright reflections and diffractions at the steam zone.