Anisotropy survey for reservoir definition

Summary In the context of Franco-Soviet cooperation, a seismic survey was carried out on the Romashkino reservoir in the Tatar Republic (USSR). This survey involved evaluating azimuthal anisotropy parameters from S-wave VSPs recorded on three wells and from a surface seismic line, the latter in order to monitor any lateral variations in the parameters. In this paper we present results which indicate in particular that for the two wells in which oil production has been established, the anisotropy rate appears to be proportional to production figures. This seems to confirm the hypothesis that variations in production are asociated with the presence of subvertical fractures which cause S-wave birefringence. By processing the reflected converted P-S waves of a surface seismic line, it is possible to monitor lateral variations in the anisotropy parameters and well ties effectively confirm differences revealed by the S-wave VSP data.