Abstract and subjects
Injection and migration of CO 2 within geologic formations and its reactions with reservoir rocks cause changes in seismic velocities, density, and attenuation, and thus seismic scattering or diffraction. We use reverse-time migration (RTM) of time-lapse walkaway vertical seismic profiling (VSP) data to study scattering changes in the reservoir caused by CO (sub 2) injection and migration. The data were acquired at the SACROC CO (sub 2) -Enhanced Oil Recovery field in Scurry County, Texas. We employ the statics correction to remove the effects of surface topography and lateral variations of P-wave velocity. In addition, we use a spectrum analysis method to balance the amplitudes of the repeat VSP data set with those of the baseline VSP data set. Our angle-domain imaging results significantly remove image artifacts and noise. Observations from our migration results are (1) the top and bottom boundaries of the reservoir are clearly imaged at depths of 1.87 km and 2.22 km; and (2) the imaging differences are mainly located within the reservoir. The results demonstrate that changes in seismic diffraction/scattering caused by CO (sub 2) injection and migration can be effectively monitored by time-lapse walkaway VSP surveys.