Seismic reflection imaging over a thermally enhanced oil recovery site

In recent years it has become increasingly important to develop a capability for monitoring Enhanced Oil Recovery (EOR) processes as they are occurring within the reservoir. A knowledge of the developing processes in real time allows the possibility of controlling and/or modifying the processes involved. During thermal EOR operations, such as steam stimulation or steamflooding, the reservoir formations undergo a number of thermally and mechanically induced physical alterations. These changes cause various petrophysical parameters to produce amplitude anomalies on seismic reflected energy. The amplitude anomalies occur as bright spots, zones of attenuated energy and as interference phenomena. They may be due to large changes in reflection coefficients due to the presence of gas or hot steam and/or steam condensate.;The elastic equations may need to be modified due to enhanced anisotropy and the change in velocity which creates "lenses" which focus or defocus acoustic or elastic waves and produce interference phenomena on stacked sections.;Synthetic seismograms were computed for P-SV and SH wave propagation in transversely isotropic media adapted for the vector CDC-205 supercomputer. The algorithms are based on the fourth order accurate MacCormack type splitting scheme. Examples indicate that anisotropy plays an important role in modeling the kinematic and the dynamic properties of the wave propagation and should be taken into account when necessary.;A new type of migration before stack has been developed which is relatively cost effective and successful in imaging diffracted elastic waves. It is a simple and yet robust seismic common shot gather depth migration operating in the frequency-space (;A seismic experiment consisting of three reflection lines was carried out by Esso Resources in February of 1984 over a steam injection research site near Cold Lake, Alberta. Analysis of the field data showed that large variations in reflected scattered energy occurred as a function of angle of incidence in areas affected by the steam zone. An Amplitude-versus-Angle (AVA) analysis, over the steam injection location showed encouraging results and established that seismic reflection methods, when well designed and carefully processed, can be used to map the invaded steam zones in steam stimulation EOR operations. The results are imaged on a new type of display called ARPA (Amplitude Ratio for Partial Angle), which illustrates reflections zones with low-high Poisson's ratio or equivalent high/low gas saturation with a CMP stack section plotted as the background.