Time-Lapse Seismic Crosswell Monitoring of Steam Injection in Tar Sand
Time-lapse tomography of crosswell seismic data can be used to monitor hydrocarbon reservoirs for P-wave velocity changes due to production over time. A finite frequency wave theory for phase and amplitude attributes is applied in the forward modelling part. In the inversion part, the common problem of poor illumination in crosswell tomography is taken into account. The developed tomographic imaging technique is used on real data in a crosswell experiment with two source wells and two receiver wells (i.e., in total there are four cross sections).
Hot steam was injected via a horizontal pipeline going through a reservoir of tar sand during 72 days between the baseline and monitor survey. The time delay and relative amplitude variation observed in the time-lapse data were used separately and jointly to estimate the time-lapse velocity models for all four cross sections. In general, the four cross sections show a negative velocity anomaly close to the pipeline location. This observation is in agreement with rock physics modelling experiments that a temperature increase results in a velocity reduction of heavy oil reservoirs.