Seismic inversion tracks in situ combustion: A case study from Balol oil field, India

Abstract In situ combustion is one of the approaches used for secondary recovery of heavy oil in which time-lapse seismic data might be used to track the production process. We have analyzed three time-lapse seismic surveys carried out at a time interval of one year during pre- and postcombustion phases of in situ combustion at the Balol field in India. Interpretation of these land time-lapse data using standard seismic amplitude differences in terms of reservoir changes during production and injection can be erroneous. The Balol data, in particular, lacked calibration and had poor repeatability. We have addressed these issues by demonstrating the applicability of independent prestack inversion of baseline and monitor surveys to derive elastic attributes that help to produce clearer images of fluid movement. Independent estimates of wavelets from the baseline and two monitor surveys were used in prestack inversion to estimate acoustic impedance, shear impedance, and Poisson's ratio. The results show unexpected movement of the thermal front away from the injection wells toward the north and northwest of the injection wells, farther from the production wells. These results have been confirmed by well production data from the field north and northwest of Balol.