Towards Quantitative Evaluation of Gas Injection using Time-lapse Seismic

Of particular concern in the monitoring of gas injection for the purposes of storage, disposal or IOR is the exact spatial distribution of the gas volumes in the subsurface. In principle this requirement is addressed by the use of 4D seismic data, although it is recognised that the seismic response still largely provides a qualitative estimate of moved subsurface fluids. Exact quantitative evaluation of fluid distributions and associated saturations remains a challenge to be solved. Here, an attempt has been made to produce mapped quantitative estimates of gas volume injected into a clastic reservoir. Despite the accuracy of the calibration using three repeated seismic surveys, time-delay and amplitude attributes reveal fine-scale differences though large-scale agreement in the estimated fluid movement. These differences indicate disparities in the nature of the two attributes themselves and highlight the need for a more careful consideration of amplitude processing for quantitative 4D seismic interpretation.