| This thesis presents a case study on time-lapse seismic monitoring. The target area is located at East Senlac in the vicinity of Alberta and Saskatchewan border, a heavy oil reservoir in the Western Canadian Sedimentary Basin. In order to observe rock property related seismic anomalies, two perpendicular seismic lines have been set up. One seismic line along the N-S direction is subject to Steam Assisted Gravity Drainage (SAGD) while the other seismic line along the W-E direction is not affected. This case study covers the subjects of feasibility study, processing strategy, repeatability evaluation, seismic attribute analysis, and impedance inversion.; Systematic feasibility study is conducted by prediction of rock properties based on Gassmann's equation, technical risk assessment, forward modelling and seismic survey design. The first stage simulation of oil substitution by steam indicates that it is feasible to perform time-lapse seismic monitoring project, but great challenge might be encountered. Continuous gas injection barely induces seismic variations. In the aspect of seismic data processing, better seismic quality is obtained by employing the prestack simultaneous processing (PSP) strategy. The three metrics, Pearson correlation, normalized root-mean-squares and predictability are employed to quantify the post-stack seismic repeatability. Higher repeatability along the W-E direction than along the N-S direction shows different local geology environment. The non-uniform CMP stack fold distribution is found the main factor to affect seismic repeatability. The seismic attribute, power spectra calculated from the N-S seismic surveys demonstrate that higher frequency energy tend to increase with time due to the possible decrease in pore pressure and pore temperature. On the other hand, the inverted impedance using the recently proposed hybrid data transformation shows mixed impedance variations. The continuous gas injection and the simultaneous drop in temperature and pressure are possibly the main reason to result in this mixed impedance variations. |
