Time-lapse seismic monitoring of a heavy oil reservoir undergoing steam injection is a critical step in the evaluation of production efficiency, where pressure, temperature and fluid changes in the reservoir can be monitored remotely over a large spatial area without drilling costly observation wells. Seismic amplitude data can be used to image changes in the reservoir, providing a qualitative view of production related effects and their spatial extent, however, the physical cause of the changes cannot be determined from amplitude data alone. The use of pre-stack simultaneous AVO inversion of 4D seismic data, in conjunction with rock physics analysis, has the ability to quantify changes in reservoir conditions, bridging the gap between seismic amplitudes, elastic properties and reservoir parameters.
This study outlines the workflow implemented to quantify changes in reservoir conditions due to steam injection and production of an Athabasca Oil Sands bitumen reservoir. A holistic approach to interpretation was implemented, encompassing unconsolidated rock physics analysis, pre-stack 4D simultaneous AVO inversion to quantify elastic changes in the reservoir, and subsequent rock physics driven probabilistic lithology classification to separate our elastic changes into steam or gas, water, and mobile oil. Ultimately, the identification of various production related effects such as steam chamber development and mobile oil leads to improved reservoir optimization opportunities, allowing for an increase in bitumen production.
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