It is becoming increasingly common to use 4D Seismic surveys on SAGD projects to characterize the steam chamber size, shape and growth. The use of this type of survey in history matching SAGD simulation models has also grown significantly, allowing engineers to match not only the volumes, temperatures and pressures, but the shapes of the steam chambers as well. In the authors’ experience, however, before 4D Seismic surveys can be used confidently to history match the steam chamber shapes, we need to understand what 4D seismic represents. Prior proposals suggest steam or gas chamber volume, stress change volume or temperature change volume. To investigate this, the current study examines the impact of various physical property changes impacting the surveys (in particular, geomechanical effects), so that the appropriate 4D seismic history matching criterion are established.
To determine how the above factors impact the 4D seismic surveys, this study investigates the relative impact of various property changes that occur in-situ during the SAGD process, with the intent to determine what changes have the biggest impact on seismic velocity. A number of SAGD simulation runs were conducted using typical oil sands geology with fully coupled geomechanics. Afterwards, the change in pressure-wave velocity and shear-wave velocity at the simulation grid blocks at various times during the simulation was calculated. The property changes of temperature, pressure, stresses, saturations and fluid properties were also calculated, and then categorized in terms of the significance each factor has to the 4D Seismic data. This categorization serves to identify the appropriate SAGD history matching criterion, to improve the quality, confidence and predictability of a SAGD simulation model.
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