ABSTRACT

The cold production process, driven by a depletion in a mobile heavy oil fields, is characterized by limited recovery rates of about 10 %. To improve the production efficiency, thermal recovery techniques such as Steam Drive (SD) or Steam Assisted Gravity Drainage (SAGD) have been developed. During the steam flooding process, it is important to monitor the growth and migration of steam chambers to optimize the process. Time-lapse seismic monitoring has been one of the efficient methods to detect steam chambers. In most cases, the seismic velocities of a steam-saturated reservoir show very low compared to the oil-saturated case. However, in our study, it was found that free gas exists everywhere in the reservoir due to the long period of cold production prior to a steam injection. The velocity change after steam flooding is relatively low, less than 3 %. Thus, seismic monitoring of the steam chamber becomes a challenging issue in such conditions. Our modeling study shows that it requires a high signal-to-noise ratios, greater than 10 dB, to estimate an accurate dimension of the steam chamber. In addition, we observe that the time-lapse seismic images give insights about the variations in hydrocarbon gas saturation.

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