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Seismic data plays a crucial role in reservoir characterization. Quantitative seismic reservoir characterization workflow aims to extract reservoir properties from seismic data to identify sweet spots for exploration, appraisal and development drilling. This is all the more true if the data is to be used in 4D seismic surveys (Time-lapse seismic) for reservoir monitoring. 4D seismic data can help to capture the reservoir change, realize the reservoir dynamic characterization and facilitate an enhanced understanding for reservoir potential, so as to have the better business decisions and optimized field development plans. In this study, use a SAGD (Steam-Assisted Gravity Drainage) field to demonstrate how to extract reservoir dynamic change and evaluate the reservoir performance from 4D seismic data.

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The hydrocarbon-bearing formation of Miano gas field belongs to the Early Cretaceous and it is bounded by two shale intervals, which are considered as maximum flooding surfaces (MFS). The hydrocarbon-bearing interval includes two reservoir units: a tight gas reservoir and its overlying conventional reservoir. Core samples, borehole logs, and well production performance revealed that the two reservoirs present reversed trends in reservoir quality through the gas field without obvious barriers. The average shale volume of the tight gas reservoir changes from 24.3% to 12.2% and the average permeability changes from 32.65 mD to 0.02 mD from the south to north. However, the average effective porosity of the overlaying conventional reservoir increases from 20% to 26% and the average permeability increases from 10 mD to 300 mD. The reversed trends in the two reservoirs lead to challenges in production forecast and development well proposals in the tight gas reservoir. Therefore, reservoir characterization and a predictive reservoir model are essential for further exploitation of Miano gas field. The geological genesis analysis integrating cores, borehole logs, and three-dimensional (3D) seismic data reveals that the producing interval of the tight gas reservoir is tidal-influenced shore facies deposition with intergranular pore space reduced by mineral cementation during burial diagenesis, while the overlaying conventional reservoir is fluvial-influenced deltaic deposition with abundant, well-connected intergranular macropores, which leads to a better reservoir quality. A reservoir model containing both the tight gas reservoir and the conventional reservoir is constructed considering the reservoir nature understanding, and the accuracy of the model is confirmed by reservoir surveillance activities with the simulation model. The study will be critical to the further reservoir development and hydrocarbon production in Miano gas field.

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