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Multi-Vintage Time-Lapse Seismic Interpretation Method Used to Understand Dynamic Behaviors of Deep-Water Turbidite Reservoirs in Dalia Field, Angola
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
Time-lapse seismic has been proven as an effective tool to monitor reservoir dynamics, in a turbidite environment. Dalia field is an ideal case for applying a 4D seismic since it has shallow burial depths and unconsolidated sands. However, a main challenge in 4D interpretation of Dalia is gas coming out of solution since the reservoir pressure is below the gas bubble point once production begins. This gas dramatically decreases seismic velocity and masks all other 4D seismic anomalies such as injected water. In this paper, we introduce a method to remove this gas-masking effect in order to enhance the water breakthrough anomalies. In Dalia, there exist five seismic monitors. The 4D inversions with two vintage data sets are computed to measure the relative velocity changes for all possible combinations of the vintage data, such as the 5th seismic monitor combined with the 2nd monitor. Then, the optimal 4D inversion vintage with the minimum gas-masking effects is selected; in this case, both sets of vintage data have similar amounts of pressure depletion, which indicates similar amounts of gas coming out. The pressure in the field is not spatially uniform, thus this method should be applied only to a small local area.