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J. Jane Shyeh1, Dave H. Johnston1, John E. Eastwood1, Mashiur Khan2, Larry R. Stanley2
(1) Exxon Production Research Co, Houston, TX
(2) Western Geophysical

Abstract: Interpretation and modeling of time-lapse seismic data: Lena Field, Gulf of Mexico

Description of Paper: Recent results from a time-lapse 4D seismic research project may have the potential to inject new life into Lena, a mature field in the Gulf of Mexico. This project is a collaborative effort of multi-disciplinary and multi-company personnel. As a result of this work, areas bypassed by injected gas have been identified as opportunities for infill drilling to recover additional oil. Furthermore, a drilling plan guided by time-lapse seismic data can greatly reduce risks (drilling cost is more than $4MM per well at Lena).

Results, Observations, and Conclusions: Two seismic surveys, one obtained in 1983 by Exxon before production and one obtained in 1995 by Western Geophysical, are used in this study. Methods and tools have been developed to remove seismic data differences originating from seismic acquisition and seismic data processing variations for the two 3D seismic surveys. The methodology has greatly improved the significance of the calculated time-lapse seismic differences.

We also calculated rock/fluid seismic properties from average pressure and saturation changes in four regions of the Lena B80 reservoir. Our analysis indicates that oil displaced by gas will cause a large change in the seismic response, and will appear as an anomaly on a seismic difference map. The presence of gas in waterflooded regions makes it difficult to detect the water front. This is because the reservoir pressure had been reduced below the bubble point of the oil early in production liberating solution gas throughout the field.

The time-lapse seismic data have been interpreted to indicate where injected gas is accumulated. This interpretation has been validated by field data for the Lena-B80 reservoir. Flow simulations also validate the time-lapse seismic results.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana