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ABSTRACT: The Change of Keutapang sand-gas reservoir physical parameters calculated using surface seismic data on AVO anomaly

Santoso, Djoko, Susanti Alawiyah, and W. G. A. Kadir , Institut Teknologi, Bandung, Indonesia

Keutapang formation is one of the important gas producers in the North Sumatra Basin. It is a group of sedimentary rocks consist of sandstone layers with shale intercalation. Structurally, the basin is characterized by northwest-southeast trending folds. Keutapang Formation was deposited in the coastal environment during Middle Miocene age. The thickness of this formation is in the range of 500-1300 m.

The gas was found on the sandstone reservoir of Keutapang Formation. It was trapped within the porous zone. In the surface seismic data the existence of gas could be identified by the AVO anomaly. Application of the Shuey's equation to the AVO anomaly using marquard inversion technique, the seismic parameters such as P wave velocity (Vp), D Vp (velocity different of upper and lower layers), r (density), D r (density different of upper and lower layer) and s can be estimated.

Using the calculated value of density and velocity the acoustic impedance of the reservoir layer can be calculated. The plot between CDP of the surface seismic line to the density, velocity and acoustic impedance values gives an interesting result. The significant change of these three parameters is found where the gas formation is located.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia