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3-D seismic interpretation of thin gas sandstone reservoirs using multiattribute analysis on poststack and AVO data, offshore SE Sumatra

Repsol-YPF, Jakarta, Indonesia

Rocky Roden

Repsol-YPF, Houston, Texas, U.S.

Corresponding author: R. Hidalgo, RHIDALGO@email.ypf.com.ar

The first 20% of the full text of this article appears below.

3-D, AVO, and poststack multiattribute analysis have been used successfully to define the internal character of a gas sandstone reservoir in Banuwati Field, offshore Sumatra. The field produces from Early Miocene "A" and "B" sandstones of the Upper Gita member, Talang Akar Formation, at a depth of 5500 ft. The range of reservoir channel sandstone thickness is 20–70 ft; the gas column is as tall as 200 ft. The main data set is the 1993 "3-D Gas Area" survey—280 km² of 3-D prestack time-migrated seismic data.

A fieldwide structural and stratigraphic analysis was begun in 1998 to more accurately estimate reserves and optimize the development plan. The 3-D survey was reprocessed as part of this study. The processing flow had two benefits: (1) to derive AVO seismic data and (2) to improve the quality of the poststack data and gain higher resolution and better signal-to-noise ratio at the main target interval. The reprocessing helped us to better define the field stratigraphy.

After careful well calibration, seismic modeling, and examination of the mapped seismic geometries, the distance between two adjacent troughs, or trough-to-trough distance (TTDT) proved the most sensitive poststack seismic attribute to discriminate sand from shale inside the channel complex.

Both AVO and zero-offset forward modeling were necessary to validate the multiattribute analysis work.

	Geologic setting

 
The area is in Sunda Basin, offshore southeastern Sumatra (Figure 1), a prolific back-arc basin between the islands of Sumatra and Java. Banuwati Field is in the flank of the depocenter of Sunda Basin, next to the Seribu half graben. The operator has produced oil from both Sunda and nearby Asri Basin for 30 years.

View larger version (30K): [in this window] [in a new window]   Figure 1. Location of Banuwati Field and the 3-D survey.