Abstract

The 3D data interpretation tools provide new ways to track and visualize geophysical data. This paper describes the process of building a depositional model by using 3D seismic data over the Selat Asam field in Malacca Strait PSC. The aim of this study is to interpret depositional features and delineate the extent of hydrocarbon reservoir in this field. The petroleum system is Lower Miocene fluvio-deltaic Sihapas Formation reservoir sands trapped in a Mid-Miocene low relief anticline, sealed by Mid-Miocene Telisa shale, and charged during end of Mid-Miocene from Upper Eocene lacustrine shale source rock of Pematang Formation.

The Selat Asam field was discovered by Selat Asam-1 well in 1985. Five significant stacked reservoirs were penetrated and tested a maximum cumulative rate of 14,000 BOPD. This success marked the beginning of the Low Relief Play exploration phase in the Malacca Strait PSC. Immediately following this success three appraisal wells were drilled, but only one well intersected a commercial oil column in that structure. Although further evaluation was constrained by severe static problems in the 2D seismic data, it was believed that a stratigraphic component is dominated the trapping mechanism. The field was put on production from two wells in 1990. In 1998 Kondur Petroleum S.A., as the new operator of the block, conducted a 406 sq km 3D seismic survey which covered this field.

In analyzing a depositional model the effects of structure need to be removed. This can be done by flattening the interpreted seismic horizon that marks the objective reservoir. The time slice section of the flattened seismic horizon might display the spatial distribution of seismic attributes over a layer. The depositional model can then be created based on the seismic attribute distribution map. These techniques have been shown to have a powerful ability to reveal depositional features such as bars and channels.

With the interpretation of a fluvial-deltaic system, the relatively larger oil column in Selat Asam - 1 well is attributed to an additional element of stratigraphic entrapment related to the draping of a tidal channel sandstone body encased in lower delta plain mudstone over the Selat Asam structure. The two failed appraisal wells are not located within this sand system. This model can be used as a basis for a reservoir characterization study or even a field development scenario.