Abstract

Since the 1970's, Total Indonesie has been intensely studying the modern Mahakam River delta in East Kalimantan as a possible working model, the attributes of which could then be applied to the Miocene deltaic series, the primary objective within our exploration permits. The key to this linkage of the modern delta analogue to the Miocene delta is the comparison of geological and geophysical models derived from surface information to available seismic data.

Do depositional environments have distinctive seismic signatures? A valuable tool to attempt an answer to this question is the 3D seismic data recently acquired over some of our fields. The high resolution exhibited by the shallow portion of the 3D data is more than sufficient to reveal valuable information concerning sedimentary bodies, their shapes, their history and their acoustic response. Attribute maps can be interpreted from the shallow 3D seismic data in terms of stratigraphy and sedimentology and the comparison with the modern delta analogue increases the confidence in the interpretation. This interpretational tool, comparison of shallow 3D seismic data with the modern delta analogue endows models with powerful seismic imaging: we know what could be the acoustic signature of environments and, furthermore, we know that shallow data caries reliable information.

Subsequent to the establishment of relationships between the shallow 3D seismic data and the modern delta analogue, the second step is to look for analogies between shallow data and deep data (within the Miocene series). Attribute maps of deep horizons are low quality. Signal/noise ratio is low, images are fuzzy and unfocused, and it is often almost impossible to recognize or understand patterns in attribute maps without any reference. The documentation of analogies as a result of the "step down" method, an initial comparison of the high resolution shallow 3D seismic data and the surface model information allows the establishment of workable acoustic images, so that they become easy to apply to deep attribute maps.

If no reference to the modern Mahakam delta analogue is established, these high resolution shallow attribute maps remain the only witness of "new" environments, non-illustrated by present-day delta (erosive periods, distal sedimentation) and can be reliably applied to the deeper series. Looking for analogies by a gradual stepping down through the 3D seismic data is one of the only ways to reach the Space and Time evolution of almost every kind of environment. Using appropriate processing sequences and display tools, the understanding and imaging of Miocene sedimentation and structure is better than ever.