Abstract

In the Kutei Basin (Indonesia), the depositional sequences of the Late Pleistocene Mahakam delta were analyzed using the shallow portions (0-250 milliseconds TWT) of approximately 650 km² of 3-D seismic data together with serveral high-resolution 2-D seismic profiles in order to study their depositional geometries, overall evolution, and relative positions to one another in sequence stratigraphic terms. This was done in hopes of understanding the depositional behavior of the lowstand delta sequences in response to sea level changes and tectonic movements, and also to compare their differences from the modern, highstand delta that is currently used as an analog for predicting reservoir geometries in the deeper Miocene-aged reservoirs.

Tracking on continuous, locally chronostratigraphic events (i.e. maximum flooding surfaces, emergence surfaces, etc) and creating seismic time and attribute maps with these surfaces permitted a visual interpretation of paleodepositional environments and the description of paleomorphologies that are not present in the modern highstand Mahakam delta. Paleomorphologic reconstructions of the lowstand delta evolution allowed the formulation of ideas on delta response to syn-depositional tectonics, sea level changes, and the relationships between the highstand/lowstand delta systems. Results show that syn-sedimentary tectonics play an important role in directing the hydrodynamic gradients of the delta, affecting sediment transport and ultimately, the reservoir geometries.