Abstract

The Attaka Field, which lies about 125 kms to the North East of Balikpapan, is within the Kutei Basin area and belongs to a Production Sharing Contract between Unocal Indonesia Company and Pertamina. The study areas have long been investigated, mainly due to their central role within one of the most potential and productive oil basins in Indonesia. However, enigmatic problems still remain pertaining to the sedimentary geology of the areas in the depositional as oil reservoirs. Larger datasets, systematically accumulated data, and more detailed characterization are required for unraveling those particular problems.

A recent study is focused on the Lower DR Sand Overpressure Sequence, at depths of 10050 – 10130 feet (TVD). An outline of the nature of sedimentary deposits of the Lower DR Sand was described using the conventional core from well Tiger-5 and wireline log data from 20 wells. The data show a deltaic depositional system, which could be divided into 5 intervals with coarsening upward units observed from the gamma ray logs.

From calibrating the core and wireline log data, the depositional environment of the Lower DR Sand was interpreted as delta front and prodelta. The Lower DR Sand in well Tiger-5 shows four types of sandstone facies, which are proximal sand bars, muddy interbar sand, distal sand bars and marine shelf.

The distribution of this sand has a prominent SW – NE orientation, as might be reflected by the general trend of the Mahakam Delta.