Abstract

Reefal facies in carbonate plays usually have a good chance for reservoir, but this is not the case for the Sopa carbonate complex in the eastern part of Musi Platform, South Sumatra Basin. Drilling in this type of facies resulted in loss of significant exploration and delineation opportunity. A different approach was used to solve the problem by using 2D seismic and well log data in a fully integrated interpretation of a geological model, 2D seismic facies, and seismic inversion. This approach has been used to predict carbonate reservoir characterization and distribution, and also to define the play concept of Baturaja Formation in this area.

Based on core data and well log correlations, the Sopa carbonate reservoirs could be divided into platform carbonate, reefal, and prograding carbonate clastic facies. These units were interpreted as transgressive and highstand systems. Diagenetic processes in the Sopa carbonate complex play an important role in reservoir quality. The platform and reefal facies are relatively tight with mainly of isolated biomoldic porosity without fractures. In contrast the prograding carbonate clastic facies is characterized by a chalky type of porosity ranging from 15% to 25% with 300-2,000 mD permeability, based on well log analysis.

Based on a geological model, reefal and prograding clastic carbonate facies have been mapped in detail by undertaking 2D seismic facies analysis, and computing average acoustic impedance gradually from 10 ms, 20 ms until 30 ms from carbonate platform. Those maps show the transgression carbonate evolution of each defined stage, the prograding clastic carbonate development and their distribution surrounding the reefal facies and marl to open marine facies. Low acoustic impedance, which was marked by toplap, downlap, and prograding seismic expression of 2D seismic facies map, represented porous reservoir of prograding clastic carbonate. While high acoustic impedance, which was marked by concordant, parallel seismic expression of 2D seismic facies map represented tight reservoir of reefal facies.

The results of the study suggested that the carbonate play concept in Sopa carbonate complexes were focused on the prograding clastic carbonate as an alternative model for hydrocarbon occurrence. The target for exploration and development in Sopa and surrounding areas of the Musi Platform, South Sumatra, is the prograding clastic carbonate, which represents good quality carbonate reservoir.