FRESH OUTLOOK OF RESERVOIR UNDERSTANDING AND IMPLICATION FOR FURTHER DEVELOPMENT STRATEGY OF MATURE FIELDS, CASE STUDY FROM SEMBERAH AND MUTIARA FIELDS, KUTEI BASIN, INDONESIA

摘要

Semberah and Mutiara fields have been producing oil and gas for more than 30 years with more than 300 wells in the crestal areas. Reservoir pressure depletion and the difficulty to find new reservoir pools in the crestal area are the main problem. This study demonstrates how the re-evaluation of old data sets are integrated and resulted with new concept that can shift a non-prospect area into an attractive development area especially for the stratigraphic trap play. This study integrates outcrops, cores, wire line logs, pressures, and production data to create new geological concept of reservoir. First, re-interpretation of old cores from multi wells combine with biostratigraphic analysis and outcrops to provide comprehensive models of reservoir characteristics. Second, re-evaluating, re- correlating, and re-mapping the well marker and try to distinguish the depositional fades of reservoir. Third, the reservoir characteristic is integrated with pressures and production data as proven validation for hydrocarbon and connectivity of each reservoir. Well known model of depositional facies as reservoirs are fluvial channel, distributary channel, and mouth bar. However, those reservoirs are likely to stack and connect each other due to high rates of sediment supply and avulsion during sedimentation process. In contrary, there are two depositional facies that is attractive to develop as stratigraphic trap and proven to hold high hydrocarbon. First facies is backfilled channel and the second one is tidal sand bar. Those two facies are interpreted to deposit during the 4th to 5th scale order of transgressive phase and proven to form isolated reservoirs. Therefore, several step out wells have been drilled into the down flank areas of Semberah and Mutiara fields up to 5 kilometers away from the crestal area and resulted with a promising outcome. Integration between depositional facies, pressures, and production history analyses may provide an adequate distinguish between isolated and nonisolated reservoirs. Finally, the new concept of isolated reservoirs is expected to unlock the remaining resources into other mature fields.