Application of geostatistical inversion for thin bed reservoir characterization on Eka field, Central Sumatra Basin, Indonesia

Application of geostatistical inversion for Bekasap Formation's thin bed reservoir characterization on Eka field has been conducted. Eka field is located in Central Sumatra Basin, the largest Indonesia's tertiary sediment basin that consists of several potential formations producing hydrocarbons. Bekasap Formation is one of which divided into 3 reservoir zones (Bekasap A, B, and C). This paper aims to identify the thin layers of reservoir and to delineate its distribution within Bekasap Formation by performing two seismic inversion methods: Deterministic Inversion (DI) and Geostatistic Inversion (GI). DI is conventional method that uses fixed mathematic formulation and results only one model while GI is a simulation method honoring seismic data, DI result, and well log data. DI result showed the blocky event on sand distribution. The limitation of deterministic inversion in vertical resolution makes it hard to differentiate the thin bed layers of reservoir which assumes the layers as one thick body sand. DI cannot resolve the non-uniqueness matter. The GI results showed the separation of reservoir's blocky layers and identified them into several thin layers which thicknesses are below the tuning thickness. Cross plot analysis showed the Acoustic Impedance (AI) cannot distinguish lithology between sand and shale in Bekasap Formation. However, AI was quite good in separating sand and shale on Bekasap A and Bekasap B. The sand lithology has the value of acoustic impedance ranges from 18213 - 25043 g/cm^3∗ft/s. The porous sand (reservoir) has additional parameter cut off which is porosity total, ranging from 0.2649 - 0.4136. GI resulted maps give a high definition imaging that can spot the distribution of the thin bed reservoirs which DI cannot. Eventually, the maps were used to determine the next well drilling location.