| Summary: | This research utilizes reservoir data from an oilfield in Indonesia, which is characterized by shaly sand and low salinity formation water. Both low salinity and shaliness reduce the resistivity contrast between oil and water. The aim of this research was to build a comprehensive interpretation algorithm to evaluate the shaly-sand reservoir in a low salinity formation water using limited well log data.
Shaly-sand interpretation is still evolving with numerous researchers conducting investigations of the clay minerals effect on rock conductivity through theoretical and experimental approach. These investigations can be loosely divided into either Fractional Shale Volume models or the Cation Exchange Capacity (clay-type) models.
This research emphasizes the Cation Exchange Capacity models. Cation Exchange Capacity (CEC) is essentially a reflection of the specific surface area of clay minerals, which causes additional conductivity in shaly-sands. The modified Silva-Bassiouni model was used to interpret shaly sand formations. This model is based on the dual water concept, however it considers that the counter-ion conductivity can be represented by an equivalent sodium chloride solution. Therefore, this method eliminates the requirement for actual CEC measurements from cores. The Shale Volume based Simandoux and Indonesia models were used for comparison. The results from the Archie clean sand model were also discussed. The model was evaluated using actual production and well test data. The modified Silva-Bassiouni model was found to yield superior estimates of cation exchange capacity and fluid saturations in the reservoirs.
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