Publications

The Mundu carbonate is a unique limestone reservoir composed of Globigerina forams specifically located in the Madura Strait area of the East Java Basin. The reservoir quality and permeability is mainly controlled by the clay content. Spectral gamma ray logs from three wells representing different locations on Mundu carbonate paleo structural highs were examined to see if there was a relationship between the Mundu carbonate reservoir quality and the thorium (Th) and uranium (U) content. It is inferred that the Th/U ratio has a strong relationship to the reservoir quality (i.e. permeability) and the paleo structural high. The best quality reservoir was found in the well located high on the paleo structural high. The reservoir was composed of dominant grainstone facies and has the lowest Th/U ratio. In contrast, the poorest reservoir quality came from a well located deeper on the paleo structural high and was composed of dominant argillaceous packstone facies with the highest Th/U ratio. This study also reveals that spectral gamma ray log signature from the three wells demonstrates a good relationship with the tight/slow build up points from wireline formation test measurement. During wireline formation testing, tight/slow build up points indicating low permeability formation were often encountered, and increased drilling costs were incurred as more formation test attempts were made. It was found that a wireline formation test point located within an interval with Th/U ratio greater than 0.7, had a greater risk of having tight/slow build up points. This study has found that the spectral gamma ray log can be used for reservoir evaluation,and can lead to a better strategy for selecting the location of wireline formation test points in the Mundu reservoir for future exploration wells.