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When Diagenesis Severely Modified Reservoir Characters: A Unique Carbonate Reservoir from Alur Siwah Field, Indonesia

Ricardo, Maranu; Syarifuddin, Ismail Y.; Adhitiawan, Erham; Nurul, Nadia; Miftahurochman, Miftahurochman; Baskaraputra, Ferry F.; Luqman, Luqman; Yanto, Yudi; Lumban Tobing, Joan C.

Building geological model of Lower Miocene carbonate reservoir in South East Asia region frequently offers huge challenge in defining the depositional facies model and reservoir characterization. Dynamic depositional system combined with multiple sub-aerial exposures could give a certain degree of complication in reservoir properties, especially due to porosity modification and change in permeability transform. Bioclastic limestone with various degrees of reservoir quality are described from core data with high inconsistencies on porosity and permeability values along with depth on the same lithofacies. Multilayered porosity development was found in some wells and confirmed by well test data that multiple sub-aerial exposure is more likely occurred instead of single sub-aerial exposure. Integration of core data and petrophysical analysis in decoding this complexity into a more definite rock types has been a key process in building the input for distributing the properties from cored section to un-cored section and eventually to areas between wells supported by seismic data. A new reprocessed 3-D seismic dataset was used for structural and stratigraphic interpretation including multi-attribute analysis and seismic inversion (AI) for reservoir property prediction. Five zones of conventional interpretation have been generated, bounding internal seismic characters of transgressive, prograding and aggrading units which suggest different layering methods and probabilistic approaches have to be applied for each different unit. Seismic inversion result shows high porosity correlate with low acoustic impedance and low porosity is the opposite. Highest cross correlation (0.7) is calculated between actual and predicted effective porosity logs in the study area. The final AI model provides geologically more realistic predicted effective porosity distribution and helps in understanding the subsurface image. Advanced probabilistic approaches were applied on 3-D static model integrates the depositional facies, diagenesis process, petrophysical analysis, and seismic inversion. As a result an appropriate 3-D geological model can be constructed for unique reservoir geology.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013