Publications

This paper describes how to obtain a reliable petrophysical analysis, permeability prediction and rock types determination from core and wireline logs of Baturaja carbonate reservoir in Semoga field. Semoga is one of the mature Indonesian oil fields and will soon be subject of an EOR pilot project. A total of 153 wells have been drilled in Semoga, 145 with conventional logs and 11 with cores. The collaboration between geological concept and reservoir dynamic data was an important consideration for obtaining the best possible predictive results. In order to constrain the petrophysical analyses, an integration of core analyses and wireline log interpretation was proposed. Firstly, core analyses began with core-log depth matching, core porosity and permeability correction, electrofacies and determination of petrophysical parameters. Based on the petrophysical measurements, most of the lithofacies had similar parameters in terms of wireline log analyses. A detailed permeability predictions were generated by porosity-permeability crossplot, using linear regression and enhanced by residual simulation. The different permeability transforms were defined by flow unit, lithofacies and depositional environment. Furthermore, rock type determination for heterogeneous carbonate reservoirs in this field was more related to pore geometry from capillary pressure than geological facies. In this case, Leverett’s J-function as a rocktyping method related to permeability and porosity ratio (SQRT K/PHI) was adequate to capture the heterogeneity of carbonate. From rock type determination, three groups were defined and distributed for all wells. Finally, rock types with their associated capillary curves were used to calculate water saturation accurately. The result of reservoir property calculations, such as shale content, porosity, permeability prediction and water saturation from well logs, aligned wells with core measurements. As a result, an improved reservoir model was built with the purpose of validating reserves and optimizing EOR implementation plans.