Publications

Unlike clastic reservoirs which are dominated by interparticle porosity, the pore type of carbonate reservoirs may consist of interparticle, intraparticle, vuggy (touching and non-touching) and fractured types. Whereas the total porosity of carbonate reservoirs may be obtained from the density, or neutron, or by combination of both log, the sonic log can only measure the tortuosity in rock which reciprocates the interparticle or matrix porosity. The sonic log might determine the secondary porosity by subtracting the total porosity form density and/or neutron log. Nonetheless, the method is still debatable by looking at the validity of sonic measured and the Wylie’s time average equation as stated by Anselmetti-Eberli. Lucia and Wang (1993) already proposed an equation to predict the amount of separate vug porosity in carbonate rock. Such an equation might be valid unless the result is in agreement with the modal analysis from thin section. We tried to use the Lucia and Wang’s equation at certain types of carbonate from reefal to platform types of reservoir. The results showed that not all of types of carbonate reservoir work with that equation. Subsequently, we empirically tried to modify the Lucia and Wang’s equation and check the genuineness of Wyllie’s sonic time average equation via Petrology analysis and rock mechanic laboratory results. The modified equation which needs a basic log analysis as an input, gave more firmness when compared with the original equation after checking its consistency with more than 20 fields in the Salawati basin. The carbonate sample from the Sukowati basin in east Java is used as a blind test for the method. Finally, by solving the problem of complexity and heterogeneity in pore type of carbonate reservoir, further analysis such as seismic inversion, attribute analysis and determining the secondary porosity in carbonate reservoir provided better understanding.