Publications

Developing a versatile carbonate rock physics model is an important phase in furthering geophysical methods in carbonate reservoirs. Seismic attributes analysis, AVO analysis, inversion analysis and also 4D Seismic will benefit fromcorrect P-wave and S-wave velocity values which are very pertinent to a correct rock physics model. However, there are several obstacles in characterizing carbonate rocks. The Kais Formation in the Salawati Basin has undergone diagenetic processes such as dissolution and cementation. As a result of dissolution, pore type such as interparticle, intraparticle, moldic, vuggy and fracture may exist in the formation. The diagenetic process definitely affects velocity, porosity and seismic impedance. Previous studies by Anselmetti-Eberli and Xu-Chako have shown that both sonic and seismic velocities are strongly affected by pore type geometry. Secondly, Gassmann’s fluid substitution method in carbonate may or may not be correct regarding the Gassmann’s model which was initially created to solve Gas-Sand inclastic reservoirs. Thirdly, a method to quantify invasion effect in wireline data is necessary, especially the sonic data, since its effect in carbonates is more significant than in clastics. In this paper, we utilized petrophysical analysis as an input for the rock physics model. Thus, we calibrated the results of Gassmann’s and Xu-Payne methods by using rock mechanic laboratory results and digital rock physics. The core limestone samples from the Salawati Basin were used to predict the P-wave and S-Wave velocity in rock mechanic laboratory analysis and digital rock physics. We found that the rock physics model that accommodated the effect of pore type in elastic properties was the most appropriate one regarding its ability to predict the condition of borehole and/or the mud invasion effect for sonic wave velocity. Also, the selected rock physics model would give the correct P-wave velocity value which was highly related to a better well seismic-tie.