IJOG 131 Indonesian Journal on Geoscience Vol. 8 No. 1 April 2021: 131-146 How to cite this article: Rosid, M.S., Muliandi, Y., and Al Hafeez, 2021. Pore Type Inversion and S-Wave Velocity Estimation for the Characterization of Salawati Carbonate Reservoir . Indonesian Journal on Geoscience, 8 (1), p.131-146. DOI: 10.17014/ijog.8.1.131-146 INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Mineral Resources Journal homepage: hĨp://ijog.geologi.esdm.go.id ISSN 2355-9314, e-ISSN 2355-9306 Indexed by: SCOPUS (Q3) Pore Type Inversion and S-Wave Velocity Estimation for the Characterization of Salawati Carbonate Reservoir M. Syamsu Rosid 1 , Yogi Muliandi 1 , and Al Hafeez 2 1 Department of Physics, Universitas Indonesia 2 J.O.B PERTAMINA-Petro China Salawati Corresponding author: syamsu.rosid@ui.ac.id Manuscript received: May, 18, 2018; revised: July, 15, 2019; approved: September, 8, 2020; available online: March, 29, 2021 Abstract - A rock physic study was conducted in Salawati Basin, Papua, Indonesia. This feld produces hydrocarbons from coral reef formation. The carbonate reservoir has a very heterogeneous and complex pore type. This study used data from ten wells. Two wells (K-2 and Z-1) have Vs data, while the other eight do not. This study was done to identify the pore type of the reservoir rock, and to estimate the Vs log data in this area. The characterization of the carbonate reservoir was carried out using the DEM (Differential Effective Medium) inversion method. In calculating the bulk (κ) and shear (μ) modulus, the DEM method is supported by the HSW (Hashin-Shtrikman-Walpole) formula in the form of its rock matrix model and Gassmann's relation for its fuid contents. The inversion results show that in eight wells the reservoir is dominated by crack pore type, and in the other two wells the reservoir is dominated by stiff pore type. As for the Vs data, at reference wells K-2 and Z-1, the estimated Vs corresponds very well to the actual Vs, with RMS error of less than 2 m/s and 3 m/s respectively. Another qualitative verifcation shows that the pore type inversion results are almost perfectly consistent with thin-layer lithology data. Keywords: carbonate reservoir, Hashin-Shtrikman-Walpole (HSW), modifed DEM, S-wave velocity, Salawati Basin © IJOG - 2021 Introduction Carbonate-dominated felds nowadays con- tribute as much as half of the world total hy- drocarbon lifting volume. However, the main challenge that engineers and geoscientists alike often face is the fact that carbonate rocks are notoriously elusive to characterize completely. Carbonate reservoir space formed throughout the entire deposition process, the dissolubility, and instability of carbonate reservoirs. It makes the evolution of their pore spaces complicated. Pore type varies over small distances and multiple pore types exist in the same formation. Pores are often affected and reformed by multiple factors. Carbonate rocks have a variety of pore types, such as moldic, vuggy, interparticle, intraparticle, and fracture (Verwer et al., 2010). Unlike clastics and sandstone that are easier to characterize through several established theories, for example the Xu-White theory (1995), carbonate rocks require scientists to layer many theories to better approxi- mate carbonate pore types. Accurate calculations of carbonate pore types are invariably important, because seismic responses depend quite heavily