PROCEEDING, SEMINAR NASIONAL KEBUMIAN KE-10 PERAN PENELITIAN ILMU KEBUMIAN DALAM PEMBANGUNAN INFRASTRUKTUR DI INDONESIA 13 – 14 SEPTEMBER 2017; GRHA SABHA PRAMANA 431 LITHO-SEISMIC CLASSIFICATION BASED ON ELASTIC ROCK PARAMETERS: CASE STUDY – SOUTH PECIKO FIELD OFFSHORE MAHAKAM DELTA Santika Satya Widita 1 Didiek Budhy Prabowo 2 Hilfan Khairy 2 1 Geophysics Sub-department, Universitas Gadjah Mada 2 Total E&P Indonésie ABSTRACT Simultaneous seismic inversion was performed using the PSTM (Pre-stack Time Migration) data from Peciko field which is located at offshore Mahakam PSC. The study concentrated in the Peciko Main Zone area with 3km of burial depth. Five wells data which stand on the deltaic environment are used for this study. Sedimentary rocks are mostly found on the study area. The main objective of this study is to analyze the probability of facies in the study area based on lithology classification from elastic rock parameters that gained from seismic inversion IP (P-Impedance) and PR (Poisson Ratio). Every lithology such as sandstone, shale, or carbonate has its own different physical characteristic and can be distinguished by using well data (density and sonic log) and seismic inversion data (IP and PR cubes). Besides, cross-plot between IP and PR can also be the tools to differentiate fluid inside the formation, such as gas- or water-bearing sand reservoir. The analysis of lithology classification which based on the elastic rock parameter showed the information that can be used to more understand the lithology probabilities in the study area, also geological model. Distinguish the lithologies in the study area is quite challenging due to the depth of burial which is relatively deep and increase the compaction among the rocks. It impacted the result of seismic inversion IP and PR which shown a less correlation between those two elastic parameters therefore hardly to do the upscaling. In the other side, deltaic and shelf environment have contrast lithology which made it as one of the challenges that need to be resolved in this study. Cross-plot between IP and PR showed the lithology classification that fitted with its real model then the Probability Density Function (PDF) is used as the statistical approach to determine the facies’ probability. The result can be used for future well development. Keywords: Simultaneous Seismic Inversion, Poisson Ratio, P-Impedance, PDF 1. Introduction Seismic reservoir characteristic is started with feasibility study based on the log data which done to understand if the elastic rock parameters (IP and PR) are able to differentiate the lithology below the surface. Meanwhile, the inversion process can be used as the estimation of elastic rock properties which derived from seismic data. The inversion result can be transformed into the qualitative and quantitative of reservoir properties such as facies, porosity, volume of clay, etc. The technique that will be used for transforming the inversion result into the reservoir properties is called as litho-seismic classification and will be applied on this study. South Peciko is one of the Mahakam PSC which is discovered in 1983, with gas as its product. It locates on the offshore of prolific Kutai basin at Mahakam delta, East Kalimantan, Indonesia (Figure 1a). Upper Miocene fluvial and deltaic front environment are the depositional environments of South Peciko field. Peciko Main Zone is deposited in the delta front to pro-delta environment which consists of mouth-bar stacking (Lambert, 2003). Simultaneous seismic inversion was performed using the PSTM (Pre-stack Time Migration) angle stacks (Near, Mid, Far, Ultra-Far angle stack), resulted the Poisson Ratio (PR) and Acoustic Impedance (IP) cube. Five wells were also used in this study to correlate with seismic data (Figure 1b). Cross-plot between IP and PR cubes could distinguish the lithologies due to its elastic rocks characteristic. Burial of Peciko Main Zone is relatively deep, thus crossplot of elastic