Analysis of 2D Seismic and Final Log to Identify Hydrocarbon Prospect, “MAHERA” Field, Lower Keutapang Formation, North Sumatera Basin

Abstract

Oil and gas still have an important role in supplying the energy need of human being. Therefore, the exploration and exploitation are still done continuously to solve the decreasing of oil and gas reserve every time. One of Tertiary basin that produces hydrocarbon is North Sumatra basin. This basin was formed at the end of Paleogen by pull apart force (pull apart basin). The research focus is done in the “Mahera” field from “Keutapang Bawah”. The purpose of the research is to know the rock type of reservoir, dispersion and thickening of reservoir layer influenced by geological structure, and to determine the area of hydrocarbon prospectively with estimation of reservoir. The method that is used in this research is the descriptive method and the analysis method that include an analysis of seismic data, geological structure, and geometry (dispersion and thickening of reservoir layer), and supported with well data (final log). The data used are the primary data (seismic data, regional geology and well data). This research is done based on an analysis of seismic and final log. Based on time contour structure map, it can be interpreted that there are five horizon that become horizon marker. They are Lower Keutapang Middle Equivalen horizon, ZA horizon, ZB horizon, ZC horizon, Lower Keutapang Bottom horizon. The hydrocarbon accumulation produced from sandstone layer of Lower Keutapang Formation. The structural geology in research area is normal fault that relative direction of northeast – southwest and north – south which one of factor controlling trapped of hydrocarbon at one particular trap as structural trap. Based on correlation of three wells that is ERA#6 well, MD#4 well, and ERA#2 well can be interpreted that ERA#6 well stay on lower position than MD#4 and ERA#2 well. So that structurally dissociated by this normal fault and this structure is down block (graben). Depositional environment of ERA and MD structure is littoral – sub littoral with the range of age from Upper Miocene - Pliocene ( N14 - N19). The direction of dispersion and thickening of reservoir layer is south southeast – southwest north. Hydrocarbon prospectively area can be shown by closure between of fault, the closure of prospect area divided in 7 prospect area that is T1-a prospect, T1-b prospect, ZA prospect, ZB-a prospect, ZB-b prospect, ZC prospect, and T2 prospect. The calculation of probable reserves estimation with four scenarios calculation with total probable reserves estimation are 22,212 MSTBO; 13,8932 MSTBO; 20,972 MSTBO; 13,319 MSTBO.