New Hydrocarbon Prospect in the Fore-Arc Basin of West Sumatera Island, Indonesia

Sapiie, Benyamin¹
 Naryanto, Naryanto²

Previous experienced of exploration in the fore-arc basin from many locations around the world has been considered as unsuccessful attempt. As a result, fore-arc basin is concluded as non-prolific hydrocarbon area. Most of the case was blamed to source rock maturity due to low gradient geothermal. Because of that, a lot of fore-arc region was overlooked and under explored. The main objective of this paper is to discuss results of new exploration attempt using integrated approached that combine new acquired 2D seismic data, geological field mapping and subsurface modeling in the fore-arc basin of west

bounded to the east by volcano-plutonic arc and to the west by series of islands represents present-day accretionary wedge of arc-trench system. Paleogene and Neogene sedimentary sequences characterize the geology of this basin. Paleogene sequence consists of sediments was deposited within the rifting system. On the other hand, Neogene sediments consist of marine transgressive sequences that in several location formed carbonate reef complexes. The new 2D seismic datasets show evidence of some large carbonate buildup exhibiting high-amplitude characteristic suggesting possible of large gas accumulation. This evidence is supported by indication of working petroleum system discovered as seeps in several locations at the onshore part of west Sumatera. Oil seeps is used qualitatively for evaluating hydrocarbon maturity in this basin using Paleogene shale as source rocks. 2D basin modeling is developed using existing wells guiding by recent seismic interpretation and integrated with outcrops evidence. The modeling results indicate positive hydrocarbon maturity and charging toward some of the Miocene carbonate buildup in the basin. Tentatively, this study concludes significant prospects of gas accumulations occurred in Miocene carbonate reservoir. Future studies need to be done in delineated leads using advanced seismic reprocessing and analysis for locating next exploration well.