RESERVOIR AND HYDROCARBON MAPPING USING FAR-OFFSET AND EXTENDED ELASTIC IMPEDANCE SEISMIC VOLUMES, WESTERN BASIN, GULF OF THAILAND

Abstract

The study area lies in the center part of the Western Basin, Gulf of Thailand. The reservoirs in the study area are Middle Miocene sandstones of a fluvial-coastal depositional system. Mapping these types of reservoirs is known to be challenging due to rapid lateral variations and possibly complex extensional fault systems. Seismic imaging of these reservoirs using only full-stacked data still have some limitations near the study area. Therefore, rock physics analysis, post-stack seismic inversion and seismic attributes were applied using partial-angle stacked seismic data in order to map sand geometries and identify hydrocarbon-bearing zones. The rock physics analysis such as density, S-wave velocity, P-impedance, and elastic impedance cross plots show different trends of sand and shale along the well respectively. The impedance value of sand is lower than shale. The P-impedance and nearangle elastic impedance cannot distinguish clearly sand and shale lithology in the study area. However, the far-angle elastic impedance displayed a strong contrast of sand and shale trend, which can help identify lithology. The main reservoir Sand Aand secondary reservoir Sand B were observed by using the inverted volumes and seismic attributes such as RMS amplitude and sweetness. The extracted far-angle elastic impedance on vertical section along inverted elastic impedance volume may successfully map the oil-bearing sand. The RMS and sweetness attributes of the far-angle stacked volume show a stronger high amplitude contrast than near-angle and very far-angle stacked volumes. Thus, the combination of seismic attributes and inversion may successfully map reservoir distribution. This study suggests that far-angle elastic impedance can be used to map reservoir distribution and predict oil bearing-sands.