Hydrocarbon and Reservoir Mapping Using Seismic Simulated Annealing Inversion, in Southern Pattani Basin, Gulf of Thailand

Abstract

The research was conducted in southern Pattani Basin, Gulf of Thailand that is known as a mature hydrocarbon play. The sands reservoirs of sand A and sand B were studied by using seismic P-impedance inversion to image the oil-bearing reservoir distribution. Although several wells have been drilled, other areas haven’t been proven to develop the reservoir due to a lack of wells drilled in the northern and southern areas. Therefore, this research conducted to mapping the distribution of oil-bearing sand at those areas.  Rock physic analysis indicates that interest zone have low-density and can be discriminated against other lithology. Full-stack and partial stack seismic data were inverted producing absolute and relative impedance volumes which were compared to distinguish the best techniques for imaging the reservoir. Absolute impedance volume has more reliable results and is used to differentiate oil-bearing sand with other lithologies. According to rock physic and absolute p-impedance analysis, porous sand and different lithologies (tight sand and shale) have significant impedance contrast. Porous sand has low impedance value and the impedance of tight sand and shale fall in the high range. Multi-well blind tests show a reasonable match. Reservoirs distribution observed using horizon slices indicate sand A shows a large and broad reservoir zone that is hard to identify in the interest zone. The sand B is smaller and identified as alluvial fan deposited in the lacustrine environment. This research indicates that full-stack absolute impedance inverted volume can be used to identify oil-bearing sand distributions. Inverted volume cannot fully differentiate oil-bearing sand apart with wet-sand. However, in most cases, oil-bearing sand can be predicted.