Depositional System and Facies Analysis in the Central Pattani Basin, Gulf Of Thailand

Abstract

Fluvial sands comprise the main reservoirs in the Central Pattani Basin, Gulf of Thailand and they exhibit complex stratigraphic architectures which results in high uncertainties in reserve estimation and development strategies. To better understand these uncertainties this  study analyzes the distribution and depositional environments of sand reservoirs within a producing field of the Central Pattani Basin to characterize reservoir architecture and analyze sand distribution using the wireline log data from 47 development wells. Based on wireline analysis, three depositional facies were interpreted within the Early to Middle Miocene interval of interest. These were fluvial dominant, estuarine to fluvial and coastal plain environments. Sand distribution maps and well log correlations indicate the orientation of sand bodies with lateral continuity of sands in the changing depositional environments. To further delineate sand body geometries seismic RMS attribute analyses were used and these show a good relationship between high amplitude anomalies and well log derived sand interpretations. Due to an overall regression from Early to Middle Miocene the depositional environments shifted from marginal marine dominant to fluvial dominant within the interval of interest. The variation in sediment supply to the fluvial systems affected potential reservoir geometries significantly. The Early Middle Miocene C to F interval shows well developed wide meander channel belts in an estuarine to fluvial environment and is the main hydrocarbon bearing stratigraphic unit in the area of interest.