Sand Distribution and Depositional Environments Pakarang Field, Pattani Basin, Gulf of Thailand

Abstract

The study area encompasses two new development platforms, PKWA and PKWB in the Pakarang Field, Pattani Basin, Gulf of Thailand where the main reservoirs are fluvial sands. These reservoirs have complex stratigraphic architectures in terms of geometries and continuity which results in high uncertainties in reserve estimation in this field as well as elsewhere in this basin. This study attempts to predict their distribution, geometry and identify depositional environments based on an integrated investigation of wireline log data and seismic data. The 47 study wells were used to determine depositional environment, characterize reservoir architectures and investigate sand distributions. Based on wireline logs, depositional facies were interpreted as channel fills and overbank/floodplain deposits. The I to M interval shows a northeast-southwest orientation of sand channel distribution with clear sand body definition whereas the channel systems are much more variable of distribution of sands in other intervals. Seismic attribute analysis was used to predict sand body orientations, geometries and their areal distributions. The results of seismic based analysis shows a good relationship between high amplitude anomalies and sand distribution interpreted from the well logs, especially in the I to M interval. This study shows the main reasons for reserve estimation downgrading in this field is, (1) there is complex and variable fluvial sand systems and (2) complex structural style in this area. Also the sands are thin and discontinuous even though they are widely extensive at some levels. There are some good areas however, and this study could be used for future well planning in order to increase the production in this area such as by infill drilling in selected locations.