SEQUENCE STRATIGRAPHIC INTERPRETATION OF CHANNEL SAND DISTRIBUTION USING WELL LOGS FROM THE BUALUANG FIELD, GULF OF THAILAND

Abstract

The most important reservoir sandstones in the Bualaung Field, Gulf of Thailand, are fluvial channel sands with a complex stratigraphy that has resulted in uncertainties in reservoir prediction and reserve estimation. The distribution, geometry and stacking pattern of the sands within the late syn-rift to post-rift  succession was determined from sequence stratigraphic interpretation of wireline log data from twelve wells. The study interval includes two stratigraphic units: aggradationally-stacked thin channel sands with thin interbedded floodplain mudstones that underlie isolated thick channel sands interbedded with thick floodplain mudstone. The stacking pattern reflects a decrease in stream gradient with time that was caused by a relative sea level rise and/or waning of fault activity during the transition from syn-rift to post-rift. The variable sand geometry and connectivity has significant implications for field development and reserve estimation, with the well-connected, thicker sands having better reservoir potential than the stacked thinner sands. The results of this study are applicable to other areas in the Gulf of Thailand, or wherever there is a gradual syn-rift to post-rift transition.