Integrated Stratigraphic and Structural Evolution of a Fluvial-Dominated, Tide-Influenced Marginal Marine System, the North Malay Basin, Gulf of Thailand

Kumnerdsiri, Kumphon; Ainsworth, Bruce; Mitchell, Andy; Backe, Guillaume

Core, wireline-log, and 3-D seismic data from the Greater Bongkot South Field were integrated to study the inter-relation of sedimentation and structure of the ~250m thick, Middle Miocene 2-D interval. Sedimentological logs from two cored wells were used to calibrate petrophysical logs for sedimentary facies and then interpolated to nine other un-cored wells. High resolution inter-well stratigraphic correlation was carried out based on core-lithology and log motif pattern, within a framework of three interpreted seismic horizons.

From the base to the top of the cored section, ten coarsening-upward cycles of mudstone, heterolithic, very fine-medium grained sandstone, and coal lithofacies are observed. Lenticular bedding and double mud drapes are associated with the heterolithic facies which indicate tidal activity, whereas ripple cross lamination and climbing ripples to cross bedding representing fluvial processes are found in the sandstone facies . From the facies associations, it can be implied that deposition occurred in a deltaic environment where fluvial and tidal processes interacted at the shoreline. Sedimentary architecture in the study interval can be classified at various scales; from Transgressive-Regressive (T-R) sequences to Element Sets. Sixteen T-R sequences are defined. Transgressive Element Complex Assemblage Sets are generally thin with the Regressive Element Complex Assemblage Sets (RECAS) forming the bulk of the T-R Sequences. Fluvial-dominated, Tide- influenced (Ft) Mouthbar and Fluvial (F)-Channel Element Complexes dominate the RECAS.

Structurally, the interval of interest is associated with minor inversion. The degree of inversion is more pronounced in the southern part of the study area and towards the top of the 2-D interval. Two families of different fault orientation; NW-SE and NE-SW control depositional dip direction at any one time. Progradation direction of mouth bar lobes is perpendicular to fault terraces particularly at the eastern and western flanks of the basin. Inversion results in uplift and therefore regionally decreases base level. This structural inversion corresponds with more frequent regressive surfaces of erosion and increased stacking of F-Channel Element Complexes towards the top of the interval of interest. However, high fault densities limit lateral sandbody continuity.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013