Paleoenvironmental Reconstruction of Miocene Surma Succession in the Rashidpur # 04 Well of Bengal Basin Using Log Facies Interpretation

Detailed log facies studies of the Miocene Succession in the Rashidpur-04Well, Rashidpur Structure, Surma Basin, were carried out by integrating wireline logs and limited core sample data in order to reconstruct the paleoenvironment of the deposition. Based on the analysis of log motifs, grain sizes, sand/shale ratios and major changes in gamma ray log motifs, two major depositional sequences were identified in the Rashidpur-04 Well which consist of 17 para-sequence sets and 22 para-sequences. Serrated bell, funnel, cylindrical, egg/bow and linear log facies were identified in the study well. Lithology indicates that the whole well interval consists of alterations of sandstone, siltstone, shale and prodelta facies. Rashidpur Sequence-2 is thought to have been deposited in tidal flat to shallow marine conditions with prograding and retrograding delta front conditions, whereas Rashidpur Sequence-1 is assumed to have been deposited under tidal channel, distributary channel, tidal flat, mudflat, marine inter-distributary bay to shallow and deep marine conditions. Rashidpur Sequence-2 was deposited in comparatively deep water conditions while Rashidpur Sequence-1 was deposited in relatively shallow water conditions. From the present study it can be concluded that the Miocene Succession was coarsening upward in nature and may have been deposited under a prograding deltaic system.