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The application of sequence stratigraphy to resolve the miscorrelation between different genetic units in reservoir characterization in a gas field of Surma Basin is dealt with. Interpretation of available seismic and wireline logs (gamma ray, resistivity, density and neutron porosity) give the sequence stratigraphic correlation of reservoir sands. The reservoirs geometry, its extent, seal architecture and trapping styles have been revealed better with this correlation. There is juxtaposition of two reservoir sands, namely A1 and A2. A1 is located at older highstand sand, whereas A2 is in the younger lowstand sand. Lithostratigraphically they might be same but sequences stratigraphy reveals that they are different and deposited at different times. Moreover, the concept reveals that lowstand sand has better reservoir quality than any highstand and transgressive sand. Asiat. Soc. Bangladesh, Sci. 45(2): 209-216, December 2019

This study builds a high-resolution sequence stratigraphic framework for the Surma Group in the X Gas field. At first, electrofacies and depositional sequences were interpreted from wire line logs. Then, the field wide configurations of these sequences have been identified in seismic using reflection terminations (of flap, onlap, top lap and down lap relationship). Finally, wire line log and seismic interpretations were integrated to establish sequences stratigraphic framework in the Surma Group. Electrofacies analysis has revealed four major facies associations namely: (i) Bell shaped fining upward facies corresponds to retrogradational shoreface to tidal flat deposits, (ii) Funnel shaped coarsening upward facies corresponds to progradational shoreface to tidal flat, (iii) Cylindrical aggradational facies interpreted as stacked channel and (iv) Symmetrical or Bow shaped facies corresponds to heterolithic unit. The succession of Surma group of about 3100+ m has been divided into twelve depositional sequences. With exception of depositional sequence 1, 11 and 12, most of them are composed of three system tracts: sandy lowstand system tract, shaley transgressive system tract and heterolithic to shaley highstand system tract. Repetitive occurrence of incised valley, shoreface sand as well as tidal channel sand separated by transgressive system tract shelfal mud resulted in sand-shale alternation in the Surma Group. The lower depositional sequences (up to sequence-6) are shale dominated and equivalent to the Lower Surma Group. The upper six sequences are sand dominated, have more channel incisions and sequence boundary representing the Upper Surma Group

This paper deals with the rock physical analysis of primary reservoir rocks in the X gas field, which includes identifying the transition zone between mechanical and chemical compaction zones and the amount of cement in the reservoir rock. The analysis is performed by plotting different log data (Gamma-ray, density, neutron porosity, and sonic log) against depth, constructing the cross plot, and plotting of sonic and porosity logs with cement model. The transition zone, which is the boundary between mechanical and chemical compactions, indicates a sharp increase in density and a decrease in porosity with no lithological change at 2,576 m depth (Well-2). Among three gas sands, the upper gas sand and upper part of the middle gas sand are located within the mechanical compaction zone. The lower parts of the middle gas sand and lower gas sand are within the chemical compaction zone. Cement model analysis showed that the upper gas sand and upper part of the middle gas are composed of unconsolidated sand. In contrast, the lower part of middle gas sand and lower gas sand comprise of consolidated sand, having almost 2% contact cement.