Petrophysical and petrographic characteristics of Barail Sandstone of the Surma Basin, Bangladesh

Abstract

The Barail sandstone in the Surma Basin is a medium- to coarse-grained pinkish-colored rock exposed near the northeastern margin of Bangladesh. In this study, we evaluated the reservoir quality of the Barail sandstone based on its petrophysical and petrographic characteristics. Petrophysical analyses of outcropped samples showed that sandstones are made up of 16.48% porosity and 132.48 mD permeability. Sandstone density ranges from 1.94 g/cm3 to 2.37 g/cm3, with a mean value of 2.12 g/cm3, shown as moderately compacted sandstone. Integrated data such as bulk density, porosity, permeability, Rock Quality Index (RQI), Normalized Porosity Index (NPI), Flow Zone Indicator (FZI), compressive strength, etc. with their relationships indicate that Barail sandstone owing characters to become a good petroleum reservoir. The rock samples consisted mainly of quartz with an insignificant amount of rock fragments and plagioclase feldspar and are categorized as sub-arkose to sub-litharenite. The rock samples also contains lithic (andesine, microcline, muscovite, biotite, etc.) of granitic and gneissic fabric and some volcanic product like aguite, albite, andesine, garnet, spinel and ulvo-spinel indicating the source of nearby orogeny. The euhedral to subhedral shape of the quartz grain in a porphyritic texture, moderately sorted with a smaller amount of clay minerals indicating the moderately mature rock type. The iron oxide border around the quartz grain also indicates that the Barail sandstone was deposited under dry climatic condition.

Depositional Environment and Reservoir Prospect Analysis of Barail Sandstone Exposed in the Northeastern Part of Bangladesh

“…These results suggest that sediments of the Barail sandstone were derived from the orogenic belt of the proto-Himalaya in the northern part of the basin. Previous works by Johnson and Alam (1991), Islam et al (2021), andBorgohain et al (2010) studied the Barail sandstone in the Surma Basin and suggested that the sediments are derived from the proto-Himalayan orogen and early orogenic belt formed from the collision of the Indian plate and the Burmese plate of the active continental margin provenance.…”

“…The Sylhet Trough had a complex evolutionary history demonstrating a change from a passive and rifted continental setting to a flexural foreland basin (Alam et al, 2003). The formation of the trough is linked to two major tectonic events: i) pop-up of the Shillong Plateau in the northern part of the trough and ii) oblique subduction of the Indian plate below the Burmese plate (Johnson and Alam, 1991;Islam et al, 2021). The late Mesozoic and Cenozoic stratal thickness in the Sylhet Trough has been estimated to be between 13 and 17 km, with much of this layer being Neogene in age (Evans, 1964;Hiller, 1984;Fig.…”

“…A 4-meter thick laterite bed in the upper surface of the Barail Group indicates a major transgressive unconformity surface (Khanam et al, 2021). Islam et al (2021) suggested that the density of sandstones ranges from 1.94 g/cm3 to 2.37 g/cm3, and average porosity and permeability are 16.48% and 132.48 mD, respectively. Little work has been done to study the detailed sedimentology, sandbody stacking pattern, and diagenesis and their link to the reservoir properties of the sandstones.…”