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.
Highlights
Petrophysical analysis involves the investigation of physical and chemical properties and their interaction with fluids (Tiab and Donaldson 2004)
Nineteen (19) core samples were prepared for petrophysical and petrographic analyses (Fig. 2). Major petrophysical analyses such as density, porosity, permeability and rock compressibility were measured at the room temperature and ambient pressure at the Petrophysical and Geotechnical Engineering Laboratories, Department of Petroleum and Mining Engineering (PME), Shahjalal University of Science and Technology (SUST)
Porosity and permeability measured in the present study are 16.48% and 132.48 mD (Table 2) which indicate that the Barail sandstone is a goodquality reservoir rock
Summary
Petrophysical analysis involves the investigation of physical and chemical properties and their interaction with fluids (Tiab and Donaldson 2004). The Surma Group sandstone is considered reservoir rock in Bangladesh because all oil/gas production comes from it (Bokabil and Bhuban Formation). Barail sandstone is moderately mature, grayish to reddish color and experienced medium to high intensity of chemical weathering in the parent rocks under humid climatic condition (Borgohain et al 2020) to arid (Sen et al 2012). Barail sandstone might be derived from active upper continental area (Sen et al 2012; Borgohain et al 2020) resembling to graniticgneisses and were deposited in active continental margin (Sen et al 2012). These sandstones are exposed close to the border between Bangladesh and India and appear to be over-thrusted in the Dauki Fault area. Sandstones are greywhite to pinkish in color with medium to coarse grains and interspersed with fine-grained silty clay
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