Unconventional petroleum resource is rather a new term in the world of hydrocarbon where petroleum is extracted from the source rock itself without expecting any trap, reservoir and migration pathways. As of Bangladesh’s perspective, we have only been successful in exploiting structural traps (saying anticlinal traps would be more perfect). In this growing industrialization, exploring unconventional resources or new petroleum plays is a must to meet with the current demand, as Bangladesh is likely to run out of indigenous fuel by 2030s.

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Unconventional Petroleum Resource Potentiality in the Bengal Basin Page 1
Unconventional Petroleum Resource Potentiality in the Bengal Basin
What is unconventional? Why unconventional?
Unconventional petroleum resource is rather a new term in the world of hydrocarbon where petroleum is
extracted from the source rock itself without expecting any trap, reservoir and migration pathways (Fig.
1A). As of Bangladesh’s perspective, we have only been successful in exploiting structural traps (saying
anticlinal traps would be more perfect). In this growing industrialization, exploring unconventional
resources or new petroleum plays is a must to meet with the current demand, as Bangladesh is likely to
run out of indigenous fuel by 2030s (Imam, 2013).
Fig. 1B (modified after Snedden et al., 2003) is self explanatory that displays the necessity to work on
unconventional plays. Production sky rockets when conventional plays are exploited but it must come to a
halt as the discovery of conventional wells also diminish with time and production ceases. As soon as
new technology or unconventional resources come into action, production also comes out of the still state.
The game changer: Hydraulic fracturing:
In unconventional resources hydrocarbon is extracted from the source rock that is impermeable and has
negligible porosity. Fracturing of the rock layer is a must to allow the fluid to escape (Fig. 1A).
Horizontal drilling is introduced as it allows larger drainage area, larger contact and high reserve
production (Zou et al., 2013).
Potential in Bengal Basin:
As mentioned earlier, only structural traps have been explored in Bengal Basin (BB) let alone any
unconventional resources. But there is some possibility with Coal bed methane, Thin bed reservoirs,
Biogenic gas, Shale gas and Tight gas reservoirs. Possible locations are shown in Fig. 2.
Coal Bed Methane (CBM):
Methane is formed by thermal maturation of coal beds at depth under high temperature and pressure and
it remains intact in the coal seams. The coal rich region is located at the north-western part of the country
where five coal fields are proven coal reserves. Barapukuria coal is being extracted for a time being but
the largest coal field, Jamalganj (1053 million metric ton) is not assumed feasible to extract coal from
such depth (640-1158m). Jamalganj coal contains high amount of methane, coal seams are thick and also
lies within the optimum depth for CBM development (Imam, 2013).
1A 1B

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Unconventional Petroleum Resource Potentiality in the Bengal Basin Page 2
Thin Bed Reservoirs:
Hydrocarbon from thin bed reservoir has already been extracted in BB. Observing the logs of Sangu-1
and Sangu-5 well, it clearly proves that the Sangu gas field is a thin bed reservoir and there is further
potential to extract from the virgin thin beds that still remains (Shahriar et al., 2020). On the other hand,
the heterolithic (interbedded sands and shales) formations are massively encountered in the Eastern Fold
Belt of Bangladesh. These thin but numerous beds should be taken into account for new development.
Biogenic Gas:
Biogenic gas occurs at shallow depth in small pockets due to bacterial action rather than thermal
maturation. This is a common phenomenon in recent sediments and the gas is exhausted after burning for
few days. This type of gas is reported from Comilla-Brahmanbaria, Noakhali-Lakhsmipur, Kishoreganj,
Greater Sylhet, Faridpur, Magura, Satkhira, Barguna, Shahbazpur (Bhola) while drilling water wells.
Although shallow gas is known as drilling hazard, it has gained reserve status in some countries like
Canada, Russia and China (Rahman et al., 2018). Study says that, biogenic gas is more prone to
accumulate in fluvio-deltaic region as well as at places where groundwater salinity is more than average
(Imam, 2013). So, the coastal belt of Bangladesh can be a good target of it.
Shale Gas:
Hrdrocarbon extracted from underground shale formations which are rich in TOC is referred as shale gas
resources. The targeted shale formations for possible gas production in BB are Kuchma-Paharpur
formation, Kopili shale, Jenum shale and Bhuban-Boka Bil. But the observation shows, Bhuban-Boka Bil

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formations are too shallow and too immatured for gas formation, Kuchma-Paharpur formation has
required maturity but the beds are too thin (<4m), Kopili shale and Jenum shale has the maturity and
thickness (>20m) but they reach maturities at depth more than 5000m (Loske: DMT final report, 2013).
But a conclusive comment should not be issued as the data analyzed are historic and up to date work is
still missing. The shelf part of BB near the hinge zone, containing high amount of TOC and thermally
matured Kopili shale can be a good possibility (Imam, 2013).
Tight Gas Reservoirs:
Tight sandstones where porosity is largely occupied by authigenic mineralization, cementation or clay
mineralization is very common throughout the samples from BB. These samples often depicts petroleum
shows but are discarded due to poor porosity and negligible permeability. Now in the era of hydraulic
fracturing these sites should be revisited and concrete decision should be made.
Conclusion:
Utilizing modern technology and providing noble effort, petroleum industry can only add to the fastest
ever growing rate of Bangladesh. To meet with the increasing need, unconventional resources should be
taken into account as soon as possible. The previous abandoned fields or the fields that have been
destroyed by blowouts should also be considered to be developed through unconventional manner as
some of them were proven to be economic.
References:
Imam B., 2013, Energy Resources of Bangladesh, 2nd
edition, University Grants Commission of
Bangladesh, Dhaka, Bangladesh.
Loske B., Teigler E. B., 2013, Preliminary Study on Shale Gas Potentiality in Bangladesh, DMT GmbH
& Co. KG, Project Number: GB-13-042.
Rahman M., Kabir S. M. M., Imam B., Haque A. K. M. E., Amin M. A., 2018, Occurrence, Distribution
and Origin of Shallow Biogenic Gas in Late Quaternary Unconsolidated Sand Deposit of Shahbazpur
Structure, Southern Bangladesh, Petroleum and Coal, vol. 60 (6), p. 1216-1227.
Shahriar M. U., Hossain D., Hossain M. S., Rahman M. J. J., Kamruzzaman, 2020, Geophysical
Characterization of the Sangu Gas Field, Offshore, Bangladesh: Constraints on Reservoirs, Journal of
Petroleum Geology, vol. 43 (4), p. 363-382.
Snedden J. W., Sarg J. F., Ying X., 2003, Exploration Play Analysis from a Sequence Stratigraphic
Perspective, Search and Recovery Article, No. 40079.
Zou C., Zhu R., Tao S., Hou L., Yuan X., Song Y., Niu J., Dong D., Liu S., Jiang L., Wang S., Zhang G.,
2013, Unconventional Petroleum Geology, Petroleum Exploration Development, vol. 40 (4), p. 413-
428.