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Open AccessArticle

Diagenetic Clay Minerals and Their Controls on Reservoir Properties of the Shahbazpur Gas Field (Bengal Basin, Bangladesh)

1
Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, USA
2
Department of Geological Sciences, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
3
Department of Geology, Southern Illinois University, Carbondale, IL 62901, USA
*
Author to whom correspondence should be addressed.
Geosciences 2020, 10(7), 250; https://doi.org/10.3390/geosciences10070250
Received: 9 April 2020 / Revised: 25 June 2020 / Accepted: 29 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue Sand(stone)s Quantitative Provenance Analysis)
Clay mineralogy and diagenesis affect the reservoir quality of the Neogene Surma Group in the Hatiya trough of Bengal Basin, Bangladesh. X-ray diffraction and scanning electron microscopic analyses of diagenetic clay minerals from Shahbazpur#2 well reveal that on average illite is the dominant clay mineral (50%), followed by chlorite (24%), kaolinite (23%) and smectite (2.50%). The absence of smectite at Core-2 (3259.80 m to 3269 m) results from the total transformation of smectite to illite owing to burial depth and high K–feldspar. The diagenetic changes are a result of chemical processes such as cementation, chlorite authigenesis, dissolution, alteration and replacement that have significantly affected the reservoir properties. Cementation plays an important role in reducing reservoir properties with pore and fracture filling cement. The relative percentage of illite and smectite minerals (>90% illite in I/S mixed layer) and Kübler index value (0.34° to 0.76° Δ2θ) indicate a diagenetic zone with subsurface temperatures of 120–180 °C in the studied samples. The temperature range determined using clay percentages and the Kübler index as a geothermometer is supported by observed diagenetic features such as quartz overgrowths, smectite to illite transformations and chlorite coatings. The diagenetic features cause variable reservoir porosity and permeability that are critical in planning exploration and development programs of this field or analog fields across the Bengal Basin. View Full-Text
Keywords: clay minerals; reservoir heterogeneity; diagenesis; geothermometer; Kübler index clay minerals; reservoir heterogeneity; diagenesis; geothermometer; Kübler index
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Hasan, M.N.; Yeasmin, R.; Rahman, M.J.J.; Potter-McIntyre, S. Diagenetic Clay Minerals and Their Controls on Reservoir Properties of the Shahbazpur Gas Field (Bengal Basin, Bangladesh). Geosciences 2020, 10, 250.

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