Diagenesis and its impact on the reservoir quality of Miocene sandstones (Surma Group) from the Bengal Basin,Bangladesh |
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| Institution: | 1. Dept. of Geological Sciences, Jahangirnagar University, Dhaka, Bangladesh;2. Dept. of Earth, Ocean and Ecological Sciences, University of Liverpool, L69 3GP, United Kingdom;1. Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain;2. Dipartimento di Scienze della Terra, Università della Calabria, Cubo 15b, 87036 Calabria, Italy;3. Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain;1. Department of Petroleum Engineering, Faculty of Engineering, Soran University, Soran, The Kurdistan Region, Iraq;2. Department of Earth Sciences, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates;4. AGR Petroleum Services, Karenslyst Allé 4, 0278, Oslo, Norway;5. Departimant of Petroleum Engineering, Czech Academic City, Erbil, The Kurdistan Region, Iraq;6. Dipartimento di Fisica e Scienze della Terra, Universita'' di Ferrara, Ferrara, Italy;1. School of Geoscience, China University of Petroleum, Qingdao 266580, China;2. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;1. School of Geosciences, China University of Petroleum, Qingdao, Shandong, 266580, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China;3. Research Institute of Petroleum Exploration & Development, Beijing, 100083, China |
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| Abstract: | Rapid supply and deposition of 1000's of meters of Miocene and Pliocene sediment tend to lead to a different set of controls on reservoir quality than older, more slowly buried sandstones. Here we have studied Miocene fluvial-deltaic Bhuban Formation sandstones, from the Surma Group, Bengal Basin, buried to >3,000 m and >110 °C, using a combination of petrographic, geochemical and petrophysical methods in order to understand the controls on Miocene sandstone reservoir quality to facilitate improved prediction of porosity and permeability. The main conclusions of the study are that mechanical compaction processes are the dominant control on porosity-loss although early calcite growth has led to locally-negligible porosity in some sandstones. Mechanical compaction occurred by grain rearrangement, ductile grain compaction and brittle grain fracturing. Calcite cement, occupying up to 41% intergranular volume, was derived from a combination of dissolved and recrystallized bioclasts, an influx of organic-derived carbon dioxide and plagioclase alteration. Clay minerals present include smectite-illite, kaolinite and chlorite. The smectitic clay was probably restricted to low energy depositional environments and it locally diminishes permeability disproportionate to the degree of porosity-loss. Kaolinite is probably the result of feldspar alteration resulting from the influx of organic-derived carbon dioxide. Quartz cement is present in small amounts, despite the relatively high temperature, due to a combination of limited time available in these young sandstones, grain-coating chlorite and low water saturations in these gas-bearing reservoir sandstones. Reservoir quality can now be predicted by considering primary sediment supply and primary depositional environment, the magnitude of the detrital bioclast fraction and the influx of organic-derived carbon dioxide. |
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| Keywords: | Diagenesis Sandstone Reservoir quality Miocene Surma group Bengal basin Mechanical compaction Calcite cement |
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