Diagenesis and its impact on the reservoir quality of Miocene sandstones (Surma Group) from the Bengal Basin, Bangladesh. (November 2016)

• Record Type: Journal Article
• Authors: Rahman, M. Julleh J.; Worden, Richard H.
• Is Part Of: Marine and petroleum geology. Volume 77(2016:Nov.)
• Page Start: 898
• Page End: 915
• Publication Date: 2016-11
• Subjects: Diagenesis -- Sandstone -- Reservoir quality -- Miocene -- Surma group -- Bengal basin -- Mechanical compaction -- Calcite cement; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2016.07.027
• Languages: English
• ISSNs: 0264-8172

Abstract

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. Highlights: Reservoir quality of Miocene deltaic-marine sandstones from Bangladesh buried up to 3200 m and 115 °C was studied. Depth and ductile grain content control compaction and porosity-loss. Calcite is the dominant cement, growing from meteoric water at low temperature. Quartz cement is minor due to limited time for growth and chlorite grain coats. Rapid burial (150 m/myr) and mineralogical immaturity of primary sediment are the master controls on reservoir quality.