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Introduction
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
Stratigraphic traps may also be developed by diagenesis of sediments. However, the diagenesis effect is more prominent in limestone (carbonates) rather than sandstone. Leaching and cementation of sediments owing to the presence of active fluid with different pH play a major role in the process of diagenesis. The alkaline solution is more active in siliceous system for dissolution in the upper zone and successive cementation in the lower portion of the bed owing to the loss of acidic nature. Whereas acidic solution is more active in carbonate systems and carbonate dissolution takes place from the upper zone owing to the acidic nature of the solution. After reaction, the solution loses its acidity and the cementation takes place in the lower area of the bed. Thus, as a whole, chances of increase in porosity are there in the upper portion of a layer whereas development of a non-porous zone may occur in the lower portion which may lead to the generation of a seal zone. Except these, recrystallisation of minerals also may play important roles in the variation of porosity in sediments.
Sedimentary rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Sedimentary petrography usually refers to the study of sedimentary rocks under the microscope. It is important since it is often the only easily available method of studying the detailed mineralogy and grain types of sediments. It can reveal the original source of the eroded fragments of terrigenous clastic rocks (provenance) and shed light on the depositional environment of limestones. Microscopic studies are particularly important in understanding post-depositional changes which occur in sediments. These changes, known as diagenesis, include physical and chemical modifications which occur during burial as a result of increasing load pressure and the passage of fluids through the sediment. Diagenesis may profoundly affect porosity (the percentage of pore space in a bulk volume of rock) and permeability (ability of a rock to allow fluid to flow through it). This is of great relevance to the study of aquifers and hydrocarbon reservoirs.
Minerals and rocks
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Diagenesis is the name given to processes that alter the character of a sedimentary rock after it has been deposited, either by interreactions between constituent minerals or by reactions between constituent minerals and pore fluids or other liquids circulating through the sedimentary material. Diagenesis is a low-temperature process, which can occur when the sediment is still in contact with the sea or lake water after its deposition, and also later when direct contact with the original water has been removed. The process continues until the constituents and pore fluids are in chemical equilibrium.
Diagenesis impact on a deeply buried sandstone reservoir (Es1 Member) of the Shahejie Formation, Nanpu Sag, Bohai Bay Basin, East China
Published in Australian Journal of Earth Sciences, 2019
M. Kashif, Y. Cao, G. Yuan, W. Jian, X. Cheng, P. Sun, S. Hassan
Diagenetic mechanisms have a substantial impact on reservoir quality and play a major role in petroleum exploration (Wang, Shen, & Zhao, 2011). Mechanical compaction is a physical process whereas mineral dissolution and precipitation are chemical processes that gradually change the porosity and permeability through burial (Bjørlykke & Jahren, 2012; Taylor et al., 2010; Thyne, 2001). Commonly, compaction in the primary stages of diagenesis causes a significant loss of porosity, whereas porosity and permeability are enhanced by dissolution and fracturing in later stages and are key factors for exploration and development in deeply buried hydrocarbon-bearing reservoirs (Wang et al., 2011). Deeply buried sandstone reservoirs are more problematic because of import and export of material associated with chemical diagenesis (Bjørlykke & Jahren, 2012; Gluyas & Witton, 1997; Taylor et al., 2010; Tournier, Pagel, Portier, Wazir, & Fiet, 2010). Quantitative diagenetic processes, sinks of dissolve minerals and sources of cement are critical for prediction of deeply buried reservoir sandstone quality (Taylor et al., 2010). Due to complex burial history, the evolution of reservoir quality and the formation mechanism of secondary pores are debated.
Diagenesis factor that effect the reservoir properties and gas accumulation in the 4th member of Xujiahe formation, Western Sichuan Basin, China
Published in Petroleum Science and Technology, 2019
Mengyao Li, Zhanghua Lou, Yi Gong, Aimin Jin, Rong Zhu
Reservoir quality is one of the key controls on prospectivity during hydrocarbon exploration. Diagenesis, which comprises a broad range of physical, geochemical, and biological post-depositional processes, has an immense impact on the reservoir properties of tight sandstones, as it readily leads reductions in porosity and permeability (Rahman and Worden 2016). Research on diagenetic processes will be crucial to improving our understanding of the factors controlling quality in tight sandstones.
The effect of diagenetic environment on hydrocarbon generation based on diagenetic mineral assemblage in mudstone
Published in Petroleum Science and Technology, 2018
Jiazong Du, Jingong Cai, Guoli Wang, Xiang Zeng, Yujin Bao, Fei Liu
The findings above indicate that clay minerals and ankerite, which can be formed through mineralization during diagenesis, are diagenetic minerals. They are the result of the synthetic effect of the diagenetic environment and often contain information on diagenetic environmental changes. Therefore, the evolution of diagenetic minerals and the changes of mineral assemblages can be excellent indicators of the diagenetic environmental changes during diagenesis.