Rocks diagenesis

Carbonate reservoir rock is usually found at the place of formation ( in situ ). Carbonate rocks are susceptible to alteration by the processes of diagenesis. 

Carbonate rocks are not normally transported over long distances, and we find carbonate reservoir rocks mostly at the location of origin, in situ . They are usually the product of marine organisms. However, carbonates are often severely affected by diagenetic processes. A more detailed description of altered carbonates and their reservoir properties is given below in the description of diagenesis . 

Detailed analysis of the DDIF spectra showed a constant microporosity for almost all samples. This lends strong support to the hypothesis that the original rocks after burial, compaction and the initial diagenesis had a common pore geometry. Such a base rock appears to be dominated by the micropores with approximately 2/3 micropores, 1 /3 mesopores and very few macropores. The effect... 

Diagenesis is the set of processes by which sediments evolve after they are deposited and begin to be buried. Diagenesis includes physical effects such as compaction and the deformation of grains in the sediment (or sedimentary rock), as well as chemical reactions such as the dissolution of grains and the precipitation of minerals to form cements in the sediment s pore space. The chemical aspects of diagenesis are of special interest here. 

Porosity can be primary or secondary. Primary porosity develops as the sediment is deposited and includes inter- and intraparticle porosity (Figure 3.1). Secondary porosity develops after deposition or rock formation and is referred to as diagenesis (Figure 3.2). 

FIGURE 3.6 Point-bar geologic model showing the influence of a sequence of rock textures and structures in a reservoir consisting of a single point-bar deposit on horizontal permeability, excluding effects of diagenesis. (Modified after Ebanks, 1987.)... 

V Diagenesis refers to the sum total of processes that bring about charges in sediment or sedimentary rock subsequent to deposition in water. The processes may be physical or chemical or biological in nature and may occur at any time (Berner, 1986). 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

Calcium also has isotopic variations stemming from the radioactive decay of " K to " Ca. These variations can be used for geochronology and may also be useful for studies of rock weathering, soil formation, magma genesis, diagenesis, and metamorphism. 

Following burial, marine sediments are recycled via two pathways a crustal route or a mantle route. In the crustal route, burial followed by diagenesis, catagenesis, and metagenesis transfers sediments into either sedimentary or metamorphic rocks. These rocks are eventually uplifted onto land by crustal motions associated with plate tectonics. In the mantle recycling route, sediments and sedimentary rocks are subducted at... 

In order to determine the source composition of sediments using trace elements, it is necessary to ascertain that the element is immobile under conditions of diagenesis and weathering (Spalletti 2008). Several ratios and plots may be used to define the source rocks. The felsic source rock compositions are found in the Co/Th vs. La/Sc diagram (Fig. 3 Table 1). Other trace element characteristics of sedimentary rocks also place some constrains on the nature of the source rock. Floyd Leveridge (1987) used a La/Sc vs. Hf plot to discriminate between different source compositions. In this plot, most data fall in the felsic source to mixed felsic/basic source field (Fig. 4 Table 1). 

FIoeve, J. Quirt, D.FI. 1984. Mineralization and Flost Rock Alteration in Relation to Clay Mineral Diagenesis and Evolution of the Middle- Proterozoic, Athabasca Basin, northern Saskatchewan, Canada. Saskatchewan Research Council, SRC Technical Report 187, 187 p. 

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