Pore Morphology
A minute opening or tiny hole between the constituent grain of particles of a body. Which admits the passage of fluid (Oil, gas, water ). Theoretically the measure of void space is defined as porosity of the rock.
Classification of porosity types
1. Primary / pre depositional porosity
- Inter granular Porosity
- Intragranular Porosity
- Intercrystalince Porosity
- Fenestrial Porosity
- Mouldic Porosity
- Vuggy porosity
- Fracture Porosity
Primary Porosity
Primary Porosity is that which by definition forms when sediment is towards take down. It is the natural porosity types found in petroleum reservoir sands or rocks. It is characterized or recognised by two types -
1. Inter-Granular Porosity
It occurs in the spaces between the detridal grain which form the frame work. of a sedimentary rocks, It is the very important porosity type. It is present initially in almost all sediment, It is generally progressively reduced by diagenesis in many carbonate, But it is dominated porosity types found in sand stone.
2. Intragranular / Inter Particle Porosity
In carbonate sands particularly those of skeleton origin , Primary porosity may be present within the grains. For example - Cavities of Molluscs , Bryo Zoans, Ammonites and macro fossils etc can all be classes as intra granular / Intra particular porosity.
However the Chemical instability of the carbonate host grains of an leads to their intra particle pores being modified or obliterated by subsequent diagenesis.
3. Secondary Porosity ( Post Depositional Porosity)
It is that which by definition which form after the sediment was deposited , It is a result of Geological Process Like diagenesis after deposition of sediment, It is more diversed in Morphology, and more complex in genesis then primary porosity.
The magnitude, shape, size, interconnection of the pores may have no direct relation to the form of original sedimentary particles. It is more commonly found in carbonates.
1. Inter-crystalline porosity
It means the porosity between crystal of approximately equal size although the simple definition would apply, in a strict sense to almost all porosity in carbonate. Intercrystalline normally restricted to porosity between the Individual crystal, It is charecteristics of dolomite.
2, Fenestrial Porosity
Lens shape porosity develop in carbonate due to the presence of fenestrial porosity, rocks with fenestrial porosity will not form good reservoir rocks unless the penestry we interconnected, to permit a good permeability to be establish. Elongated fenestrial pores may developed into rotting of organic material.
3. Mouldic Porosity
Mould are pores form by the selective disolution of individual constituent grains of coasals in carbonate rock, it is all the grains of a particular type that is dissolved. It is typically found in carbonate.
4. Vuggy Porosity
Vuggs are larger size than moulds. Porosity produced by dis-solution of the rock by the formation water, to generate patchy cavity. Vuggs tend to larger than moulds. It is most common in carbonates.
5. Fracture Porosity
Porosity resulting from fracture develop by tectonic forces between the rock, is Called fracture porosity. This porosity type is charecteristics of rocks , that we strongly lifted. Therefore they are generally form, later than the other varieties of porosity. It is important to knows that fracture porosity is not only found in well cemented sand stone and carbonate but may also be present in shales and igneous and metamorphic rock.
Notes:- Data is collected from our universities notes-books and persons experienced. Main purpose of this article is to help peoples.
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