Changes

Pores are open spaces between grains, matrix, and cement. Then, porosity is the ratio of total pore space to total volume.

Pores are open spaces between grains, matrix, and cement. Then, porosity is the ratio of total pore space to total volume.

:Porosity = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑇𝑜𝑡𝑎𝑙 𝑃𝑜𝑟𝑒 𝑆𝑝𝑎𝑐𝑒 x 100 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑅𝑜𝑐𝑘 𝑆𝑎𝑚𝑝𝑙𝑒

:<math>\text{Porosity} = \text{Volume of total pore space } \times 100 \text{ Volume of Rock Sample}</math>

Porosity has both primary and secondary origin. Primary porosity originates from deposition and arrangement of grains. Intergranular and intragranular porosity make up primary porosity. Intergranular porosity exists between grains, mostly affected by fabrics. Variables affecting intergranular porosity include grain size, sorting, and shape. Increasing grain size coincides with decreasing porosity. Lee (1919) in Selley (1976) states that ancient sedimentary rock porosity increasing with decreasing grain size. Finer grain tends to have angular shape, enabling greater pore spaces. Sorting certainly affects porosity in the proportion of grain sizes and how they are arranged. Well-sorted sandstone tends to have greater porosity due to higher percentage of grain to matrix. Less sphere grain tends to produce greater porosity since it is hardly closely packed.

Porosity has both primary and secondary origin. Primary porosity originates from deposition and arrangement of grains. Intergranular and intragranular porosity make up primary porosity. Intergranular porosity exists between grains, mostly affected by fabrics. Variables affecting intergranular porosity include grain size, sorting, and shape. Increasing grain size coincides with decreasing porosity. Lee (1919) in Selley (1976) states that ancient sedimentary rock porosity increasing with decreasing grain size. Finer grain tends to have angular shape, enabling greater pore spaces. Sorting certainly affects porosity in the proportion of grain sizes and how they are arranged. Well-sorted sandstone tends to have greater porosity due to higher percentage of grain to matrix. Less sphere grain tends to produce greater porosity since it is hardly closely packed.

Secondary porosity (Selley, 1976) encompasses intercrystalline porosity, fenestral porosity, moldic porosity, vuggy porosity, and fractured porosity. Types of porosity commonly occur in sandstone are intercrystalline and fractured porosity. The other three types of porosity are typically found in carbonate rocks. Intercrystalline porosity occurs between crystals precipitated in diagenesis. On the other hand, fractured porosity is related to post-sedimentary structures and tectonics. Post-sedimentary structures are able to produce sedimentary faults and folds. A distinct example of fractured porosity due to tectonics occurs in anticline. Outer arc of a fold bears extension, generating tensional fractures and faults. Inner arc of a fold experiences compression, producing compressive fractures.

Secondary porosity (Selley, 1976) encompasses intercrystalline porosity, fenestral porosity, moldic porosity, vuggy porosity, and fractured porosity. Types of porosity commonly occur in sandstone are intercrystalline and fractured porosity. The other three types of porosity are typically found in carbonate rocks. Intercrystalline porosity occurs between crystals precipitated in diagenesis. On the other hand, fractured porosity is related to post-sedimentary structures and tectonics. Post-sedimentary structures are able to produce sedimentary faults and folds. A distinct example of fractured porosity due to tectonics occurs in anticline. Outer arc of a fold bears extension, generating tensional fractures and faults. Inner arc of a fold experiences compression, producing compressive fractures.





==Permeability==

==Permeability==

Related property of sandstone with porosity is permeability. Permeability is effective amount of pore spaces. Selley (1976) defines permeability as the ability of a liquid or gas to flow through a porous solid. Darcy’s law defines the calculation of permeability

Related property of sandstone with porosity is permeability. Permeability is effective amount of pore spaces. Selley (1976) defines permeability as the ability of a liquid or gas to flow through a porous solid. Darcy’s law defines the calculation of permeability