JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II PETROLEUM GEOLOGY Previous Question Paper (December - 2018 - R16)

Diagenesis refers to all the physical, chemical, and biological changes that occur in sediments after their initial deposition, during and after lithification, but excluding metamorphism and weathering. It involves processes such as compaction, cementation, dissolution, and replacement that transform loose sediment into sedimentary rock at relatively low temperatures and pressures.

Clay stone is a fine-grained sedimentary rock composed primarily of clay minerals. Its key physical properties include:

• Texture: It possesses a very fine-grained or argillaceous texture, with individual particles typically smaller than 0.004 mm, making them indistinguishable to the naked eye.
• Fissility: Unlike shale, clay stone is typically non-fissile, meaning it lacks the tendency to split into thin, parallel layers or laminae.
• Hardness and Plasticity: It is generally soft with low Mohs hardness. When dry, it is brittle, but it exhibits significant plasticity when wet, becoming moldable and cohesive due to the presence of clay minerals like kaolinite or illite.
• Porosity and Permeability: While it has high porosity due to its fine-grained nature, it exhibits extremely low permeability, which makes it an effective seal or cap rock in petroleum systems.