Kerogen is often considered to be a fully hydrocarbon-wet constituent of mudrocks . Type I kerogen is rare and predominantly composed of hydrogen-rich organic matter. It mainly consists of lacustrine sources. Type II kerogen has predominantly marine depositional origin with some land components. It contains relatively high hydrogen content. Type III kerogen consists of woody terrestrial source and typically contains low hydrogen content. They are mostly prone to gas generation. During thermal maturation of kerogen, it evolves from hydrogen-rich organic matter into hydrogen-poor residual carbon ). This promotes transformation in the chemical structure of kerogen with a gradual increase in sp 2 /sp 3 carbon hybridization ratio, leading to aromatization . At very high thermal maturity, the kerogen structure condenses to mainly aromatic units in sp 2 hybridized graphitic structures . With increasing thermal maturity, carbonyls and alkyls decrease while aromatics increase (Mao et al. 2010).