Characteristic of homodrimane and maturity of organic matter in the low mature source rocks

Bicyclic sesquiterpenoids are mostly used to illustrate the origins of organic matter and genetic types of crude oil presently. In this paper, the relationship between distributions and compositions of C-16 homodrimane in immature to mature source rocks and evolution of organic matter was studied, and the correlation between C-16 homodrimane at immature to low mature stages and thermal evolution of organic matter was analyzed. The results show that in terrestrial facies depositional system, the ratio of 8 alpha(H)-homodrimane to 8 beta(H)-homodrimane has a high sensitivity about the maturity's minor changes at immature to low mature stages. It is found that when the vitrinite reflectance R-0< 0.7%, the ratio significantly decreases with increasing burial depth or maturity. This kind of phenomenon reveals that these parameters may be the useful maturity indicators for determining the relative maturation of organic matter at immature to low mature stages, and have certain practical value in biogeochemical and environmental geochemical research on low mature oil and gas.