Effects of inorganic salts on the hydrocarbon generation from kerogens

The minerals and salts existing in the sediments during kerogen maturation have important effects on petroleum generation. They may catalyze or restrain thermal decomposition of kerogen, thereby altering the yield and composition of petroleum. Therefore, the work on this field has been the subject of much research in recent years. In this paper, a series of thermal simulation experiments on isolated kerogen and mixtures of kerogen salts are carried out to investigate the effects of inorganic salts on kerogen degradation using Rock Eval and Py GC. The kerogen samples are prepared from source rocks in Songliao Basin and Dongying Depression, China. On the basis of experimental data, a kinetic model of kerogen degradation is developed which takes into account the effects of the added salts on kinetic parameters. It is found that the inorganic salts have different effects on kerogen degradation. Among the several salts used, salt chlorides including MgCl2, CaCl2 and SrCl2 exhibit inhibition effects on the kerogen degradation to decrease the hydrocarbon yields. The other salts including NaHCO3, MgSO4 and K2CO3 promote the hydrocarbon generation to increase the hydrocarbon yields in kerogen degradation. Because of the catalytic effects of the salts, activation energies are decreased, or in some cases, frequency factors are increased. The inorganic salts have no effects on the composition of hydrocarbon generated from kerogens. Finally, the catalysis action of inorganic salts on the kerogen degradation can be tentatively accounted for by electron inducement mechanism. According to this mechanism, salt ions enter into intra or inter molecule of kerogen to make the electronic configuration and charge distribution changed to some extent. These changes result in shifting of the charges from place to place, increase the polarity of covalent bonds (C—C or C—H) and polar bonds (C—O or C—S) and thus promote cleavage of some bonds. Further research on this subject is necessary in the future to understand the more details of the mechanism of salt catalysis.