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Monterey Formation and Green River Formation kerogens (types II and I, respectively) were isolated, mixed with common sedimentary minerals, and pyrolyzed under dry and hydrous conditions for various times and temperatures. Analysis of all the pyrolyses products were conducted to perform a material balance and to infer reaction kinetics and mechanisms.
Material balance of the pyrolyses products, in the presence and absence of minerals, reveals that the kerogen degradation results in the formation of bitumen rich in high molecular weight compounds in the initial stages, followed by additional cracking of kerogen and bitumen. However, amount and type of hydrocarbons in the pyrolyses products of kerogen in the presence of montmorillonite are markedly different from those produced by heating kerogen alone or with other minerals. The initial amount of products in the presence of montmorillonite, and in particular the quantities of low molecular weight hydrocarbons, are higher than those in the presence of illite, calcite, and kerogen alone. The composition of these low molecular weight compounds is dominated by branched hydrocarbons, ind cating catalytic cracking via carbonium ion mechanism, which is initiated on acidic sites of the clay. Compositional differences are evident also in the distribution of n-alkanes and in the pristane/phytane ratio. The catalytic effect of montmorillonite, however, disappears in the presence of excess water.
These differences may have important implications for the composition and quantities of petroleum generated from source rocks with different mineralogies.
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