Page 164 - Geology and Geochemistry of Oil and Gas

STUDIES OF SOLUBLE AND INSOLUBLE PORTIONS OF ORGANIC MATTER 133
heavier: the amount of initial matter in the experiments by Rohrback et al. (1984)
was limited by the size of the sample, whereas it does not have to be limited in
nature. In other words, when the amount of initial matter is sufficient, during the
formation of products (CH 4 and H 2 S in these cases), the bonds with the matter are
severed first for the light isotopes, and only then for the heavier ones.
In the initial rock–water–organic matter system, the last link (OM) is highly
sensitive to the changes during diagenesis and subsequent catagenesis (epigenesis).
The direction of processes transforming the organic matter during diagenesis and
catagenesis and the resulting products are clear. Obviously, the most stable com-
ponents accumulate. It may be suggested that this link (OM) loses energy (increase in
entropy) during diagenesis and catagenesis. However, the organic matter transfor-
mation processes and their effect on the energy status of the entire system is not
clear. The potential role of the spontaneous reactions upon overcoming the energy
threshold is also not clear. The studies that have been initiated in the effects of
sources other than heat energy on the organic matter transformation are discussed
later in this book.