Print this pageThe Role of Organic-Inorganic Interactions in Clastic Diagenesis
SURDAM, RONALD C.
A decade ago organic acids/acid anions/CO[2], and organic-inorganic interactions were suggested as being responsible for many of the dissolution reactions documented by petrographers in clastic hydrocarbon reservoir rocks. The strongest evidence supporting this suggestion was the presence of significant quantities of organic acids/acid anions in oil field waters. Initially, the source of these organic acids/acid anions/CO[2] was attributed to the maturation of kerogen in source rocks. However, critics of the organic-inorganic interaction explanation for dissolution reactions rightly pointed out that there was a problem with the oxygen balance - there was insufficient oxygen in associated kerogen to generate the quantity of organic acids/acid anions CO[2] required to cause the amount of dissolution observed in adjacent reservoir rocks. As a consequence the role of organic-inorganic interactions in clastic diagenesis was discounted by some investigators.
It is now known that organic acids/acid anions/CO[2] associated with oil field waters can be derived from a variety of processes (i.e., redox reactions involving mineral oxidants and kerogen; redox reactions involving hydrocarbons and mineral oxidants; kerogen-water reactions; hydrocarbon-water reactions; as well as thermal maturation of kerogen). It is concluded that oxygen contained in kerogen no longer needs to be considered as a constraint on the amount of organic acids/acid anions/CO[2] available in clastic diagenetic systems. Simulating these oil-water-rock- interactive processes using hydrous pyrolysis techniques allows the retrieval of the kinetic parameters necessary to model organic-inorganic interactions during progressive burial and diagenesis of source/reservoir rock systems. These modelling techniques when combined with a sedimentological framework result in significant reduction of uncertainty in predicting porosity/permeability distributions in source/reservoir rock systems.