Summary

COLOMBO: Dr. HEDBERGs concept of "source sequence", as opposed to that of source rocks, is particularly valuable. We could go a little farther and deny that the origin of petroleum, as such, is synonymous with the origin of the components of petroleum.

If this view is correct, while hydrocarbons are generated in the source beds, petroleum is actually formed in the trap environment. Should we not, therefore, regard the traps as having an active source function, rather than as being merely passive containers ? SALVADOR: Probably the most controversial aspect of the origin of oil and gas is still the understanding of the mechanism or mechanisms of primary migration by which the hydrocarbons move from their source rocks to the reservoirs. Could Dr. HEDBERG give us his views on this matter? HEDBERG: I have indeed used the term "sourcesequence" because it has a more general connotation which better includes the whole source system of sediments and fluids which may be associated with the origin of any particular petroleum.

With respect to the still highly controversial matter of primary migration, I can only say that personally I believe that a large part of primary migration is associated with the moderately early stages of compaction and water expulsion; that effects of increasing pressure and temperature are continuously involved; and that primary migration of petroleum (or certain constituents of petroleum) may take place variably in the form of free oil, or in a colloidal state, or in water solution, or in gaseous solution, depending on the stage attained and the conditions of origin.

DUPUY DE LOME: In connection with Dr.

HEDBERGs remarks on coals, do you think there is a relationship between the large recent gas discoveries in the North Sea and the process of "decarbonization" of the coal beds underlying the reservoirs ? HEDBERG: It seems to me quite reasonable to suppose that much of the Permian gas of the North Sea is indeed related to a "re-coalification" of carboniferous coal beds, as suggested by Patijn for the Groningen gas of Holland.

HODGSON: Would Dr. HEDBERG care to comment on the contribution of hydrocarbon material from terrigenous sources as distinct from marine organisms ? Since the inorganic constituents of recent Sediments come from the land surface, is it not 74 Origin of Oil and Gas reasonable to accept a land-surface origin for the organic matter as well? HEDBERG: I have mentioned the strikingly widespread empirical relation between high wax content of oils (commonly reflected in high pour point) and probable fresh and brackish water source-sequences, usually of the shale-sandstone lithologic type. I am inclined to believe that this high wax content is fundamentally related not so much to salinity as to conditions favouring contribu

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