SECTIONAL TRANSACTIONS.—C. 391 
Wednesday, September 30. 
Discussion on The Genesis of Oil Pools in the Sedimentary Cycle. (Prof. 
V. C. Ittine ; Prof. P. G. H. Boswett, O.B.E., F.R.S.; Prof. W. 8. 
Bovutton ; Dr. G. M. Lers; Dr. J. V. Harrison.) 
Prof. V. C. Iturna. 
That oil is produced from the organic matter in sediments is now accepted 
generally as the only reasonable theory. Where diversity of opinion enters is, 
firstly, as to the type of organic material involved and, secondly, the cause of the 
transformation. So far as the present discussion is concerned, the first problem 
will be glossed over, accepting merely the broad statement that the basic material 
is organic and may include a diversity of chemical compounds. So far as the 
mechanics of the change is concerned, the different views may be broadly assembled 
into two camps. The first postulates heat or other internal physical agencies as the 
reacting agent, the second considers that the process of change is biochemical. One 
of the essential differences in these two theories lies in the fact that the one presupposes 
oil formation as a separate and later process after the sediments have been changed 
into rocks, whereas the biochemical theory considers oil formation as a part of the 
process of sedimentation, a change taking place in the sediment as it is being laid 
down. 
The metamorphic theory has the sanction of the chemists as a perfectly feasible 
process, though there are geological arguments which render its application doubtful ; 
the biochemical theory has not yet been proved as a possibility, but it has gained 
many adherents on the indirect evidence. A theory is not necessarily true because it 
is simple, but when a series of separate ideas can be linked together to forma chain 
of evidence, the probability of the theory is greatly increased. 
In this case the speaker puts forward as a support of the biochemical theory the 
fact that it, and it alone, links up satisfactorily with the experimental evidence of 
migration to explain the characteristics of our oil accumulations. Origin, migration 
and accumulation linking up as a complete chain of events without any interlude. 
Tt is now many years since Munn put forward his Hydrostatic theory of migration ; 
but it has never been emphasised sufficiently that the migrating water currents which 
he presupposes are so much more general in the phase of compaction, that it is only 
on a theory of oil formation pari passu with sedimentation that the Hydrostatic 
theory can receive its full development. 
One of the basic facts of oil accumulation is that the oil always occurs in the 
coarsest available rocks ; Dolomite in limestone, sands in clays, or coarse sands in 
fine sands, the essential being a coarser porous rock surrounded by a finer non-porous 
or water-bearing rock. This has been explained as due to the greater surface tension 
of water and the displacement of the oil from the finer strata, but such displacement 
is difficult to reproduce experimentally and it is quite possible experimentally to 
reverse the liquids. 
During the course of experimental work on the subject, it has been found that 
when two immiscible fluids are forced from a fine to a coarse rock, there is an un- 
interrupted passage of both liquids, but when the flow is reversed the fluid which wets 
the grains passes freely from the coarse to the fine, while the other liquid is retained 
at the coarse-fine interface and can be accumulated and concentrated there. By 
suitable arrangements it was found possible to trap completely the gas and oil carried 
by water in sand pockets, and to concentrate oil from very dilute mixtures. 
Such free migration is only possible before the clays are thoroughly compacted, 
and it appears probable that the processes of oil formation, migration and accumulation 
can be linked into one continuous chain initiated and continued through the phase 
of sedimentation. 
Prof. W.8. Bouton. 
During the last 20 years or so of oil-field development, the great accumulation of 
geological fact and experience has given us a reasonable explanation of the con- 
centration of oil into pools from the areas in their immediate vicinity. ‘The relative 
