Dr MEHMET AKKUS (Turkey) read a summarised version of a paper by himself and co-author Dr FIKRET KURTMAN (Turkey) entitled "Inter-Mountain Basins in the Eastern Anatolia (Turkey) and their Oil Possibilities". He pointed out that there were four large, deep, tertiary filled intermontane basins in the Anatolia-Taurid belt of Eastern Anatolia, which, because of marked facies changes in their Sediments, should contain stratigraphic traps. The presence of oil seeps encouraged him to think that these might be prospective.
Dr N. A. EREMENKO (U.S.S.R.) and Dr I. M.
MICHAILOV (U.S.S.R.) presented a comment entitled "Pools caused by Tectonic Sealing of the Reservoir". There was no provision made in the programme for the discussion of other types of trap than stratigraphic. But the problems associated with tectonically sealed pools are still inadequately investigated although such pools are widespread in nature.
Pools sealed up dip by impermeable material in a bounding fault zone are well known. Other cases, in which the trap is due to a capillary pressure difference across a permeable fault zone, have been described by D. A. Smith (Bull AAPG, v. 50, No. 2, 1966). But there are still other phenomena, connected with the rheological properties of the fluids, which also cause trapping against a permeable fault surface under suitable conditions.
The initial pressure gradient is the limit below which the flow of oil or gas through a porous medium will not start. This operates for both Newtonian and non-Newtonian fluids; it is clearly demonstrated mainly in reservoirs with some argillaceous admixture.
The theory of this gradient is fully discussed in Special Paper No. 9 [Volume 4 of Proceedings] presented to this Congress by A. KH. MIRZADJAN- ZADE et al.
Hydrocarbon entrapment due to the initial pressure gradient effect is dependent on fluid and reservoir properties, In nature, capillary pressure and initial pressure gradient act together and simultaneously.
Pools associated with both capillary pressure and initial pressure gradient are called "pools of initial pressure gradient" for short.
There are also special types of hydrodynamic traps against fault zones with good permeability. In such traps the pressure at the apex of the oil accumulation is balanced by the pressure of the water in the fault zone. It follows that the bottom waters of the pool must be underpressured, as the oil column, with its lighter density, would normally give rise to an excess pressure. Such is indeed found to be the case. It is further observed that such underpressured reservoirs are in rocks of reduced permeability while the more permeable beds abutting the fault zone are in pressure equilibrium with the fault zone waters.
Pools of this sort are widespread in the Dniepetrovsk-Donetsk depr
