The book presents much irrefutable evidence for processes of formation and accumulation of oil beginning in early diagenesis and essentially culminating in the brown-coal stage of catagenesis.
This concept is backed up by such factors as the formation of commercial accumulations of oil and gas in sediments of the Pleistocene, the occurrence of oil-bearing rocks the depth of burial of which does not exceed “diagenetic” depths (600-1200 m), the occurrence of asphalt balls washed out of lower occurring oil-bearing sediments, the uncemented character of many oil sands and correspondingly the formation of sand “plugs” during production of oil pools. Post-depositional changes in accessory minerals of productive sandstones and many other such phenomena indicate the possibility of an early stage of formation and accumulation of oil. Particularly persuasive in this respect are the results of studies of the direction of the process of alteration of organic matter in modern and Pleistocene sediments from wells drilled offshore. In sediments of the Kvalyn and Khazar horizons of Quaternary age were found bitumens that are in considerable degree reduced with clear traces of migration of their hydrocarbon components.
At the same time in the gas phase of various facies of modern sediments were found not only methane but also the entire gamut of heavy hydrocarbons from ethane to hexane, inclusively.
At the same time, as presented in further chapters of the book, the direction of the process of conversion of organic matter depending on facies of the sediments is quite variable, and these variations begin during early diagenesis. Demonstration of this conclusion is based on conditions of distribution of oil in areas of the middle Pliocene basin of Azerbaydzhan. Two facies groups are recognized here: 1) facies of a single intracontinental basin (Apsheron, Kobystan, and Nizhne-Kura), which are regionally oil-bearing; and 2) marginal facies of the basin (Peri-Caspian-Kuban, Lengebiz, Yuzhno-Mugan, and Muradkhanly), which is characterized by oxidizing conditions and is devoid of oil shows. This example thus is a clear example of the significance of facies as the main factor determining oil occurrence in one place and its absence in another.
Arguing for the culmination of the process of formation and accumulation of oil at the brown coal stage, the author cites several oil-bearing formations where the pays are associated with beds of brown coal. In those cases where the oil-bearing formations of young (Cenozoic) age are expressed by alternation of paralic and shallow-water facies, the presence of beds of brown coal is typical and characteristic.
The conclusions drawn here have not only scientific but also practical importance. They indicate that prospects for oil should not be limited by the depth barrier (greater than 600-1200 m), which now prevails. The author thinks that such depths are not necessary.
In later chapters of the book the scale of migration of oil necessary for commercial accumulations is estimated. The leading role of lateral migration is recognized here. The conditions of formation and migration of oil in carbonate facies is examined. There is great interest in the genetic relationship of oil of reef facies to organic matter of these reefs.
Finally, attention is given to the dependence of the maximum content of oil in clastic sandy-silty sediments on median diameter of their grains. Maximum possible concentrations of oil are in areas of fine-grained sands and coarse-grained siltstones.
Moscow, Nedra, 1978.
D. M. Suleymanov
Source
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