Niektóre zagadnienia geologii ropnych złóż

Karol Bohdanowicz

Abstract


Some problems of petroleum geology

A comparative compilation of material pertaining to oil fields in various countries compels taking a critical attitude towards some thesis widely propagated in petroleum geology. Seemingly „revelatory“ discoveries of Russian scientists, concerning biochemical accidents of the Black Sea, failed to give anything new as regards the p art of biochemical factors in the formation of fluid crude oil. Conclusions drawn from McKenzie Taylor’s investigations cannot be taken to deny the tremendous influence exercised by chemical reactions in the process of formation and evolution of coal and crude oil in the course of geologic time. Sediments may presumably be sapropellites of the type found at the bottom of the Black Sea, however, it would be unjustified exaggeration to look for source beds solely among analogies with bottom of that sea. Investigations by Hackford, Berl, Treibs, Haseman and others, abolish the principal argument against the possibility of crude oil originating not only from vegetable and animal plankton, but also from huic products from the cellulose of green plants, as has been, in its time (1918), inferred by late R. Zuber, senior, on the basis of geologic observations. The extreme conception of the principal cause of crude oil accumulating in reservoirs exclusively or principally through deformation of unconsolidated sediments and of consolidated sediments at the time of folding or finally by vertical migration — such a conception fails to take into consideration other accidents the at lead to reservoirs becoming closed, nor does it take into account actual geologic material concerning oil fields. Coordinated investigations of geologic conditions of crude oil deposits and of peculiarities displayed by crudes, will lead to the conclusion the at differentiations of crude oil cannot be explained unless the heterogeneous character of the primary organic substance is taken into consideration. In spite of divergent opinions advanced by modern geologists as regards the p a rt played by various factors in the formation of individual peculiarities of crude oils, the hypothesis may be risked th a t there are no general laws that would seemingly prejudicate the uniformity of the primary organic substance, a generally uniform process of crude oil accumulation in deposits, or a generally uniform direction of evolution of crude oil. Negation of such general laws arises from know ledge of crudes and of crude oil deposits becoming more and more profound. The complex of coordinate investigations in Petroleum Geology and Engineering, must, conforming to the ideas of late D. White, become the object of research work by institutes broadly organised and correspondingly equipped as regards both means and men. Crude oils from the various Polish oil pools belong to a number of different types: 1) Cretaceous, including the crudes from Jamna horizons, asphalt-base (non-paraffine) light and heavy, and, less frequently, semi-paraffine and light. 2) Eocene asphalt-base light, semi-paraffine and paraffine-base heavier. 3) In the series of Menilite shales we have paraffine-base crudes and such semi-paraffine, heavier and lighter ones; no non-paraffine crudes have been observed in this iseries. 4) The Krosno light asphalt-base crudes, with heavier ones being rather scarce. 5) From among the stratigraphie series just enumerated, the Menilite series displays the most uniform facial character, beginning at the fields of Libusza—Lipinki on the west as fa r as the Bitków region on the southeast, and it is just this series that generally contains crudes of the most uniform character. 6) Variation of the crudes belonging to more or less the same chemical type, as for example the non-paraffine crudes (Harklowa, Węglówka, Grabownica, Iwonicz, Równe, Rogi, Kosmacz), is based principally upon a different content of light gasoline and lubricating fractions, and this finds expression in the prices paid normally for those crudes, — the prices standing in an inverse ratio to the specific gravity of each particular crude. 7) In spite of a chemical variation of crudes belonging to one and the same stratigraphie series, there may be distinguished certain geochemical types of crudes within the confines of the Polish Carpathian petroliferous province. 8) In the cross section of the Borysław fields, the geologic series, except the strictly Menilite series exclusive the Borysław sandstone, differ in their facial formation from approximately synchronic series found upon larger areas of the western and eastern Polish Carpathians. The crudes from each series, as found at the Borysław field, show few differences between each other except crude coming from the shallow parts of the overthrust, however, they display a character different from that of crudes in synchronic formations. The crude from the shallow parts of the Cretaceous overthrust (series a), approaches the heavy Cretaceous crudes of Węglówka and Kosmacz. 9) Crude oil fields occur upon tectonic structures which range from more or less normal folds (Potok, Równe, Rogi), and folds inclined at various angles, to folds entirely recumbent (Borysław). Those various shapes may be divided into two groups: a) Disharmonie foldings with extrusions of the deeper older formations compressed into diapiric uplifts (Potok, Grabownica, Stara Wieś, Bobrka, Rogi), or such re taining the shape of more gentle folds (Lipinki, Węglówka). b) Disharmonie foldings with older formations thrust over younger (Borysław, Rypne, Bitków). In some cases both types may combine as for instance in Harklowa. 10) The forms of group (b) are the expression of the highest degree of orogenic tension, and dependently on this condition deposits show the highest paraffine content (Borysław, Rypne, Bitków), and the primary character of various crudes has the greatest homogenity (Borysław). 11) Variations in specific gravities of crudes — those having a paraffine-base as well as those non-paraffine — cannot be subordinated to the „Dichteregel“ by Krejci-Graf, and especially if the changes in the specific gravity brought about by long exploitation periods are taken into consideration. For paraffine-base crudes it might be expected th a t with increasing depth the specific gravity would normally decrease, while reversely with non-paraffine crudes the specific gravity would under those conditions increase (Węglówka, Grabownica, Iwonicz), which would be contrary to „Dichteregel“.12) Non-paraffine crudes occurring in Grabownica and Bobrka above those having a paraffine base might, if it were possible to prove their transitory character from paraffinebase crudes, furnish examples of asphalt „caps“ resting upon paraffine-base crudes; there are also cases of a reverse relation of paraffine crudes above non-paraffine ones (Rajskie, Iwonicz, Schodnica).

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