Perspektywy poszukiwań złóż węglowodorów w północnej części strefy Teisseyre'a-Tornquista

Abstract

PERSPECTIVES OF SEARCH FOR HYDROCARBONS IN NORTHERN PART OF THE TEISSEYRE-TORNQUIST ZONE Summary The results of regional studies and search for hydrocarbons showed that Tuchola-Płock area, situated in contact zone of the Paleozoic and Precambrian platforms, northern part of the Teisseyre-Tornquist Zone, is highly perspective. In that area, series perspective from the point of view of search for oil and gas include upper sub-Zechstein strata: Rotliegendes, Carboniferous and Devonian. Older strata of both the folded and platform Paleozoic may be regarded as barren. The question of perspectives of strata belonging to the Zechstein-Mesozoic complex is beyond the scope of this paper. The perspectives of search for oil and gas in the above mentioned strata are presented at the background of deep geological structure of this area as well as lithostratigraphic and facies characteristics and thickness distribution of the Lower Paleozoic, Devonian, Carboniferous and Permo-Mesozoic. The sub-Permian geological structure is mainly characterized by a pattern of blocks elongated in NW-SE direction and bounded by still poorly controlled faults (the Z1’ reflector, interpreted as related to the base of the Zechstein, still remains to be the lowermost of the reliable ones as reflection seismic surveys just started to supply some data on sub-Zechstein strata). The major tectonic element in this area is an elongate Devonian block which contacts folded Silurian strata in NE and Carboniferous ones in SW. Erosional upper surface of the strata is. discordantly overlain by the Rotliegendes. This pattern, formed in times of syn-Variscan movements (Late Carboniferous -Early Permian), may extend as far as regional strike-slip zone in the Kutno area (central Poland). Borehole data show that traces of oil (spots and oil seepages) are quite common in the Devonian (Givetian, Frasnian and Famennian). The oil inflow from the Famennian knobby limestones in the borehole Unisław IG 1 (depth. 4760-4808 m) is the first discovery in the Devonian in Poland which occurred. Under conditions of very high (853 at.) pressure, in well tests over 62 m3 of oil have been hitherto obtained. Moreover, a uneconomic accumulation of gas (56,9% of hydrocarbons) with deposit pressure of 823 at. has been found in Rotliegendes rocks in the same borehole. A few gas deposits have been found in the Carboniferous in the Pomeranian Basin and traces of gas - at western margin of the studied area (Zabartowo). The paper presents critical analysis of the thesis put forward by J. Znosko (51). According to that author, there are no large oil and gas deposits in the Polish Lowlands as those existing in the past became destroyed due to mobility of the Teisseyre-Tornquist Zone, along which the Old Platform was uplifted in Early Permian. It is emphasized that processes of generation and migration of hydrocarbons from Devonian-Carboniferous structural complex were taking place in post-Permian times ( 4, 36 - 42). lt follows that syngenetic deposit accumulations still did not exist in Devonian-Carboniferous strata in area of the Paleozoic Platform in times of major syn-Variscan movements. Therefore, any destructive processes could not affect them but deposits related to the Lower Paleozoic only. The presented positive indices for oil-and gas-bearing of sub-Zechstein Paleozoic make it possible to state that both the Teisseyre-Tornquist zone and adjoining part of the Polish Lowlands are perspective from the point of view of search for hydrocarbons. In the Tuchola-Płock area, there are some perspectives for discovery of gas deposits with resources of the order of some dozens milliards m3 in the Rotliegendes and Carboniferous, and oil deposits with resources of some millions tons in the Devonian.