Poszukiwania ropy naftowej i gazu ziemnego w północno-zachodniej Polsce w latach 1955-1985
Abstract
EXPLORATION FOR OIL AND GAS IN NW POLAND IN THE YEARS 1955-1985
Summary
The paper presents a short review of the exploration for hydrocarbons carried on in northwestern Poland during the period 1956-1985. There are several exploration targets in the area: Lower Devonian clastics, Middle and Upper Devonian carbonates, Lower Carboniferous sandstones and oolitic limestones, Upper Carboniferous and Rotliegendes sandstones, and Zechstein carbonates (mainly Hauptdolomit). So far oil fields in the Hauptdolomit have been discovered, as well as gas fields in the Lower and Upper Carboniferous horizons, and minor gas pools in the Rotliegendes sandstones. About 260 boreholes have been drilled, c. 15% of which have been successful (Fig. 3).
The progress of works in the first ten years was slow (Figs. 1 and 2). They were accelerated only in the period 1966 -1970 and concentrated on the investigations of the sub-Permian sequences in the Koszalin-Chojnice tectonic zone. During the next five years (1971-1975), because of oil findings in the Hauptdolomit of the adjacent areas, the exploration was aimed at this horizon within the Kamień Pomorski Błock. It resulted in the discovery of the most prolific oil field in the Polish Lowlands. Later on (1975- 1985) the search for oil was shifted southwards, to the carbonate barrier of the Hauptdolomit and to the fore-barrier zone, and the search for gas was focused on the Carboniferous of the Kołobrzeg Block.
In spite of the relatively high effectiveness of exploration some disadvantages should be stressed. Lack of distinct seismic reflectors from beneath the Zechstein greatly hampers the exploration in the Devonian and Carboniferous strata. The tectonics of this complex remains unknown - the so far revealed gas traps are located at the erosional sub-Permian surface and are sealed either by the impermeable Zechstein rocks or by the rejuvenated faults. Secondly, the deficiencies result sometimes from the excessive concentration of works on the immediate economic goals with neglect of more general geologic research.
Unsolved problems in the sub-Permian are: the existence and possible extent of the Devonian carbonate buildups, the character of the gaps at the Devonian - Carboniferous boundary and the relations between shaly, sandy and carbonate facies in the Lower Carboniferous. In the Permian succession they are: the mapping of the most favorable sandstone facies of the Rotliegendes, the role of matrix in these sandstones for the reservoir parameters, the extent of the Zechstein carbonate barrier in the eastern part of the area and the problem of the epigenetic improvement of the reservoir characteristics in the basinal slope of the carbonate platform due to migration of waters enriched in CO2.
Summary
The paper presents a short review of the exploration for hydrocarbons carried on in northwestern Poland during the period 1956-1985. There are several exploration targets in the area: Lower Devonian clastics, Middle and Upper Devonian carbonates, Lower Carboniferous sandstones and oolitic limestones, Upper Carboniferous and Rotliegendes sandstones, and Zechstein carbonates (mainly Hauptdolomit). So far oil fields in the Hauptdolomit have been discovered, as well as gas fields in the Lower and Upper Carboniferous horizons, and minor gas pools in the Rotliegendes sandstones. About 260 boreholes have been drilled, c. 15% of which have been successful (Fig. 3).
The progress of works in the first ten years was slow (Figs. 1 and 2). They were accelerated only in the period 1966 -1970 and concentrated on the investigations of the sub-Permian sequences in the Koszalin-Chojnice tectonic zone. During the next five years (1971-1975), because of oil findings in the Hauptdolomit of the adjacent areas, the exploration was aimed at this horizon within the Kamień Pomorski Błock. It resulted in the discovery of the most prolific oil field in the Polish Lowlands. Later on (1975- 1985) the search for oil was shifted southwards, to the carbonate barrier of the Hauptdolomit and to the fore-barrier zone, and the search for gas was focused on the Carboniferous of the Kołobrzeg Block.
In spite of the relatively high effectiveness of exploration some disadvantages should be stressed. Lack of distinct seismic reflectors from beneath the Zechstein greatly hampers the exploration in the Devonian and Carboniferous strata. The tectonics of this complex remains unknown - the so far revealed gas traps are located at the erosional sub-Permian surface and are sealed either by the impermeable Zechstein rocks or by the rejuvenated faults. Secondly, the deficiencies result sometimes from the excessive concentration of works on the immediate economic goals with neglect of more general geologic research.
Unsolved problems in the sub-Permian are: the existence and possible extent of the Devonian carbonate buildups, the character of the gaps at the Devonian - Carboniferous boundary and the relations between shaly, sandy and carbonate facies in the Lower Carboniferous. In the Permian succession they are: the mapping of the most favorable sandstone facies of the Rotliegendes, the role of matrix in these sandstones for the reservoir parameters, the extent of the Zechstein carbonate barrier in the eastern part of the area and the problem of the epigenetic improvement of the reservoir characteristics in the basinal slope of the carbonate platform due to migration of waters enriched in CO2.