In Poland, major gas fields were discovered in area of the Polish Lowlands. Large gas fields are also known from the Carpathian Foreland and smaller ones – from the Carpathian Mts and Polish economic zone of the Baltic Sea (map). About three quarters of the gas resources are related to plays involving Miocene and Rotliegend formations and the remaining resources – to plays in the Cambrian, Devonian, Carboniferous, Zechstein, Jurassic and Cretaceous formations.
In the Polish Lowlands, gas fields are related to the Permian in the Fore-Sudetic and Wielkopolska regions and the Carboniferous and Permian in the Western Pomerania. In these regions gas occurs in massive and block-type reservoirs with water or gas drive mechanism. In that area only four gas fields contain high methane gas. The remaining gas fields are characterized by presence of nitrogen natural gas with content of methane ranging from about 30 % up to over 80 %, that is nitrogen-methane or methane-nitrogen mixtures.
Gas fields containing natural gas with nitrogen content over 90 %, called as „high nitrogen natural gas” (HNNG), are discussed in a separate section.
In the Carpathian Foreland, natural gas fields are related to plays involving the Jurassic, Cretaceous and Miocene formations. The fields usually contain high methane natural gas with low content of nitrogen. The exception are here few natural gas fields containing high nitrogen concentrations. In this region gas occurs in structural-lithological multi-layer traps or, sometimes, massive-type reservoirs with gas drive mechanism.
In the Carpathians, natural gas occurs in gas and oil-gas and oil-gas-condensate fields related to plays in the Cretaceous and Tertiary formations. The Carpathian fields are exploited using standard gas depletion drive mechanism. Produced gas is characterized by high content of methane (usually over 85 %) whereas average content of nitrogen is a few percent at the average.
In the Polish economic zone of the Baltic Sea, there are two gas fields (B4 and B6) and two oil-gas fields (B3 and B8).
At present the Polish Lowlands region accounts for 69 % of proven domestic resources of natural gas and the Carpathian Foreland – for 26 % of those resources. The resources of the Polish economic zone of the Baltic Sea and the Carpathians are subordinate, being equal 4.0 and 1.0 % of the proven domestic resources, respectively.
Table 1 shows exploitable resources of natural gas and degree of exploration and development of the gas and oil and condensate fields in individual parts of the country. The data given in this table refer to resources of natural gas actually present in the gas fields and are not converted to those of high methane gas (high methane gas = extracted reserves x combustion heat of real gas / combustion heat of high methane gas, that is about 34 MJ/m3).
In the year 2011, exploitable resources of natural gas were found to be 144,881 million m3 (anticipated economic and anticipated sub-economic resources), that is 2,51 million m3 less than one year earlier. In 2011 there were new deposits documented: Lisewo (989.50 million m3 of exploitable resources), Gajewo (18.30 million m3) and Kamień Mały (129.85 million m3).
Resources of exploited fields were estimated at 120,24 billion m3, which corresponds to 83 % of total amount of all the exploitable resources. In the year 2011, economic resources of natural gas were estimated at 62.96 billion m3.
The total domestic resources given above include those of gas fields which are planned to be converted for use as underground natural gas storage facilities. Production from these gas fields has been stopped in order to use the remaining gas as gas cushion (base gas) throughout the time of operation of the storage sites. The Brzeźnica (45.59 million m3), Daszewo (27.72), Husów (372.88), Strachocina (121.5), Swarzów (28.80) and Wierzchowice (5,557.12) gas fields were selected for conversion into underground storage facilities. In December 2010 Bonikowo Underground Natural Gas Storage Facility was officially opened. Total reserves of natural gas to be used as gas cushions are estimated at 6.48 billion m3. Underground natural gas storage facilities are also built in salt (Mogilno II and Kosakowo facilities) and hard coal deposits (Nowa Ruda facility). The Mogilno II facility is the first of that type already in use for natural gas storage and the Kosakowo facility is under construction. In turn, the Góra facility is used for storage of liquid fuels. Up to now, 11 licenses for running underground natural gas and liquid fuel storage facilities were issued.
In the year 2011, domestic production of natural gas from exploitable gas resources was 5,646 million m3 (see Table 2), being 150 million m3 bigger than in 2010.
The figure given below shows changes in domestic resources and production of natural gas in Poland in the years 1989-2011.
Domestic production of natural gas covers about 40 % of annual consumption.
Shale gas accumulations are likely to occur in the Upper Ordovician-Lower Silurian formations in the Baltic and Lublin-Podlasie Basins, as well as in the Lysogory and Bilgoraj-Narol blocks. These formations are currently subject to industry exploration activity. Polish Geological Institute-National Research Institute in cooperation with U.S. Geological Survey on the basis of data from the period 1950-1990 estimated resources of gas and oil in the Upper Ordovician-Lower Silurian formations in the Baltic and Lublin-Podlasie Basins. Total exploitable resources of gas can be maximum 1,920 million m3 and oil 535 million tones. Taking into account all parameters of the evaluation, resources can be estimated with the highest probability in the range of 346 – 768 billion m3 of gas and 215 – 268 million tonnes of oil(1) .
Presence of tight gas accumulations is the most probable in the north-eastern rim of the Fore-Sudetic Monocline in the Rotliegend sediments developed in eolian facies. A few wells drilled in 2009-2011 east of Poznan confirmed presence of gas in Rotliegend tight sandstones in that region.
Prepared by: Martyna Czapigo-Czapla
(1)Polish Geological Institute – National research Institute, 2012 – Ocena zasobów wydobywalnych gazu ziemnego i ropy naftowej w formacjach łupkowych dolnego paleozoiku w Polsce (basen bałtycko – podlasko – lubelski).