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EN
In terms of oil reserves of Poland, the Lubiatów oilfield in the Międzychód area is the second largest after BMB oilfield. The discovery of this structural-lithological trap in a toe-of-slope position in relation to the Main Dolomite (Ca2) carbonate platform opened a new hydrocarbon opportunities in this unit. One of the conditions for trap occurrence in the "Lubiatów-type" deposits of the toe-of-slope zone in relation to Ca2 carbonate platforms and microplatforms is the presence of appropriate reservoir facies. These facies are characterized by occurrence of thick packets of porous Main Dolomite rocks (Ca2 lithosomes) composed mostly of sublittoral, redeposited carbonate sands (packstones, floatstones, sporadic rudstones), deposited below wave-base and resulting from activity of traction and suspension currents and gravity flows. The only method to detect such facies is via high resolution seismic images, preferably from three-dimensional (3D) surveys. Unfortunately, intensive exploration studies carried out in this zone between 2005-2008 did not bring measurable effects, that is discovery of new hydrocarbon deposits. Several boreholes drilled in Ca2 lithosomes found water-bearing horizons only. In several other dry holes, none of the facies assumptions made prior to drilling were confirmed. Comparison of seismic images of area of those dry holes made it posssible to find a geometric criterion for seismic detection of Ca2 lithosomes located at the toe-of-slope of carbonate platforms and microplatforms. This geometric criterion, along with the seismological one, should constitute an important interpretational premise in identifying or excluding areas with potential hydrocarbon traps in the Main Dolomite rocks in the area under study.
EN
The Miocene Carpathian foredeep basin in Poland (CFB) developed in front of the Outer Carpathian fold-and-thrust belt, at the junction of the East European craton and the Palaeozoic platform. 3D seismic data, cores and well logs from Sokołów area (vicinity of Rzeszów) were used in order to construct new depositional model of the Miocene succession of the Carpathian foredeep. The gas-bearing Miocene infill of the CFB is characterized by a shallowing-upward trend of sedimentation and consists of hemipelagic, turbiditic and deltaic and nearshore-to-estuarine facies associations. Lowermost part of the Miocene infill seems to has been deposited from the North. Such direction of sediment supply was related to influence of existing relief of the pre-Miocene basement, where very deep (up to 1,5 km) erosional valleys cut into the pre-Miocene (Precambrian) basement due to inversion and uplift of the SE segment of theMid-Polish Trough are located. Upper part of theMiocene infill reflects sediment progradation from the South, from the Carpathian area into the foredeep basin. In the Rzeszów area existence of the so-called anhydrite-less island, i.e. relatively large area devoid of the Badenian evaporitic cover caused by the post-Badenian uplift and widespread erosion of evaporites,has been postulated for many years. Interpretation of 3D seismic data showed that such model should be abandoned. In the studied part of the CFB, Late Badenian evaporitic sedimentation was restricted to the axial parts of deep paleovalleys. Evaporites deposited in these valleys have been rarely encountered by exploration wells as such wells were almost exclusively located above basement highs separating erosional paleovalleys, hence giving incorrect assumption regarding regional lack of evaporitic cover. It is possible that in axial parts of these valleys important gas accumulations might exist, charged from the South and sealed by the Badenian evaporites.
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