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Comparative Analysis of Shale Gas/Oil Resources in the Baltic and the Lublin Basins (Poland) Based on 3-D Static Modelling

Abstract

The presented study concerns the Baltic Basin (BB) and the Lublin Basin (LB) in Poland, being a part of the system of the Lower Paleozoic sedimentary basins developed along the western slope of the East European Craton (EEC). The basins originated with the late Neoproterozoic rifting, followed by the post-rift thermal sag basin (Cambrian – Middle Ordovician). Since late Ordovician throughout Silurian oblique collision of the Avalonia with the Baltica led to development of the extensive flexural foredeep basin along the western slope of the EEC. The basins are filled with a thick complex of the Silurian mudstone-claystone-marl sediments. The Variscan evolution of the BB and LB was considerably different, resulting with significantly higher degree of tectonic deformation and denser grid of faults and natural fractures in the later one. For this reason in the LB risk of gas release from the shale reservoir is considerable. In the BB majority of faults terminates at the base of Silurian, increasing probability of gas preservation. The main target of shale gas/oil exploration in the BB are the TOC rich lowest Llandovery and Caradoc deposits, and to lesser degree also the Wenlock ones. In the LB of the key interest with respect to shale gas/oil are the Wenlock and the Landowery intervals, while the Caradoc is here of marginal interest. For the selected parts of the basins, quantitative 3D static modelling were completed. The regional-scale models covered 3806 km2 in the BB and 7340 km2 in the LB. The models integrate lithostratigraphy, petrophysical data, geochemical data, well logs, and seismic data. Modelled parameters include bulk density (RHOB), porosity (PHI) and water saturation, present and original TOC, shale and brittle minerals volumes models, and in the LB additionally vitrinite reflectance (Ro), RockEval S1+ S2 and HI. Hydrocarbon resources were calculated separately for the oil, liquid and gas windows, GIIP estimates were performed involving the volumetric, the genetic Schmocker and the USGS assessment methods. In a case of the BB mean risked resources estimated with the latter method are equal to 4 M tone of oil/km2, ~2 MMcm of gas/km2 in oil window, ~3.9 M tone of oil/km2 and 0.9 MMcm of gas/km2 in liquid window, ~29 MMcm of gas/km2 in gas window, while for the LB this is 26.4 M tone of oil/km2, 9.2 MMcm of gas/km2, 26.4 M tone of oil/km2, 2.2 MMcm of gas/km2, 6, 23 MMcm of gas/km2 respectively. Financed by the NCBR, Blue Gas (BG1/LUPZAS/13).