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3-D geological model of Jurassic deposits from the Lublin Basin, E Poland

JURASSICA XII 4th IGCP 632 meeting and Workshop of the ICS Berriasian Working Group April 19th-23rd, 2016, Smolenice Castle, Slovakia
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The 3D geological model of Jurassic deposits from the Lublin Basin is a part of the 3D model of the region comprising the geological profile from Ediakarian to Quaternary. The model has been recently constructed in the Polish Geological Institute – NRI as a part of the program of sedimentary basins modelling by a team consisting of regional geologists, geophysicists and experts in modeling. Mapped regional structure covers the area of 260x80 km located between Warsaw and Polish-Ukrainian border, along NW–SEtrending margin of the East European Craton. Within the basin, the Paleozoic beds with coalbearing Carboniferous and older formations containing hydrocarbons and unconventional prospects are covered unconformably by Permo-Mesozoic and younger rocks. Vertical extent of the regional model is set from topographic surface to -6000 m ssl and at the bottom includes some Proterozoic crystalline formations of the craton. The project focuses on internal consistency of the models in different scales – from basin (small) scaleto field-scale (large-scale). The models, nested in the common structural framework, are being built with regional geological knowledge, ensuring smooth transition in the 3D model resolution and amount of geological detail. Modeled Jurassic strata reaches 700 m of thickness in the western part of area. Overmost of the area, they overlie the Palaeozoic (Carboniferous, Devonian) and are covered by the  Upper Cretaceous.The first stage of the modelling process was a data integration and an update of the database with geological information derived from boreholes and geophysical interpretation. Structural modelling of top and base of Jurassic was based on 2D seismic interpretation and data from 420 wells. Internal stratification of the units was modeled with borehole data only. In order to make the detailed Jurassic model, data inspection and verification was done for selected 163 wells, of which 155 included Jurassic deposits. The parameters that were used to build the model comprised stratigraphy, well picks of layers, lithology and depositional environment interpretation. For most well profiles we used chronostratigraphic record from the Boreholes section of the Central Geological Database ( Borehole data and geophysical logs permitted to correlate tops and bases of Lower, Middle and Upper Jurassic deposits. Additionally, formal lithostratigraphic units (Formations) of Lower and Upper Jurassic were distinguished. In 56 boreholes, units from CBDG database were used and in 99 boreholes, formations were identified on the basis of geophysical logs and description of the cores contained in archival record. Also, thickness of individual lithological types – based on data from geophysical log interpretation and core descriptions and cutting samples from all 155 boreholes – were included in the model. Joint analysis of all available literature data and own research and observations permitted to interpret depositional environments and connect them to litho and chronostratigraphic units in individual wells. Data relating to porosity and permeability of Jurassic deposits, derived from the analysis of core and geophysical logs, were also included in the model database. Structural arrangement of the Lublin basin has been analyzed on about 1000 2-D seismic lines, where selected seismic horizons have been traced in the entire depth of the model. For Jurassic the depth and geometry of the top and base as well as the presence and shape of faults displacements were interpreted from the seismic. Thus, top and bottom of Jurassic as well as internal horizons were characterized in much greater detail than would be possible with borehole data alone. Final model was based on the geological conceptual outlines of the Lublin Basin, well data, well logs and seismic data interpretations, calibrated to model resolution and spatial extension and corrected for known depositional features, hiatuses etc. It shows spatial distribution of the chrono- and lithostratigraphic units, depositional environments, lithofacies and petrophysical parameters. Lithofacies model of the Upper Jurassic was built in three steps from the most general to the most detailed. First, the lithostratigraphy was modeled in chronostratigraphic framework. The chronostratigraphic domain was discretized in the gird of 250x250 m horizontal dimension. Vertically the grid is discretized accordingly to total unit thickness and generally grid layers do not exceed 10 m. The resulting grid was used to model depositional environments and finally lithofacies were modeled. The model can be used to predict and communicate the lithology and other attributes of sedimentary rocks at any point or at any line section. It may help to observe changes of structural and thickness trends of formations and to determine the anticipated depositional environments and petrophysical properties in the profile of the Jurassic. Detailed structural characteristics of the layers in the entire model above and below Jurassic show trends of subsidence, what allows identifying zones with possible synsedimentary active faults. The model was created as a future multidimensional platform for common research and studies related to sedimentary rocks attributes and petrophysical properties. Its generalized image will be presented in the web application available to public and detailed version will be available on demand with dedicated 3D viewer application.

The Project was financed by NFOŚiZN no 22-2209-1201-00-1.