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The New Opportunity of Gas Exploration From Tight Mudstone and Shale Dominated Sequences in Miocene, Carpathian Foredeep, Poland


The Polish Carpathian Foredeep (CFD) is a part of the large sedimentary basin that stretches from Vienna (Austria) to the Iron Gate (Romania) on a distance ~1300 km. CFD is an asymmetric basin, filled with mainly clastic sediments of the Miocene age, thickness of which in Poland is up to 3000 m. The CDF is an important gas province of Poland. Gas accumulated here is of biogenic origin. Its production started in 1959, and reached totally 100 ×109 m3 from conventional fields exclusively, recently mostly depleted. Lack of new discoveries and decreasing production, accompanied with very common gas shows in mudstones lead to the new prospection concept. During last years exploration was focused on massive mudstone and shale dominated complexes, underlying conventional gas fields. Preliminary generation modelling allowed to estimate yet to find resources of gas as ~150 ×109 m3. Currently Siedleczka and Kramarzówka gas fields were discovered (recoverable resources ~1.8 ×109 m3 and ~1.3 ×109 m3, respectively). The fields are producing commercially gas from > 100 m thick, almost impermeable mudstone – shale interval, comprising very scarce and thin sandstone layers, which could be classified as tight or hybrid reservoir. To improve the knowledge of this unconventional hydrocarbon system, and to indicate next prospects location the new project was lunched comprising among others detailed 3D geomodelling of the wide area (~4500 km2) of CFD, located along Carpathian front. It is based on structural analysis, as well as seismic and well log data interpretation. The model comprise 5 complexes: - Lower Badenian clastics, -Badenian evaporates, - fine grained deposits; -turbiditic sequences; - deltaic sequences and their overburden (Upper Badenian and Sarmatian). This is the framework of the generalized regional, generation and migration 3D model, as well as of the local detailed models. The latter will restore precisely sedimentological and petrophysical characteristics of the Miocene sequences, in particular fine grained and turbiditic series. The models aim to visualize spatial variability of unconventional reservoir, gas saturation patterns, and to perform some dynamic simulations, including testing of fracking effectiveness or simulation of production from horizontal interval. Financed by research program NCBR Blue Gas (BG2/ShaleFore/14).