Genetic correlation between source rocks and natural gas in the western part the Polish Outer Carpathians and Paleozoic-Mesozoic basement

Abstract

Geochemical characteristics (content, genetic type, maturity and petroleum potential) of organic matter in the profiles of Lower Cretaceous–Lower Miocene strata of the Dukla, Silesian and Sub-Silesian tectonic units of the Polish Outer Carpathians and Lower Devonian, Mississippian and Jurassic strata of Paleozoic-Mesozoic basement in the Kraków–Brzesko–Nowy Sacz area were established based on Rock-Eval, isotopic and biomarker analyses of 275 core samples. The Oligocene Menilite Shales have the highest organic carbon content in the Dukla Unit, up to 5.9 wt.%; however, the residual hydrocarbon potential is low. The TOC content in the Cretaceous Upper Cieszyn and Grodziszcze beds of the Sub-Silesian Unit is moderate and the residual hydrocarbon potential is low. The Oligocene Menilite Shales of the Silesian Unit have the best hydrocarbon potential of all formations in the study area. Upper Cretaceous-Paleocene Lgota, Godula and Istebna beds in the Silesian Unit have poor hydrocarbon potential. The Lower and Middle Devonian strata are lean in organic matter. The Upper Devonian strata, Mississippian carbonate facies and Middle Jurassic strata have the variable TOC content and residual hydrocarbon potential. The clastic facies of the Mississippian strata are statistically richer in TOC then carbonate facies. The Upper Jurassic strata are probably lean in organic matter. Seven natural gas samples from the Upper Cretaceous-Miocene sandstones of the Silesian and Dukla units and eight natural gas samples from the Mesozoic basement were collected and analysed for molecular and stable isotope compositions. Gaseous hydrocarbons accumulated both in the Silesian and Dukla units of the Outer Carpathians and their Paleozoic-Mesozoic basement are genetically related to thermogenic and microbial processes. Gases accumulated in the Dukla Unit were generated during both high-temperature and low-temperature thermogenic processes from mixed Type-II/III kerogen of the Menilite Shales. Methane from Dolszyce accumulations in the Oligocene-Lower Miocene Krosno and Upper Cretaceous-Paleocene Istebna Beds of the Silesian Unit and from the Upper Cretaceous sandstone reservoirs of the Brzezowiec gas field was generated during microbial carbon dioxide reduction process and migrated from the autochthonous Miocene strata of the Carpathian Foredeep, filling up the traps within the Outer Carpathians and Mesozoic basement strata, respectively. Other gases from the Upper Cretaceous sandstone and Upper Jurassic carbonate reservoirs of the Mesozoic basement are genetically related to thermogenic processes. The thermogenic gases were generated during both high-temperature and low-temperature thermogenic processes from the mixed Type-III/II kerogen from the Middle Jurassic source rocks. Moreover the thermogenic gases migrated from the Outer Carpathians and at least partly filling the traps within the Mesozoic basement. The research has been financially supported by the Polish Ministry of Science and High Education grant No. 5 T12B 017 25 and statutory research of the Faculty of Geology, Geophysics and Environmental Protection at the AGH University of Science and Technology (project No. 11.11.140.175).

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015