Organic Matter Thermal Maturity Versus Variability of the Present-Day Thermal Gradient of the Eastern Part of Polish Outer Carpathians—The Key to the Success or Failure of Hydrocarbon Generation Processes

Abstract

This study presents an integrated analysis of organic matter (OM) maturity proxies, including Rock-Eval pyrolysis, vitrinite reflectance, and the spore color standard (SCS), in conjunction with a pre-existing 3D numerical model of the present-day temperature field. Our research, focused on the eastern Polish Outer Carpathians, aimed to unravel the potential distribution of the mature source rocks in the region. Specifically, we sought to verify the timing of maturation (pre- or post-orogenic), delineate extensively uplifted areas, assess the role of the current thermal structure in catagenesis, and understand the origin of thermal anomalies. The 3D thermal model, derived from over 500 well thermal logs, was re-evaluated using isotherm depth maps (80°C, 130°C, and 160°C) to characterize catagenesis stages. The SCS method was introduced as a robust and cost-effective tool for OM maturity determination, offering the unique advantage of tracing multi-sourcing and redeposition. Our findings reveal relatively low maturity in the Silesian and Skole Units, generally mirroring the present-day thermal field. We infer that the mature source rocks responsible for existing hydrocarbon accumulations are likely situated deeper, beneath the basal thrust of the topmost nappes. Localized “hot spots” in the present-day thermal gradient, coinciding with anomalously high OM maturity, indicate irregular heat transfer within the study area. A prominent high heat-flow zone in the southeastern Silesian and Dukla Units (Bieszczady and Bystre Subunit areas) may be linked to significant tectonic uplift or a deep-seated heat source, potentially of magmatic origin. This analysis demonstrates that understanding present-day thermal gradient irregularities can effectively highlight regions of elevated paleotemperatures, indicative of mature source rocks. The presented integration of diverse methods offers a powerful approach for enhanced source rock maturity assessment, benefiting the Carpathian petroleum industry.