Abstract
The objective of this paper is to evaluate the relationship between the distributions of direct and indirect, surface geochemical indices in the selected part of the Outer Carpathians. The research included analysis of molecular composition of soil gas samples and calcite contents as well as the measurements of magnetic susceptibility and pH of soil samples. The survey contained 96 soil gas samples collected from 1.2 m depth and 96 soil samples taken from interval 0.7–0.8 m depth. The maximum concentrations of methane, total alkanes C2–C5 and total alkenes C2–C4 were: 2100, 10.43 and 0.772 ppm. The magnetic susceptibility values changed from 3.6 to 21.5 x 10–8 m3/kg. The calcium carbonate contents varied from 0.02 to 29.92 wt% and the pH values measured in soil solutions obtained changed from 4.5 to 8.3. Although the results demonstrate no correlation between the direct soil gas anomalies and the indirect geochemical indicators, the integrated profiles in Fig. 7 suggest possible haloes in the calcite/magnetic data that could be related to hydrocarbons migrating from depth. There are, however, various independent mechanisms that might control the appearance of these mineral anomalies. Secondary changes of mineral composition of soils disclosed by the indirect methods, even if controlled by hydrocarbon migration throughout geological time, might cause some closure of migration pathways, influencing the location of active hydrocarbon migration pathways. Comprehensive interpretation of the results obtained by direct and indirect methods in this paper provides another positive example helping to better understand the complicated mechanism of hydrocarbon migration and the potential usefulness of indirect methods suitable for hydrocarbon exploration.
Highlights
Many world petroleum provinces, which host conventional petroleum deposits, reveal much higher hydrocarbon potential confirmed by the discovery and the assessment of unconventional deposits: shale gas, shale oil, tight gas and tight oil (Boyer et al 2011; Zou 2013; U.S EIA 2019)
According to Kozimor et al (2017), such accumulations may occur, among others, in the Carpathian Foredeep and in the Outer Carpathians belonging to the Małopolska Petroleum Province of southern Poland (Karnkowski 2007)
That is why the Polish part of the Outer Carpathians is still regarded as a promising target of petroleum exploration, despite its 150-year-long history of discovery and exploitation of hydrocarbon deposits (Kuśmierek 1990; Dziadzio et al 2006; Pawlewicz 2006; Ślączka et al 2006; Karnkowski 2007)
Summary
Many world petroleum provinces, which host conventional petroleum deposits, reveal much higher hydrocarbon potential confirmed by the discovery and the assessment of unconventional deposits: shale gas, shale oil, tight gas and tight oil (Boyer et al 2011; Zou 2013; U.S EIA 2019). A significant potential may be provided by so-called “hybrid” hydrocarbon accumulations. These objects integrate the features of both the conventional and the unconventional plays (Kozimor et al 2017). According to Kozimor et al (2017), such accumulations may occur, among others, in the Carpathian Foredeep and in the Outer Carpathians belonging to the Małopolska Petroleum Province of southern Poland (Karnkowski 2007). That is why the Polish part of the Outer Carpathians is still regarded as a promising target of petroleum exploration, despite its 150-year-long history of discovery and exploitation of hydrocarbon deposits (Kuśmierek 1990; Dziadzio et al 2006; Pawlewicz 2006; Ślączka et al 2006; Karnkowski 2007). Still improving, this method shows limitations due to insufficient quality of seismic records caused by fold-and-thrust structure of the Carpathian orogenic belt (Roure et al 1993; Pawlewicz 2006; Kuśmierek 2010; Kuśmierek and Baran 2016; Kováč et al. Vol.:(0123456789)
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