Assessment of hydrocarbon potential of Jurassic and Cretaceous source rocks in the Tarnogród-Stryi area (SE Poland and W Ukraine)

Abstract

Abstract:The Jurassic/Cretaceous stratigraphic complex forming a part of the sedimentary cover of both the eastern Małopolska Block and the adjacent Łysogóry-Radom Block in the Polish part as well as the Rava Rus'ka and the Kokhanivka Zones in the Ukrainian part of the basement of the Carpathian Foredeep were studied with geochemical methods in order to evaluate the possibility of hydrocarbon generation. In the Polish part of the study area, the Mesozoic strata were characterized on the basis of the analytical results of 121 core samples derived from 11 wells. The samples originated mostly from the Middle Jurassic and partly from the Lower/Upper Cretaceous strata. In the Ukrainian part of the study area the Mesozoic sequence was characterized by 348 core samples collected from 26 wells. The obtained geochemical results indicate that in both the south-eastern part of Poland and the western part of Ukraine the studied Jurassic/Cretaceous sedimentary complex reveals generally low hydrocarbon source-rock potential. The most favourable geochemical parameters: TOC up to 26 wt. % and genetic potential up to 39 mg/g of rock, were found in the Middle Jurassic strata. However, these high values are contradicted by the low hydrocarbon index (HI), usually below 100 mg HC/g TOC. Organic matter from the Middle Jurassic strata is of mixed type, dominated by gas-prone, Type III kerogen. In the Polish part of the study area, organic matter dispersed in these strata is generally immature (T max below 435 °C) whereas in the Ukrainian part maturity is sufficient for hydrocarbon generation.

Burial history, thermal history and hydrocarbon generation modelling of the Jurassic source rocks in the basement of the Polish Carpathian Foredeep and Outer Carpathians (SE Poland)

“…In the Mesozoic profile in the southeastern part of Poland only the Middle Jurassic strata show rock complexes that meet the quantitative criteria of source rocks (Kosakowski et al 2012b). The geochemical analysis performed in those strata revealed that the Triassic, Upper Jurassic and Cretaceous strata present generally very low TOC and hydrocarbon (S 1 +S 2 ) contents, and low thermal maturity of organic matter additionally reduced their source rock potential.…”

“…The organic matter is immature, or mature in the early phase of the "oil window". The maturity of kerogen increases towards to Outer Carpathians (Kosakowski et al 2012b). …”

“…The Middle Jurassic source rocks show much higher TOC and hydrocarbon contents up to 17.0 wt. % and 53.4 mg HC/g rock, respectively (Kosakowski et al 2012b). This potential is variable, but the maximum values indicate the presence of good and very good source rocks.…”

“…60 mW/m 2 in its western and central parts. The maturity modelling was calibrated with thermal maturity measurements, Rock-Eval T max temperature (Kosakowski et al 2012b) and vitrinite reflectance R o (Table 1). A significant incompleteness in the stratigraphic section in the study area makes it impossible to create one unique thermal-erosional model.…”

Genetic correlation of source rocks and natural gas in the Polish Outer Carpathians and Paleozoic–Mesozoic basement east of Kraków (southern Poland)

“…Al though the Up per Ju ras sic strata in the study area are lean in or ganic mat ter, in the Ukrai nian part of the Me so zoic base ment (Kosakowski et al, 2012b) and the Pol ish Low lands (Wiêc³aw, 2016) their hy dro car bon po ten tial is lo cally very high and the dom i nant oil-prone Type-II kerogen is ca pa ble of pe troleum gen er a tion. Wiêc³aw (2011) and Wiêc³aw et al (2012b) con sid ered them as most prob a bly the source rock of heavy oils ac cu mu lated in the Up per Ju ras sic car bon ate de pos its in the Pol ish-Ukrai nian bor der area (Lubaczów, Kokhanivka and Orchovichi de pos its).…”