Abstract
The petroleum generation potential of Upper Jurassic to Lower Cretaceous organic rich shales from the southwestern Barents Sea was evaluated using bulk and quantitative pyrolysis analysis. Fifteen thermally-immature samples from the Hekkingen Formation with differing organic facies, as defined by maceral composition, were subjected to total organic carbon, Rock-Eval pyrolysis, pyrolysis gas chromatography, bulk kinetics, and micro-scale sealed vessel pyrolysis analyses. The results were employed to characterize differences in source rock kerogens, gross petroleum type, and the compositional evolution of the generated fluids as well as their physical properties (i.e. gas to oil ratio, saturation pressure, and formation volume factor) as a function of increasing maturity.The investigated samples contain varying proportions of kerogen type II and III. Heterogeneities in the kerogen composition result in different orders of thermal stability, with the onset of petroleum generation predicted to occur over a high and broad temperature range from 123 °C to 144 °C (at 3.3C⁰/Ma). Reduced kerogen stability associated with elevated sulfur contents is only documented in a few samples. Most of the analyzed samples have the potential to generate low GOR oils of an intermediate to aromatic, low wax paraffinic-naphthenic-aromatic (P–N-A) composition and variable amounts of wet gas. Petroleums of similar compositional and physical properties are predicted to have been generated from the natural maturation sequence of various organic facies in thermally mature areas of the Hammerfest Basin and the Ringvassøy-Loppa High and Bjørnøyrenna fault complexes. Vitrinite-rich sources in the Fingerdjupet Sub-basin and the Troms-Finnmark Fault Complex have potential for gas and condensate generation.
Highlights
The Norwegian Barents Sea hosts various petroleum source rock intervals ranging in age from Carboniferous to Early Cretaceous (Hen riksen et al, 2011a; Ohm et al, 2008; Abay et al, 2017)
The Total organic carbon (TOC) contents of the fifteen source rock samples selected for artificial maturation experiments range from 2.2 to 23 wt% with Hydrogen indices (HI) values in the range of 115–378 mg HC/g TOC (Table 1)
High HI values are mostly associated with elevated TOC contents, while comparatively lower HI values correspond to low TOC contents (Fig. 3A)
Summary
The Norwegian Barents Sea hosts various petroleum source rock intervals ranging in age from Carboniferous to Early Cretaceous (Hen riksen et al, 2011a; Ohm et al, 2008; Abay et al, 2017). The clastic rocks of the Upper Jurassic Hekkingen Formation constitute the most widespread and one of the most prolific sourcing intervals These extended deposits are records of a Late Jurassic epicontinental sea inundating vast areas of the western Barents Shelf (Fig. 1). Geochemical characterization of oils in the southwestern Barents Sea has been conducted by Ohm et al (2008), Duran et al (2013a), Killops et al (2014), Murillo et al (2016) and Lerch et al (2016). Non-isothermal open-system pyrolysis is used for modeling bulk kinetic parameters of primary petroleum generation from fifteen samples cho sen to capture the variability in organic facies, as defined by maceral compositions, within the Hekkingen Formation. The results of this study can be readily implemented in basin and petroleum system studies of the Barents Sea and other basins alike
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