Oil charge and biodegradation history in an exhumed fractured reservoir, Devonian, UK

Abstract

The distribution of oil residues in fractured Upper Devonian reservoir sandstones of Caithness help us to understand relationships between oil charge and episodes of fracturing. The sandstones are cut by an extensive set of tightly cemented deformation bands in the vicinity of the Brough Fault, and calcite-mineralized open fractures. The deformation bands compartmentalized the reservoir, which subsequently was charged by oil to varying extent in different compartments. Petrographic and biomarker data distinguish two charges of oil. The first charge of oil was unaltered. The later mineralized fractures introduced a heavier biodegraded oil that spread into the sandstone pores and displaced/overprinted the earlier oil. Two distinct oil charges are also evident from two generations of oil fluid inclusions, firstly in overgrowths on quartz grains, and secondly in the calcite veins, exhibiting distinct fluorescence characteristics. Migration and trapping of oil depended on the combination of two fracturing episodes of different character, in which the first episode created sealed compartments which were then filled by oil introduced by the second episode.

Copper, Uranium and REE Mineralisation in an Exhumed Oil Reservoir, Southwest Orkney, Scotland

“…Mineralisation was, therefore, complete before the uplift event during the end-Carboniferous to early Permian Hercynian Orogeny. Burial history reconstructions [3,33,78] show that oil had been generated during the latest Devonian-early Carboniferous, so are consistent with the later exhumation and biodegradation of oil reservoirs in the Orcadian Basin during the uplift event [79,80].…”

The application of surface enhanced Raman scattering to the detection of asphaltic petroleum in sediment extracts: deconvolving three component-mixtures using look-up tables of entire surface enhanced Raman spectra

“…13,14 This is consistent with previous work describing the presence of petroleum source rocks and oil-baring sandstones at Brough. 19 The ion chromatograms (Fig. 3b) also contain a well-resolved homologous series of hopanes with structural congurations typically found in oil (e.g.…”

“…Under subsurface conditions, were the oil within the sandstone saturated with gas, it would be considered analogous to a petroleum reservoir. 19 At surface conditions this is not the case and the petroleum is never a free-owing liquid phase (even during summer), instead it is a solid phase within the sandstone or bound to the surfaces of sand formed from the weathering of the petroleum impregnated sandstone. For all samples, from the perspective of a SERS-assay, a number of analytical interferences are naturally present; endoliths within the sandstone (visible as green and purple colouration beneath the surface of the sandstones, Fig.…”

Insight into Polycyclic Aromatic Hydrocarbons in Unconventional Oil via Concentration-Resolved Fluorescence Spectroscopy Coupled with Data Mining Techniques

“…Given the current analytical condition, the chemical composition of the unconditional oil is still not well-understood and requires comprehensive and in-depth investigation. Gas chromatography–flame ionization detector (GC–FID) and gas chromatography–mass spectrometry (GC–MS) are widely used tools for routine oil analysis, such as oil exploring and refining, forensic oil spill identification, and their environmental fate and behavior. − However, the previous techniques mainly focusing on hydrocarbon components with good separation property now encounter bottlenecks because of their limited peak capability and the low-resolution ratio of the heavy components of unconventional oil. The baseline of gas chromatography is often elevated to form a hump of unresolved complex mixtures (UCMs), which makes many biomarkers concealed and unable to be detected …”