ALBERT

Description: As part of the Onshore Energy Systems Group’s program, organic maturation levels were determined using polar compounds from potential source rocks from the Georgina and Canning basins. The Early Paleozoic organic matter is devoid of the vitrinite maceral so unsuitable of the measurement of the industry-standard vitrinite reflectance (Ro%) measurement.

Description: The formation of viscous oil and tar mats in oilfield reservoirs has substantial consequences in the production of oil. For example, aquifer sweep can be precluded in such an occurrence, impacting field development planning. Several processes can give rise to accumulations of heavy ends in reservoirs, namely, the asphaltenes and other high-molecular-weight polar compounds. Multiple, incompatible charge fluids can enter a reservoir, causing instability, migration, accumulation, and phase separation of heavy ends. Two adjacent reservoirs in Norway evidently exhibit different stages of tar formation from incompatible charge: in one reservoir, asphaltenes deposit as a result of an excess asphaltene concentration, and in the second reservoir, asphaltenes deposit from solution gas expulsion. Here, ultrahigh-resolution mass spectrometry is used to analyze heavy ends from both reservoirs in crude oils and rock core chips. The heavy ends or asphaltenes in crude oils and associated core deposits from each reservoir are analyzed and shown to be compositionally very similar. In addition, the two crude oils are examined by two-dimensional gas chromatography, confirming that the hydrocarbon liquid-phase components closely resemble one another. Importantly, there are only subtle chemical differences between heavy ends that underwent phase separation in the reservoir versus heavy ends that remained in the crude oil, a result that is consistent with heavy end chemical speciation and solvation characteristics. The combination of thermodynamic and compositional considerations proves to be very effective in elucidation of reservoir fluid geodynamic processes that have a significant impact on oil production.

Description: We have recently shown that molecular hydrogen generation from organic matter occurs at high maturity levels (vitrinite reflectance 3–5%) in Lower Cretaceous shales of the Songliao Basin. To evaluate and extend these implications to a wider range of source rock types and organofacies, we report on two Paleozoic maturity suites from Australia, namely the Permian Patchawarra Formation (fluviodeltaic; Type-III; Cooper Basin) and the middle Cambrian Arthur Creek Formation (marine; Type-II; Georgina Basin), and additional mature marine source rocks from Europe and the USA. It can be inferred from high resolution mass spectrometry that rapid growth of aromatic ring systems is the major pathway for the formation of thermogenic molecular hydrogen from all organic matter types. Extensive open system pyrolysis experiments indicate that the main generation pulse occurs in the vitrinite reflectance range 3.5–5.0%. Kinetic parameters were constructed by subtracting the hydrogen associated with hydrocarbon formation from total hydrogen in the open-system experiments via adjustment factors defined by the relative yields of CH4 and H2. A cumulative H2 potential of 20 mg/g TOC is found with maximum rates of generation that are sufficient for feeding the deep biosphere. Back of the envelope calculations indicate ∼3.5E+10 tonnes of in-place accessible H2 globally, which is an order of magnitude lower than in-place shale gas resource estimates. Regionally, inferred here for the Patchawarra Formation in the Nappamerri Trough (Cooper Basin), yields per unit rock volume resemble those of economic shale gas in the Barnett Shale, Fort Worth Basin, USA. Organic particles are, at the SEM-scale (〉30 nm), barren of secondary porosity in the case of terrigenous samples at all maturity stages, but show sponge-like porosity in the investigated marine source rocks exhibiting vitrinite reflectance 〉∼2.0%. Presence of such meso- and macropores is crucial for H2 storage in marine shales, as microporosity (〈2 nm) yielding sorptive storage space for H2, is usually much higher in mature terrigenous kerogens.

Description: The oil-bearing fluid inclusions (FIs) in reservoir sandstones in the Skarv field in the Haltenbanken region offshore Norway recorded a complex oil charge and leakage history. Inclusion oils, hosted in quartz cements, and corresponding adsorbed residual oils on mineral surfaces from the Jurassic Garn and Tilje Formation (Fm) sandstones have been investigated using coupled gas chromatography-mass spectrometry, coupled gas chromatography-isotope ratio mass spectrometry and, as a new technique for FI oil analysis, Fourier transform-ion cyclotron resonance-mass spectrometry. The biomarker, stable carbon isotope and nitrogen, sulfur and oxygen-containing compound results suggest that FI oils from both the Garn and Tilje Fms and adsorbed (Ad) oil from the Tilje Fm were derived from the same source, whereas Ad oil from the Garn Fm shows a lower maturity level and differences in facies indicators. The similar geochemical signals for the FI oils from the Garn and Tilje Fms point to a first charge from the same source rock i.e. the late-Jurassic/earliest-Cretaceous Spekk Fm (Oxfordian to Ryazanian age). The fact that the Ad oil in the Tilje Fm is also similar to the respective FI oil indicates that the Tilje Fm was charged only once. In contrast, differences between the FI and Ad oils in the Garn Fm suggest that first charged oil has leaked and was replenished by a later charge sourced from a spatially different and less mature kitchen area of the Spekk Fm.

Description: The origins of hydrocarbons occurring in oil-bearing fluid inclusions (FIs) have been studied in detail over the last four decades, but very little is known about co-occurring nitrogen, sulfur and oxygen (NSO)-containing compounds. Here, we outline a new method for gathering valuable information on NSO-compounds using the Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS) in combination with Atmospheric Pressure Photoionization in positive ion mode (APPI (+)) and Electrospray Ionization in negative ion mode (ESI (−)). A key element was to develop a rigorous acid-free cleaning protocol to make oil inclusions from a broad range of host materials accessible to the very sensitive FT-ICR-MS technique. Although oil contamination from surrounding organic matter could not be entirely eliminated, the procedure enables distinction of external contaminants and identification of affected NSO-compound classes allowing a conditional interpretation of the FT-results of FI samples, especially for compounds measured in the APPI (+) mode. First insights into the high molecular weight hydrocarbons and NSO-compounds in FI oils are presented here using examples from Germany, Tunisia, Pakistan and Mexico.