ALBERT

Description: The 3D basin modelling of the Southwestern Barents Sea was planned with the aim of addressing the masses of petroleum generated, migrated, accumulated and lost during the basin evolution. The first model was constructed for the Hammerfest Basin considering three source rocks, which correspond to the Upper Jurassic Hekkingen Formation and the Triassic Snadd and Kobbe formations. The highest maturities for the three source rocks were reached in the western and northwestern margin of the basin. The model reproduced satisfactorily the hydrocarbon phases and distribution of the main fields and discoveries. Two events of petroleum re-distribution occurred in the basin: the first corresponds to the oil re-distribution (during the Oligocene–Miocene); the second corresponds to the gas leakage (during the Pliocene–Pleistocene) in connection to the glacial–interglacial cycles. At least 0.247 Gt of thermogenic gas leaked from the main reservoir and reached the sediment interface. The analysis of the volumetric proportions of oil and gas contributions to each field and discovery, suggest that the gas contribution stems mainly from Triassic source rocks, while the oil phases contain variable proportions from both the Jurassic Hekkingen Formation and the Triassic source rocks. Available fluid geochemical data from the main fields in the Hammerfest Basin allowed testing these results. The interpretation of gas isotopes and maturity related biomarker ratios confirms the maturity trends derived from basin modelling; and light hydrocarbons indicate the influence of secondary processes. However, age related biomarker ratios did not provide a clear separation when evaluating a contribution from Jurassic versus Triassic source rocks. The 3D basin modelling was extended to include the Loppa High as well as some other important frontier exploration areas; taking into account the same source rocks. Calibrated model predictions indicate that the three source rocks are overmature in the western margin and also have high maturities in the deepest parts of the Maud Basin to the east. However, in the Bjarmeland platform, only the Triassic source rocks have entered the oil window. Recent generation has been observed in the eastern part around the Bjarmeland Platform and generative potential is still available at present–day. The timing of generation in the western part is different in comparison to the east, with the Kobbe Formation starting to generate during the Late Triassic–Early Jurassic, the Snadd Formation during Late Jurassic–Early Cretaceous and the Hekkingen Formation during Middle Cretaceous. The three source rocks do not have any generative potential left; therefore, it is necessary to rely on younger source rocks. Additional results indicate that the main drainage directions do not change drastically during the evolution of the area, not even during the glacial–interglacial cycles. The model output shows changes in the sizes of the relative oil versus gas quantities in the modelled accumulations during the glacial cycles.

Description: In March 2010, the project CoCoCo (incipient COntinent-COntinent COllision) recorded a 650 km long amphibian N-S wide-angle seismic profile, extending from the Eratosthenes Seamount (ESM) across Cyprus and southern Turkey to the Anatolian plateau. The aim of the project is to reveal the impact of the transition from subduction to continent-continent collision of the African plate with the Cyprus-Anatolian plate. A visual quality check, frequency analysis and filtering were applied to the seismic data and reveal a good data quality. Subsequent first break picking, finite-differences ray tracing and inversion of the offshore wide-angle data leads to a first-arrival tomographic model. This model reveals (1) P-wave velocities lower than 6.5 km/s in the crust, (2) a variable crustal thickness of about 28 - 37 km and (3) an upper crustal reflection at 5 km depth beneath the ESM. Two land shots on Turkey, also recorded on Cyprus, airgun shots south of Cyprus and geological and previous seismic investigations provide the information to derive a layered velocity model beneath the Anatolian plateau and for the ophiolite complex on Cyprus. The analysis of the reflections provides evidence for a north-dipping plate subducting beneath Cyprus. The main features of this layered velocity model are (1) an upper and lower crust with large lateral changes of the velocity structure and thickness, (2) a Moho depth of about 38 - 45 km beneath the Anatolian plateau, (3) a shallow north-dipping subducting plate below Cyprus with an increasing dip and (4) a typical ophiolite sequence on Cyprus with a total thickness of about 12 km. The offshore-onshore seismic data complete and improve the information about the velocity structure beneath Cyprus and the deeper part of the offshore tomographic model. Thus, the wide-angle seismic data provide detailed insights into the 2-D geometry and velocity structures of the uplifted and overriding Cyprus-Anatolian plate. Subsequent gravity modelling confirms and extends the crustal P-wave velocity model. The deeper part of the subducting plate is constrained by the gravity data and has a dip angle of ~ 28°. Finally, an integrated analysis of the geophysical and geological information allows a comprehensive interpretation of the crustal structure related to the collision process.

Description: The Barents Sea is a frontier for hydrocarbon exploration where activity has been renewed after recent oil discoveries. However, previously this province has been dominated by gas finds, with the largest discoveries being Snøhvit, Albatross and Askeladd gas fields, located in the Hammerfest Basin. Cenozoic erosion and high latitude Quaternary glaciations are thought to have driven the hydrocarbons out of the traps and contribute thus to the lack of significant oil discoveries. Hydrocarbon leakage is a widespread phenomenon and has significant impact on climate, marine ecosystem, geotechnical installations and petroleum exploration. In this study, we aim to elucidate the impact of Cenozoic erosion and Pliocene-Pleistocene glaciations on the dynamics of hydrocarbon leakage from the thermogenic reservoirs. We use high resolution and vintage 3D seismic reflection datasets to analyse hydrocarbon plumbing system above the Snøhvit and Albatross gas fields to investigate the geo-morphological manifestation and the dynamics of leakage from the reservoir. We then use 3D Petroleum Systems Modelling (PSM) to simulate the basin history in terms of generation, migration and leakage of hydrocarbons through time in response to erosion, glacial loading and deglaciations. Based on this integrated approach, we then are able to compare numerical modelling results with seismically observed leakage indicators. Numerous EW trending reactivated faults are present in the study area which link the Jurassic hydrocarbon reservoirs of the Snøhvit and Albatross field with the shallow Paleocene strata. Reactivation of polygonal fault networks has formed an interconnected network of Paleocene faults, which served as migration avenues for thermogenic fluids in the vicinity of deep reactivated tectonic faults. Numerous pockmarks and mega pockmarks on the seabed and buried pockmarks on the base Quaternary Upper Regional Unconformity (URU) provide evidence of migration pathways as they are connected to seismic blow out pipes, Paleocene fault networks and deep reactivated tectonic faults. A gas cloud anomaly has been interpreted as a Bottom Simulating Reflector (BSR), whose depth coincides with the estimated base of the hydrate stability field for a thermogenically-derived gas hydrate with around 90 mol % methane. At least two fluid venting episodes have been inferred based on seabed and URU pockmark distributions, following the Last Glacial Maximum ~17-16 ka and prior to the Late Weichselian, older than ~0.7 Ma. Results of the 3D PSM modelling show that hydrocarbon leakage from the Jurassic reservoirs takes place through faults during each deglaciation, with most of accumulated mass lost (60-80 %) during the first instance of fault dilation. Subsequent leakage during deglaciations results in a sequential loss of remaining accumulated mass in the Snøhvit reservoir. The first modeled leakage event (0.8-0.78 Ma) coincides with a major fluid escape event at the time of a major regional unconformity (URU older than ~0.7Ma), and is in agreement with shallow subsurface hydrocarbon leakage indicators such as pockmarks, shallow gas clouds and blow out pipes observed in the seismic data analysis.

Description: We study segregation of the subducted oceanic crust (OC) at the core mantle boundary and its ability to accumulate and form large thermochemical piles (such as the seismically observed Large Low Shear Velocity Provinces - LLSVPs). Our high-resolution numerical simulations suggest that the longevity of LLSVPs for up to three billion years, and possibly longer, can be ensured by a balance in the rate of segregation of high-density OC-material to the CMB, and the rate of its entrainment away from the CMB by mantle upwellings. For a range of parameters tested in this study, a large-scale compositional anomaly forms at the CMB, similar in shape and size to the LLSVPs. Neutrally buoyant thermochemical piles formed by mechanical stirring - where thermally induced negative density anomaly is balanced by the presence of a fraction of dense anomalous material - best resemble the geometry of LLSVPs. Such neutrally buoyant piles tend to emerge and survive for at least 3Gyr in simulations with quite different parameters. We conclude that for a plausible range of values of density anomaly of OC material in the lower mantle - it is likely that it segregates to the CMB, gets mechanically mixed with the ambient material, and forms neutrally buoyant large scale compositional anomalies similar in shape to the LLSVPs. We have developed an efficient FEM code with dynamically adaptive time and space resolution, and marker-in-cell methodology. This enabled us to model thermochemical mantle convection at realistically high convective vigor, strong thermally induced viscosity variations, and long term evolution of compositional fields.

Description: Assumed comparable environmental conditions of early Mars and early Earth in 3.7 Ga ago – at a time when first fossil records of life on Earth could be found – suggest the possibility of life emerging on both planets in parallel. As conditions changed, the hypothetical life on Mars either became extinct or was able to adapt and might still exist in biological niches. The controversial discussed detection of methane on Mars led to the assumption, that it must have a recent origin – either abiotic through active volcanism or chemical processes, or through biogenic production. Spatial and seasonal variations in the detected methane concentrations and correlations between the presence of water vapor and geological features such as subsurface hydrogen, which are occurring together with locally increased detected concentrations of methane, gave fuel to the hypothesis of a possible biological source of the methane on Mars. Therefore the phylogenetically old methanogenic archaea, which have evolved under early Earth conditions, are often used as model-organisms in astrobiological studies to investigate the potential of life to exist in possible extraterrestrial habitats on our neighboring planet. In this thesis methanogenic archaea originating from two extreme environments on Earth were investigated to test their ability to be active under simulated Mars analog conditions. These extreme environments – the Siberian permafrost-affected soil and the chemoautotrophically based terrestrial ecosystem of Movile cave, Romania – are regarded as analogs for possible Martian (subsurface) habitats. Two novel species of methanogenic archaea isolated from these environments were described within the frame of this thesis. It could be shown that concentrations up to 1 wt% of Mars regolith analogs added to the growth media had a positive influence on the methane production rates of the tested methanogenic archaea, whereas higher concentrations resulted in decreasing rates. Nevertheless it was possible for the organisms to metabolize when incubated on water-saturated soil matrixes made of Mars regolith analogs without any additional nutrients. Long-term desiccation resistance of more than 400 days was proven with reincubation and indirect counting of viable cells through a combined treatment with propidium monoazide (to inactivate DNA of destroyed cells) and quantitative PCR. Phyllosilicate rich regolith analogs seem to be the best soil mixtures for the tested methanogenic archaea to be active under Mars analog conditions. Furthermore, in a simulation chamber experiment the activity of the permafrost methanogen strain Methanosarcina soligelidi SMA-21 under Mars subsurface analog conditions could be proven. Through real-time wavelength modulation spectroscopy measurements the increase in the methane concentration at temperatures down to -5 °C could be detected. The results presented in this thesis contribute to the understanding of the activity potential of methanogenic archaea under Mars analog conditions and therefore provide insights to the possible habitability of present-day Mars (near) subsurface environments. Thus, it contributes also to the data interpretation of future life detection missions on that planet. For example the ExoMars mission of the European Space Agency (ESA) and Roscosmos which is planned to be launched in 2018 and is aiming to drill in the Martian subsurface.