Triassic and Jurassic sediments from two cores in the Nordkapp Basin, Barents Sea, were analyzed by sedimentological, petrographic, SEM and XRD methods. The objective of the study was to gain better understanding of the depositional environments of the Upper Triassic-Jurassic, Snadd-, Fruholmen- and Stø formations with emphasis a mineralogical shift in the transition between the Snadd and Fruholmen formations, and try to relate the differences to depositional environment, climatic changes and diagenesis.The studied sediments of the Snadd and Fruholmen formations represent a transition from tidal flat, shoreline and inner shelf deposits. And the Stø Formation mainly represents inner shelf deposits, with exception of some fluvial deposits due to a local variation in one of the cores. The deposits represent an overall transgressive trend.The diagenetic processes differ in the three formations due to dissimilar depositional environment. In the Snadd Formation rhizocretions have been observed in combination with rootlets,and high levels of iron and manganese indicate influence by fresh-water. XRD analyses of mudstones showed no great compositional differences the Snadd and Fruholmen formations supporting observations from sandstone compositions of similar provenance and environment above and below the formation boundary.The largest compositional variation is seen between the Fruholmen and Stø formations, this is in accordance with other studies conducted in the Nordkapp Basin. The distinct increase in maturity may be due to extensive reworking connected with a regional transgression and sea-level rise.

A palaeodepositional model and an analysis of the diagenetic evolution of the Upper Triassic Snadd Formation in the Barents Sea are here presented. Attention has especially been given to the pedogenic structures dominating the sediments. The interpretations are based on core logging and thin section analyses including three shallow, stratigraphic wells from the south- western Barents Sea area. The data from the Nordkapp Basin represent a sediment succession of only a few meter thicknesses, and the main interpretation is therefore based on data from the Bjarmeland Platform core, which covers the upper 108.9 m of the Snadd Formation of Carnian to Norian age. Sandstones are mineralogical immature, fine- grained lithic arenites. Main carbonate cements include siderite, calcite and ankerite. Iron carbonates formed early in the diagenetic evolution and a progressive decrease in the Fe- content of the system with time has been evidenced. Kaolinite is a dominating, early diagenetic mineral, and indicates an overall humid climate. Regional interpretations of the Upper Triassic palaeoclimate, are that there was a switch from arid to humid on the Triassic- Jurassic border, and this goes well with the observations made in this study. Alternating sand and mud layers dominate the Upper Triassic strata and are suggested to represent deltaic sequences formed as a consequence of autocyclic switching of lobes on the delta plain. Sedimentary structures indicate a tidally influenced environment, while thin coal deposits and abundance of root structures indicate a transitional to continental setting. In the Bjarmeland Platform core there is a switch from coarsening upward units dominated by tidal structures in the lower portions to dominantly fining upward units with rooted horizons and lack of tidal influence in the upper portion, suggesting a transition from lower delta plain to mid/upper delta plain. The Nordkapp Basin cores bear resemblance to the upper portion of the Bjarmeland Platform succession and a similar setting has been interpreted for these deposits. The depostional model correlates well with former interpretations of a large- scale delta system prograding in a westward direction in Late Triassic. Mottled sediments clearly modified by pedogenic processes are found inbetween smaller fining upward or coarsening upward sand units. The interpreted delta plain environment is a favourable setting for pedogenesis and several micro-textures e.g. carbonate-coated grains, alveolar textures, circumgranular cracking and Microcodium have been identified in the polarization microscope. Coal beds are often associated with dark grey to black carbonaceous mudrocks reflecting high water table and reducing conditions during pedogenesis. The alternations between oxidized ferruginous palaeosols with carbonate concretions and carbonaceous palaeosols most likely reflects variation in ground-water level, caused by avulsion of channels on the delta plain. Oxidized palaeosols probably formed during low-water table while carbonaceous palaeosols were formed during high ground-water table perhaps in small pools on the delta plain. The well- preserved soil profiles indicate subaerial exposure for a sufficient period of time, followed by lack of subsequent erosion. Extensive carbonate cementation at an early stage has probably enhanced the preservation of the soils.

This master thesis presents a hierarchical modelling workflow in a slope canyon of the turbidite sandstone reservoir in the Formation X at the PA field in the Gulf of Mexico. The Formation X with approximately 400 m thick was deposited during Late Paleocene to Late Middle Eocene and composed of alternating shale and sandstone intervals. Depositional lithofacies, petrophysical well characteristics, 3D seismic data and geological facies models have been used for characterizing and evaluating of this turbidite reservoir. The reservoir properties and heterogeneities are typically controlled by facies architecture. Depositional lithofacies have been interpreted using core description in few wells, and have been tried to link with the predicted electrofacies from well logs. Two main logs representing depositional heterogeneity -GR and Vsh- have been interpreted using neutron and density logs and have been used to predict electrofacies in the Formation X. Three electrofacies have been predicated and considered as facies associations. The facies associations include sand, shaly-sand and shale. The core descriptions, regional studies and seismic data are valuable data to understand the conceptual geological model that can be used a guide to distribute the facies associations between the wells. Well tops from well logs have been interpreted by variations in depositional characteristics and have been tied to seismic surfaces in order to construct the stratigraphic framework. A total of eight surface resulted in defining seven geological zones to populate reservoir properties.The geological grids have been defined according to the possible depositional heterogeneities in lateral and vertical directions. Well data including facies and porosity in a scale of 15 cm have been scaled-up to geological grids with 1 m thick. Due to uncertainty in the conceptual depositional model two different alternative facies modelling methods have been tried in order to learn the modelling processes and to understand the challenges which may influence the final results. Object-based models have been used to model the sand facies as channel, shaly-sand facies as overbank and shale facies as background. The pixel-based facies models have been built based on random distribution of the facies according to the results from data analysis in available wells.Petrophysical models have been constrained to the pixel-based facies models using random function simulation algorithm. According to data analysis and the results from modelling, the depositional facie control reservoir properties. Sand facies have higher porosity values than shaly-sand and shale facies.The result from geological description, petrophysical evaluation, seismic interpretation and property modelling has shown that the Formation X is a complex turbidite system. Such complexities results in higher uncertainty in the results and thus uncertainty assessments are necessary in this kind of reservoirs.

The mid-Norwegian Vøring and Møre margins are listed as the type example of volcanic rifted margins, with their formation usually related to the influence of the Icelandic plume. Recent studies have shown that these margins have more in common with non-volcanic rifted margins than the scientific community used to think, which opens the discussion on their architecture and evolution. As the rifting mechanisms are not yet fully constrained, a wide variety of extensional models have been proposed in the literature. The evolution of the rifting models requires updated studies based on the new concepts and the new high resolution datasets now available. Despite the large amount of geophysical data acquired on the Vøring and Møre margins during the past decades, the ambiguity with respect to the deep structures, and especially in detecting sub-basaltic basement structures, where intrusions and lava flows perturb the seismic imaging, is still a matter of concern. This study illustrates the benefit of the combination of seismic and potential field modeling results. The forward gravity and magnetic modeling significantly improves the model accuracy and provides a valuable tool to estimate sub-basaltic deep crustal structures.

Petrographic composition, diagenesis and reservoir quality of the Upper Triassic fluvial to marginal marine Fruholmen Formation, the Middle and Upper Triassic estuarine and coastal plain Snadd Formation, and the Middle Triassic estuarine Kobbe Formation have been examined in wells 7131/4-1 and 7222/11-1 located on the western Bjarmeland Platform and on the eastern Finnmark Platform in the southern Barents Sea. Twenty-nine thin-sections from the Fruholmen Formation, sixty-eight from the Snadd Formation and eleven from the Kobbe Formation were studied with a petrographic microscope, forty were point-counted, and six were studied with a cathodoluminescence microscope. The petrographic observations were compared with plug measurements of porosity and permeability.The Fruholmen Formation sandstones are moderately well and well sorted fine-, medium- and coarse-grained quartz arenites. The Snadd Formation sandstones are moderately well and well sorted and fine- and medium-grained, and the Kobbe Formation sandstones are mostly well sorted and fine-grained. Both the Snadd and Kobbe Formations comprise sublitharenites and lithic arenites with common to abundant metasedimentary rock fragments, but the Snadd Formation contains both K-feldspar and plagioclase, whilst the Kobbe Formation contains plagioclase only. These compositional differences between the three formations may largely be a result of the Snadd and Kobbe formations having had an eastern source area (Uralides), and the Fruholmen Formation a more southerly source area (Scandinavia), although a shift to a more humid climate in the Late Triassic may also have influenced sand composition.The Fruholmen Formation sandstones contain very little diagenetic cement, typically 1-2% quartz overgrowths, traces of pyrite cement, and occasionally 1-2% authigenic kaolin. The main diagenetic cement in the Snadd Formation is early diagenetic chlorite that occurs as grain coatings and more rarely as pervasive microporous pore-filling cement. Siderite is present in most Snadd Formation samples in amounts of 1-6%, and a few thin zones are strongly calcite-cemented. Up to 3% authigenic kaolin is commonly present, and traces of pyrite cement and quartz overgrowths occur. The Kobbe Formation sandstones contain the same diagenetic minerals as the Snadd Formation, plus a few albitic overgrowths on plagioclase. However, the total volumes of diagenetic minerals in the Kobbe Formation are typically very low, 1-5% in the point-counted samples.Diagenetic chlorite or poorly crystalline chlorite precursors may have formed from iron-rich colloidal material brought in by rivers and flocculated where fluvial waters mixed with marine waters. These colloids may also have been the main source for iron in early diagenetic siderite. Partly dissolved biogenic carbonate is still present in the Snadd and Kobbe formations, and carbonate fossils are probably the source of the calcite cement. The calcite cement engulfs and therefore postdates chlorite grain coats, siderite cement and authigenic kaolin. Quartz overgrowths were sourced from dissolution of quartz grains at stylolites evolved from clay laminae when temperatures reached 70-80°C.Reservoir quality is largely excellent in the Fruholmen Formation sandstones (25-32% helium porosity, 1 000-38 000mD permeability) because contents of detrital clay and diagenetic minerals are almost zero. Snadd Formation porosities are also in most cases high to very high, 26-36%, partly due to the chlorite coatings inhibiting quartz cementation. Permeabilities are mostly 100 to 5 000mD, but where microporous diagenetic chlorite fills the pore system permeabilities are very low to low, 0.1-15mD. The Kobbe Formation sandstones have been more deeply buried than the overlying formations, approximately 3.5km, content of soft components (detrital and authigenic clay, mica-rich rock fragments) is high, and compaction has therefore been severe. Porosities are consequently quite low, 15-21%, even in the best of the cored Kobbe Formation sandstones, and together with the fine grain size this results in low permeabillities, 1-20mD.Burial depth for the shallowest examined cores is only 0.4 and 0.56km, and present temperatures are around 30°C. The consolidated nature of these cores and the presence of quartz overgrowths that normally start forming at 70-80°C therefore suggest that the sandstones have been more deeply buried than at present. Lack of illitization of kaolin in the deepest samples indicates that they have not been subjected to temperatures above 130°C. Together with the degree of quartz cementation in the various examined samples this suggests uplift of around 1.5km in well 7131/4-1 and 1.7km in well 7222/11-1. Comparison of the present porosities in the quartz arenites of the Fruholmen Formation with the porosity depth trend for the Garn Formation also suggests 1.5km of uplift in well 7131/4-1.

Hydrocarbon generation and migration modelling from the northern North Sea

<p>This dissertation deals with (1) experimental measurements on petrophysical reservoir engineering and morphological properties of Ekofisk chalk, (2) numerical simulation of core flood experiments to analyze and improve relative permeability data, (3) stochastic reconstruction of chalk samples from limited morphological information, (4) extraction of pore space parameters from the reconstructed samples, development of network model using pore space information, and computation of petrophysical and reservoir engineering properties from network model, and (5) development of 2D and 3D idealized fractured reservoir models and verification of the applicability of several widely used conventional upscaling techniques in fractured reservoir simulation. </p><p>Experiments have been conducted on eight Ekofisk chalk samples and porosity, absolute permeability, formation factor, and oil-water relative permeability, capillary pressure and resistivity index are measured at laboratory conditions. Mercury porosimetry data and backscatter scanning electron microscope images have also been acquired for the samples. </p><p>A numerical simulation technique involving history matching of the production profits is employed to improve the relative permeability curves and to analyze hysteresis of the Ekofisk chalk sample. The technique was found to be a powerful tool to supplement the uncertainties in experimental measurements. </p><p>Porosity and correlation statistics obtained from backscatter scanning electron microscope image are used to reconstruct microstructures of chalk and particulate media. The reconstruction technique involves a simulated annealing algorithm, which can be constrained by an arbitrary number of morphological parameters. This flexibility of the algorithm is exploited to successfully reconstruct particulate media and chalk samples using more that one correlation function. A technique based on conditional simulated annealing has been introduced for exact reproduction of vuggy porosity in chalk in the form of foraminifer shells. A hybrid reconstruction technique that initialized the simulated annealing reconstruction with input generated using the Gaussian random field model has also been introduced. The technique was found to accelerate significantly the rate of convergence of the simulated annealing method. This finding is important because the main advantage of the simulated annealing method, namely its ability to impose a variety of reconstruction constraints, is usually compromised by its very slow rate of convergence.</p><p>Absolutely permeability, formation factor and mercury-air capillary pressure are computed from simple network models. The input parameters for the network models were extracted from a reconstructed chalk sample. The computed permeability, formation factor and mercury-air capillary pressure correspond well with the experimental data. The predictive power of a network model for chalk is further extended through incorporating important pore-level displacement phenomena and realistic description of pore space geometry and topology. Limited results show that the model may be used to compute absolute and relative permeabilities, capillary pressure, formation factor, resistivity index and saturation exponent. The above findings suggest that the network modeling technique may be used for prediction of petrophysical and reservoir engineering properties of chalk. Further works are necessary and an outline is given with considerable details.</p><p>Two 2D, one 3D and a dual-porosity fractured reservoir models have been developed and an imbibition process involving water displacing oil is simulated at various injection rates and with different oil-to-water viscosity ratios using four widely used conventional upscaling techniques. The upscaling techniques are the Kyte & Berry, Pore Volume Weighted, Weighed Relative Permeability, and Stone. The results suggest that the upscaling of fractured reservoirs may be possible using the conventional techniques. Kyte & Berry technique was found to be the most effective in all situations. However, further investigations are necessary using realistic description of fracture length, orientation, connectivity, aperture, spacing, etc. </p> / Paper 3,4 and 5 reprinted with kind persmission of Elsevier Science, Science Direct.

This dissertation deals with (1) experimental measurements on petrophysical reservoir engineering and morphological properties of Ekofisk chalk, (2) numerical simulation of core flood experiments to analyze and improve relative permeability data, (3) stochastic reconstruction of chalk samples from limited morphological information, (4) extraction of pore space parameters from the reconstructed samples, development of network model using pore space information, and computation of petrophysical and reservoir engineering properties from network model, and (5) development of 2D and 3D idealized fractured reservoir models and verification of the applicability of several widely used conventional upscaling techniques in fractured reservoir simulation. Experiments have been conducted on eight Ekofisk chalk samples and porosity, absolute permeability, formation factor, and oil-water relative permeability, capillary pressure and resistivity index are measured at laboratory conditions. Mercury porosimetry data and backscatter scanning electron microscope images have also been acquired for the samples. A numerical simulation technique involving history matching of the production profits is employed to improve the relative permeability curves and to analyze hysteresis of the Ekofisk chalk sample. The technique was found to be a powerful tool to supplement the uncertainties in experimental measurements. Porosity and correlation statistics obtained from backscatter scanning electron microscope image are used to reconstruct microstructures of chalk and particulate media. The reconstruction technique involves a simulated annealing algorithm, which can be constrained by an arbitrary number of morphological parameters. This flexibility of the algorithm is exploited to successfully reconstruct particulate media and chalk samples using more that one correlation function. A technique based on conditional simulated annealing has been introduced for exact reproduction of vuggy porosity in chalk in the form of foraminifer shells. A hybrid reconstruction technique that initialized the simulated annealing reconstruction with input generated using the Gaussian random field model has also been introduced. The technique was found to accelerate significantly the rate of convergence of the simulated annealing method. This finding is important because the main advantage of the simulated annealing method, namely its ability to impose a variety of reconstruction constraints, is usually compromised by its very slow rate of convergence. Absolutely permeability, formation factor and mercury-air capillary pressure are computed from simple network models. The input parameters for the network models were extracted from a reconstructed chalk sample. The computed permeability, formation factor and mercury-air capillary pressure correspond well with the experimental data. The predictive power of a network model for chalk is further extended through incorporating important pore-level displacement phenomena and realistic description of pore space geometry and topology. Limited results show that the model may be used to compute absolute and relative permeabilities, capillary pressure, formation factor, resistivity index and saturation exponent. The above findings suggest that the network modeling technique may be used for prediction of petrophysical and reservoir engineering properties of chalk. Further works are necessary and an outline is given with considerable details. Two 2D, one 3D and a dual-porosity fractured reservoir models have been developed and an imbibition process involving water displacing oil is simulated at various injection rates and with different oil-to-water viscosity ratios using four widely used conventional upscaling techniques. The upscaling techniques are the Kyte &amp; Berry, Pore Volume Weighted, Weighed Relative Permeability, and Stone. The results suggest that the upscaling of fractured reservoirs may be possible using the conventional techniques. Kyte &amp; Berry technique was found to be the most effective in all situations. However, further investigations are necessary using realistic description of fracture length, orientation, connectivity, aperture, spacing, etc. / Paper 3,4 and 5 reprinted with kind persmission of Elsevier Science, Science Direct.