1,721,534 research outputs found
Permeability model of tight reservoir sandstones combining core-plug and miniperm analysis of drillcore; longyearbyen co2lab, Svalbard
No full textPermeability measurements in Mesozoic, low-permeability sandstone units within the strata cored in seven drillholes near Longyearbyen, Svalbard, have been analysed to assess the presence of aquifers and their potentials as reservoirs for the storage of carbon dioxide. These targeted sandstones are located in the Upper Triassic-Lower Jurassic De Geerdalen and Knorringfjellet formations, with some permeability found in the Cretaceous Rurikfjellet and Helvetiafjellet formations situated within otherwise impermeable cap-rocks. Permeability and porosity data were acquired from drill plugs, analysed in the laboratory by flooding of H2O, He and Hg, and compared with direct measurements collected manually from cores with a Miniperm instrument. The sandstones are tight (<2 mD) due to extensive diagenesis. The two methods produced permeability results of up to one order difference in magnitude; however, when correlated, these methods offer a robust linear relationship that can be applied as a correction function. Detailed mapping of drillcore with Miniperm, corrected by the proposed function, allows analysis of tight reservoir permeability on a very detailed scale, which identify otherwise unrecognised permeable zones. In the analysed reservoir sandstone succession, 2 out of 30 m has recognisable permeability above the threshold of the Miniperm. In the upper part of the reservoir (Knorringfjellet Formation), where data are from three closely spaced wells, the permeability field can be divided into through-going and isolated zones, of which c. 10% is through-going. In the explored Upper Triassic to Cretaceous succession of Central Svalbard, the Knorringfjellet Formation sandstones and conglomerates have the best matrix properties for storage of carbon dioxide
Evidence of overpressured fluids in the thrust zone of the "Bobbio Window" (Trebbia Valley, Northern Apennines)
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The Epiligurian wedge-top succession in the Enza Valley (Northern Apennines): evidence of a syn-depositional transpressive system
No full textWe here discuss the Early Oligocene–Middle Miocene evolution of the Epiligurian wedge-top basin system cropping out in the middle Enza Valley (Northern Apennines, Italy). Newly acquired stratigraphic and structural data, backed up by literature review, highlight that during the Rupelian to Serravallian time span, sedimentation was controlled by a left-lateral transpressive system. This system, here named as the Enza Valley Deformation Zone (EVDZ), is SW–NE directed and trends obliquely to the main regional NW–SE-directed structural axis characterizing this part of the Northern Apennines nowadays. The syn-sedimentary activity is testified by: (1) local to regional stratigraphic unconformities, (2) lateral variations of sedimentary facies associations, (3) thickness changes of the stratigraphic units and (4) the occurrence of mass transport deposits. This study suggests that structural lineaments like the EVDZ, transversal to the main regional tectonic trends, may have played a long-term control on the syn-orogenic sedimentation atop the evolving Apennine orogen
Asymmetrical cross-current turbidite facies tract in a structurally-confined mini-basin (Priabonian-Rupelian, Ranzano Sandstone, northern Apennines, Italy)
No full textThis work discusses the stratigraphy and facies analysis of the Ranzano Sandstone, in the northern Apennines (Italy), a confined low-efficiency turbidite system deposited in a series of small piggy-back basins, which show strong analogies with intraslope minibasins commonly observed in divergent margins. The detailed physical stratigraphy of these deposits, which are the counterpart of the Annot Sandstone of the classic “Trilogie Priabonienne” cropping out in the western Alps, shows a cross-current asymmetrical distribution of the facies related to basin morphology. In an E-W oriented transect, roughly perpendicular to the general paleocurrents directed towards SSW, coarse-grained amalgamated massive sandstones that onlap against the eastern basin margin, grade towards the west, over very short distances, into a stratigraphic succession dominated by coarse-grained sandstones reworked in megaripples. This westward lateral facies change is also associated with: a) progressive deviation of the megaripple paleocurrents towards the west, b) progressive eastward increase in the sandstone/mudstone ratio, impact flow structures and beds with mudstone clasts, and c) progressive westward decrease in bed thickness characterizing massive facies. This cross-current transition is interpreted as related to bipartite turbidity currents experiencing deceleration against a relatively steeper eastern margin, producing flow decoupling and consequent bypass of upper turbulent flows that can spread out towards the less steep western bounding slope. The lateral spreading of turbulent flows causes reworking of the coarse-grained massive facies, producing tractive structures that indicate westward flow divergence. The lack of medium, fine-grained sands and mud testifies that these grain sizes must have been transported by turbulent flows into another adjacent basin, allowing the described deposits to be interpreted as recording a “flow stripping” phase as found in the ponded intraslope basins of the Gulf of Mexico and other confined settings, such as wedge-top basins and inner foredeeps
Mass transport-related stratal disruption within sedimentary mélanges: Examples from the northern Apennines (Italy) and south-central Pyrenees (Spain)
No full textWe report here mass transport-related disruption processes and their artifacts within sedimentary mélanges. The case studies include the early Oligocene wedge-top mass transport deposits in the northern Apennines (Italy) and the Eocene foredeep carbonate megabreccias from the south-central Pyrenees (Spain). These "chaotic" units commonly share a block-in-matrix fabric expressed by variously deformed slide blocks of different size, lithology, age and shape, embedded in a fine-grained matrix. Geophysical studies of modern continental margins have characterized many of these deposits, which, however, remain still relatively poorly described in term of meso-scale characteristics. The prominent feature of the analyzed mass transport deposits is the occurrence of an unsorted, strongly mixed, relatively fine-grained clastic matrix, infilling space between large clasts and blocks. This matrix shows either fluidal structures related to simple shear, or a structureless, homogeneous fabric, both probably related to liquefaction/fluidization processes and thus, to the internal strength of the mixed lithologies. We interpreted this phase as a liquefied mixture of water and sediment, characterized by high mobility due to overpressured conditions, as evidenced by both lateral and vertical injections. On a much larger scale this kind of matrix could represent the acoustically "transparent" facies separating slide blocks of many seismic examples. The inferred generating mechanism is that of a progressive soft sediment deformation, linked to different phases of submarine landslide evolution (i.e. failure, translation, accumulation and post-depositional stages), leading to an almost complete stratal disruption of involved bedded sequences, either within the slide mass and in the underlying substrate. In this framework the down-slope movement is favored by the development of ductile, overpressured shear zones, both internally and along the basal sliding horizon. Therefore, this matrix signature represents a possible discriminating factor to separate sedimentary and tectonic mélanges within accretionary systems and, moreover, to distinguish fast- from slow-rated generating processes. © 2011 Elsevier B.V
High-resolution fracture characterization of a siliciclastic aquifer targeted for CO2 sequestration, Svalbard, Norway
No full textThe target siliciclastic aquifer investigated by the Longyearbyen CO2 Lab as a possible test-scale CO2 storage unit is a dual-permeability reservoir characterized by fractured, tight lithologies. By integrating borehole and outcrop data, the reservoir section has been subdivided in intervals defined by 5 lithostructural units (LSUs), each one characterized by different lithologies and fracture sets interpreted to represent pseudo-geomechanical units. Due to their contrasting features, these LSUs are believed to have a crucial influence on subsurface fluid migration. Our results indicate that fractured shale intervals control lateral fluid flow (predominance of low-angle fracture) whereas sandy and coarser intervals seem to control vertical fluid flow (predominance of high-angle fractures), locally enhancing the contribution of the matrix porosity. Horizontal and vertical high permeability conduits can be found at the LSUs' interfaces, along the chilled margins of igneous sills and dykes, and along the damage zone of mesoscopic faults, due to the localized enhanced fracturing (fracture corridors). A large database containing structural data on fractures has been acquired and analyzed in order to extrapolate calibrated parameters for numerical modeling and flow simulations. These in turn allow reservoir volumetric calculations, assessment of seal integrity and forecasting of vertical/lateral connectivity of the reservoir
Fracture systems and mesoscale structural patterns in the siliciclastic Mesozoic reservoir-caprock succession of the Longyearbyen CO2 Lab project: Implications for geological CO2 sequestration in Central Spitsbergen, Svalbard
No full textCarbon dioxide injection: The importance of natural fractures in a tight reservoir for potential CO2 storage: A case study of the upper triassic - Middle Jurassic Kapp Toscana Group (Spitsbergen, Arctic Norway)
No full textSubstrate deformation and incorporation in sedimentary mélanges (olistostromes): examples from the northern Apennines (Italy) and northwestern Dinarides (Slovenia)
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