Norwegian Geotechnical Institute (NGI) Digital Archive
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Caprock characterization of Upper Jurassic organic-rich shales using acoustic properties, Norwegian Continental Shelf
Get PDFOur analysis of a comprehensive well log database and complementary mineralogical and geochemical information indicates that the risk for Upper Jurassic shales on the Norwegian Continental Shelf (NCS) to permit severe leakage of hydrocarbons from the reservoir is generally low, even in the case of substantial uplift. The content of brittle minerals, organic content, and compaction are dominant factors that explain the observed discrepancies in acoustic properties of organic-rich caprock shales. In particular, variations in silt-clay content in clay-dominated shales are found to primarily influence sonic velocity and to correlate closely with gamma-ray where the uranium contribution is limited (“grey shales”). Changes in organic content exhibit a stronger density-component and are seen to counteract or mask the compaction effect on velocity and density in Kimmeridgian black shales. The Hekkingen, Draupne and Tau formations are distinctly different from the underlying grey shale formations in acoustic properties, despite that the latter group also contains significant amounts of organic matter. Based on the low permeability and high capillary sealing capacity of clay-dominated shales, we conclude that even for a silty seal, migration through the caprock matrix is highly unlikely. Furthermore, tectonic fracturing is an ineffective leakage mechanism when the seal is poorly consolidated/cemented prior to uplift. Brittleness, related to both mineralogical composition and consolidation, is consequently a crucial parameter for predicting seal integrity in exhumed basins. Our rock physics framework and interpretations relate this rather qualitative parameter to acoustic properties, and thus, to seismic data.publishedVersio
Design and performance of the Quxue asphalt-core rockfill dam
Get PDFThe design and performance of the 174-m high Quxue asphalt-core rockfill dam in Sichuan Province, China, are presented. An extensive field monitoring program was implemented. During construction, the asphalt core settled more than the adjacent transition zones, but no more than 20 mm due to strong interlocking with the coarser gravel particles in the transition zones. The lateral displacements of the core were recorded during the impoundment. The measured shear displacements were less than 10 mm between the core and the plinth along the steep abutments (about 70°), and the interface remained watertight. The dam was constructed in about one year, and the reservoir impoundment up to about 100 m height was done in two months. The performance monitoring documents that the asphalt core type of dam is suitable for high embankment dams even in narrow valleys with steep abutments. The core exhibits flexible and ductile behavior without cracking, and internal core erosion is not an issue of concern.publishedVersio
Mind the Gap: Towards a Typology of Climate Service Usability Gaps
Get PDFLiterature on climate services presents a large diversity of different services and uses. Many climate services have ‘usability gaps’: the information provided, or the way it is visualized, may be unsuitable for end users to inform decision-making processes in relation to adaptation against climate change impacts or for the development of policies to this end. The aim of this article is to contribute to more informed and efficient decision-making processes in climate adaptation by developing a typology of usability gaps for climate services. To do so, we first present and demonstrate a so-called ‘climate information design’ (CID) template with which to study and potentially improve the visual communicative qualities of climate services. Then, two climates services are selected for a further, qualitative explorative case study of two cases in the north and south of the Netherlands. A combination of focus group sessions and semi-structured interviews are used to collect data from Dutch governmental stakeholders as well as private stakeholders and NGOs. This data is then coded to discover what usability gaps are present. We then present twelve different types of usability gaps that were encountered as a typology. This typology could be used to improve and redesign climate servicespublishedVersio
Effects of acidic water on hydro-mechanical properties of asphalt concrete
Get PDFAsphalt concrete is widely used in road and airport pavements and more recently also in the construction of impervious facings and central cores in dams and dykes. Asphalt concrete may be subjected to strongly acidic water when used in connection with storage of mine tailings (tailings dams). Acidic water reacts with bitumen and mineral materials and may cause deterioration of the behavior of asphalt concrete with time. The present study investigated effects of acidic water with time on aggregate-bitumen adhesion, bitumen penetration value, softening point and ductility, mass change of asphalt materials, and change in tensile strength for porous and impervious asphalt concrete. The test results show that impervious, hydraulic asphalt concrete is very resistant to acidic water and show insignificant deterioration of properties during the 3-year testing period used in the experiments.publishedVersio
Frictional Properties and Seismogenic Potential of Caprock Shales
Get PDFFractures and faults are critical elements affecting the geomechanical integrity of CO2 storage sites. In particular, the slip of fractures and faults may affect reservoir integrity and increase potential for breach, may be monitored via the resulting seismicity. This paper presents an experimental study on shale samples from Draupne and Rurikfjellet formations from the North Sea and Svalbard, Norway, using a laboratory test procedure simulating the slip of fractures and faults under realistic stress conditions for North Sea CO2 storage sites. The motivation of the study is to investigate whether the slip along the fractures within these shales may cause detectable seismic events, based on a slip stability criterion. Using a direct shear apparatus, frictional properties of the fractures were measured during shearing, as a function of the shear velocity and applied stress normal to the fracture. We calculated the friction coefficient of the fractures during the different stages of the shear tests and analysed its dependency on shear velocity. Information on velocity-dependent friction coefficient and its evolution with increasing slip were then used to assess whether slip was stable (velocity-strengthening) or unstable (velocity-weakening). Results showed that friction coefficient for both Draupne and Rurikfjellet shales increased when the shear velocity was increased from 10 to 50 µm/s, indicating a velocity-strengthening behaviour. Such a behaviour implies that slip on fractures and faults within these formations may be less prone to producing detectable seismicity during a slip event. These results will have implications for the type of techniques to be used for monitoring reservoir and caprock integrity, for instance, for CO2 storage sitespublishedVersio
Probabilistic Tsunami Hazard Analysis: High Performance Computing for Massive Scale Inundation Simulations
Get PDFProbabilistic Tsunami Hazard Analysis (PTHA) quantifies the probability of exceeding a specified inundation intensity at a given location within a given time interval. PTHA provides scientific guidance for tsunami risk analysis and risk management, including coastal planning and early warning. Explicit computation of site-specific PTHA, with an adequate discretization of source scenarios combined with high-resolution numerical inundation modelling, has been out of reach with existing models and computing capabilities, with tens to hundreds of thousands of moderately intensive numerical simulations being required for exhaustive uncertainty quantification. In recent years, more efficient GPU-based High-Performance Computing (HPC) facilities, together with efficient GPU-optimized shallow water type models for simulating tsunami inundation, have now made local long-term hazard assessment feasible. A workflow has been developed with three main stages: 1) Site-specific source selection and discretization, 2) Efficient numerical inundation simulation for each scenario using the GPU-based Tsunami-HySEA numerical tsunami propagation and inundation model using a system of nested topo-bathymetric grids, and 3) Hazard aggregation. We apply this site-specific PTHA workflow here to Catania, Sicily, for tsunamigenic earthquake sources in the Mediterranean. We illustrate the workflows of the PTHA as implemented for High-Performance Computing applications, including preliminary simulations carried out on intermediate scale GPU clusters. We show how the local hazard analysis conducted here produces a more fine-grained assessment than is possible with a regional assessment. However, the new local PTHA indicates somewhat lower probabilities of exceedance for higher maximum inundation heights than the available regional PTHA. The local hazard analysis takes into account small-scale tsunami inundation features and non-linearity which the regional-scale assessment does not incorporate. However, the deterministic inundation simulations neglect some uncertainties stemming from the simplified source treatment and tsunami modelling that are embedded in the regional stochastic approach to inundation height estimation. Further research is needed to quantify the uncertainty associated with numerical inundation modelling and to properly propagate it onto the hazard results, to fully exploit the potential of site-specific hazard assessment based on massive simulations.publishedVersio
Modelling of shallow landslides with Machine Learning algorithms
Get PDFThis paper introduces three machine learning (ML) algorithms, the 'ensemble' Random Forest (RF), the 'ensemble' Gradient Boosted Regression Tree (GBRT) and the MultiLayer Perceptron neural network (MLP) and applies them to the spatial modelling of shallow landslides near Kvam in Norway. In the development of the ML models, a total of 11 significant landslide controlling factors were selected. The controlling factors relate to the geomorphology, geology, geo-environment and anthropogenic effects: slope angle, aspect, plan curvature, profile curvature, flow accumulation, flow direction, distance to rivers, total water content, saturation, rainfall and distance to roads. It is observed that slope angle was the most significant controlling factor in the ML analyses. The performance of the three ML models was evaluated quantitatively based on the Receiver Operating Characteristic (ROC) analysis. The results show that the 'ensemble' GBRT machine learning model yielded the most promising results for the spatial prediction of shallow landslides, with a 95% probability of landslide detection and 87% prediction efficiency.Modelling of shallow landslides with Machine Learning algorithmspublishedVersio
GADL1 is a multifunctional decarboxylase with tissue-specific roles in β-alanine and carnosine production
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Experimental investigation of natural fracture stiffness and flow properties in a faulted CO2 bypass system (Utah, USA)
Get PDFFracture stiffness and flow properties have been measured in the laboratory using naturally fractured fault rock samples from the Little Grand Wash fault, Utah, USA. We compare fracture closure and related flow change during isotropic loading of two fractures which have been subject to various amounts of paleo‐reactive flow. The two tested fractures are described as (i) a small‐aperture fracture (0.1 mm) with negligible geochemical alterations of the fracture surface and (ii) a large‐aperture fracture (0.53 mm) where precipitates are observed on the fracture surface. X‐ray imaging is used for quantification of fracture aperture and fracture surface contact distribution. The petrographical characterisation using scanning electron microscopy and x‐ray powder diffraction is performed pre‐test and describes burial and uplift diagenesis as well as pulses of reactive fluid flow within the fault. The stress dependent flow and deformation experiment provides new data on fracture stiffness and flow for naturally developed fractures in siliciclastic rock. Fracture stiffness is found to be highest for the small‐aperture fracture due to its high fracture contact ratio and well‐developed surface mating during closure. For the naturally altered and rougher, large‐aperture fracture, fracture stiffness is lower and a highly stress dependent decay in flow is observed during initial closure. The results illustrate that a natural fracture with high contact ratio and well mated surfaces will close during loading, whereas a fracture associated with high flow rates and affected by previous geochemical alteration maintains a high flow rate compared to the host rock during similar loading.Experimental investigation of natural fracture stiffness and flow properties in a faulted CO2 bypass system (Utah, USA)publishedVersio
Ingeniørgeologiske vurderinger og kostnadsestimat for tunnelalternativ
Get PDFNGI er engasjert av NVE for å foreslå hvordan man kan bygge en dreneringstunnel med mål om å drenere Åknes fjellside. Hovedmålet er å foreslå forslag til konsept, og deretter
utføre et kostnadsestimat. I foreliggende rapport er et forslag til dreneringsløsning med boring av dreneringshull i vifteform valgt.
Tre tunnelalternativer er vurdert, og etter en gjennomgang ble et alternativ med påhugg i Strandadalen ved ca. 426 m o.h. valgt. Adkomst- og dreneringstunnel er estimert til henholdsvis 3640 m og 160 m, der dreneringstunnelen er lagt horisontalt på høyde 550
m o.h. under vestre del av Åknes fjellside. Helningen på adkomsttunnelen er 3,38 % (1,94 grader).
Adkomsttunnelen er planlagt å ha tverrsnitt på 20,3 m2, mens tverrsnittet til dreneringstunnelen er 39,1 m2. Dette for å få noe bedre plass der dreneringshullene skal bores i vifter fra flere posisjoner langs dreneringstunnelen. Omfang og design av vifter av dreneringshull er fleksibelt og kan justeres etter behov.
Det er beregnet at forventet byggekostnad for dreneringstunnelen blir ca. 129 millioner kroner med et standardavvik på ca. 10 millioner kroner, og usikkerheten er antatt å være rundt 8 %.Norges vassdrags- og energidirektorat (NVE