We investigate the relationship between tectonic activity and sedimentation in minibasins with syn-halokinetic continental deposition in a semi-arid Triassic climate on a regional scale. For the central North Sea, seismic data, well logs, cores, and well reports have been used to define four stratal geometries (bowls, wedges, and tabular geometries, as well as post-depositional anticlines), within five minibasin morpohologies. Pod and deep-toed minibasins dominate around the Jæren High and the Cod Terrace along the eastern slope of the Central Graben, and polygonal, fault-bounded, and linear minibasins occur east of the pod and deep-toed minibasins. The variation in development of the five minibasin morphologies resulted from differences in salt deformation, extensional tectonic influence, and sediment transport. The well-log facies and stratal geometries of the Triassic strata suggest that fine-grained and coarse-grained lithologies are equally common in the upper part of the minibasins and that interfingering lithologies represent the Triassic stratigraphy. This is different from both the official layer-cake model and the J-member model for the Norwegian and UK central North Sea, respectively. Thus, the commonly used lithostratigraphy is incompatible with our observations. Consequently, the identified stratal geometries within minibasins affect interpretations of both sediment transport and the depositional style in this continental region. The understanding of salt-tectonic and sedimentary interactions is key to properly address the energy exploration and storage potential for continental minibasin systems in semi-arid climates.
Strength of knowledge (SoK) judgments are a key component in characterising risks from an uncertainty-based risk perspective. A commonly applied assessment scheme for this purpose involves evaluating the SoK based on several criteria: the reasonableness of assumptions, the availability and reliability of data, the degree to which phenomena are understood, the level of expert agreement, and the extent to which the knowledge has been scrutinised. The applicability of this scheme has been widely discussed and debated in the risk research literature. However, less attention has been given to its actual use and to risk practitioners' evaluations. In Norway, many practitioners regularly apply the SoK scheme to address real-world risk problems, as various public and private sectors have incorporated it into their risk assessment standards and guidance documents. In this paper, we examine how 22 risk practitioners use the SoK scheme and assess its utility. The study aims to provide insights into the challenges and benefits of applying the SoK scheme in practical contexts, thereby enhancing its applicability for practitioners and informing its ongoing development within the research community. Key findings relate to the scheme’s practical value in structuring uncertainty assessments and informing risk management, alongside identified needs for improved guidance to support consistent judgment and effective communication.
This paper develops a discrete-time framework for quadratic repulsiveness in linear time-invariant (LTI) systems with respect to a prescribed, possibly indefinite, quadratic form. The concept characterizes whether system trajectories are driven toward decreasing values of an indefinite quadratic form associated with a prescribed undesirable region, while preventing re-entry once its complement has been reached. Unlike the continuous-time case, discrete-time dynamics require not only a decrease of the quadratic function in the undesirable region, but also forward invariance of its complement, since trajectories may otherwise jump across the quadratic boundary and re-enter the undesirable region. We introduce a definition of discrete-time quadratic repulsiveness and derive necessary and sufficient matrix-inequality conditions using the S-procedure. For diagonalizable state matrices, we show that quadratic repulsiveness imposes a precise ordering constraint on the eigenstructure: the eigenvectors associated with the eigenvalues of largest modulus must lie in the negative side of the prescribed quadratic form, whereas the remaining eigenvectors must lie in its positive side. As a consequence, almost every trajectory leaves the undesirable region in finite time and remains outside it. The only exceptions correspond to initial conditions belonging to the invariant subspace spanned by the eigenvectors lying on the positive side of the quadratic form, which has zero Lebesgue measure. We then address state-feedback synthesis, deriving exact design conditions formulated as bilinear matrix inequalities (BMIs), while tractable sufficient conditions are obtained through convex inner approximations leading to linear matrix inequality (LMI)-based procedures. The framework is further extended to systems with polytopic uncertainty through vertex-wise sufficient conditions for robust analysis and control design. Numerical examples illustrate the proposed synthesis method and confirm the predicted eigenstructure and trajectory behavior.
Underground hydrogen storage in porous reservoirs requires accurate prediction of hydrogen-cushion gas mixing during cyclic injection, storage, and withdrawal, both to preserve the purity of produced hydrogen and to minimize downstream purification costs. This mixing is governed by dispersion - the combined effect of molecular diffusion and mechanical mixing - which, through Darcy's law, is strongly controlled by the viscosity of the gas mixture; yet this viscosity-dispersion coupling has not been quantified at the pressures and temperatures representative of storage operations. The objective of this study is to quantify that coupling for two candidate cushion gases and to establish a viscosity model capable of representing it. The work proceeds in two steps. First, several viscosity correlations are benchmarked, and the best-performing correlation is coupled with a onedimensional advection-dispersion solver. Dispersion coefficients are then estimated by matching the simulated H2 breakthrough profiles to the analytical Ogata-Banks solution for H2 paired with CH4 and CO2 at pressures of 5-25 MPa and temperatures of 40-120 degrees C. The widely used Chung et al. [13] correlation, combined with Wilke's mixing rule, is shown to systematically misrepresent H2 and H2-cushion gas viscosities at elevated pressures, whereas the Pedersen corresponding-states model reproduces the measurements accurately and is therefore adopted for the transport simulations. The resulting dispersion coefficients increase with temperature and decrease with pressure, and mechanical mixing accounts for up to 92 % of the total. H2-CH4 systems consistently exhibit higher dispersion than H2-CO2 systems, reflecting the lower viscosity of the former. To the authors' knowledge, this is the first study to show that the medium dispersivity - conventionally assumed to be a property of the rock alone - instead depends on cushion-gas composition, pressure, and temperature, all mediated through the gas-mixture viscosity. By isolating this viscosity control within a computationally efficient framework, the study provides quantitative input for estimating hydrogen losses and for selecting cushion gases in the design and operation of underground hydrogen storage sites.
In recent years, considerable efforts have been made to better incorporate knowledge aspects into risk assessment. A variety of methods have been proposed, drawing on diverse attributes and both qualitative and quantitative approaches and methods. A central concept in this development is the "strength of knowledge" (SoK), which evaluates the strength of the knowledge base underpinning probability and risk judgments. This paper critically examines the SoK concept and argues for methodological advancement by expanding the focus beyond the mere strength of the supporting knowledge to also encompass the quality of the transformation process from that knowledge into the final probability and risk judgments. To address this, a new concept-"strength of justification" (SoJ)-is introduced. SoJ integrates both the quality of the knowledge itself and the rigor of the transformation steps leading to the probability and risk judgments. By adopting the SoJ framework, the paper derives enhanced methods for characterizing individual uncertainty judgments, as well as overall risk descriptions, offering a more comprehensive approach to assessing and communicating risk.
