Janos Urai

RWTH Aachen University and German University of Technology in Oman · Structural Geology, Tectonics and Geomechanics

Constitutive laws to predict long-term deformation of solution-mined caverns and radioactive-waste repositories in rock salt play an important role in the energy transition. Much of this deformation is at differential stresses of a few megapascals, while the vast majority of laboratory measurements are at much higher differential stress and require...

Metamorphic limestones in Namibia and Oman were found to be consumed inside the rock mass by microbiological activity of a thus far unknown nature that created bands of parallel tubules. Tubule of up to 0.5 mm wide and 30 mm long collectively form bands of tens of meters long. These bands formed along fractures in the rock and only surfaced after e...

Tight carbonate rocks are important hydrocarbon and potential geothermal reservoirs, for example, in CO2-Enhanced Geothermal Systems. We report a study of outcrop samples of tectonically undeformed tight carbonates from the upper Jurassic “Malm ß” formation in Southern Germany near the town of Simmelsdorf (38 km NE of Nuremberg) to understand bulk...

The input sediments of the North Sumatra subduction zone margin, drilled during IODP Expedition 362, exhibit remarkable uniformity in composition and grain size over the entire thickness of the rapidly deposited Nicobar Fan succession (seafloor to 1500 m b.s.f.), providing a unique opportunity to study the micromechanisms of compaction. Samples wer...

Plain Language Summary Fluids in the Earth's crust can alter permeability and porosity, precipitate and dissolve minerals, transport material and interact with deformation. This affects the transport and mechanical properties of the rock system and in turn has consequences for example, in subsurface engineering applications. In this work we simulat...

The reaction of serpentinized peridotite with CO2-bearing fluids to form listvenite (quartz–carbonate rock) requires massive fluid flux and significant permeability despite an increase in solid volume. Listvenite and serpentinite samples from Hole BT1B of the Oman Drilling Project help to understand mechanisms and feedbacks during vein formation in...

Constitutive laws of rock salt are required for the prediction of long-term deformation of radioactive waste repositories and solution mined caverns, which are used for energy storage and play an important role in the energy transition. Much of this deformation is at differential stresses of a few MPa. The vast majority of laboratory measurements o...

Carbonated serpentinites (listvenites) in the Samail Ophiolite, Oman, record mineralization of 1–2 Gt of CO2, but the mechanisms providing permeability for continued reactive fluid flow are unclear. Based on samples of the Oman Drilling Project, here we show that listvenites with a penetrative foliation have abundant microstructures indicating that...

Most models of brittle boudinage predict a dependency of fracture spacing on thickness of the boudinaged layer. This basic relationship can be distorted in the case of multiphase boudinage, where structural inheritance, possibly combined with time evolution of rheology affects boudin geometries, but is not recognized in 2D outcrops. Here we present...

Tight carbonate rocks are important potential although unconventional geothermal and hydrocarbon underground storage reservoirs and prospective CO 2 -EGS sites. We study these rocks by using the Upper Jurassic “Malm ß” in Southern Germany as an outcrop analog example to understand bulk properties in relation to microstructure and to test a variety...

The way rocks deform under changing stress conditions can be described by different deformation modes, which is fundamental for understanding their rheology. For Opalinus Clay, which is regarded as a potential host rock for nuclear waste, we investigate the failure mode as a function of applied effective stress in laboratory experiments. Therefore,...

The present work showcases a comprehensive phase-field study on the formation of multi-crack-seal veins in quartz microstructures. The microstructure simulation framework Pace3D incorporates the modeling of both fracturing and sealing in polycrystalline rock systems, where crystallographic anisotropies, crack resistances and growth velocities of di...

The KEM-17 project of the Dutch State Supervision of Mines presented a critical review of concepts of cavern abandonment and related science. It recommended that analyses of cavern abandonment are done as an integrated project, addressing (i) micro-scale physical processes, (ii) cavern scale models based on field scale experiments and numerical mod...

Organic-rich carbonate mudrocks are among the most important petroleum source rocks in the world, sourcing most of the hydrocarbons of Arabia and many other oil provinces. Hydrocarbon generation and migration in organic-rich carbonate source rocks and the governing geological processes have previously been widely discussed. However, only a few stud...

The way rocks deform under changing stress conditions can be described by different deformation modes, which is fundamental for understanding their rheology. For Opalinus Clay, which is considered as a potential host rock for nuclear waste, we investigate the failure mode as a function of applied effective stress in laboratory experiments. Therefor...

The input sediments of the North Sumatra subduction zone margin, drilled during IODP Expedition 362, exhibit remarkable uniformity in composition and grain size over the entire thickness of the rapidly deposited Nicobar Fan succession (sea-floor to 1500 mbsf depth), providing a unique opportunity to study the micromechanisms of compaction. Samples...

This paper provides an overview of research on core from Oman Drilling Project Hole BT1B and the surrounding area, plus new data and calculations, constraining processes in the Tethyan subduction zone beneath the Samail ophiolite. The area is underlain by gently dipping, broadly folded layers of allochthonous Hawasina pelagic sediments, the metamor...

We investigate the magnetic fabrics and microstructures of diamagnetic rocksalt samples from the Sedom salt wall (diapir), Dead Sea Basin, as possible strain markers. A comprehensive study of anisotropy of magnetic susceptibility (AMS), combined with magnetic, microtextural, geochemical and mineralogical analyses allows us to depict the deformation...

The reaction of serpentinized peridotites with CO2-bearing fluids to listvenite (quartz-carbonate rocks) requires massive fluid flux and significant permeability despite increase in solid volume. Listvenite and serpentinite samples from Hole BT1B of the Oman Drilling Project help to understand mechanisms and feedbacks during vein formation in this...

Building on recent developments in phase-field modeling of structural diagenesis, we present an analysis of single-seal syntaxial calcite vein microstructure in a variety of limestones. We focus on the effects of fracture aperture, intergranular versus transgranular fracturing, crystal habit and the presence of second phases in the host rock, to sy...

Most models of brittle boudinage predict a dependency of fracture spacing on thickness of the boudinaged layer. This basic relationship can be distorted in the case of multiphase boudinage, where structural inheritance, possibly combined with time evolution of rheology affects boudin geometries, but is not recognized in 2D outcrops. Here we present...

Rock fractures organize as networks, exhibiting natural variation in their spatial arrangements. Therefore, identifying, quantifying, and comparing variations in spatial arrangements within network geometries are of interest when explicit fracture representations or discrete fracture network models are chosen to capture the influence of fractures o...

A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, impo...

At laboratory timescales, rock salt samples with different composition and microstructure show variance in steady-state creep rates, but it is not known if and how this variance is manifested at low strain rates and corresponding deviatoric stresses. Here, we aim to quantify this from the analysis of multilayer folds that developed in rock salt ove...

The published article is available at: https://www.nature.com/articles/s41467-022-31049-1

https://onlinelibrary.wiley.com/share/author/NACKDF2WTAPRUIUKZU3H?target=10.1029/2021TC006850 In salt-detached fold-and-thrust belts, contractional modification of salt structures may include decapitation by thrusting, but examples are not well known in the subsurface and undocumented in outcrop. Here we present a surface exposure of an intrasalt,...

The Lilstock outcrop in the southern Bristol Channel provides exceptional exposures of several limestone beds displaying stratabound fracture networks, providing the opportunity to create a very large, complete, and ground-truthed fracture model. Here we present the result of automated fracture extraction of high-resolution photogrammetric images (...

Analysis and prediction of deformations in salt tectonics and salt engineering require information about the mechanical properties of rocksalt at time scales far longer than possible in the laboratory. It is known that at laboratory time scales, rocksalt samples with different composition and microstructure show a variance in steady-state creep rat...

A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical laboratory tests have been performed to characterize the bulk mechanical, hydro-mechanical and failure behaviour of Opalinus...

We investigate the spatial variation of 2D fracture networks digitized from the well-known Lilstock limestone pavements, Bristol Channel, UK. By treating fracture networks as spatial graphs, we utilize a novel approach combining graph similarity measures and hierarchical clustering to identify spatial clusters within fracture networks and quantify...

Outcrop studies of fracture networks are important to understand fractured reservoirs in the subsurface, but complete maps of all fractures in large outcrops are rare due to limitations of outcrop and image resolution. We manually mapped the first full-resolution UAV-based, Gigapixel dataset and DEM of the wave-cut Lilstock Benches in the southern...

Salt deposits are extremely potent seals for hydrocarbon reservoirs present in the sedimentary basins worldwide. Large rock inclusions (stringers) encased within various salt bodies may adopt diverse modes of deformation and displacement. Analyzing the movement and segmentation of these elastic and viscous stringers provides a comprehensive underst...

Salt diapirs/bodies are remarkable structures often presenting a rich internal structure, with features like isoclinal folds, sheath folds, curtain folds, boudinage, etc. Salt structures are themselves valuable as a resource but are also often associated with significant hydrocarbon accumulations, as well as valuable as storage sites. While signifi...

Vein microstructures contain a wealth of information on coupled chemical and mechanical processes of fracturing, fluid transport, and crystal growth. Numerical simulations have been used for exploring the factors controlling the development of vein microstructures; however, they have not been quantitatively validated against natural veins. Here we...

A comprehensive characterization of clay shale behaviour requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: i) pore pressure oscillation, ii) pressure pulse decay, and iii) pore pressure e...

Liassic limestones at the Somerset coast (UK) contain dense arrays of calcite microveins with a common but poorly understood microstructure, characterized by laterally wide crystals that form bridges across the vein. This paper investigates the formation mechanisms and evolution of these wide-blocky vein microstructures by a combination of high-res...

In salt-detached fold-and-thrust belts, contractional modification of salt structures may include decapitation by thrusting, but examples are not well known in the subsurface and unreported in outcrop. Here we present a surface exposure of an intrasalt, sub-horizontal shear zone at the boundary between the Tarcau and Subcarpathian nappes in the Rom...

Hole BT1B of the Oman Drilling Project provides a continuous sampling from listvenite into the metamorphic sole that preserves the deformation, hydration, and carbonation processes of oceanic mantle peridotite at the base of the Samail ophiolite, Oman. We present evidence of multistage brittle deformation in listvenites and serpentinites based on f...

We review the status of a 1.4 GW, 8 GWh U-PHS project in the southern Netherlands, 17 which has been under development since the 1980s. Its history shows how the prospect of a large-18 scale U-PHS for the Netherlands (a country whose proverbial flatness prohibits PHS) has been 19 attractive in every decade, based on proven technology in a subsurfac...

The 100 000m2 wave-cut pavement in the Bristol Channel near Lilstock, UK, is a world-class outcrop, perfectly exposing a very large fracture network in several thin limestone layers. We present an analysis based on manual interpretation of fracture generations in selected domains and compare it with automated fracture tracing. Our dataset of high-r...

Outcrop studies of fracture networks are important to understand such networks in the subsurface, but completemaps of all fractures in large outcrops are rare due to limitations of outcrop and image resolution. We present thefirst full-resolution UAV-based, Gigapixel dataset and DEM of the wave-cut Lilstock Benches in the southern Bristol Channel b...

Hole BT1B of the Oman Drilling Project provides a continuous sampling from listvenite into the metamorphic sole that preserves the deformation, hydration and carbonation processes of oceanic mantle peridotite at the base of the Samail ophiolite, Oman. We present evidence of multistage brittle deformation in listvenites and serpentinites based on fi...

Abstract. The 100,000 m² wave-cut pavement in the Bristol Channel near Lilstock, UK, is a world-class outcrop, perfectly exposing a very large fracture network in several thin limestone layers. We present an analysis based on manual interpretation of fracture generations in selected domains and compare this with automated fracture tracin...

Slip planes and slip directions of subsequent generations of faults were measured and analysed in the interaction damage zone of two abutting faults in porous sandstones in order to understand the palaeostress/palaeostrain evolution. The Courthouse branch point of the Moab Fault in SE Utah (USA) is a much-studied, spectacular outcrop of two abuttin...

Over-pressured salt solution mining caverns and leakage mechanisms Phase 1: micro-scale processes

The work of Trusheim in the early 1950s in the German Zechstein Salt Basin laid the foundation for interpreting the kinematic evolution of salt structures. His observations connected salt diapir evolution to sed-imentation. This paper shows examples of how our understanding from Trusheim to today has evolved in the Zechstein salt giant. We discuss...

Microstructure strongly influences flow and transport properties of porous media. Flow and transport simulations within porous media, therefore, requires accurate three-dimensional (3D) models of the pore and solid phase structure. To date, no imaging method can resolve all relevant heterogeneities from the nano- to the centimeter scale within comp...

Normal faults in basalts develop massive dilatancy in the upper few hundred meters below the Earth's surface with corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDFs) are widespread in Iceland and the East African Rift, but the details of their geometry are not well documented, despite their importance f...

Boom Clay is a soft, slightly overconsolidated, uncemented claystone considered as potential host material for a radioactive waste repository in Belgium. We studied the evolution of microfabrics in samples which were shortened to 20% bulk strain in consolidated-undrained (CU) triaxial experiments at effective confining pressures of 0.375, 0.750 and...