COTEC – Teknikker for indentifisering av sikker CO2 lagring

• Petrie, Elizabeth S.; Skurtveit, Elin; Faleide, Thea Sveva; Halvorsen, Kristine; Smith, Scott Adam & Arvesen, Brock C. (2024). Development of fluid pathways and associated diagenetic variations in a natural CO2 leaking fault zone. Lithosphere. ISSN 1941-8264. 2023(14). doi: 10.2113/2023/lithosphere_2023_335. Fulltekst i vitenarkiv Vis sammendrag

  Permeability within fault zones can vary through time due to repeated deformation events and rock–fluid interactions. Understanding the history of fault zone alteration is critical when building hydrogeologic models and evaluating the risk of mechanical rock failure during subsurface storage. Newly acquired drill core recovered within the fault damage zone and fault core of the Little Grand Wash fault (LGWF) is combined with observations from outcrop, optical petrography, computerized tomography image analysis, and ultrasonic velocity measurements to characterize the rock types and preserved structural deformation features within this fault zone. These data are used to understand the history of mechanical rock failure and mineralization associated with this fluid-charged fault system. We identify multiple structural features and use their cross-cutting relationships to understand the history of deformation and their association with changes in fault zone permeability and rock mechanical properties. At the LGWF zone, structural deformation features vary temporally and are used to recognize a decoupling between fault slip and fluid flow. The formation of most open-mode veins occurred after shear failure within the LGWF zone. Early-developed shear bands are cut by carbonate veins, that are in turn cut by shear fractures, followed by a second phase of vein formation and ultimately by folding in the fault core. This sequence of formation reflects changes in mechanical rock properties due to subsurface rock–fluid interactions and indicates that the alteration of rock matrix by secondary carbonate cement results in increased unconfined compressive strength, decreased permeability, and increased ultrasonic velocity. In this fault zone, and possibly other fault zones, the changes in rock properties associated with deformation can be detected through their geophysical response.

• Liberty, Lee M.; Yelton, Jonathan; Skurtveit, Elin; Braathen, Alvar; Midtkandal, Ivar & Evans, James P. (2022). Regolith and host rock influences on CO<inf>2</inf> leakage: Active source seismic profiling across the Little Grand Wash fault, Utah. International Journal of Greenhouse Gas Control. ISSN 1750-5836. 119. doi: 10.1016/j.ijggc.2022.103742. Fulltekst i vitenarkiv Vis sammendrag

  Understanding carbon dioxide (CO2) reservoir to surface migration is crucial to successful carbon capture and sequestration approaches; especially fault/reservoir interactions under injection pressure. Through seismic imaging, we explore regolith and shallow stratigraphy across the Little Grand Wash fault. The presence of natural CO2 seeps, travertine and tufa deposits confirm modern and ancient fault-controlled CO2 leakage. We consider this an analogue for a long-failed sequestration site. We estimate bulk porosity and fracture density for host rock, regolith, and fault zone from petrophysical relationships. When combined with existing geochemical and geological data, we characterize a 60 m wide damage zone that represents the primary surface delivery channel for CO2 originating from reservoir depths. Within this damage zone, low seismic velocities suggest sediments have formed through host rock chemical dissolution or mechanical weathering. In contrast, velocities within the adjacent host rock are consistent with low fracture density clastic rocks. We measure anomalously high seismic velocities within the fault zone along one profile that best represents a sealed (cemented/plugged) low permeability, relic flow channel. This suggests that shallow fault zone permeability varies along strike. While regional stress changes may account for decadal- to millennial-scale changes in CO2 pathways, we speculate that the total fluid pressure has locally reduced the fault's minimum horizontal effective stress; thereby producing both low- and high-permeability fault segments that either block or promote fluid migration. Studying CO2 migration in this system can inform potential risks to future sequestration projects and guide monitoring efforts.

• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, J. A. Mattias (2022). Tidal dynamics in palaeo-seas in response to changes in physiography, tidal forcing and bed shear stress. Sedimentology. ISSN 0037-0746. 69(4), s. 1861–1890. doi: 10.1111/sed.12975. Fulltekst i vitenarkiv Vis sammendrag

  Simulating hydrodynamic conditions in palaeo-ocean basins is needed to better understand the effects of tidal forcing on the sedimentary record. When combined with sedimentary analyses, hydrodynamic modelling can help inform complex temporal and spatial variability in the sediment distribution of tide-dominated palaeo-ocean basins. Herein, palaeotidal modelling of the epicontinental Upper Jurassic (160 Ma, lower Oxfordian) Sundance and Curtis seas of North America reveals possible regional-scale variations in tidal dynamics in response to changes in ocean tidal forcing, physiographic configuration and bottom drag coefficient. A numerical model forced with an M2 tidal constituent at the open boundary shows that the magnitude and location of tidal amplification, and the variability in current velocity and bed shear stress in the basin, were controlled by palaeophysiography. Numerical results obtained using a depth of 600 m at the ocean boundary of the system enable the prediction of major facies trends observed in the lower Curtis Formation. The simulation results also highlight that certain palaeophysiographic configurations can either permit or prevent tidal resonance, leading to an overall amplification or dampening of tides across the basin. Furthermore, some palaeophysiographic configurations generated additional tidal harmonics in specific parts of the basins. Consequently, similar sedimentary successions can emerge from a variety of relative sea-level scenarios, and a variety of sedimentary successions may be deposited in different parts of the basin in any given relative sea-level scenario. These results suggest that the interpretation of sedimentary successions deposited in strongly tide-influenced basins should consider changes in tidal dynamics in response to changing sea level and basin physiography.

• Faleide, Thea Sveva; Braathen, Alvar; Lecomte, Isabelle Christine & Anell, Ingrid (2022). Exploring seismic detection and resolution thresholds of fault zones and gas seeps in the shallow subsurface using seismic modelling. Marine and Petroleum Geology. ISSN 0264-8172. 143. doi: 10.1016/j.marpetgeo.2022.105776. Fulltekst i vitenarkiv Vis sammendrag

  Seismic resolution and illumination issues are sources of challenges in the detailed imaging and detection of subsurface fault architecture and fluid migration. Improved constraints on resolution can provide input into monitoring requirements and detectability of CO2 leakage, and fault-sealing properties during subsurface visualization of migration pathways. This study explores detection and resolution thresholds via synthetic seismic imaging of a detailed shallow normal fault model with realistic fault architecture including sub-seismic structures of damage zones. The base fault model is built from interpretations of high-resolution P-Cable seismic data and is further developed and conditioned by outcrop-based observations and empirical laws for fracture and deformation band distribution. Damage zones of sandstone layers host deformation bands contrary to shale layers with fractures, while mixed lithologies (shaley sandstone and sandy shale) are subjected to a combination of the two deformation mechanisms. We utilize a 2D point-spread function based convolution seismic modelling to produce the synthetic seismic images. Test scenarios include one baseline fault model without a damage zone (M1), and five more advanced/detailed fault models incorporating features known from outcrops (M2-M6; damage zones, an isolated fracture corridor, and gas seeps (CO2) along damage zones of faults and in the fracture corridor). Furthermore, sensitivity analyses on two selected models test the effect of changing the illumination angle and wavelet. The results show that: (1) faults with damage zones have larger disturbances in seismic signals than faults without damage zones, (2) stronger amplitudes are distinguished for models with CO2-filled fractures, (3) a fracture corridor (5 m at it widest) is clearly visible where it crosses horizons bounding horizontal layers, (4) sensitivity tests show good imaging for illumination ≥45°, which is the average dip of the main fault segment, and (5) learnings from fault modelling offer guidance for seismic monitoring.

• Braathen, Alvar; Petrie, Elisabeth; Nystuen, Tonje; Sundal, Anja; Skurtveit, Elin & Zuchuat, Valentin [Vis alle 8 forfattere av denne artikkelen] (2020). Interaction of deformation bands and fractures during progressive strain in monocline - San Rafael Swell, Central Utah, USA. Journal of Structural Geology. ISSN 0191-8141. 141. doi: 10.1016/j.jsg.2020.104219. Fulltekst i vitenarkiv Vis sammendrag

  Folds in porous sandstone in cases allow identification of progressive deformation in an evolving strain field. In the Navajo Sandstone of the km-scale Laramide-style monocline of the San Rafael Swell (Utah, USA), four populations of small-scale structures record different kinematics and deformation mechanisms, depending on orientation to bedding within the first-order fold. Small-scale structures span from cataclastic (shear-) compaction and shear-isochoric deformation bands to dominant disaggregation (shear-) dilation bands. Extension and shear fractures record transformations from band to fracture formation, adding to the structural diversity. Early structures record semi-penetrative shear deformation guided by bedding and lamination in eolian deposits, consistent with layer-parallel shortening. Subsequent deformation is localized and at a higher angle relative to bedding, recording forward-directed and subsequently backward-directed shear structures within the east-verging monocline. Final deformation is highly localized and appears as a conjugate set of sub-vertical shear zones with shortening-extension axes oblique to the monocline. For the given conditions in a progressive shear system in highly porous sandstones, interactions of deformation bands and fractures suggest a revival of deformation bands by mutual shear band-fracture systems as developing band swarms rotate into an extensional strain sector during folding. In cases of deformation by shear-dilation strain, deformation bands may evolve directly into fractures, as grain contacts are lost.

• Skurtveit, Elin; Sundal, Anja; Bjørnarå, Tore Ingvald; Soldal, Magnus; Sauvin, Guillaume & Zuchuat, Valentin [Vis alle 8 forfattere av denne artikkelen] (2020). Experimental investigation of natural fracture stiffness and flow properties in a faulted CO2 bypass system (Utah, USA). Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125(7). doi: 10.1029/2019JB018917. Fulltekst i vitenarkiv Vis sammendrag

  Fracture 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.

• Zuchuat, Valentin; Midtkandal, Ivar; More, Miquel Poyatos; Costa, Sigrid Da; Brooks, Hannah Louise & Halvorsen, Kristine [Vis alle 9 forfattere av denne artikkelen] (2019). Composite and diachronous stratigraphic surfaces in low-gradient, transitional settings: The J-3 “unconformity” and the Curtis Formation, east-central Utah, U.S.A. Journal of Sedimentary Research. ISSN 1527-1404. 89(11), s. 1075–1095. doi: 10.2110/jsr.2019.56. Fulltekst i vitenarkiv Vis sammendrag

  Unconformities, by definition, correspond to erosional or nondepositional surfaces, which separate older strata below, from younger rocks above, encapsulating significant time gaps. However, recent studies have highlighted the composite nature of some unconformities, as well as their heterochronous and diachronous character, which challenge the use of such a definition in a four-dimensional dynamic environment. The J-3 Unconformity, separating the Middle Jurassic Entrada Sandstone from the Upper Jurassic Curtis Formation (and laterally equivalent units) in east-central Utah (USA), is laterally variable, generated by either erosion-related processes such as eolian deflation, and water-induced erosion, or by deformational processes. The J-3 Unconformity is a composite surface, formed by numerous processes that interacted and overlapped spatially and temporally. This study therefore demonstrates the heterochronous, diachronous, and non-unique nature of this surface interpreted as unconformity, where one process can be represented by varying expressions in the stratigraphic record, and conversely many processes may result in the same stratigraphic expression.

• Fan, Changyu; Braathen, Alvar; Wang, Zhenliang; Zhang, Xiaoqiang; Chen, Suiying & Feng, Nana [Vis alle 8 forfattere av denne artikkelen] (2019). Flow pathway and evolution of water and oil along reverse faults in the northwestern Sichuan Basin, China. American Association of Petroleum Geologists Bulletin. ISSN 0149-1423. 103(5), s. 1153–1177. doi: 10.1306/10261816501. Fulltekst i vitenarkiv
• Fan, Changyu; Braathen, Alvar; Wang, Zhenliang; Zhang, Xiaoqiang; Chen, Suiying & Feng, Nana [Vis alle 8 forfattere av denne artikkelen] (2019). Flow of brine and oil along reverse faults in the northwestern Sichuan Basin, China. American Association of Petroleum Geologists Bulletin. ISSN 0149-1423. 103(5), s. 1153–1177. doi: 10.1306/10261816501. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Skurtveit, Elin; Midtkandal, Ivar & Braathen, Alvar (2023). A naturally occurring CO2 laboratory in Utah. Fulltekst i vitenarkiv
• Midtkandal, Ivar (2023). COTEC-prosjektet - økt kunnskap om CO2-inneslutninger og overvåkningsteknikker. Fulltekst i vitenarkiv
• Smith, Scott Adam; Faleide, Thea Sveva; Petrie, Elizabeth S. & Skurtveit, Elin (2022). Velocity variations due to lithology and fractures in a fault zone with CO2 seepage, Utah, USA. EarthDoc. doi: 10.3997/2214-4609.202243030. Fulltekst i vitenarkiv
• Petrie, Elizabeth S.; Skurtveit, Elin; Faleide, Thea Sveva & Halvorsen, Kristine (2022). Fracture Systems and Development in an Active Fault Zone. Geological Society of America Abstracts with Programs. doi: 10.1130/abs/2022PR-376078. Fulltekst i vitenarkiv
• Dichiarante, Anna Maria; Oye, Volker & Bruland, Charlotte (2022). First results from passive seismic data at the Little Grand Wash Fault. Fulltekst i vitenarkiv
• Liberty, Lee (2022). Active source seismic profiling across the Little Grand Wash fault, Utah. Fulltekst i vitenarkiv Vis sammendrag

  Soil and rock seismic properties measurably change within a leaky CO2 fault system. • Shallow fault zone permeability varies along the Little Grand Wash fault. • Low- and high-permeability fault segments can block or promote upward CO2 migration. • Regional stresses and local fluid pressures can control fluid and gas migration.

• Skurtveit, Elin (2022). Fracture flow experiments, Little Grand Wash fault. Fulltekst i vitenarkiv
• Faleide, Thea Sveva; Smith, Scott Adam; Petrie, E. S.; Halvorsen, Kristine & Skurtveit, Elin (2022). Core characterization: CT scans, mini-perm, uniaxial compressional strength (UCS) test, P&S velocity. Fulltekst i vitenarkiv
• Petrie, Elizabeth (2022). LGW Drilling and core characterization. Fulltekst i vitenarkiv Vis sammendrag

  Summary of core-drilling and retrieval from Little Grand Wash Fault Zone, Utah

• Braathen, Alvar (2022). Fault zone architecture and seismic imaging. Fulltekst i vitenarkiv
• Faleide, Thea Sveva (2022). Exploring seismic detection and resolution thresholds of fault interpretations in the shallow subsurface using seismic modelling. Fulltekst i vitenarkiv
• Midtkandal, Ivar; Zuchuat, Valentin; Petrie, Elizabeth & Liberty, Lee (2021). COTEC. Fulltekst i vitenarkiv Vis sammendrag

  The multi-disciplinary, multi-institution approach to monitoring CO2-flow in the subsurface is presented, and represented by examples from sedimentology, structural geology, and seismic monitoring.

• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, Mattias J.A. (2021). Curtis Wars, episode IV: Return of the (Je)tide: Tidal dynamics in palaeo-seas in response to long-term changes in bathymetry, tidal forcing, and bottom shear stress. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Liberty, Lee; Petrie, Elizabeth; Hafner, Alison; Arvesen, Brock & Alterskjær, Camilla [Vis alle 10 forfattere av denne artikkelen] (2021). On CO2 monitoring techniques and the importance of collaborating during times of crisis. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, J.A. Mattias (2021). A quick a robust numerical modelling method to study the propagation of tides in palaeo-seas. Fulltekst i vitenarkiv Vis sammendrag

  Tidal dynamics in shoreline-shelf systems are dependent on the physiography (geometry and bathymetry) of a basin and its latitude. Researchers can increase their understanding of sedimentary processes in ancient shallow-marine basins, and incorporate potential variations in tidal dynamics in response to an anthropogenically-driven relative sea level change by studying the impact that changes in physiography have on tides. In order to conduct such an analysis in the epicontinental Upper Jurassic Sundance and Curtis Seas, we developed a workflow that everyone can use to model the propagation of tides in ancient basins, to understand the evolution of tidal dynamics in a basin with respect to change in its physiography, or to test the feasibility of certain geological interpretations. The numerical simulations of tides are run in the open-source Deltares Delft3D software, and one of the primary input that the software requires is palaeobathymetric data. Since these data might not exist for the study of ancient marine systems, we developed a simple Python code that extracts the colour-value of every pixel in a georeferenced image, before attributing it a depth value depending on how light- or dark-colour the pixel was: the lighter-coloured the pixel is, the shallower the attributed depth is (and vice-versa). Various tidal constituents can then be forced into the system, either at the same time, if the control on the different tidal constituents in the system is robust, or individually in order for example to minimise assumptions. Such a workflow can quickly test if and how tides can propagate in any given ancient seas, which allows for the testing of certain geological interpretation of the rock record. Our Python-code allows for the very quick generation of multiple palaeobathymetries, by varying the maximum depth attributed to the darkest-coloured pixel of the image, which can then be used to study by proxy the impact of relative sea-level variations on the propagation of tides in ancient seas. The sensitivity of the models can then be tested by varying different input parameters, such as the initial open-ocean tidal forcing, or the bottom drag coefficient values. Delft3d can notably simulate the tidal amplitude and the flow speed anywhere in the system and at any time, but the distribution of sedimentary facies can be predicted for each of the simulation, using the modelled maximum bed shear stress as a proxy. The map of the predicted distribution of sedimentary facies can then be compared to the real distribution of sedimentary facies in the rock record. The study of the Upper Jurassic Sundance and Curtis Sea using this simple but robust workflow allowed us to identify the primary control that the physiographic configuration had on the propagation of tides in the system. This workflow also allowed quantifying how tidal dynamics would evolve with respect to change in palaeophysiographic configuration, which has highlighted the importance of considers the effects of palaeophysiographic changes related to relative sea-level variations and their associated impact on tidal dynamics, which will certainly help improving and refining models of tide-dominated basins and their evolution.

• Zuchuat, Valentin; Midtkandal, Ivar; More, Miquel Poyatos; Costa, Sigrid Da; Brooks, Hannah Louise & Halvorsen, Kristine [Vis alle 9 forfattere av denne artikkelen] (2021). Mind The Gap: Composite and diachronous stratigraphic surfaces in low-gradient, transitional settings: The J-3 “unconformity” and the Curtis Formation, east-central Utah, U.S.A. Fulltekst i vitenarkiv
• Slivicki, Stephen & Liberty, Lee (2021). Seismic Response of Natural CO2 Gas Migration Through the Little Grand Wash Fault, Utah. Fulltekst i vitenarkiv
• Yelton, Jonathan & Liberty, Lee (2021). Seismic Imaging of Active and Ancient CO2 Pathways in the Little Grand Wash Fault. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, J.A. Mattias (2021). Variations in physiography, tidal forcing, and bottom shear stress in palaeo-seas: lessons learned from numerical modelling. Fulltekst i vitenarkiv Vis sammendrag

  The physiography (geometry and bathymetry) of a basin and its latitude are the primary parameters that dictate the tidal dynamics in shoreline–shelf systems. Understanding the impact that changes in physiography have on tides allows researchers to 1) improve interpretations of historical sedimentary processes in shallow-marine basins, and 2) better predict potential variations in tidal dynamics in response to an anthropogenic-driven relative sea level change. Here, we present an analysis of numerical modelling of tidal propagation in the Upper Jurassic Sundance and Curtis Seas demontrating that basin-scale amplification and dampening of tides occurred in different palaeophysiographic configurations, and more localised amplification relating to tidal harmonics occurred in certain physiographic scenarios. Consequently, palaeophysiography was the primary control on both the magnitude and location of tidal amplification, flow speed, and bed shear stress, whereas secondary controls were initial tidal forcing and bottom drag coefficient. Simulation results for the palaeophysiography with a 600 m depth at the mouth of the system suggest a distribution of sedimentary facies comparable to those documented in the Upper Jurassic lower Curtis Formation, apart from the innermost Curtis Sea, near to the palaeoshoreline. Sediments potentially supplied by aeolian processes during regression and increased aridity were likely reworked by tides during a subsequent a transgression as the climate became more humid. The palaeophysiography with a 600 m depth at the mouth of the system can therefore be considered a realistic palaeophysiographic configuration for the Sundance and Curtis Seas given the similarities that exist between the predicted distribution of sedimentary facies and their actual distribution in the lower Curtis Formation. In this palaeophysiography, the Sundance Sea and the Curtis Sea would have thus attained a maximum depth of ~240 m and 40-45 m, respectively. In this context, the simulated tidal range in the Curtis Sea would have reached 2.60 m, which would classify the Curtis Sea as a meso-tidal system (2x 1.30 m tidal amplitude). Finally, using change in palaeophysiographic configuration as a proxy for relative sea-level variations revealed the non-uniqueness (sensu Burgess & Prince, 2015) of sedimentary successions deposited in tide-dominated basin, given that tidal amplification in the system was controlled by palaeophysiographic configuration: one specific succession could be the product of several, equally-valid relative sea-level histories. Reciprocally, the impact of relative sea-level change on different successions is non-unique, since local tidal harmonics and the characteristics of coeval deposition may vary significantly during relative sea level changes.

• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, J.A. Mattias (2021). Ancient tides and physiography: time to update sequence-stratigraphic models? Fulltekst i vitenarkiv Vis sammendrag

  Tidal dynamics are dependent on the physiography (geometry and bathymetry) of a basin and its latitude. By studying the impact that changes in physiography have on tides, scientists can improve their understanding of sedimentary processes that occurred in palaeo-seas, and incorporate potential variations in tidal dynamics in response to relative sea level changes to their interpretation. We developed a workflow that everyone can use to model the propagation of tides in ancient basins, to understand the evolution of tidal dynamics in a basin with respect to change in its physiography, or to test the feasibility of certain geological interpretations. This methods was tested in the epicontinental Upper Jurassic Sundance and Curtis Seas, which extended from today’s British Columbia to today’s east-central Utah, where tidal currents strongly impacted the deposition of certain sedimentary units preserved in the rock record. The numerical simulations of tides were run in the open-source Delft3D software by Deltares, and one of the initial input that the software requires is palaeobathymetric data. Because palaeobathymetry data might not exist for the study of ancient seaways, we developed a simple Python code that extracts the colour-value of every pixel in a georeferenced image, before attributing it a depth value depending on how light- or dark-colour the pixel was: the lighter-coloured the pixel is, the shallower the attributed depth is (and vice-versa). The results of numerical modelling of tidal propagation show that changing the palaeophysiographic configuration of the basin controls both the magnitude and the location of tidal amplification. Some palaeophysiographic configurations resulted in an overall increase in tidal amplitude in the seaway (with various degrees of amplification) but potentially link to the onset of resonance in (part of) the basin, whereas other palaeophysiographic configurations led to a general decrease of the tidal amplitude. Further, certain palaeophysiographic configurations resulted in a heterogeneous spatial distribution of the tidal amplification across the basin as additional tidal harmonics only appeared in certain parts of the basin, but were absent from others. This results in the resurgence of tidal amplification or dampening with different periods at different locations, with increasing spatial variations the deeper the basin is. As a result, the stacking pattern of the various architectural elements would differ from one margin of the basin to the other, despite a similar relative sea-level history. Consequently, the interpretation of the relative sea-level history across an entire basin necessitates caution when tides are one of the main process active at the time of deposition, especially when data points are scarce or limited to a portion of the basin only.

• Faleide, Thea Sveva; Braathen, Alvar; Lecomte, Isabelle; Mulrooney, Mark Joseph; Anell, Ingrid Margareta & Midtkandal, Ivar [Vis alle 7 forfattere av denne artikkelen] (2020). Testing seismic interpretation of faults by modelling; viable geometries versus seismic resolution in the subsurface. EAGE extended abstracts. 2020. doi: 10.3997/2214-4609.202011930. Fulltekst i vitenarkiv
• Buckley, Simon John; Ringdal, Kari; Lecomte, Isabelle; Anell, Ingrid Margareta & Braathen, Alvar (2020). Virtual field trip to seismic scale outcrops of the Triassic, Edgeøya, Svalbard. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Steel, Elisabeth; Mulligan, Ryan P.; Collins, Daniel S. & Green, Mattias J.A. (2020). Does it still make sense to apply classical, sequence-stratigraphical concepts to tide-dominated basins? Fulltekst i vitenarkiv
• Faleide, Thea Sveva; Braathen, Alvar; Lecomte, Isabelle; Anell, Ingrid Margareta; Midtkandal, Ivar & Planke, Sverre (2020). Seismic modelling of faults; viable geometries vs seismic resolution in the subsurface. Fulltekst i vitenarkiv Vis sammendrag

  Resolution and illumination issues in seismic data curtails identification of fault geometries and fault-initiated rock damage when mapping subsurface faults. Seismic modelling can be utilized to bridge the gap in identifying what can be imaged with certainty in seismic data, with respect to the original geology, especially when also comparing to outcrop data. In this study, we explore how seismic modelling can distinguish between real structures versus seismic artefacts. 2(3)D Point-Spread-Function based convolution modelling is used in a sensitivity study. One input is detailed fault interpretations of high-resolution P-Cable data and comparable conventional 3D seismic data from the Hoop area in the Barents Sea. Another dataset comes from detailed fault geometries observed in outcrops, which were used to build geological models as input to the seismic modelling. In addition to the host-rock lithofacies, parameters of importance for the geological model building include overall fault geometry and the distribution of architectural elements (fault facies) within the fault zone. By varying fault input, lithofacies, a wide range of frequencies, and illumination, we analyse a variety of synthetic seismic images. Finally we compare our modelled outcomes with seismic data from the Hoop area. The scope of the workflow is to increase confidence in seismic interpretations and to identify limitations in the analysis of steep, normal faults in seismic data.

• Zuchuat, Valentin (2020). If Cream knew how to code: psychedelic simulations of tides in the Proto-Western Interior Seaway. Fulltekst i vitenarkiv
• Faleide, Thea Sveva (2020). Seismic modelling of faults; viable geometries vs seismic resolution in the subsurface. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Midtkandal, Ivar; More, Miquel Poyatos; Costa, Sigrid Da; Brooks, Hannah L & Halvorsen, Kristine [Vis alle 9 forfattere av denne artikkelen] (2020). Brexit, Megxit, and the J-3 Unconformitexit: how they all lost it. Fulltekst i vitenarkiv Vis sammendrag

  Unconformities, by definition, correspond to non-depositional or erosive surfaces, separating older strata below, from younger rocks above, and encapsulating significant time gaps. However, recent studies have emphasized the composite nature of some unconformities, as well as their heterochronous and diachronous character, which restricts the use of such a definition to a near one-dimensional setting. This study analyses the nature of the J-3 Unconformity, which separates the Middle Jurassic Entrada Sandstone from the Late Jurassic Curtis Formation (and laterally equivalent units) in east-central Utah (USA). Our detailed mapping and characterization indicates the J-3 “Unconformity” is in fact a composite surface generated by either erosion-related processes such as eolian deflation, and water-induced erosion, or by deformational processes. These multiple mechanisms interacted and overlapped in time and space, which demonstrates the composite and diachronous and non-unique nature of such boundaries. This contact has been historically interpreted as an unconformity, but our results show that this key stratigraphic surface is a time-transgressive flooding-ravinement surface that formed shortly before and during a series of transgressions that flooded the area during the Late Jurassic. Consequently, the regionally extensive, composite, heterochronous, and diachronous J-3 Unconformity does not fit the classic unconformity definition, after which an unconformity universally separates older from younger strata basin-wide. The J3 “Unconformity” case study highlights the fact that one process can be represented by varying expressions in the stratigraphic record, and conversely many processes may result in the same stratigraphic expression. Consequently a revised definition of unconformity is discussed, focusing on processes and associated environmental changes, while abandoning its time-barrier aspect. This investigation also exemplifies some of the implications on subsurface analyses that the inaccurate characterization of the subseismic complex characters of such major stratigraphic bounding surfaces can have. These inaccuracies may lead to imprecise timing and sediment budget predictions, and ultimately have strong implications for basin evolution and reservoir models. Key words: Unconformity, transitional basin, composite surface, ravinement, time-transgressive

• Zuchuat, Valentin; Hafner, Alison; Osmond, Johnathon L.; Liberty, Lee; Petrie, Elizabeth & Arvesen, Brock [Vis alle 11 forfattere av denne artikkelen] (2020). CO2 containment and monitoring techniques along Little Grand Wash Fault, east-central Utah, USA. Fulltekst i vitenarkiv Vis sammendrag

  Our current understanding of sub-surface CO2 storage feasibility derives mainly from valuable small-scale projects, which have mostly been working at injection or human time scales. These projects, however, have not been operational long enough to fully assess flow and/or seepage at longer time scales relevant for subsurface CO2 sequestration (e.g. > 10 kY). Many examples of fluid escape have been documented in the offshore subsurface environment (e.g. seismic chimneys), and active or relict natural seeps on land offer informative analogues to subsurface fluid migration. Of note are the natural seeps located in east-central Utah, USA that are easily accessible and represent suitable onshore counterparts to the offshore fluid escape features. These seeps can be studied to improve our understanding of geological and geomechanical factors controlling subsurface CO2 containment and the expression of fluid escape in geophysical images. A critical concern in CCS is how to account for features that are detrimental to subsurface storage containment and are at scales below seismic resolution. This multidisciplinary project aims to address the challenge by collecting surface and subsurface datasets at mesoscopic scales that, through upscaling, will be implemented in seismic investigations and reservoir-seal models. The project builds upon previous studies detailing the complex development of the Jurassic sedimentary basin in question (Zuchuat et al. 2018; 2019a; 2019b) but is also relevant for analogous settings such as the Norwegian Continental Shelf (e.g. Horda Platform region). Overall, this next research phase specifically focuses on the detailed, post-depositional history of the targeted interval in Utah, addressing one fundamental question: what are the thresholds for detecting CO2 seeps in the subsurface? This encompasses more targeted questions: • What does the fault core and the fault damage zone of the leaking Little Grand Wash Fault consist of? • What is the detailed geological footprint of CO2 flow along strata, faults, and fractures? • How did the CO2 flow migrate through a heterogeneous and transitional, faulted reservoir-seal complex? • Can seepage from the storage compartments and fluid saturation be identified by seismic imaging? Zuchuat, V., Sleveland, A. R., Sprinkel, D. A., Rimkus, A., Braathen, A., & Midtkandal, I. (2018). New Insights on the Impact of Tidal Currents on a Low-gradient, Semi-enclosed, Epicontinental Basin—the Curtis Formation, East-central Utah, USA. Geology of the Intermountain West, 5, 131-165. Zuchuat, V., Sleveland, A.R.N., Pettigrew, R.P, Dodd, T.J.H., Clarke, S.M., Braathen, A., & Midtkandal, I. (2019a). Overprinted Allocyclic Processes by Tidal Resonance in an Epicontinental Basin: the Upper Jurassic Curtis Formation, East-Central Utah, USA. The Depositional Record, 5(2), 272-305. Zuchuat, V., Midtkandal, I., Poyatos-Moré, M., Da Costa, S., Brooks, H.L., Halvorsen, K., Cote, N., Sundal, A., & Braathen, A. (2019b). Composite and Diachronous Stratigraphic Surfaces in Low-Gradient, Transitional Settings: the J-3 “Unconformity” and the Curtis Formation, East-Central Utah, U.S.A. Accepted in The Journal of Sedimentary Research.

• Zuchuat, Valentin; Sleveland, Arve; Sprinkel, Douglas; Pettigrew, Ross P.; Dodd, Thomas J.H. & Clarke, Stuart M. [Vis alle 8 forfattere av denne artikkelen] (2020). When Utah was a blue state: the sedimentology of the tidally-influenced Upper Jurassic Curtis Formation. Fulltekst i vitenarkiv Vis sammendrag

  The sedimentary record of east-central Utah during the Middle/Late Jurassic shows that arid conditions prevailed, punctuated by episodic incursions of the Sundance Sea from the north. It is some of these incursions that terminated the Entrada aeolian system, and deposited the overlying shallow-marine Curtis Formation in a tide-dominated, semi-enclosed basin. The shallow-marine system was neighboured by a coastal aeolian system belonging to the Moab Member of the Curtis Formation, and a fluvially-starved, sporadically-flooded, paralic belt of the Summerville Formation. These paralic deposits progressively blanketed the shallow-marine strata of the Curtis Formation as the sea regressed northward. This study deconstructs and analyses the continental to shallow-marine deposition during one transgressive-regressive cycle. Our analysis sub-divides the Curtis Formation into three informal units: the lower, middle and upper Curtis. Allocyclically-driven, short-lived relative sea-level variations, along with episodes of uplift and deformation, dominated over autocyclic processes of the Curtis Sea as the lower Curtis was deposited. The system entered into tidal resonance following the onset of the major transgression that defines the base of the middle Curtis, as the flooded basin reached an optimal length that corresponded to an odd multiple of one quarter tidal wavelength. This high-energy resonant system overprinted the effects of allocyclic forcing within the middle Curtis. By contrast, the neighbouring coastal systems continued to record allocyclic signals preserved as five stacked aeolian sequences of the Moab Member of the Curtis Formation, and a cyclical pattern recognised within the supratidal Summerville Formation. By documenting a resonant stage in a tide-influenced basin that overprints the otherwise dominant allocyclic processes, this study highlights the importance of assessing coeval depositional systems in order to build complete stratigraphic basin histories. Keywords: allocyclic, autocyclic, Curtis Formation, stratigraphic surfaces, tidal resonance, aeolian sequences, Utah.

• Zuchuat, Valentin; Braathen, Alvar; Midtkandal, Ivar; Liberty, Lee; Skurtveit, Elin & Evans, James R. [Vis alle 10 forfattere av denne artikkelen] (2020). COTEC students seminar. Fulltekst i vitenarkiv
• Faleide, Thea Sveva; Midtkandal, Ivar; Planke, Sverre; Corseri, Romain; Faleide, Jan Inge & Nystuen, Johan Petter [Vis alle 8 forfattere av denne artikkelen] (2019). High-resolution seismic imaging and modelling of structural and stratigraphical features in the SW Barents Sea. Fulltekst i vitenarkiv Vis sammendrag

  Poster at the AAPG 2019 conference, San Antonio, Texas, USA

• Faleide, Thea Sveva; Midtkandal, Ivar; Planke, Sverre; Corseri, Romain; Faleide, Jan Inge & Nystuen, Johan Petter [Vis alle 7 forfattere av denne artikkelen] (2019). Barremian delta and Early Cretaceous faulting revealed by high resolution 3D seismic data in the southwestern Barents Sea. NGF Abstracts and Proceedings of the Geological Society of Norway. Fulltekst i vitenarkiv
• Zuchuat, Valentin; Osmond, Johnathon L.; Sundal, Anja; Midtkandal, Ivar; Skurtveit, Elin & Petrie, Elizabeth [Vis alle 9 forfattere av denne artikkelen] (2019). CO2 containment and monitoring techniques along Little Grand Wash Fault, east-central Utah, USA. Fulltekst i vitenarkiv Vis sammendrag

  Our current understanding of sub-surface CO2 sequestration feasibility derives mainly from valuable small-scale projects, which have mostly been working at injection or human time scales. These projects, however, have not been operational long enough to fully assess flow and/or seepage at longer time scales relevant for subsurface CO2 storage (e.g. > 10 kY). Many examples of fluid escape have been documented in the offshore subsurface environment (e.g. seismic chimneys), and natural seeps found on land, both active and relict, offer informative analogues to subsurface fluid migration. Of note are the natural seeps located in east-central Utah, USA that are easily accessible and represent suitable onshore counterparts to the offshore fluid escape features. These seeps can improve our understanding of geological and geomechanical factors controlling subsurface CO2 containment and the expression of fluid escape in geophysical images. A critical concern is how to account for features that are detrimental to subsurface storage containment and are at scales below seismic resolution. This multidisciplinary project aims to address the challenge by collecting surface and subsurface datasets at mesoscopic scales that, through viable upscaling, will be implemented in seismic investigations and reservoir-seal models. Moreover, the project builds upon previous studies detailing the complex development of the Jurassic sedimentary basin in question (Zuchuat et al. 2018; 2019; in press) but is also relevant for the Horda Platform region (Aurora and Smeaheia) or other prospective North Sea CO2 storage sites. Overall, this next research phase specifically focuses on the detailed, post-depositional history of the targeted interval in Utah, addressing one fundamental question: what are the thresholds for detecting CO2 seeps in the subsurface? This encompasses more targeted questions: • What is the detailed geological footprint of CO2 flow along strata, faults, and fractures? • How did the CO2 flow migrate through a heterogeneous and transitional, faulted reservoir-seal complex? • Can seepage from the storage compartment be identified by seismic imaging? • Can detailed geological datasets and related geophysical models verify the existence of – and facilitate quantification of CO2 volumes (saturation) required to create offshore geophysical chimneys, and thereby improve integrity assessment of prospective North Sea CO2 reservoirs? Zuchuat, V., Sleveland, A. R., Sprinkel, D. A., Rimkus, A., Braathen, A., & Midtkandal, I. (2018). New Insights on the Impact of Tidal Currents on a Low-gradient, Semi-enclosed, Epicontinental Basin—the Curtis Formation, East-central Utah, USA. Geology of the Intermountain West, 5, 131-165. Zuchuat, V., Sleveland, A.R.N., Pettigrew, R.P, Dodd, T.J.H., Clarke, S.M., Braathen, A., & Midtkandal, I. (2019). Overprinted Allocyclic Processes by Tidal Resonance in an Epicontinental Basin: the Upper Jurassic Curtis Formation, East-Central Utah, USA. The Depositional Record, 5(2), 272-305. Zuchuat, V., Midtkandal, I., Poyatos-Moré, M., Da Costa, S., Brooks, H.L., Halvorsen, K., Cote, N., Sundal, A., & Braathen, A. (in press.). Composite and Diachronous Stratigraphic Surfaces in Low-Gradient, Transitional Settings: the J-3 “Unconformity” and the Curtis Formation, East-Central Utah, U.S.A. Accepted in The Journal of Sedimentary Research.

• Zuchuat, Valentin; Midtkandal, Ivar & Braathen, Alvar (2019). Continental to Shallow Marine Transition in a Tide-Dominated, Low Accommodation Basin - Controlling Factors and Depositional Architecture. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Modern tide-dominated, regressive shorelines featuring deltas estuaries and lagoons are well characterised and distinctive from wave or fluvial dominated systems. However, some ancient tidedominated basins and their associated sedimentary successions do not relate well to any of the above-mentioned, present-day systems. The Utah-Idaho Trough a semi-enclosed, narrow, and shallow foreland basin flooded during the Upper Jurassic by the Curtis Sea is one of these exceptions. The main target of this doctoral thesis is the Upper Jurassic, tide-dominated Curtis Formation, which outcrops in east-Central Utah, where it overlies the Middle Jurassic, aeolian deposits of the Entrada Sandstone. The Curtis Formation is defined at its base by the J-3 Unconformity and is conformably overlain by supratidal sabkha deposits of the Summerville Formation. The Entrada-Curtis-Summerville is subdivided into eight facies associations (FA 1-8), with six subfacies associations (FA 1a, 1b, 3a, 3b, 4a, 4b). Based on the specific three-dimensional arrangement of these facies associations, it is proposed to separate the Curtis Formation into three informal subunits: The lower, middle and upper Curtis. The lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud- (FA 3a) and sand-dominated heterolithic subtidal flat sediments (FA 3b),

• Zuchuat, Valentin (2019). Continental to Shallow Marine Transition in a Tide-Dominated, Low Accommodation basin - Controlling Factors and Depositional Architecture. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  This study presented in this doctoral thesis addresses the development of the Upper Jurassic Curtis Formation, outcropping in east-central Utah. The study suggests a separation of the Curtis Formation in three geological sub-units, each characterised by specific constituents, and diagnostic sedimentary architectures: the lower-, the middle-, and the upper Curtis. The lower Curtis was deposited as the semi-enclosed Curtis sea was flooding the arid coastal Entrada plains and dunes. It is characterised by thin beds of alternating mudstone and sandstone. It reflects three short-lived episodes of relative sea-level oscillations. It is capped by the middle Curtis, which consists nearly entirely of sandstone. The well-defined beds of the lower Curtis are replaced over time by an amalgamation of dunes and tidal channel deposits, reflecting a much higher energy level in the sea than the conditions that prevailed during the deposition of the lower Curtis. This dramatic increase in energy is thought to be a consequence of the basin entering into tidal resonance, which amplified the tides to such a degree that the signatures of short-lived relative sea-level variations were completely erased. As the Curtis sea was regressing, the energy level decreased, and the middle Curtis was subsequently replaced by the finer sediments of the upper Curtis, while the aeolian dunes of the Moab Member of the Curtis Formation were migrating next to the sabkhas of the Summerville Formation. The effects of these relative sea-level variations, absent from the middle Curtis, kept being recorded by the neighbouring and contemporaneous units above-mentioned, highlighting the importance of considering adjacent sedimentary systems in order to obtain the most complete knowledge of a basin’s history.

• Costa, Sigrid Da; Zuchuat, Valentin & Midtkandal, Ivar (2018). The complexity of regional erosion; incision, faulting, and deposition during the development of the J-3 unconformity, Utah, USA. Universitetet i Oslo. Fulltekst i vitenarkiv
• Bromander, Nikoline; Sundal, Anja; Midtkandal, Ivar & Zuchuat, Valentin (2018). Facies-controlled reservoir quality and preferential deformation in sandstone reservoirs; a case study from the Entrada Sandstone, Utah, USA. Universitetet i Oslo. Fulltekst i vitenarkiv
• Tveterås, Susanne; Braathen, Alvar; Midtkandal, Ivar & Zuchuat, Valentin (2018). Fault style and deformation mechanisms caused by sand mobility in the Entrada Sandstone and Curtis Formation, Utah, USA. Universitetet i Oslo. Fulltekst i vitenarkiv
• Halvorsen, Kristine; Zuchuat, Valentin; Midtkandal, Ivar & Braathen, Alvar (2018). Sand tectonics – sand mobility linked to faulting and the influence on depositional systems. Universitetet i Oslo. Fulltekst i vitenarkiv
• Halvorsen, Kristine; Braathen, Alvar; Midtkandal, Ivar & Zuchuat, Valentin (2018). Sand tectonics – sand mobility linked to faulting and the influence on depositional systems. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Mobility of sand by fluidization, so-called sand tectonics, can drive surface movements and thereby have a significant impact on depositional environments. Deformation related to sand mobilization is a typical understudied component in geology, yet important because it has implications for sediment distribution and sand body geometry. Previous studies imply regional, large-scale impacts as triggering events. This study consider the potential of local, smaller-scale drivers for sand mobilization. Improving the understanding of sand tectonic related processes is therefore necessary to better comprehend their dynamics and impact on sedimentary systems. Three outcrops in the Middle Jurassic Entrada Sandstone and Upper Curtis Formation in Utah (USA) have been used to characterize the structural and sedimentary response to the underlying mobilization of sand. Data show that mild sand mobilization results in meter-scale, gentle sags and up-warps, which can be linked to distinct depositional environments and erosional processes. With an increased localization of deformation, faults nucleate and small fault-bound grabens develop. Overall, growth sequences attest to fault movement events, demonstrating the structural control on the basin. Many of the faults in upper parts of the grabens are however removed by erosion and overlain by late basin fill. The results from this study may provide important input on deformation in near surface settings, applicable to both CO2 storage operations and the petroleum industry.

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