Jonathon Osmond

• Osmond, Johnathon; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2022). Structural traps and seals for expanding CO<inf>2</inf> storage in the northern Horda platform, North Sea. American Association of Petroleum Geologists Bulletin. ISSN 0149-1423. 106(9), s. 1711–1752. doi: 10.1306/03222221110. Fulltekst i vitenarkiv Vis sammendrag

  Development and maturation of geological carbon dioxide (CO2) storage projects along the Norwegian Continental shelf is ongoing, but even more storage locations are needed to reach climate mitigation goals by 2050. To augment the future Aurora injection site and expand CO2 storage in the northern Horda platform of the North Sea, the region’s potential must be assessed. Here, we leverage the latest wellbore and seismic data to map storage aquifers, identify structural traps, and assess possible top and fault seals associated with Lower and Upper Jurassic storage complexes in four major fault blocks. Our results indicate that both storage complex aquifers are preserved throughout the study area. From our minimum size criteria, we have identified a total of 95 Lower and 64 Upper Jurassic traps representing approximately 2.37 × 1010 and 5.80 × 1010 m3 in gross rock volume, respectively. Mapping, modeling, and formation pressure analyses suggest that top seals are sufficiently thick over the majority of structural traps and provide vertical pressure barriers between storage aquifers. Across-fault juxtaposition seals are abundant but dominate the Upper Jurassic storage complexes. Lower Jurassic aquifers, however, are often upthrown against Upper Jurassic aquifers, but apparent across-fault pressure differentials and shale gouge ratio values >0.15 correlate, suggesting fault rock membrane seal presence. Aquifer self-juxtapositions, however, are likely areas with poor fault seal. Overall, our work provides added support that the northern Horda platform represents a promising location for CO2 storage expansion, carrying the potential to become a future storage hub in the North Sea.

• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Braathen, Alvar; Skurtveit, Elin & Sundal, Anja (2022). Structural characterization and across-fault seal assessment of the Aurora CO<inf>2</inf> storage site, northern North Sea. Petroleum Geoscience. ISSN 1354-0793. 28(4). doi: 10.1144/petgeo2022-036. Fulltekst i vitenarkiv Vis sammendrag

  Faults play an essential role at many potential CO2 storage sites because they can act as conduits or barriers to fluid flow. To contribute to the evaluation of the Aurora storage site in the northern North Sea, we perform a structural characterization and assessment of across-fault seals that displace the Lower Jurassic storage complex. We find that first-order faults are predominately north–south striking and west dipping, with throws greater than the thickness of the primary seal (>85 m). In contrast, second-order faults have lower throws (15–50 m), and variable strike and dip directions. Due to the dip of the storage complex, injected CO2 is likely to migrate northwards before encountering the first-order Svartalv Fault Zone on its footwall side, which juxtaposes the storage units against younger sand-rich units. However, shale gouge ratio values exceed 0.30 at the depth of the storage complex, suggesting that a fault membrane seal may be present. Furthermore, second-order NE-dipping faults create juxtaposition seals and, in places, small-scale structural traps (24–48 m) along the Svartalv Fault Zone. Overall, we suggest that faults within the Aurora storage site could provide barriers to plume migration, allowing more CO2 to become trapped and thereby increasing the storage capacity.

• Würtzen, Camilla Louise; Osmond, Johnathon; Faleide, Jan Inge; Nystuen, Johan Petter; Anell, Ingrid & Midtkandal, Ivar (2021). Syn- to post-rift alluvial basin fill: seismic stratigraphic analysis of Permian-Triassic deposition in the Horda Platform, Norway. Basin Research. ISSN 0950-091X. doi: 10.1111/bre.12644. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Structural analysis of the Smeaheia fault block, a potential CO2 storage site, northern Horda Platform, North Sea. Marine and Petroleum Geology. ISSN 0264-8172. 121. doi: 10.1016/j.marpetgeo.2020.104598. Fulltekst i vitenarkiv Vis sammendrag

  Smeaheia, a prominent fault block located on the Horda Platform, northern North Sea is identified as a potential subsurface CO2 storage site. We utilise the GN1101 3D seismic survey to generate a high-resolution subsurface geomodel to inform the structural style and evolution of the fault block, to investigate geological controls on proposed CO2 storage and provide a geometric framework as a basis for future analyses. Two basement-involved (first-order) north-south trending fault systems, the Vette Fault Zone (VFZ) and the Øygarden Fault Complex (ØFC), bound the 15 km-wide fault block. The VFZ bifurcates down-section where it is hard-linked with two separate basement structures, a phenomenon we term as “dual rooted”. Apart from activity during the Permo-Triassic (Rift Phase 1) and the Late Jurassic–Early Cretaceous (Rift Phase 2), we present evidence that rifting in this part of the North Sea continued into the Late Cretaceous with minor reactivation in the Palaeocene–Eocene. Two segments of the VFZ interacted and linked at a relay ramp during Rift Phase 2. Second-order (thin-skinned) faults show basement affinity and developed during Rift Phase 2 in two distinct pulses. A population of polygonal faults intersects the overburden and developed during the Eocene to middle Miocene. We have revised the areal extent of two structural closures that define the Smeaheia fault block, Alpha (VFZ footwall) and Beta (ØFC hanging wall) which consist of Upper Jurassic Viking Group target formations. Simplified cross-fault juxtaposition analysis of the VFZ and second-order intra-block faults are presented and inform pressure communication pathways between the Smeaheia and Tusse fault block, as well as reservoir integrity and compartmentalisation. The geomodel further identifies important geological controls on CO2 storage in the fault block including a thinning caprock above the Alpha structure, and identification of hard-linkage between deep tectonic faults and shallow polygonal faults.

• Horne, Elizabeth A.; Hennings, Peter H.; Osmond, Johnathon L. & DeShon, Heather R. (2020). Structural characterization of potentially seismogenic faults in the Fort Worth Basin. Interpretation. ISSN 2324-8858. 8(2), s. T323–T347. doi: 10.1190/INT-2019-0188.1. Fulltekst i vitenarkiv Vis sammendrag

  From 2006 through mid-2018 there have been 125 Mw = 2.5 recorded earthquakes within the Fort Worth Basin and the Dallas-Fort Worth metropolitan area. There is general scientific consensus that this increase in seismicity has been induced by increases in pore fluid pressure from waste water injection and from cross-fault pore pressure imbalance due to injection and production. Previous fault stress analyses show that many of the faults are critically stressed, therefore careful consideration should be taken when injecting in close proximity to these structures. Understanding the structural characteristics that control geomechanical aspects of these earthquake-prone faults is vital to characterizing this known hazard. To improve the understanding of faults in the system we provide a characterization using a new basin-wide fault interpretation and database that has been assembled through the integration of published data, 2D and 3D seismic surveys, outcrop mapping, earthquakes, and interpretations provided by operators resulting in a 3D structural framework of basement-rooting faults. Our results show that a primary fault system trends NE-SW, creating a system of elongate horsts and grabens. Fault architectures range from isolated faults to linked and cross-cutting relay systems with individual segments ranging in length from 0.5 to 80 km. The faults that have hosted earthquakes are generally less than 10 km long, trend towards the northeast, and exhibit over 50 meters of normal displacement. The intensity of faulting decreases to the west away from the Ouachita structural front. Statistical analysis of fault length, spacing, throw, and linkage tendency enables a more complete characterization of faults in the basin which can be used to mitigate the seismic hazard. Finally, we show that a significant percentage of the total population of faults may be susceptible to reactivation and seismicity as those that have slipped recently.

• Osmond, Johnathon Lee & Meckel, Timothy A. (2019). Enhancing trap and fault seal analyses by integrating observations from HR3D seismic data with well logs and conventional 3D seismic data, Texas inner shelf. Geological Society Special Publication. ISSN 0305-8719. doi: 10.1144/SP496-2018-142. Fulltekst i vitenarkiv Vis sammendrag

  An understanding trap and fault seal quality is critical for assessing hydrocarbon propspectivity. To achieve this, modern analytical techniques leverage well data and conventional industry-standard 3D seismic data to evaluate the trap and any faults displacing the reservoir and top seal intervals. Above all, geological interpretation provides the framework of trap and fault seal analyses, but can be hindered by data resolution, quality, and acquisition style of the conventional seismic data. Furthermore, limiting the analysis to only the petroleum system at depth may lead to erroneous perceptions because interpreting overburden features, such as shallow faults or gas chimneys, can provide valuable observations with respect to containment performance and can help validate trap and fault seal predictions. A supplement to conventional 3D data are high-resolution 3D seismic (HR3D) data, which provide detailed images of the overburden geology. This study utilizes an HR3D seismic volume in the San Luis Pass area of the Texas inner shelf, where shallow fault tips and a sizeable gas chimney are interpreted over an unsuccessful hydrocarbon prospect. Static post-drill fault seal and trap analyses suggest that the primary fault displacing the structural closure could have withheld columns of gas ∼100 m high, but disagrees with our HR3D seismic interpretations and dry-well analyses. From our results, we hypothesize that tertiary gas migration through fault conduits reduced the hydrocarbon column in the prospective Early Miocene reservoir, and may have resulted from continued movement along the intersecting faults. Overall, this study reinforces the importance of understanding the overburden geology and geohistory of faulted prospects, and demonstrates the utility of pre-drill HR3D acquisition when conducting trap and fault seal analyses.

• Hennings, Peter H.; Snee, Jens-Erik Lund; Osmond, Johnathon Lee; DeShon, Heather R.; Dommisse, Robin & Horne, Elizabeth [Vis alle 8 forfattere av denne artikkelen] (2019). Injection-induced seismicity and fault-slip potential in the Fort Worth Basin, Texas. Bulletin of The Seismological Society of America (BSSA). ISSN 0037-1106. 109(5), s. 1615–1634. doi: 10.1785/0120190017. Fulltekst i vitenarkiv Vis sammendrag

  The rate of seismicity in the hydrocarbon‐producing Fort Worth Basin of north‐central Texas, which underlies the Dallas–Fort Worth metropolitan area, increased markedly from 2008 through 2015, coinciding spatiotemporally with injection of 2 billion barrels of wastewater into deep aquifers. Although the rate of seismicity has declined with injection rates, some earthquake sequences remained active in 2018 and new clusters have developed. Most of this seismicity occurred away from regionally mapped faults, challenging efforts to constrain the continuing hazards of injection‐induced seismicity in the basin. Here, we present detailed new models of potentially seismogenic faults and the stress field, which we use to build a probabilistic assessment of fault‐slip potential. Our new fault map, based on reflection seismic data, tens of thousands of well logs, and outcrop characterization, includes 251 basement‐rooted normal faults that strike dominantly north‐northeast, several of which extend under populated areas. The updated stress map indicates a relatively consistent north‐northeast–south‐southwest azimuth of the maximum horizontal principal stress over seismically active parts of the basin, with a transition from strike‐slip faulting in the north to normal faulting in the southeast. Based on these new data, our probabilistic analysis shows that a majority of the total trace length of the mapped faults have slip potential that is equal to or higher than that of the faults that have already hosted injection‐induced earthquake sequences. We conclude that most faults in the system are highly sensitive to reactivation, and we postulate that many faults are still unidentified. Ongoing injection operations in the region should be conducted with these understandings in mind.

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• Holden, Nora; Alaei, Behzad; Skurtveit, Elin; Braathen, Alvar; Midtkandal, Ivar & Osmond, Johnathon L. [Vis alle 8 forfattere av denne artikkelen] (2024). CO2 storage on the Horda Platform - Assessing structural complexities and fault-seal integrity. Fulltekst i vitenarkiv
• Holden, Nora; Skurtveit, Elin; Braathen, Alvar; Alaei, Behzad; Midtkandal, Ivar & Osmond, Johnathon L. [Vis alle 8 forfattere av denne artikkelen] (2024). CO2 storage on the Horda Platform. Fulltekst i vitenarkiv
• Holden, Nora; Alaei, Behzad; Skurtveit, Elin; Braathen, Alvar; Midtkandal, Ivar & Osmond, Johnathon L. [Vis alle 8 forfattere av denne artikkelen] (2024). Structural de-risking of CO2 storage sites on the Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Holden, Nora; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2024). Beyond Aurora and Smeaheia; structural traps and seals for additional CO2 storage within Jurassic Horda Platform aquifers. Fulltekst i vitenarkiv Vis sammendrag

  Summary: Geological carbon dioxide sequestration (CCS) is a relatively small, yet viable solution for reducing CO2 emissions as we approach the year 2050. This is particularly true for emissions resulting from industrial operations that likely cannot be rendered into emissionless processes, such as cement production. The Aurora CO2 storage site located in the northern Horda Platform of the Norwegian North Sea is part of the Longship project, one of the world’s first to demonstrate the full CCS value chain. Injection and containment of CO2 is scheduled take place by 2024 within the Lower Jurassic storage complex comprised of Dunlin Gp siliciclastic saline aquifers capped by mudrocks and shales. While current well tests at Aurora suggest favorable conditions for injection rates of 5 megatons per year, more storage sites are required and under development. Roughly 40 km east of Aurora, a second CO2 storage exploitation license has recently been awarded in the Smeaheia area. In contrast to Aurora, injection is likely to transpire within an Upper Jurassic storage complex, with aquifers of the Viking Gp overlain by fine-grained rocks of the Viking Gp and Lower Cretaceous Cromer Knoll Gp, similar to parts of the nearby Troll field. While storage complexes in both areas are fairly well-established, less is certain about whether or not the same concepts could be utilized throughout greater northern Horda Platform, and what other areas have potential. In order to address the possibility of expanding the northern Horda Platform into a larger CO2 storage hub, we utilized 3D seismic reflection and wellbore data to study the Lower and Upper Jurassic storage complexes with a regional structural trap and seal approach. Here, we show Lower and Upper Jurassic storage aquifers presence, and highlight the array of fault-bound structural traps. We also present top seal thickness variations and evidence of their effectiveness, where we consider fine-grained Cretaceous Shetland Gp and Paleocene Rogaland Gp rock as additional seals of the Upper Jurassic storage complex. Furthermore, because faults have generally been observed to provide barriers or conduits to across-fault fluid migration, we have assessed the lateral fault seals critical for containing injected CO2 within the mapped traps. While across-fault juxtaposition seals are of high confidence and are critical for the Upper Jurassic storage complex, we go on to illustrate that membrane seals are also necessary for success in the Lower Jurassic storage complex, but both pressure data and empirical modeling imply their seal effectiveness. Finally, as the Aurora and Smeaheia storage sites develop and technical work continues to be carried out, the results from this study suggest that the Upper and Lower Jurassic storage complexes could be utilized to develop northern Horda Platform CO2 into a larger storage hub.

• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Sundal, Anja & Braathen, Alvar (2023). Structural characterization and across-fault seal assessment of the Aurora CO2 storage site. Fulltekst i vitenarkiv
• Osmond, Johnathon; Mulrooney, Mark Joseph; Würtzen, Camilla Louise; Cruz, E. De La; Skurtveit, Elin & Faleide, Jan Inge [Vis alle 7 forfattere av denne artikkelen] (2022). Upper Jurassic through Lower Cretaceous seal characterization in the northern Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Leon, Elias H.; Cruz, Erika H. de La & Würtzen, Camilla Louise [Vis alle 9 forfattere av denne artikkelen] (2022). Containment derisking of a potential CO2 storage hub in the Horda Platform, Norwegian North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2022). Screening traps and seals for CO2 storage expansion in the northern Horda Platform, Norwegian North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Evaluation and development of new and exciting CO2 storage opportunities on the Norwegian Continental Shelf is on the rise. Of note is the Aurora site located in northern Horda Platform of the Norwegian North Sea, where injection is scheduled to commence in 2024 under project Longship. While the planned injection volumes at Aurora are over 1.5 megatonnes per year, many more storage locations are required in order to meet international climate mitigation targets by 2050. Other parts of the northern Horda Platform show CO2 storage potential, but additional subsurface characterization is required. As a contribution towards this effort, I present two possible Jurassic storage complexes (Lower and Upper), where I discuss the presence of available storage aquifers, structural traps, as well as top and fault seals. Overall, our work supports the notion that the northern Horda Platform may be capable of hosting a future CO2 storage hub for northern Europe.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2022). Structural traps and seals for expanding CO2 storage in the northern Horda Platform, North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Full-scale CO2 storage within the Norwegian Continental Shelf is scheduled to commence in 2024 at the Aurora site under project Longship and the Northern Lights JV. While tens of megatons of injected CO2 are anticipated over the coming years, many more storage locations are required in order to meet international climate mitigation targets by 2050. In the event of success at Aurora, the northern Horda Platform region could be further developed into a North Sea CO2 storage hub, but more subsurface evaluation is needed to identify prospective sites. Here, I present two possible Jurassic storage complexes (Lower and Upper), and discuss the presence of available storage aquifers, structural traps, as well as top and fault seals based on the latest 3D seismic and wellbore data. Our results indicate that both storage complex aquifers are preserved throughout the study area, and we have identified a total of 95 Lower and 64 Upper Jurassic fault-bound traps. Mapping, modeling, and formation pressure analyses suggest that top seals are sufficiently thick over the majority of identified traps, and provide vertical pressure barriers between storage aquifers. While across-fault juxtaposition seals appear to dominate the Upper Jurassic storage complexes, Lower Jurassic aquifers are often up-thrown against Middle and Upper Jurassic aquifers, posing a potential risk to CO2 containment for many Lower Jurassic footwall traps. However, I go on to show that apparent across fault pressure differentials and shale gouge ratio values >0.15 correlate at such juxtapositions, suggesting fault rock membrane seal presence. Moreover, I illustrate that aquifer self-juxtapositions are likely zones of poor fault seal within the study area. Overall, our work provides added support that the northern Horda Platform represents a promising location for CO2 storage expansion, carrying the potential to become a future storage hub for northern Europe.

• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Braathen, Alvar & Sundal, Anja (2022). Structural characterization and across-fault seal assessment of the Aurora CO2 storage site, northern North Sea. Fulltekst i vitenarkiv
• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Braathen, Alvar & Sundal, Anja (2022). Structural characterization and across-fault seal assessment of the Aurora CO2 storage site, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Leon, Elias H.; Cruz, Erika H. de La & Würtzen, Camilla Louise [Vis alle 9 forfattere av denne artikkelen] (2021). Structural traps, seals, and other geologic adventures — entertaining CO2 storage exploitation of the northern Horda Platform, North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Leon, Elias H.; Holden, Nora; Mulrooney, Mark Joseph; Skurtveit, Elin & Faleide, Jan Inge [Vis alle 7 forfattere av denne artikkelen] (2021). Geological derisking of a potential CO2 storage hub for Europe in offshore Norway. Fulltekst i vitenarkiv Vis sammendrag

  A Norwegian demonstration of the full-scale CCS value-chain is scheduled to commence in 2024. Carbon-dioxide captured from industrial sites in eastern Norway will be transported west, processed, and injected into the subsurface at the Aurora site in the northern North Sea. While Aurora represents a sizeable CO2 storage location, many more are needed in order to significantly reduce global emissions and meet climate mitigation goals. Ideally, developing additional storage sites within the vicinity of Aurora would expand on its soon-existing infrastructure, and create a potential CO2 storage hub for Norway and northern Europe. However, geological risks to CO2 containment must be identified and assessed before such a development could take place. Here, a summary of ongoing subsurface characterization work is presented in support of the storage hub concept in this region.

• Osmond, Johnathon L.; Holden, Nora; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2021). Regional containment derisking for future CO2 storage in the Horda Platform, Norwegian North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Full-scale CO2 storage within the Norwegian Continental Shelf is scheduled to commence in 2024 at the Aurora site under project Longship and the Northern Lights JV. While tens of megatons of injected CO2 are anticipated over the coming years, many more storage locations are required in order to meet international climate mitigation targets. In the event of success at Aurora, the remaining Horda Platform region could be further developed into a larger North Sea CO2 storage hub, but more subsurface evaluation is needed to identify prospective sites. Here, I present two possible Jurassic storage complexes (reservoirs and seals) and discuss some of my ongoing PhD work related to derisking traps, seals, and overburden geology in the region. It is hoped that these results can later be leveraged for more site-specific analyses so that new prospects can be matured to help supplement the storage volumes at Aurora site and to further develop CCS operations in the North Sea.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin & Braathen, Alvar (2021). Top and lateral seals for CO2 storage in Jurassic saline aquifers of the Horda Platform. Fulltekst i vitenarkiv Vis sammendrag

  Full-scale CO2 storage within the Norwegian Continental Shelf is scheduled to commence in 2024 at the Aurora site under project Longship and the Northern Lights consortium. While tens of megatonnes of injected CO2 are anticipated over the project lifespan, many more storage locations are required in order to meet international climate mitigation targets. In the event of success at Aurora, the Horda Platform could be further developed into a larger North Sea CO2 storage hub. Lower and Upper Jurassic sandstone aquifers offer ample pore space for sequestration, and structural mapping within the region reveals a collection of possible storage traps distributed within three large-scale fault blocks. As it is imperative to characterize seals enveloping potential CO2 storage traps, we have undertaken a regional screening of top seal presence and lateral seal types associated with Lower and Upper Jurassic intervals of the Horda Platform. The solitary top seal formation above the Lower Jurassic aquifer thins considerably to the northwest, lowering confidence in seal presence above traps in those parts of the study area. In contrast, a culmination of several top seal formations provide a relatively thick regional seal above the Upper Jurassic aquifer. Fault-bound traps in the study area exhibit two lateral relationship types; 1) fault juxtapositions where the envisaged storage aquifer is in contact with downthrown top seals or 2) juxtapositions where the storage aquifer is in contact with sandstone aquifers above the top seal. Though the first type represents simple juxtaposition seal, the second implies that fault membrane seal is required at sandstone-to-sandstone contacts. Type two relationships are prevalent along Lower Jurassic traps, but SGR analyses and recent aquifer pressure measurements in the region suggest that such faults may enjoy some membrane seal potential. All Upper Jurassic faulted traps express type one relationships, and are perceived to possess lower-risk seals based on analogous relationships observed at nearby hydrocarbon fields (e.g., Troll East). However, fewer Upper Jurassic traps are readily available for CO2 storage due to the risk of up-dip contamination of hydrocarbon accumulations, and are therefore restricted to the eastern-most fault block until the end of production.

• Osmond, Johnathon L.; Leon, Elias H.; Mulrooney, Mark Joseph & Braathen, Alvar (2021). Geological controls over stacked Quaternary pockmark distributions above the Horda Platform, northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Pockmarks are fluid escape structures that indicate paleo-expulsion events within sedimentary basins. The Troll pockmark field is one of the world’s largest, and is located in the Horda Platform area within Norwegian Channel of the northern North Sea. The Quaternary succession hosts a set of stacked pockmarked surfaces, providing a viable opportunity to elucidate the potential geological controls over pockmark distributions in the region at different stages of the Quaternary Period. We mapped buried and seafloor pockmarks above the Horda Platform in order to determine pockmark density trends and assess potential correlations with relevant geological features above and below the Upper Regional Unconformity (URU). Positive correlations then provide evidence that further corroborate the possibility that thermogenically sourced methane drove Quaternary pockmark formation.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2021). Distribution of faulted Mesozoic and Tertiary seals for CCS in the Horda Platform, northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  The presence of Upper Jurassic through Lower Paleogene sealing units in the Horda Platform has been assessed and established for the purpose of derisking the Alpha CO2 storage prospect in the Smeaheia fault block. The nearby Troll East field closure provides as an excellent analogue for evaluating seals surrounding the Alpha closure. Analysis of mapped horizons and trap-bounding faults indicates that all sealing units are required to retain the hydrocarbons trapped at Troll East. Contrastingly, only the Draupne Formation and Cromer Knoll Group are needed to seal the top of Alpha, while the Cromer Knoll is needed to laterally seal the closure. Overall, if the Troll East analogy holds true for Alpha, the arrangement of top and lateral seals appears suitable for CCS at Smeaheia.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Leon, Elias H.; Cruz, Erika H. de La & Würtzen, Camilla Louise [Vis alle 9 forfattere av denne artikkelen] (2021). Containment derisking of a potential CO2 storage hub in the Horda Platform, Norwegian North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2021). Top and lateral seal characterizations for CCS in Jurassic saline aquifers, Horda Platform, Northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Capture of industrially sourced CO₂ and transport to the Aurora subsurface storage site in the northern North Sea are approved to commence in 2024 under the direction of the Longship and Northern Lights projects. Results from well 31/5-7 drilled in early 2020 within exploitation license EL001 confirmed suitable parameters at Aurora (e.g., porosity, injectivity, etc.). While the geology of the site proves promising for CCS, it remains imperative to mature additional locations in order to meet current climate mitigation targets and establish the Horda Platform as a European storage hub. Planned injection and containment at Aurora will be hosted by the Lower Jurassic Dunlin Gp stratigraphic storage complex (storage aquifer and seals), however, the Upper Jurassic Viking Gp represents an additional storage complex. Moreover, Aurora is located in the western-most of three large, basement-rooted fault blocks, each showing storage potential. Hundreds of thick- and thin-skinned faults create two- and three-way structural traps for both storage complexes in all three fault blocks. Some Viking Gp traps contain hydrocarbons (e.g., Troll field), providing direct analogs, but should be avoided for CO₂ storage until the end of their production life around 2050. Nevertheless, the remaining structural traps currently make the most attractive storage prospects, as they can focus injected CO₂ in a predicable fashion, particularly during the early stages of the sequestration process before other trapping mechanisms take over (e.g., residual trapping). As both top and lateral seals must completely envelop the storage aquifer, understanding the distribution and nature of the seals is critical for predicting subsurface CO₂ containment. In order to provide insight towards additional CCS potential in the Horda Platform, we present a summation of top and lateral seal mapping, modeling, and observations for the Dunlin and Viking Gp storage complexes in the three major fault blocks. For the Dunlin Gp storage complex, interpretation of its top seal distribution from 3D seismic and wellbore data confirm seal presence in all three fault blocks, including that of the Aurora site. The majority of small thin-skinned faults at the Jurassic stratigraphic level and create aquifer juxtapositions against the top seal, while larger thick-skinned faults must provide membrane seals along the largest closures. In these latter cases, the Dunlin Gp sandstone aquifer is up-thrown and juxtaposed against the overlying Viking Gp sandstone aquifer, but shale gouge ratio analysis and regional aquifer pressures suggest favorable membrane fault seal potential. Top seal formations above the Viking Gp aquifer are determined to be present throughout the Horda Platform, but only the eastern-most fault block is currently prospective for CO₂ storage, given the high risk of contaminating producing fields in adjacent fault blocks. Fault seals in this case appear to be juxtaposition-controlled, even for thick-skinned faults, which are analogous to Troll East. Considering the availability of structural traps for expanding storage activities in the Horda Platform, our work infers that the presence top and lateral seals is probable for both the Dunlin and Viking Gp storage complexes.

• Würtzen, Camilla Louise; Osmond, Johnathon L.; Faleide, Jan Inge; Nystuen, Johan Petter; Anell, Ingrid Margareta & Midtkandal, Ivar (2021). Syn- to post rift alluvial basin fill: seismic stratigraphic analysis of Permian-Triassic deposition in the Horda Platform. Fulltekst i vitenarkiv
• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Sundal, Anja & Skurtveit, Elin (2021). Structural characterization of the Aurora prospect, a potential CO2 storage site in the northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Significant uncertainties occur through varying methodologies when interpreting faults using seismic data. These uncertainties are carried through to the interpretation of how faults may act as baffles/barriers or increase fluid flow. How fault segments are picked when interpreting structures, i.e. what seismic line spacing is specified, as well as what surface generation algorithm is used, will dictate how detailed the surface is, and hence will impact any further interpretation such as fault seal or fault growth models. We can observe that an optimum spacing for fault interpretation for this case is set at approximately 100 m. It appears that any additional detail through interpretation with a line spacing of ≤50 m simply adds further complexities, associated with sensitivities by the individual interpreter. Hence, interpreting at a finer scale may not necessarily improve the subsurface model and any related analysis, but in fact lead to the production of very rough surfaces, which impacts any further fault analysis. Interpreting on spacing greater than 100 m often leads to overly smoothed fault surfaces that miss details that could be crucial, both for fault seal as well as for fault growth models. This contribution is a case example showing how different picking strategies influence analysis of a bounding fault in terms of CO2 storage assessment. This is an example from the Horda Plaform: the Smeaheia potential storage site, 20 km East of Troll East. This is a fault bound prospect, and hence this bounding fault is required to have a high seal potential and a low chance of reactivation upon CO2 injection, increasing the pore pressure. Uncertainty in the seismic interpretation methodology will follow through to fault seal analysis, specifically for analysis of whether in situ stresses combined with increased pressure through CO2 injection will act to reactivate the faults, leading to up-fault fluid flow / seep. We have shown that changing picking strategies significantly alter the interpreted stability of the fault, where picking with an increased line spacing has shown to increase the overall fault stability. Surprisingly, differences in picking strategy show little influence on the overall fault seal (i.e. shale gouge ratio) of the fault.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2021). Top and lateral seal assessment for CCS in Dunlin Group sandstones within the Tusse fault block, Horda Platform. Fulltekst i vitenarkiv Vis sammendrag

  Demonstration of the full-scale CCS value chain along the Norwegian Continental Shelf is scheduled to begin in 2024 as a result of both Longship and Northern Lights projects. Subsurface geological characterization and results from well 31/5-7 recently confirmed favorable storage conditions at the Aurora storage site (exploration license EL001), which is located roughly 11 km south of the Troll West hydrocarbon field and 8 km east of the Tusse Fault Zone. Supercritical CO2 will be injected into the Lower Jurassic Dunlin Group storage complex comprised of Johansen and Cook Formation sandstones, which are sealed by overlying Drake Formation mudstones and shales. Confidence is relatively high with respect to the geology controlling successful CCS operations at Aurora, however, little work has been done to extrapolate satellite storage potential of the Dunlin Group throughout the Horda Platform. This is especially true for the envisaged top and lateral seals that are critical for reliable containment of the injected CO2, as previous contributions instead focused on understanding the Johansen and Cook storage formations. In order to utilize local infrastructure and encourage further development of the Horda Platform as a European CCS hub, we present an assessment of potential top and lateral seals in the neighboring Tusse fault block east of Aurora and underneath the Troll East field. Relevant horizons and faults defining three potential storage traps are mapped using well logs and 3D seismic data, and are used to build a local structural model. Thickness maps indicate that the Drake top seal is present throughout the study area, but thickness decreases from over 125 m at the Aurora site to approximately 65 m along the eastern edge of the Tusse fault block. Log readings from nine wells within the Tusse fault block also suggest adequate seal properties for CO2 storage, particularly in the lower part of the Drake Formation. All three traps are dependent on lateral fault seals, however, their nature is primarily determined by the amount of displacement occurring along them and the regional stratigraphy. A number of small faults (throw < 50 m) displace the traps, creating local zones where up-thrown Johansen and Cook sandstones are juxtaposed against Drake mudstones. Contrastingly, displacements along larger trap-bounding faults (e.g., the Tusse Fault Zone) exceed 75 m, juxtaposing up-thrown Dunlin Group sandstones with thick Upper Jurassic Viking Group sandstones (Troll reservoir). These larger faults, therefore, must provide continuous membrane seals at sandstone-on-sandstone juxtapositions, and shale gouge ratio (SGR) analysis suggests that their membrane seal potential is favorable for retaining injected CO2. Assuming good regional reservoir quality within Johansen and Cook formations, these results infer that ample seals are present for leveraging Tusse fault block traps as supplemental CO2 storage sites in the Horda Platform.

• Osmond, Johnathon L.; Holden, Nora; Leon, Elias H.; Mulrooney, Mark Joseph; Skurtveit, Elin & Faleide, Jan Inge [Vis alle 7 forfattere av denne artikkelen] (2021). Top and lateral seal characterizations for CO2 storage in Jurassic saline aquifers of the Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2021). Potential top and lateral seals for supplemental CO2 storage in Dunlin Group sandstones of the Tusse fault block, northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Top and lateral seals are imperative for subsurface containment of injected CO2 during CCS operations. This is especially true for initial stages of the sequestration process because structural trapping delivers the primary CO2 trapping mechanism. A full-scale CCS value chain is scheduled to be demonstrated along the Norwegian sector of the northern North Sea in 2024 under both Longship and Northern Lights projects. Injection of supercritical CO2 will take place at the Aurora storage site in the Horda Platform, about 11 km south of the Troll West hydrocarbon field. Appraisal well 31/5-7 confirmed favourable storage conditions and previous geological assessments of the Aurora site. The storage complex is comprised of the Lower Jurassic Dunlin Group, where Johansen and Cook Formation sandstones are capped by lower permeability Drake Formation mudstones and shales. While confidence in storage potential at Aurora is fairly high, viability of the storage complex in nearby Horda Platform structures remains uncertain, particularly with respect to top and lateral seal potential. Assuming that CCS operations are demonstrated successfully at Aurora, further development of the Horda Platform as a European CO2 storage hub will require a greater understanding of suitable traps and seals in the region. As a contribution towards this effort, we present an assessment of top and lateral seal potential in the neighbouring Tusse fault block, approximately 8 km east of the Aurora, and underneath the producing Troll East field. Relevant stratigraphic horizons and faults are mapped from 3D seismic data and petrophysical data from regional boreholes are used to identify three potential closures, as well as characterize top seal presence and lateral seal types. Thickness mapping of the Drake Formation indicates the top seal decreases in thickness eastward from over 125 m to roughly 65 m, while log readings suggest favourable petrophysical properties throughout the study area. Each of the potential storage closures are dependent lateral fault seals, where the faults fall into two general populations. Within the Tusse fault block, thin-skinned intra-trap faults with throws less than 50 m create local juxtaposition seals, with the Drake mudstones downthrown onto Johansen and Cook sandstones. In contrast, larger trap-bounding faults with throws greater than 50 m are thick-skinned (e.g., the Tusse Fault Zone), and juxtapose thick, non-producing Upper Jurassic Viking Group sandstones (Troll reservoir) onto Dunlin Group sandstones in the footwall. These larger faults, therefore, must provide membrane seals that are continuous along these high-risk juxtapositions. Shale gouge ratio analyses indicate that zones where displacement is greater than 50 m are characterized by SGR values greater than 0.2, suggesting favourable membrane seal potential. Considering the compilation of the results herein, we infer that ample seals are present for utilizing the Tusse fault block as a supplemental Horda Platform CO2 storage site, assuming good Dunlin Group reservoir quality within the study area and baring more detailed studies.

• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2021). Structural analysis of the Smeaheia fault block, a potential CO2 storage site, northern Horda Platform. Fulltekst i vitenarkiv Vis sammendrag

  Smeaheia, a prominent fault block located on the Horda Platform, northern North Sea is identified as a potential subsurface CO2 storage site. We utilise the GN1101 3D and regional 2D seismic surveys to generate a high-resolution subsurface geomodel to inform the structural style and evolution of the fault block, to investigate geological controls on proposed CO2 storage and provide a geometric framework as a basis for future analyses. Two basement-involved (first-order) north-south trending fault systems, the Vette Fault Zone (VFZ) and the Øygarden Fault Complex (ØFC), bound the 15 km-wide fault block. Apart from activity during the Permo-Triassic (Rift Phase 1) and the Late Jurassic–Early Cretaceous (Rift Phase 2), we present evidence that rifting in this part of the North Sea continued into the Late Cretaceous with minor reactivation in the Palaeocene–Eocene. Two segments of the VFZ interacted and linked at a relay ramp during Rift Phase 2. Second-order (thin-skinned) faults show basement affinity and developed during Rift Phase 2 in two distinct pulses. A population of polygonal faults intersects the overburden and developed during the Eocene to middle Miocene. We have revised the areal extent of two structural closures that define the Smeaheia fault block, Alpha (VFZ footwall) and Beta (ØFC hanging wall) which consist of Upper Jurassic Viking Group target formations. Cross-fault juxtaposition analysis of the VFZ and second-order intra-block faults are presented and inform pressure communication pathways between the Smeaheia and Tusse fault block, as well as reservoir integrity and compartmentalisation. The geomodel further identifies important geological controls on CO2 storage in the fault block including a thinning caprock above the Alpha structure, and identification of hard-linkage between deep tectonic faults and shallow polygonal faults. Fault reactivation analysis was conducted on depth-converted faults to determine the risk of up-fault CO2 migration. Hydrostatic and depleted scenarios were modelled. Faults are modelled as classic cohesionless structures but also utilising parameters (cohesion and friction angle) derived from host rock mechanical analysis.

• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Braathen, Alvar & Sundal, Anja (2021). Structural characterization and across-fault seal assessment of the Aurora CO2 storage site. Fulltekst i vitenarkiv
• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Braathen, Alvar & Sundal, Anja (2021). Structural characterization and across-fault seal assessment of the Aurora CO2 storage site, northern North Sea. Fulltekst i vitenarkiv
• Holden, Nora; Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Braathen, Alvar & Sundal, Anja (2021). Across-fault seal assessment of the Aurora CO2 storage site, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L. & Meckel, Timothy A. (2021). Fault seal and containment failure by way of continued displacement of an Early Miocene structure in the San Luis Pass area, offshore Galveston Island, Texas Inner Shelf. Fulltekst i vitenarkiv Vis sammendrag

  Understanding trap and seal quality in faulted siliciclastic reservoirs is imperative for determining subsurface hydrocarbon presence as faults have been documented to either seal buoyant fluids or serve as conduits for fluid migration. Sophisticated techniques, such as shale gouge ratio (SGR) analysis, have been developed for evaluating containment failure mechanisms, but data limitations can restrict workflows and interpretation precision, especially within shallow overburden sediments. Furthermore, containment failure analyses are typically conducted under the assumption that recent slip along a fault has not affected the petroleum system. These two factors may lead to optimistic and erroneous volumetrics, and potentially, dry holes. This study promotes the use of nested seismic datasets of variable resolution in tandem with well log data for containment failure analysis by providing a case study of a faulted Early Miocene structure with recent slip history located along the Texas Inner Shelf, 11.2 km offshore from Galveston Island. Unique high-resolution 3D seismic data (HR3D P-Cable) acquired in 2013 resolves features that are unapparent within available industry 3D seismic data. They include near-surface fault tips projecting from deep-rooted normal faults and seismic amplitude anomalies that resemble vertical gas chimneys above the structure. These observations, coupled with nine dry holes targeting the structure suggest that hydrocarbons within the Early Miocene 2 (EM2) reservoir interval have migrated out into the shallow overburden. The largest fault displacing the structure (Fault A) is thought to play a significant role in the leakage scenario, and six potential containment failure mechanisms are evaluated by way of 3D structural modeling to determine the likely cause of leakage. Results from static fill-to-spill, juxtaposition, SGR, and top seal analyses suggest that the San Luis Pass structure should indeed retain methane column heights between 100–300 m. The lack thereof, however, signifies a mechanical reason for leakage, and CHIRP data collected in 2015 confirms Late Pleistocene movement along Fault A. Therefor, reactivation of Fault A may have triggered leakage from EM2 reservoirs through fault conduits, emphasizing the importance of understanding geologic history when evaluating traps and seals, and supporting the use of multiple seismic datasets with variable resolutions to improve fault interpretation and reduce predrill uncertainty.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Holden, Nora; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2021). Structural derisking for CO2 storage in the northern Horda Platform, Norwegian North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Ongoing top and lateral seal characterizations for CO2 storage in the Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2020). Top and lateral seal variation along the Horda Platform, northern North Sea: implications towards CO2 storage in Viking Gp sandstones. Fulltekst i vitenarkiv Vis sammendrag

  Full-scale geologic CO2 storage will be demonstrated along the Norwegian Continental Shelf within the next few years to promote climate mitigation technologies. While Lower Jurassic sandstones are the current storage formation target south of the Troll West hydrocarbon field at the Aurora site, Upper Jurassic Viking Group sandstones remain a subsidiary storage option in the Horda Platform of the North Sea. This study focuses on the Alpha prospect within the Smeaheia fault block. The trap is a large three way closure bounded by the Vette fault zone on its western flank. This structural configuration draws similarity to the adjacent Tusse fault zone, which seals the >200m Troll East gas accumulation. Moreover, the Alpha and Troll East traps are overlain by time-equivalent fine-grained Upper Jurassic through Lower Paleogene strata, which are also juxtaposed along the bounding fault zones. This relationship provides a useful analogy for seal quality at Alpha since comparable seals are proven at Troll East, however, seal thickness varies across the regionally. To address this, we utilize 3D seismic data and well ties to determine top and lateral seal presence, and help derisk CO2 containment within Alpha. A 3D structural model is built from mapped faults and horizons to characterize structure and thickness of the sealing formations, as well as model across-fault juxtaposition along the Alpha and Troll East closures. Overall, we find that the possibility of CO2 leakage due to seal thickness heterogeneity and unfavorable across-fault juxtaposition is qualitatively low given the seals are proven at Troll East.

• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2020). Fault stability of seismic-scale normal faults: Implications for CO2 storage on the northern Horda Platform. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2020). HordaPlatform: New Learnings 2020. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Summary of manuscript: Structural analysis of the Smeaheia fault block, a potential CO2 storage site, northern Horda Platform, North Sea. Fulltekst i vitenarkiv
• 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.

• Osmond, Johnathon L. (2020). PhD progress update. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Horda Platform geology and CCS research discussion. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Leon, Elias H.; Mulrooney, Mark Joseph & Braathen, Alvar (2020). Stacked Quaternary pockmark distributions above the Horda Platform, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Holden, Nora; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Ongoing top and lateral seal characterizations for CO2 storage in the Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Horda Platform geology and CCS research discussion. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin; Faleide, Jan Inge & Braathen, Alvar (2020). Horda Platform geology and CCS research discussion. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Leon, Elias H.; Mulrooney, Mark Joseph & Braathen, Alvar (2020). Stacked Quaternary pockmark distributions above the Horda Platform, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L. & Meckel, Timothy A. (2020). Trap and seal geohistory informed from integrated overburden interpretation, Texas inner shelf. Fulltekst i vitenarkiv Vis sammendrag

  Characterizing fault and seal potential is imperative for derisking the presence of subsurface hydrocarbon accumulations in faulted siliciclastic reservoirs. Although several notable techniques are often used to evaluate both fault and top seals at depth, special attention should also be given to features within the overburden sediments. Gas chimneys and deep-rooted faults propagating into the overburden strata above a prospect can imply both local hydrocarbon presence and recent movement along trap-bounding faults, respectively. With regard to trap and seal performance, however, gas chimneys and near-surface faulting also provide important details about geohistory and can indicate that an accumulation may be compromised. Conventional 3D seismic data is often capable of imaging these features, yet high-resolution 3D seismic (HR3D, e.g. P-Cable) and chirp data acquisition allow for more accurate interpretation of the overburden stratigraphy where conventional acoustic datasets may be lacking sufficient fidelity. This study supports the acquisition of nested seismic datasets of variable resolution together with wireline data for inspecting the overburden geology and assessing trap and seal potential. We present local HR3D seismic data that resolves features above a faulted Early Miocene structure with recent slip history along the Texas inner shelf, which are unapparent from available conventional seismic data. Vertical gas chimneys appear to emanate from the trap where wells tested the prospect and were deemed dry, suggesting that hydrocarbons within the Early Miocene reservoir have migrated vertically into the overburden strata. The primary fault bounding the trap (Fault A) is thought to have had significant influence on breaching the containment system, but results from static fill-to-spill, juxtaposition, SGR, and top seal analyses predict that the closure could have withheld gas column heights up to 300 m. Nevertheless, imagery from the HR3D data indicates that Fault A and accessory faults displacing the Early Miocene reservoir have propagated through Late Pleistocene strata near the seafloor, suggesting progressive fault slip may have compromised the trap and seal. Overall, our results demonstrate the potential value of comprehensive overburden interpretation when investigating the geohistory of traps and seals, and the usefulness of high-resolution datasets for reducing uncertainty in exploration.

• Osmond, Johnathon L.; Leon, Elias H.; Mulrooney, Mark Joseph & Braathen, Alvar (2020). Quaternary pockmark distributions informed by 3D seismic interpretation above the Horda Platform, northern North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Pockmarks in offshore settings record the expulsion of fluids sourced from the subsurface. The northern North Sea hosts one of the world’s largest seafloor pockmark fields above the Horda Platform where Troll hydrocarbon fields and prospective CO2 storage sites are located. Previous workers have used data from multi-beam bathymetry surveys, shallow boreholes, and ocean-bottom sediment samples to better understand the distribution, timing, and potential causative mechanisms related to the seafloor pockmarks directly above Troll East field. It has been proposed that these seafloor pockmarks formed ~10 ka during the latest deglaciation period, possibly by gas expulsion from destabilized methane hydrate paleo-accumulations in underlying strata, but little has been done to characterize the greater affected area or to determine if there were earlier pockmark-forming events. We expand on previous work by using 4,770 km2 of conventional 3D seismic data to 1) map the regional extent and density of the seafloor pockmarks, and 2) to investigate other potential fluid-escape structures preserved within Quaternary strata below the seafloor. Over 35,000 seafloor pockmarks are interpreted inside the study area, where they abruptly appear and gradually cease from west to east. All mapped seafloor pockmarks lie within the Norwegian Channel, where the highest densities are above the hanging wall of the Tusse fault zone and the Troll West field underneath the regional Quaternary unconformity (URU). More novel is that we have identified a prominent seismic reflector roughly 200 ms below the seafloor hosting more than 2,500 buried pockmarks confined to a thin and discontinuous intra-Quaternary deposit along the eastern side of the study area. Interestingly, the location of seafloor pockmarks seldomly overlap those that are buried, suggesting that the two populations formed during separate expulsion events, although we are currently unable to determine if they formed by the same proposed mechanism. The present arrangement of Quaternary sediments and underlying geologic features correlate with pockmark distributions, demonstrating possible stratigraphic and structural controls on their distribution. Furthermore, while the original source (microbial or thermogenic) of methane thought to have been frozen and expelled from the destabilized paleo-hydrates remains unresolved, we discuss how the pockmark distributions and other observations constrain up-dip paleo-fluid migration routes from possible thermogenic sources and surrounding hydrocarbon fields (e.g. Troll). If the source is indeed thermogenic, evidence of paleo-fluid expulsion through the Quaternary interval has implications towards buoyant fluid flow regionally, as it indicates that deeply sourced fluids have migrated through it over time.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2020). Arrangement of top and across-fault seal intervals within the Horda Platform: implications towards CCS in Viking Group sandstones. Fulltekst i vitenarkiv Vis sammendrag

  Effective traps require seals to be vertically and laterally continuous around the hydrocarbon reservoir or CO2 storage formation. Moreover, traps that require faults to laterally seal the closure must be scrutinized adequately enough to draw confidence in its seal quality. Although useful, techniques for predicting the presence and quality of low-permeability fault membrane seals or fault rocks are speculative. Across-fault juxtaposition seal analysis remains a more simplistic, yet effective means of determining lateral seal presence. Upper Jurassic Viking Group sandstones of the Horda Platform in the northern North Sea contain large quantities of trapped hydrocarbons, particularly within the greater Troll field. The Viking Group also possesses sufficient quality and high CO2 storage potential along the eastern Horda Platform. This study focuses on the Alpha CO2 storage prospect within the Smeaheia fault block 5 km east of the Troll East gas field. The trap is a large three-way closure with unproven seals and is bound by the Vette fault zone on its western flank. This structural configuration draws similarity to the adjacent Tusse fault zone, which seals the >200 m Troll East gas column. Equivalent fine-grained Upper Jurassic through Lower Paleogene strata overlie the Alpha and Troll East traps and are also juxtaposed along the bounding Vette and Tusse fault zones, respectively. This relationship provides a useful analogy for CO2 top and lateral seal quality at Alpha since comparable seals hold hydrocarbons at Troll East. However, thickness changes occur regionally among individual sealing intervals, especially within the Cretaceous growth strata in the hanging walls of the bounding fault zones. We use 3D seismic data and wireline logs to map the distribution of four top and lateral seal intervals between the Tusse and Smeaheia fault blocks in an effort to derisk CO2 containment within the Alpha closure. Regional thickness maps indicate several areas where individual top seals are absent, while across-fault juxtaposition maps (Allan diagrams) establish the arrangement of top and lateral seals along the Tusse and Vette faults. While a combination the four seal intervals appears to trap the hydrocarbons at Troll East, only the two lower-most intervals would be required to trap CO2 at Alpha. Overall, if lithological properties are laterally consistent, we find that the possibility of CO2 leakage at Alpha due to unfavorable top seal or across-fault juxtaposition conditions is low given that similar seals at Troll East are proven.

• Osmond, Johnathon L. (2019). Current perspectives on structural derisking the Smeaheia area for full-scale geological CO2 storage. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2019). Horda Platform: New Learnings. Fulltekst i vitenarkiv
• Leon, Elias H.; Osmond, Johnathon L.; Mulrooney, Mark Joseph & Braathen, Alvar (2019). Distribution and spatial statistics of pockmarks in Quaternary sediments above the Smeaheia CO2 storage area. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2019). Comparison between two Late Jurassic CO2 storage prospects with respect to structural derisking, Smeaheia area, Norwegian North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L. (2019). Addressing across-fault and top seal potential for CCS in Viking Group sandstones of the Horda Platform. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2019). 3D geologic framework and structural derisking of two offshore CO2 storage prospects in the Smeaheia area, Norwegian North Sea. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Leon, Elias H. & Braathen, Alvar (2019). A reduced capacity Smeaheia prospect – Structural risks associated with an Alpha-only storage scenario. Fulltekst i vitenarkiv Vis sammendrag

  Smeaheia, a potential subsurface storage unit situated in the northern North Sea, east of Troll East was previously considered as the most suitable location for storage of CO2 for a proposed full-chain CCS project in Norway. The site was preferable owing to the adjacency to existing pipe-line infrastructure, a lack of potential for interfering with Troll field production, and a large estimated storage capacity. Originally, two closures, the Alpha (to the west) and Beta (to the east) where defined. CO2 injected into the Alpha structure was envisaged to fill the structure (approx. 100 Mt) and spill over to the Beta structure (an additional 100 Mt capacity). Juxtaposition of the potential storage unit (the Jurassic Sognefjord Fm), however, against Caledonian basement adjacent to the Beta closure has been considered too high risk for the Beta structure to be considered for the full-chain CCS project. Moreover, the Alpha structure alone is not considered to have sufficient capacity, and has lead to an alternative site being chosen. The Alpha structure, however, prevails as a potential storage site for more modest-scaled CCS projects. Key to the success of Alpha is the nature of cross-fault juxtaposition of the Vette Fault Zone (Figure 1) where the storage unit in Alpha is primarily self-separated across the fault zone, and juxtaposed with mixed siliciclastic-carbonate successions of the Cretaceous overburden. A complex relay zone of several Vette Fault Zone segments to the south primarily exhibit cross-fault self-juxtaposition of the storage unit. This relay zone likely provides pressure communication between Smeaheia and the Troll field suggesting Smeahiea is depleted. Subsidiary faults that intersect the storage unit in Alpha pose potential baffles to CO2 migration and require consideration when positioning injector wells. A small population of tectonic faults, including the prospect bounding fault, continue up section where they intersect the caprock and overburden. These faults provide potential caprock-bypass risk, and as such the likeliness of their reactivation under various pressure regimes is considered. Moreover, a network of low-displacement polygonal faults that intersect the overburden have been mapped, and in places are hard-linked to tectonic faults. Finally, the distribution of pock-marks both on the seafloor and on intra-Quaternary horizons are considered in relation to underlying faults to discern whether these paleo-seepage events are from significant depths or from shallow methanogenic gas. Acknowledgments: This contribution has been produced with support from the NCCS Centre, performed under the Norwegian research program Centres for Environment-friendly Energy Research (FME). The authors acknowledge the following partners for their contributions: Aker Solutions, ANSALDO Energia, CoorsTek Membrane Sciences, Gassco, KROHNE, Larvik Shipping, Norcem, Norwegian Oil and Gas, Quad Geometrics, Shell, Equinor, TOTAL, and the Research Council of Norway (257579/E20). We gratefully acknowledge Schlumberger Software for the provision of academic licenses for the Petrel E&P Software Platform and Midland Valley for the provision of academic licenses for the Move Software Suite.

• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2019). Addressing across-fault and top seal potential for CCS in Viking Group sandstones of the Horda Platform. Fulltekst i vitenarkiv
• Horne, Elizabeth; Hennings, Peter H. & Osmond, Johnathon L. (2019). Characteristics of Potentially Seismogenic Faults in the Greater Fort Worth Basin. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2019). Analogous Juxtaposition of Mixed Lithologies Against a Siliciclastic Hydrocarbon Reservoir and Proposed CO2 Storage Formation in the Norwegian North Sea. Fulltekst i vitenarkiv Vis sammendrag

  Thorough characterization and evaluation of potential seals is essential for derisking any geologic CO2 storage prospect. In particular, prospects with traps that require bounding faults to act as lateral seals for facilitating containment demand great attention. One such prospect, known as Alpha, is located within the tilted normal fault block of Smeaheia in the Norwegian North Sea. The Alpha trap is an elongate 3-way closure bounded on its western flank by the westward-dipping Vette Fault Zone. The proposed CO2 storage formation and seal intervals are comprised of Late Jurassic Viking Group sandstones and overlying shaley units, respectively. The maximum structural closure is ~80 m high at the footwall cutoff, however, no hydrocarbons were encountered in the solitary well that tested it. Furthermore, mixed Cretaceous siliciclastic and carbonate overburden lithologies in the hanging wall are juxtaposed against the Jurassic footwall sandstones. Given that these overburden rocks are poorly characterized locally, and that Vette Fault Zone seal quality remains unproven, a critical concern is whether the Fault Zone can seal CO2 injected into Alpha. Analogous to the Vette Fault Zone is the Tusse Fault Zone, which bounds the western side of the Troll East Field 17 km west of Alpha. Unlike Vette, the Tusse Fault Zone originally sealed a ~250 m fill-to-spill gas column in equivalent Jurassic footwall sandstones. Despite this difference, both fault zones have similar throw magnitudes (>500 m) and juxtapose comparable footwall and hanging wall stratigraphies, although minor juxtapositions with Early Paleogene-aged units are also observed along the Tusse Fault. As fault seal is imperative for the success of the Alpha CO2 prospect, we have utilized the analogous Tusse Fault Zone sealing Troll East to assess fault seal potential of the unproven Vette Fault Zone by employing a fault juxtaposition approach. We have determined lithologic properties of juxtaposed stratigraphy and constructed a 3D framework based on seismic data, well logs, and cuttings to generate detailed Allan diagrams. A key component of this analysis is the identification and qualification of potential leakage points along each fault zone. We find that several areas of seemingly higher juxtaposition leakage risk are present in both cases, but that juxtaposition leak may not have a significant impact for CO2 storage at Alpha assuming negligible leakage and recharge is occurring at Troll East.

• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2019). Smeaheia – structural uncertainty. Fulltekst i vitenarkiv
• Osmond, Johnathon L. (2019). Helping build the seismic network for Texas and a 3D structural model for the Fort Worth Basin as a backbone for induced seismicity research. Fulltekst i vitenarkiv
• Osmond, Johnathon L. (2019). Addressing top and across-fault juxtaposition seal potential for CCS in Viking Group sandstones of the Horda Platform. 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.

• Osmond, Johnathon L. (2018). Characterization of overburden faults and features above the Alpha CO2 storage prospect, Smeaheia area, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L. & Mulrooney, Mark Joseph (2018). First-pass modeling of the faults displacing the Sognefjord Formation within the Alpha CO2 storage prospect and Vette relay ramp areas / Interpretation of overburden horizons and faults, Smeaheia, northern North Sea. Fulltekst i vitenarkiv
• Braathen, Alvar; Mulrooney, Mark Joseph & Osmond, Johnathon L. (2018). Fault studies - challenges and applications. Fulltekst i vitenarkiv
• Osmond, Johnathon L. (2018). Characterization of overburden faults and features above the Alpha CO2 storage prospect, Smeaheia area, northern North Sea. Fulltekst i vitenarkiv
• Osmond, Johnathon L.; Mulrooney, Mark Joseph; Skurtveit, Elin & Braathen, Alvar (2018). First-pass 3D geologic interpretation and structural modeling of the Alpha CO2 storage prospect in the Smeaheia area, Norwegian North Sea. Fulltekst i vitenarkiv
• Skurtveit, Elin; Mulrooney, Mark; Osmond, Johnathon Lee; Choi, Jung Chan & Braathen, Alvar (2018). Structural derisking for Smeaheia - Improved fault characterization workflow. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon Lee; Skurtveit, Elin; Wu, Long & Braathen, Alvar (2018). Smeaheia, A Potential Northern North Sea CO2 Storage Site: Structural Description And De-Risking Strategies. Fulltekst i vitenarkiv
• Skurtveit, Elin; Choi, Jung Chan; Osmond, Johnathon Lee; Mulrooney, Mark Joseph & Braathen, Alvar (2018). 3D fault integrity screening for Smeaheia CO2 injection site. Fulltekst i vitenarkiv Vis sammendrag

  Task leader, Elin Skurtveit presents the GHGT paper "3D fault integrity screening for Smeaheia CO2 injection site" together with plans for future work.

• Hennings, Peter H; Osmond, Johnathon L.; Dommisse, Robin & Nicot, Jean-Philippe (2018). Development of a deterministic seismicity potential assessment of the Fort Worth Basin. Fulltekst i vitenarkiv
• Skurtveit, Elin; Choi, Jung Chan; Mulrooney, Mark; Osmond, Johnathon Lee & Braathen, Alvar (2018). 3D fault integrity screening for Smeaheia CO2 injection site. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2017). Structural observations from The Smeaheia Prospect: Sites of structural complexity and gaps in the geological knowledge. Fulltekst i vitenarkiv
• Mulrooney, Mark Joseph; Osmond, Johnathon L.; Skurtveit, Elin & Braathen, Alvar (2017). Smeaheia case study – first assessments: Sites of structural complexity and gaps in the geological knowledge. Fulltekst i vitenarkiv
• Leon, Elias Heimdal; Braathen, Alvar; Mulrooney, Mark Joseph & Osmond, Johnathon L. (2019). Distribution and spatial statistics of pockmarks above the Smeaheia CO2 storage area: Evaluating Quaternary sediments as a secondary seal. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Understanding geologic risks that could hinder successful geologic CO2 capture and storage (CCS) in a prospective area is imperative before moving forward with a storage project. Containment of injected CO2 requires the storage formation, top seal, and fault seals to be of sufficient quality, but the stratigraphic overburden must also be characterised thoroughly in order to appreciate the entire storage system fully. Two CO2 storage prospects are located within the Smeaheia, 4 km east of the Troll East offshore gas field along the west coast of Norway. Above the idealised Jurassic storage units are the Cretaceous and Tertiary overburden strata, which could provide either secondary seals or conduits to flow if containment of the CO2 were to fail. Of particular interest are the Quaternary sediments, which lie above the Upper Regional Unconformity (URU), and preserves many pockmarks and glacial features. Since pockmarks are indicators of paleo-fluid seepage, the distribution of pockmarks on the seabed and within the Quaternary interval, can provide insight towards how buoyant paleo-fluids may have migrated through the subsurface and help determine if parts of the overburden geology could act as a secondary seal for any leaking CO2 injected into the Smeaheia storage prospects. To achieve this, pockmarks and other overburden features are interpreted from high-quality 3D seismic data, and statistics are gathered and analysed to understand the distribution of the pockmark geometries and map their areal densities. The seabed surface hosts a total of 679 pockmarks and can be divided into three groups; (A) medium pockmarks with a mean width of 77 m, (B) large pockmarks with a mean of 129 m, and (C) giant pockmarks with a mean width of 214 m. An additional 2476 buried pockmarks are identified on six older seismic horizons under the seabed down to the URU. These horizons are dominated by medium-sized pockmarks with mean widths between 75 to 81 m, while large pockmarks increase in size with depth and have mean widths ranging from 122 to 191 m. It is proposed that the formation of large and mega pockmarks are associated with significant expulsion events and occasionally correlate with interpreted seismic pipes, while the ubiquity of the medium-sized pockmarks suggests that they may have formed in the wake of more significant expulsion events or from more passive buoyant fluid build-ups within the Quaternary stratigraphy. Furthermore, quadrat and kernel density maps are used to display pockmark density distribution. These density maps, together with qualitative observations from the available 3D seismic data below the URU, suggest that there are two main domains for pockmarks-forming fluid sources, east and west of the Øygarden Fault Complex (ØFC). Pockmarks east of the ØFC appear to originate from basement-rooted faults along the footwall of the ØFC, while pockmarks west of the ØFC could have multiple points of origin. Most of the pockmarks west of the ØFC are present between Top Sele Fm and Top Shetland Gp horizon subcrops under the URU, which are also above a dense network of Tertiary polygonal faults and deeper WNW-ESE rending faults associated with a Late Jurassic to Early Cretaceous rifting event. No data was available to determine whether the buoyant fluids that formed the pockmarks were biogenic or thermogenic, and no hydrocarbons were encountered by the two wells drilled in the Smeaheia fault block. However, the Cretaceous and Tertiary layers subcroping the URU are all westward-dipping, suggesting that buoyant thermogenic fluids may have migrated up-dip from the NW or WNW from the Troll area. Additionally, mapped mega-scale glacial lineations (MSGL) and plough mark trends correlate with pockmark longest axis azimuths, which shows that glaciers may have played a vital role in triggering pockmarks formation at Smeaheia. Overall, it is evident that the Quaternary interval has periodically been compromised by buoyant fluid migration, implying that the Quaternary and underlying overburden strata might work poorly as a secondary seal for CO2 sequestration at Smeaheia over geologic timescales.

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