Pore-scale characterization and modelling of CO2 flow in tight sandstones using X-ray micro-CT; Knorringfjellet formation of the Longyearbyen CO2 lab, Svalbard

Rocks of the Knorringfjellet Formation in Central Spitsbergen form a potential storage reservoir for CO2 below Longyearbyen. They are characterised by a moderate porosity and low permeability. However, water injection tests have shown positive results and fractures are considered to facilitate fluid flow. Therefore, hard data on fracture parameters and pore characteristics schould be analysed to better understand flow characteristics. Consequently, sandstone and conglomerate samples from the Knorringfjellet Formation were sampled and characterised with High Resolution X-ray Computed Tomography (HRXCT) at the Centre for X-ray Tomography at Ghent University, Belgium (UGCT). The dataset includes samples taken from drillholes in the vicinity of Longyearbyen, drilled during the pilot phase at the Longyearbyen CO2 project, as well as from the Knorringfjellet Formation outcrops at Konusdalen and Criocerasdalen. This was done in order to compare micro-fracture and pore parameters in both settings. With HRXCT, the samples were analysed at pore scale and quantitative information of the pore network and fractures were extracted. Pore networks were used for the modelling of CO2 flow in specific samples and information on fracture aperture was obtained at a micrometre scale. The acquired dataset can be directly used for a better understanding of flow in the aquifer

the permo carboniferous oslo rift through six stages and 65 million years

The Oslo Rift is the northernmost part of the Rotliegendes basin system in Europe. The rift was formed by lithospheric stretching north of the Tornquist fault system and is related tectonically and in time to the last phase of the Variscan orogeny. The main graben forming period in the Oslo Region began in Late Carboniferous, culminating some 20-30 Ma later with extensive volcanism and rifting, and later with uplift and emplacement of major batholiths. It ended with a final termination of intrusions in the Early Triassic, some 65 Ma after the tectonic and magmatic onset. We divide the geological development of the rift into six stages. Sediments, even with marine incursions occur exclusively during the forerunner to rifting. The magmatic products in the Oslo Rift vary in composition and are unevenly distributed through the six stages along the length of the structure

Changing provenance and stratigraphic signatures across the Triassic–Jurassic boundary in eastern Spitsbergen and the subsurface Barents Sea

A change to more sandstone dominated deposits and increasing condensation across the Triassic–Jurassic boundary is generally associated with improved reservoir quality in the Barents Sea. However, spatial and temporal changes in reservoir quality in this interval shows that the composition of the sediment source, immature sedimentary rocks supplied from the east or recycled in the basin in contrast to mature arenites to the south and west, affect the reservoir quality. The regional distribution of the different sources is best constrained in the southwestern part of the Barents Sea, and hitherto there has been no direct comparison between the zircon signature in outcrop analogues and their subsurface equivalents. In this study we evaluate the stratigraphic development of formations across the Triassic–Jurassic boundary in the Barents Sea and eastern Spitsbergen to compare their provenance signatures. By coupling outcrop and core data, we tie together the regional tectono-stratigraphic evolution of this important reservoir interval and relate the variable degree of sediment reworking with the relative distribution of immature Triassic sedimentary rocks across the basin. Results show higher degrees of erosion and reworking in Spitsbergen compared to the Barents Sea, consistent with local variations in the forebulge province of Novaya Zemlya observed in the subsurface. Provenance samples from Spitsbergen also record the same change in signature as in the subsurface Barents Sea. However, mature sediments are mixed with immature sediments later in Spitsbergen, indicating a latency in progradation from mature source areas which favour southern provenance areas in Fennoscandia as opposed to Greenland. Presence of young detrital zircon grains with similar Norian ages are recorded in the Upper Triassic strata both in the southernmost Barents Sea and on Spitsbergen, suggesting that a sediment source was active east of the basin and supplied sediment uniformly to the entire basin during the late Triassic.publishedVersio

The role of shelf morphology on storm-bed variability and stratigraphic architecture, Lower Cretaceous, Svalbard

The dominance of isotropic hummocky cross‐stratification, recording deposition solely by oscillatory flows, in many ancient storm‐dominated shoreface–shelf successions is enigmatic. Based on conventional sedimentological investigations, this study shows that storm deposits in three different and stratigraphically separated siliciclastic sediment wedges within the Lower Cretaceous succession in Svalbard record various depositional processes and principally contrasting sequence stratigraphic architectures. The lower wedge is characterized by low, but comparatively steeper, depositional dips than the middle and upper wedges, and records a change from storm‐dominated offshore transition – lower shoreface to storm‐dominated prodelta – distal delta front deposits. The occurrence of anisotropic hummocky cross‐stratification sandstone beds, scour‐and‐fill features of possible hyperpycnal‐flow origin, and wave‐modified turbidites within this part of the wedge suggests that the proximity to a fluvio‐deltaic system influenced the observed storm‐bed variability. The mudstone‐dominated part of the lower wedge records offshore shelf deposition below storm‐wave base. In the middle wedge, scours, gutter casts and anisotropic hummocky cross‐stratified storm beds occur in inferred distal settings in association with bathymetric steps situated across the platform break of retrogradationally stacked parasequences. These steps gave rise to localized, steeper‐gradient depositional dips which promoted the generation of basinward‐directed flows that occasionally scoured into the underlying seafloor. Storm‐wave and tidal current interaction promoted the development and migration of large‐scale, compound bedforms and smaller‐scale hummocky bedforms preserved as anisotropic hummocky cross‐stratification. The upper wedge consists of thick, seaward‐stepping successions of isotropic hummocky cross‐stratification‐bearing sandstone beds attributed to progradation across a shallow, gently dipping ramp‐type shelf. The associated distal facies are characterized by abundant lenticular, wave ripple cross‐laminated sandstone, suggesting that the basin floor was predominantly positioned above, but near, storm‐wave base. Consequently, shelf morphology and physiography, and the nature of the feeder system (for example, proximity to deltaic systems) are inferred to exert some control on storm‐bed variability and the resulting stratigraphic architecture

Unravelling key controls on the rift climax to post-rift fill of marine rift basins: insights from 3D seismic analysis of the Lower Cretaceous of the Hammerfest Basin, SW Barents Sea

This is the pre-peer reviewed version of the following article: Marin Restrepo, D.L. et al. (2017) Unravelling key controls on the rift climax to post-rift fill of marine rift basins: insights from 3D seismic analysis of the Lower Cretaceous of the Hammerfest Basin, SW Barents Sea. Basin Research, which has been published in final form at https://doi.org/10.1111/bre.12266. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.In this study, we investigate key factors controlling the rift climax to post-rift marine basin fill. We use two- and three-dimensional seismic data in combination with sedimentological core descriptions from the Hammerfest Basin, south-western Barents Sea to characterize and analyse the tectonostratigraphy and seismic facies of the Lower Cretaceous succession. Based on our biostratigraphic analyses, the investigated seismic facies are correlated to 5–10 million year duration sequences that make up the stratigraphic framework of the basin fill. The seismic facies suggest the basin fill was deposited in shallow to deep-marine conditions. During rift climax in Volgian/Berriasian to Barremian times, a fully linked fault array controlled the formation of slope systems consisting of gravity flow deposits along the southern margin of the basin. Renewed uplift of the Loppa High north of the basin provided coarse-grained sediments for fan deltas and shorelines that developed along the northern basin margin. During the early to middle late Aptian, the input of coarse-grained sediments occurred mainly in the NW and SW corners of the basin, reflecting renewed uplift-induced topography in the western flank of the Loppa High and along the western Finnmark Platform. The lower Albian part of the basin fill is interpreted as a post-rift succession, where the remnant topography associated with the Finnmark Platform continued to provide sediments to prograding fan deltas and adjacent shorelines. During the Albian, a series of faults were reactivated in the northern part of the basin, and footwall wedges comprising various gravity flow deposits occur along these faults. During the latest Albian to Cenomanian, the south-eastern part of the Loppa High was flooded by a rise in eustatic sea-level and differential subsidence. However, the western part of the high remained exposed and acted as a sediment source for a shelf-margin system prograding towards the SE. It is concluded that the rift climax succession is controlled by: along strike variability of throw and steps of the main bounding faults; the diachronous movement of the faults; and the nature of the feeder system. The evolution of the post-rift succession may be controlled by rifting in adjacent basins which preferentially renew sources of sediments; local reactivation of faults; and local remnant topography of the basin flanks. We suggest that existing tectonostratigraphic models for rift basins should be updated, to incorporate a more regional perspective and integrating variables such as the influence of adjacent rift systems.submittedVersio

Stratigraphy and palaeosol profiles of the Upper Triassic Isfjorden Member, Svalbard

The Isfjorden Member forms the upper part of the De Geerdalen Formation in Svalbard and is well exposed throughout central and eastern Spitsbergen, including the island of Wilhelmøya. We examine palaeosol profiles identified in the Isfjorden Member and compare these to profiles seen in the remainder of the De Geerdalen Formation. In addition, we address the nuances of the Isfjorden Member, its practicality as a stratigraphic interval and attempt to constrain the unit’s presence, as well as the nature of its lower boundary throughout outcrops in Svalbard. The Isfjorden Member is easily recognised by its conspicuous beds of alternating red and green coloured palaeosols, occasional caliche profiles and bivalve coquina beds. These beds have commonly been used to identify the unit in outcrop and we explore their relevance to the formal stratigraphic definition. The lower boundary is typically difficult to identify, especially when using the original definition; however, we find that placing it at the top of the last major sandstone in the De Geerdalen Formation is a practical solution. The boundary is conformable throughout Spitsbergen with no obvious erosion or break in sedimentation observed.The abundance, thickness and maturity of palaeosols increases upwards through the De Geerdalen Formation. Mature palaeosol and occasional caliche horizons are found to dominate within the Isfjorden Member. Immature palaeosols are in general constrained to the strata below. The position of palaeosols in relation to sedimentary successions is typically restricted to floodplain and interdistributary bay deposits, or atop upper shoreface deposits. The transition from immature palaeosols with common histosols to mature palaeosols and caliche reflects the development of the delta plain from a dynamic paralic setting to a morestable proximal system.publishedVersio

Linking regional unconformities in the Barents Sea to compression-induced forebulge uplift at the Triassic-Jurassic transition

The Triassic-Jurassic transition marks an important change in the basin configuration of the Greater Barents Sea. A contiguous basin with km-thick sedimentary successions changed into a partitioned basin with uplift in the west and foreland basins in the east with significant implication for the basin infill history. Our study employs a range of different high-resolution datasets from a distal part of the basin which unravels the complex pattern of differential uplift and erosion in the basin during this period. We record for the first time distinct angular unconformities between Upper Triassic strata and overlying Lower Jurassic strata within the basin, showing that large parts of it formed topographic highs. Our study links these angular unconformities to compression induced by the Novaya Zemlya Fold and Thrust Belt. A heterolithic basement below a thick sedimentary succession where the fold belt developed created a complex uplift pattern in the basin, at the same time similar to but different from typical forebulge areas. Compression caused inversion of older basement rooted faults defining platforms and graben systems throughout western parts of the Barents Sea basin, in addition to salt remobilization that resulted in differential uplift and erosion. These local zones of uplift controlled the sediment distribution pattern to the basin at a time when the most important reservoir units in the basin were deposited. This new understanding of the basin development explains hitherto enigmatic sequence boundaries that has inspired complex paleogeographic models in the past.publishedVersio

In situ triaxial testing to determine fracture permeability and aperture distribution for CO2 sequestration in Svalbard, Norway

On Svalbard, Arctic Norway, an unconventional silicidastic reservoir, relying on (micro)fractures for enhanced fluid flow in a low-permeable system, is investigated as a potential CO2 sequestration site. The fractures' properties at depth are, however, poorly understood. High resolution X-ray computed tomography (micro-CT) imaging allows one to visualize such geomaterials at reservoir conditions. We investigated reservoir samples from the De Geerdalen Formation on Svalbard to understand the influence of fracture closure on the reservoir fluid flow behavior. Small rock plugs were brought to reservoir conditions, while permeability was measured through them during micro-CT imaging. Local fracture apertures were quantified down to a few micrometers wide. The permeability measurements were complemented with fracture permeability simulations based on the obtained micro-CT images. The relationship between fracture permeability and the imposed confining pressure was determined and linked to the fracture apertures. The investigated fractures closed due to the increased confining pressure, with apertures reducing to approximately 40% of their original size as the confining pressure increased from 1 to 10 MPa. This coincides with a permeability drop of more than 90%. Despite their closure, fluid flow is still controlled by the fractures at pressure conditions similar to those at the proposed storage depth of 800-1000 m

Time, hydrologic landscape and the long‐term storage of peatland carbon in sedimentary basins

Peatland carbon may enter long‐term storage in sedimentary basins preserved as either coal or lignite. The time required to account for the carbon in 1 – 10 m thick coal seams must represent 105 to 106 years, an order of magnitude more than previously assumed. To understand the process by which this happens requires extrapolation of our understanding of peatland carbon accumulation over timescales that greatly exceed those of Holocene peat. We analyse the consequences of extrapolating peat growth to periods of 106 years. We deduce that that key to sustained peat growth are hydrologic landscapes that can maintain a saturated peat body above the level of clastic deposition. Contrary to current stratigraphic frameworks we conclude that the generation of accommodation space at low rates of 0.1 to 0.2 mm/yr can adequately accommodate thick peat accumulation over periods >105 yrs. However, generation of accommodation space at rates >0.5 mm/yr cannot. The low rates that permit accommodation of thick peat are typical of the rates of subsidence in specific tectonic settings, particularly foreland basins, and this has implications for our understanding of the links between terrestrial carbon burial, tectonics and the carbon cycle. The long‐term stability of extensive peatland required to form coal also requires sediment bypass, modifying basin wide sediment transport and deposition. Limits to peatland growth under very low accommodation rates must exist but the relative importance of the limiting process is not understood. Finally, we discuss the consequences of these factors for predicting the future of the peatland carbon reservoir

Tectonostratigraphic development of the Upper Triassic to Middle Jurassic in the Hoop Area, Barents Sea: Implications for understanding ultra-condensed reservoir units

The most prolific reservoir intervals in the Barents Sea are found in the Upper Triassic to Middle Jurassic Realgrunnen Subgroup, deposited during a major change in the structural evolution of the basin which greatly influenced its development and distribution. The effects are evident in one of the petroleum provinces in the SW Barents Sea, the Hoop Area. Due to the condensed nature of the succession, the tectonostratigraphic evolution has been enigmatic. We use a range of different methods and dataset, including high-resolution P-Cable seismic to determine the tectono-stratigraphic evolution of the succession. Results are important for exploration and production in the Hoop Area and beyond, but also for a broader understanding of how ultra-condensed successions might evolve during long periods of non-deposition and short bursts of deposition. Seven major phases of deposition and non-deposition/erosion are defined. Stage 1 represents fluvio-deltaic deposition in the Fruholmen Formation (Norian), followed by Stage 2 with significant truncation and non-deposition, lasting up to 35 million years. Deposition resumed with the shallow marine to fluvial Nordmela and Stø formations (Pliensbachian to Bajocian), which both encapsule long periods of erosion and non-deposition (stage 3–6). Stage 7 is represented by transgression and shelf deposition in the Fuglen Formation (Bathonian). The change from a high-accommodation setting with continuous and relatively high rate of accumulation in the Triassic, to a low-accommodation setting with episodic deposition and extensive sediment cannibalization in the Jurassic, resulted in cleaner sandstones with better reservoir properties. The low-accommodation setting also enabled coarse-graded detritus from hinterlands in Fennoscandia to prograde into distal part of the basin and more amalgamation of the sands during the Jurassic. Adversely, the low accommodation setting also caused a fragmented pattern of deposition and preservation that needs to be carefully considered in subsurface datasets, often with limited resolution.publishedVersio