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Sökning: WFRF:(Juhlin Christopher 1956 )

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1.
  • Koyi, Hemin, et al. (författare)
  • Numerical models of ductile rebound of crustal roots beneath mountain belts
  • 1999
  • Ingår i: Geophysical Journal International. - : Blackwell Publishing. - 0956-540X .- 1365-246X. ; 139:2, s. 556-562
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Crustal roots formed beneath mountain belts are gravitationally unstable structures, which rebound when the lateral forces that created them cease or decrease significantly relative to gravity. Crustal roots do not rebound as a rigid body, but undergo intensive internal deformation during their rebound and cause intensive deformation within the ductile lower crust. 2-D numerical models are used to investigate the style and intensity of this deformation and the role that the viscosities of the upper crust and mantle lithosphere play in the process of root rebound. Numerical models of root rebound show three main features which may be of general application: first, with a low-viscosity lower crust, the rheology of the mantle lithosphere governs the rate of root rebound; second, the amount of dynamic uplift caused by root rebound depends strongly on the rheologies of both the upper crust and mantle lithosphere; and third, redistribution of the rebounding root mass causes pure and simple shear within the lower crust and produces subhorizontal planar fabrics which may give the lower crust its reflective character on many seismic images.
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2.
  • Niemi, Auli, et al. (författare)
  • Chapter 7: Site Characterization
  • 2017
  • Ingår i: Geological Storage Of Co<sub>2</sub> in Deep Saline Formations. - Dordrecht : Springer Netherlands. - 9789402409949 - 9789402409963 ; , s. 309-380
  • Bokkapitel (refereegranskat)abstract
    • A necessary first step in qualifying a specific site for CO2 storage and for quantifying its relevant properties is a proper site characterization. Site characterization provides the ultimate input data for reservoir modeling and for all the predictions concerning the storage complex and its surroundings. It also provides baseline information for monitoring the behavior of injected CO2. It also incorporates input from laboratory experiments described in Chap.6. This chapter gives an overview of site characterization procedures with respect to geological storage of CO2, by starting from regulatory requirements and guidelines and proceeding to specific methodologies for assessing the sites properties in terms of CO2 geological storage.
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3.
  • Alcalde, J., et al. (författare)
  • 3-D reflection seismic imaging of the Hontomin structure in the Basque-Cantabrian Basin (Spain)
  • 2013
  • Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 4:2, s. 481-496
  • Tidskriftsartikel (refereegranskat)abstract
    • The Basque-Cantabrian Basin of the northern Iberia Peninsula constitutes a unique example of a major deformation system, featuring a dome structure developed by extensional tectonics followed by compressional reactivation. The occurrence of natural resources in the area and the possibility of establishing a geological storage site for carbon dioxide motivated the acquisition of a 3-D seismic reflection survey in 2010, centered on the Jurassic Hontomin dome. The objectives of this survey were to obtain a geological model of the overall structure and to establish a baseline model for a possible geological CO2 storage site. The 36 km(2) survey included approximately 5000 mixed (Vibroseis and explosives) source points recorded with a 25 m inline source and receiver spacing. The target reservoir is a saline aquifer, at approximately 1450 m depth, encased and sealed by carbonate formations. Acquisition and processing parameters were influenced by the rough topography and relatively complex geology. A strong near-surface velocity inversion is evident in the data, affecting the quality of the data. The resulting 3-D image provides constraints on the key features of the geologic model. The Hontom n structure is interpreted to consist of an approximately 10(7) m(2) large elongated dome with two major (W-E and NW-SE) striking faults bounding it. Preliminary capacity estimates indicate that about 1.2 Gt of CO2 can be stored in the target reservoir.
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4.
  • Alcalde, J., et al. (författare)
  • Active seismic characterization experiments of the Hontomin research facility for geological storage of CO2, Spain
  • 2013
  • Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 19:0, s. 785-795
  • Tidskriftsartikel (refereegranskat)abstract
    • An active source seismic experiment was carried out as part of the subsurface characterization study of the first Spanish Underground Research Facility for Geological Storage of CO2 in Hontomín (Burgos, Spain). The characterization experiment included a 36 km2 3D seismic reflection survey and two three-component seismic profiles. The target reservoir is a saline aquifer located at 1450 m depth within Lower Jurassic carbonates (Lias). The main seal is formed by interlayered marlstones and marly limestones of Early to Middle Jurassic age (Dogger and Lias). The seismic images obtained allow defining the 3D underground architecture of the reservoir site. The structure consists of an asymmetric dome crosscut by a relatively complex fault system. The detailed characterization of the fracture system is currently under study to unravel the geometric distribution of the faults and their extent within the different formations that form the structure. The constrained model has guided the design of the injection and monitoring boreholes and provided the data for the baseline study. The resultant high resolution seismic model will be used as a reference in future monitoring stages.
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5.
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6.
  • Andersson, Magnus, et al. (författare)
  • Carbonatite ring-complexes explained by caldera-style volcanism
  • 2013
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ∼3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas.
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7.
  • Ayarza, Puy, et al. (författare)
  • Evolution of the Iberian Massif as deduced from its crustal thickness and geometry of a mid-crustal (Conrad) discontinuity
  • 2021
  • Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 12:7, s. 1515-1547
  • Tidskriftsartikel (refereegranskat)abstract
    • Y Normal incidence seismic data provide the best images of the crust and lithosphere. When properly designed and continuous, these sections greatly contribute to understanding the geometry of orogens and, along with surface geology, unraveling their evolution. In this paper we present the most complete transect, to date, of the Iberian Massif, the westernmost exposure of the European Variscides. Despite the heterogeneity of the dataset, acquired during the last 30 years, the images resulting from reprocessing the data with a homogeneous workflow allow us to clearly define the crustal thickness and its internal architecture. The Iberian Massif crust, formed by the amalgamation of continental pieces belonging to Gondwana and Laurussia (Avalonian margin), is well structured in the upper and lower crust. A conspicuous mid-crustal discontinuity is clearly defined by the top of the reflective lower crust and by the asymptotic geometry of reflections that merge into it, suggesting that it has often acted as a detachment. The geometry and position of this discontinuity can give us insights into the evolution of the orogen (i.e., of the magnitude of compression and the effects and extent of later-Variscan gravitational collapse). Moreover, the limited thickness of the lower crust below, in central and northwestern Iberia, might have constrained the response of the Iberian microplate to Alpine shortening. Here, this discontinuity, featuring a Vp (P-wave velocity) increase, is observed as an orogen-scale boundary with characteristics compatible with those of the globally debated Conrad discontinuity.
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8.
  • Basirat, Farzad, et al. (författare)
  • Hydraulic Modeling of Induced and Propagated Fractures : Analysis of Flow and Pressure Data From Hydromechanical Experiments in the COSC-1 Deep Borehole in Crystalline Rock Near Åre, Sweden
  • 2021
  • Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 57:11
  • Tidskriftsartikel (refereegranskat)abstract
    • To characterize the coupled hydromechanical behavior of rock fractures, the step-rate injection method for fracture in-situ properties (SIMFIP) was conducted with a specialized downhole probe developed by Guglielmi et al. (2014, https://doi.org/10.1007/s00603-013-0517-1). In June 2019, a field campaign was carried out near Åre, Sweden, where the SIMFIP probe was applied in the Collisional Orogeny in the Scandinavian Caledonides-1 scientific borehole to understand the dynamics of injection-induced fracture initiation, fracture opening, and shearing due to water injection-withdrawal in a borehole interval isolated by two packers. Three intervals were investigated at ∼500 m depth: (a) an unfractured section (intact rock), (b) a section with non-conductive fractures, and (c) a section with hydraulically conductive fractures. Pressure, injection flow rate, and borehole wall displacement were simultaneously measured during the tests. In the present study, the geometry of the induced fracture and deformation of existing fractures at different time stages of the tests are determined based on a hydrologic model by using the measured pressure and flow data during each time stage of the experiment. A numerical model for the fluid flow within the fracture and the packed-off borehole interval is implemented within COMSOL Multiphysics. By matching model simulations with observed data for all three sections, estimates of the induced and propagated fractures' radius and aperture at successive time stages have been obtained in each case. We could also determine the non-linear relationship between fracture aperture and pressure for values above fracture opening pressures. The model results provide insights for the understanding of pressure-induced fracture initiation and propagation in crystalline rock.
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9.
  • Bastida, F, et al. (författare)
  • A cross-section through the Zilair Nappe (southern Urals)
  • 1997
  • Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 276:1-4, s. 253-263
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • A structural transect in the Zilair-Kugarchi area involves the western part of the Suvanyak Complex, the Zilair Nappe and the eastern part of the foreland thrust and fold belt. This section has been analyzed using field, microstructural and seismic data. The cross-section shows the transition from the hinterland to the foreland in the footwall to the suture of the southern Urals. The rocks involved range from early Palaeozoic to Permian in age. A characteristic of the Zilair Nappe is the dominance of a succession of volcanic greywackes and mudrocks of Late Devonian age (Zilair Formation). The metamorphic grade decreases from east to west, from greenschist facies to diagenetic conditions. The structure of the cross-section mainly comprises west-directed thrusts and thrust-related folds with an associated cleavage. Fold vergence changes along the section depending on of the distance to the associated thrust and its geometry. The Zilair thrust which separates the Zilair Nappe from the foreland thrust and fold belt accommodated ca. 10 km displacement and the characteristics of the deformation are similar on both sides of it. The contact between the Zilair Nappe and Suvanyak Complex is a west-dipping normal fault that does not represent a major tectonic boundary.
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10.
  • Beckel, Ruth A. (författare)
  • Active and passive seismic methods for investigating the glacially-triggered Burträsk fault
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Glacially-triggered faults are of high scientific interest since their formation was likely accompanied by major earthquakes and they are still a centre of seismicity in northern Fennoscandia, today. Imaging their deeper structure mainly relies on reflection seismics since the method generally has the best resolving power at depth of all geophysical methods. This thesis uses data acquired at the glacially-triggered Burträsk fault to advance active and passive seismic imaging methods and improve the understanding of the area. Reprocessing of a vintage, crooked-line reflection dataset using a newly developed module for a local cross-dip correction improved the quality of the reflection image significantly and provided important 3D information for the interpretation of the fault and its surroundings. A fault segment to the southwest of the profile was imaged with a dip of approximately 50° but the segment intersecting the profile was not imaged, likely due to insufficient shot coverage close to the fault. Since the Burträsk area is seismically the most active area in Sweden, passive imaging using a dataset of local microearthquakes was attempted. As a first step, the earthquakes were re-located using a stacking-based location method. In spite of the poor azimuthal coverage of the array, the method yielded surprisingly good location results within 30–40 km from the array. The most important factors for success proved to be combined P- and S-wave location with down-weighted S-wave signals, and the use of a polarity-sensitive characteristic function. The distribution of the hypocentres confirmed that the trace of the Burträsk fault is the currently active fault plane. Disappointingly, passive seismic processing using reflection seismic interferometry (RSI) did not image the known reflections. To improve the planning of future studies, different aspects of imaging dipping faults with RSI were investigated using synthetic data. The results showed that reconstructing steeply dipping reflections requires sources in the hanging-wall and that the interpretation of the RSI sections is complicated due to strong artefacts caused by P-S converted arrivals. Thus, passive imaging needs careful planning and a good knowledge of the source positions for distinguishing between artefacts and subsurface structures. This knowledge can be obtained using the stacking-based location method. 
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11.
  • Beckel, Ruth A., et al. (författare)
  • Comparing the performance of stacking-based methods for microearthquake location : a case study from the Burträsk fault, northern Sweden
  • 2022
  • Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 228:3, s. 1918-1934
  • Tidskriftsartikel (refereegranskat)abstract
    • Traditional earthquake location relying on first arrival picking is challenging for microseismic events with low signal-to-noise ratio. Over the past years, alternative procedures have been explored based on the idea of migrating the energy of an earthquake back into its source position by stacking along theoretical traveltime curves. To avoid destructive interference of signals with opposite polarity, it is common to transform the input signals into positive time-series. Stacking-based source location has been successfully applied at various scales, but existing studies differ considerably in the choice of characteristic function, the amount of pre-processing and the phases used in the analysis. We use a data set of 62 natural microearthquakes recorded on a 2-D seismic array of 145 vertical geophones across the glacially triggered Burtrask fault to compare the performance of five commonly used characteristic functions: the noise filtered seismograms and the semblance, the envelope, the short-term average/long-term average ratio and the kurtosis gradient of the seismograms. We obtain the best results for a combined P- and S-wave location using a polarity-sensitive characteristic function, that is the filtered seismograms or the semblance. In contrast, the absolute functions often fail to align the signals properly, yielding biased location estimates. Moreover, we observe that the success of the procedure is very sensitive to noise suppression and signal shaping prior to stacking. Our study demonstrates the usefulness of including lower quality S-wave data to improve the location estimates. Furthermore, our results illustrate the benefits of retaining the phase information for location accuracy and noise suppression. To ensure optimal location results, we recommend carefully pre-processing the data and test different characteristic functions for each new data set. Despite the suboptimal array geometry, we obtain good locations for most events within similar to 30-40 km of the survey and the locations are consistent with an image of the fault trace from an earlier reflection seismic survey.
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12.
  • Beckel, Ruth A., et al. (författare)
  • Impact of source and receiver distributions on imaging of dipping reflectors with reflection seismic interferometry
  • 2022
  • Ingår i: Geophysical Journal International. - : Oxford University Press. - 0956-540X .- 1365-246X. ; 230:3, s. 2098-2116
  • Tidskriftsartikel (refereegranskat)abstract
    • Passive reflection seismic interferometry (PRSI) facilitates imaging the subsurface structure using passive sources but according to the general theory, the target needs to be illuminated equally from all directions to obtain a kinematically correct result. In practice, this requirement is almost impossible to meet which can introduce artefacts into the PRSI results. Our study was motivated by an unsuccessful attempt to image a couple of known dipping reflectors by applying PRSI to a data set of local microearthquakes clustering around the glacially triggered Burträsk fault. Dipping reflectors are a special case since they introduce a directionality into the seismic-interferometry problem that makes the results especially sensitive to the source azimuths. To investigate which source distributions are favourable in such a case and to study the range of artefacts occurring, we analyse a number of acoustic and elastic synthetic data sets calculated using a simple model of a dipping fault. Our results show that the main contribution for imaging such a fault with PRSI comes from sources in the hangingwall whereas contributions from the footwall are often weak and kinematically incorrect. The type and position of the occurring artefacts depend upon both the source azimuth and the type of modelling. In the acoustic case, the main artefact is a gently dipping reflection caused by insufficient cancellation of the direct reflection at the fault. In the elastic case, the artefacts are dominated by a set of both gently and steeply dipping reflections related to P–S converted waves. These artefacts are present even for ideal illumination due to the use of source records containing both P- and S-wave contributions. During interpretation, it is essential to be able to distinguish between physically meaningful reflections and artefacts. We found that both acoustic and elastic artefacts stack best at lower than expected normal moveout velocities. If data quality is insufficient for velocity analysis, our results can serve as a reference point for the interpretation of dipping features in PRSI images.
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13.
  • Beckel, Ruth A., et al. (författare)
  • The cross-dip correction as a tool to improve imaging of crooked-line seismic data : a case study from the post-glacial Burtrask fault, Sweden
  • 2019
  • Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 10:2, s. 581-598
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the development of post-glacial faults and their associated seismic activity is crucial for risk assessment in Scandinavia. However, imaging these features and their geological environment is complicated due to special challenges of their hardrock setting, such as weak impedance contrasts, often high noise levels and crooked acquisition lines. A crooked-line geometry can cause time shifts that seriously de-focus and deform reflections containing a cross-dip component. Advanced processing methods like swath 3-D processing and 3-D pre-stack migration can, in principle, handle the crooked-line geometry but may fail when the noise level is too high. For these cases, the effects of reflector cross-dip can be compensated for by introducing a linear correction term into the standard processing flow. However, existing implementations of the cross-dip correction rely on a slant stack approach which can, for some geometries, lead to a duplication of reflections. Here, we present a module for the cross-dip correction that avoids the reflection duplication problem by shifting the reflections prior to stacking. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of cross-dip correction, velocity analysis and dip-moveout (DMO) correction is repeated until the stacked image converges. Using our new module to reprocess a reflection seismic profile over the post-glacial Burtrask fault in northern Sweden increased the image quality significantly. Strike and dip information extracted from the cross-dip analysis helped to interpret a set of southeast-dipping reflections as shear zones belonging to the regional-scale Burtrask Shear Zone (BSZ), implying that the BSZ itself is not a vertical but a southeast-dipping feature. Our results demonstrate that the cross-dip correction is a highly useful alternative to more sophisticated processing methods for noisy datasets. This high-lights the often underestimated potential of rather simple but noise-tolerant methods in processing hardrock seismic data.
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14.
  • Beckel, Ruth, et al. (författare)
  • Imaging and Characterization of Glacially Induced Faults Using Applied Geophysics
  • 2021
  • Ingår i: Glacially-Triggered Faulting. - Cambridge : Cambridge University Press. - 9781108779906 - 9781108490023 ; , s. 118-132
  • Bokkapitel (refereegranskat)abstract
    • Geophysical methods have the potential to delineate and map the geometry of glacially induced faults (GIFs) in the hard rock environment of the Baltic Shield. Relevant geophysical methods include seismic, geoelectric, electromagnetic, magnetic and gravity ones. However, seismic methods have the greatest potential for determining the geometry at depth due to their higher resolving power. Seismic methods have even been used to identify a previously unknown GIF within the Pärvie Fault system. The other geophysical methods are usually employed to image the near-surface structure of GIFs. We provide a brief review of geophysical principles and how they apply to imaging of GIFs in the hard rock environment. The advantages and challenges associated with various geophysical methods are discussed through several case histories. Results to date show that it is possible to map GIFs dipping at 35–65° from the near-surface down to depths of 7–8 km. It is not clear if the limiting factor in their mapping at depth is the nature of the faults or the limitations in the seismic acquisition parameters since the mapping capacity is highly dependent upon the acquisition geometry and source type used.
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15.
  • Bergman, Björn, et al. (författare)
  • High-resolution reflection seismic imaging of the upper crust at Laxemar, southeastern Sweden
  • 2002
  • Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 355:1-4, s. 201-213
  • Tidskriftsartikel (refereegranskat)abstract
    • A major cost in exploring the upper 1–2 km of crystalline crust with reflection seismics is the drilling required for explosive sources. By reducing the charge size to a minimum, shallow inexpensive shotholes can be drilled with handheld equipment. Here, we present results from a full-scale test using small charges for high-resolution seismic surveying over a nuclear waste disposal study site (not an actual site). Two 2–2.5-km-long crossing profiles were acquired in December 1999 with 10-m shot and geophone spacing in the Laxemar area, near Oskarshamn in southeastern Sweden. After standard processing, including dip moveout (DMO), several subhorizontal to moderately dipping reflections are imaged. Many of the dipping ones can be correlated to fracture zones observed in a ca. 1700-m-deep borehole where the profiles cross and/or to fracture zones mapped on the surface. The imaged fracture zones form a complex 3D pattern illustrating the necessity of having 3D control before interpreting seismic reflection data. Analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole (granite/greenstone reflection coefficient is +0.065). These greenstones may contribute to the reflectivity when associated with fracture zones. In some cases, where they are present as larger subhorizontal lenses, they may be the dominant source of reflectivity. A set of north-dipping (10°) reflectors at 3–3.5-km depth can be correlated to a similar set observed below the island of Ävrö about 3 km to the east.
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16.
  • Bergmann, Peter, et al. (författare)
  • Combination of seismic reflection and constrained resistivity inversion with an application to 4D imaging of the CO2 storage site, Ketzin, Germany
  • 2014
  • Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 79:2, s. B37-B50
  • Tidskriftsartikel (refereegranskat)abstract
    • A combination of seismic and geoelectric processing was studied by means of a structurally constrained inversion approach. Structural constraints were interpreted from the seismic data and integrated into the geoelectric inversion through a local regularization, which allowed inverted resistivities to behave discontinuously across defined boundaries. This arranged seismic processing and constrained resistivity inversion in a sequential workflow, making the generic assumption that the petrophysical parameters of both methods change across common lithostructural boundaries. We evaluated the approach using a numerical example and a real data example from the Ketzin CO2 pilot storage site, Germany. The latter demonstrated the efficiency of this approach for combining 4D seismic and surface-downhole geoelectric data. In consistence with the synthetic example, the constrained resistivity inversions produced clearer delineated images along the boundary between caprock and reservoir formation. Near the CO2-flooded reservoir, the seismic and geoelectric time-lapse anomalies correlated well. At some distance to the downhole electrodes, however, the geoelectric images conveyed a notably lower resolution in comparison to the corresponding seismic images. Both methods confirm a northwesterly trend for the CO2 migration at the Ketzin site, although a rather northerly direction was initially expected. The results demonstrate the relevance of the presented approach for the combination of both methods for integrated geophysical CO2 storage monitoring.
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17.
  • Brodic, Bojan, et al. (författare)
  • Bedrock and Fracture Zone Delineation UsingDifferent Near-surface Seismic Sources
  • 2017
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • To delineate the bedrock surface and a fracture zone intersected by a well at c. 50 m depth, a seismic survey wasconducted using four different near-surface seismic sources. These were a 5-kg sledgehammer, a metal I-beamhit laterally, an accelerated weight drop and a prototype source tested for the first time called Udarnik. TheUdarnik source has two hammers whose impacts are initiated by an electromagnetic force of the stable coilexciting its inner moving part. Two hammers separated by a distance of approximately 50 cm successively hittwo contact plates mounted on the bottom of the source. The sweep length is adjustable and maximum 18 hitscan be made per second. In this study, we compare the performance of every source used and present reflectionseismic sections and tomography results from the high-fold (star-type acquisition was used) combinedlandstreamer and wireless recorder survey. Preliminary results indicate that bedrock was well delineated both ontomography results and stacked sections for all sources and some weak reflectivity is observed where thefracture zone is expected with most of the sources used showing the potential of the seismic methods forfracture zone imaging and near-surface characterization
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18.
  • Brodic, Bojan, et al. (författare)
  • Delineating fracture zones using surface-tunnel-surfaceseismic data, P-S, and S-P mode conversions
  • 2017
  • Ingår i: Journal of Geophysical Research - Solid Earth. - 2169-9313 .- 2169-9356. ; 122:7, s. 5493-5516
  • Tidskriftsartikel (refereegranskat)abstract
    • A surface-tunnel-surface seismic experiment was conducted at the Äspö Hard Rock Laboratoryto study the seismic response of major fracture systems intersecting the tunnel. A newly developedthree-component microelectromechanical sensor-based seismic landstreamer was deployed inside the noisytunnel along with conventional seismic receivers. In addition to these, wireless recorders were placed on thesurface. This combination enabled simultaneous recording of the seismic wavefield both inside the tunneland on the surface. The landstreamer was positioned between two geophone-based line segments, alongthe interval where known fracture systems intersect the tunnel. First arrival tomography produced a velocitymodel of the rock mass between the tunnel and the surface with anomalous low-velocity zones correlatingwell with locations of known fracture systems. Prominent wave mode converted direct and reflected signals,P-S and S-P waves, were observed in numerous source gathers recorded inside the tunnel. Forward traveltime and 2-D finite difference elastic modeling, based on the known geometry of the fracture systems, showthat the converted waves are generated at these systems. Additionally, the landstreamer data were used toestimate Vp/Vs, Poisson’s ratio, and seismic attenuation factors (Qp and Qs) over fracture sets that havedifferent hydraulic conductivities. The low-conductivity fracture sets have greater reductions in P wavevelocities and Poisson’s ratio and are more attenuating than the highly hydraulically conductive fracture set.Our investigations contribute to fracture zone characterization on a scale corresponding to seismicexploration wavelengths.
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19.
  • Brodic, Bojan, et al. (författare)
  • Innovative seismic imaging of volcanogenic massive sulfide deposits, Neves-Corvo, Portugal - Part 1 : In-mine array
  • 2021
  • Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 86:3, s. B165-B179
  • Tidskriftsartikel (refereegranskat)abstract
    • To evaluate and upscale the feasibility of using exploration tunnels in an operating mine for active-source seismic imaging, a seismic experiment was conducted at the Neves-Corvo mine, in southern Portugal. Four seismic profiles were deployed in exploration drifts approximately 650 m beneath the ground surface, above the world-class Lombador volcanogenic massive sulfide deposit. In addition to the tunnel profiles, two perpendicular surface seismic profiles were deployed above the exploration tunnels. The survey was possible due to a newly developed prototype global positioning system (GPS) time transmitter enabling accurate GPS synchronization of cabled and nodal seismic recorders, below and on the surface. Another innovative acquisition aspect was a 1.65 t broadband, linear synchronous motor (LSM) driven - electric seismic vibrator (e-vib) used as the seismic source along two of the exploration tunnels. We have evaluated the challenges and innovations necessary for active-source tunnel seismic acquisition, characterized by high levels of vibrational noise from the mining activities. In addition, we evaluated the LSM vibrator's signal and overall seismic-data quality in this hard rock mining environment. Our processing results from the tunnel data and 3D reflection imaging of the Lombador deposit below the exploration tunnels were checked for consistency through constant-velocity 3D ray-tracing traveltime forward modeling. For imaging purposes, 3D Kirchhoff prestack depth and poststack time-migration algorithms were used, with both successfully imaging the targeted deposit. The results obtained show that active-source-seismic imaging using subsurface mining infrastructure of operational mines is possible. However, it requires innovative exploration strategies, a broadband seismic source, an accurate GPS-time system capable of transmitting GPS-time hundreds of meters below the surface, and careful processing. The results obtained open up possibilities for similar studies in different mining or tunneling projects.
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20.
  • Brodic, Bojan, et al. (författare)
  • Multi-component digital-based seismic landstreamer and boat-towed radio-magnetotelluric acquisition systems for improved subsurface characterization in the urban environment
  • 2017
  • Ingår i: First Break. - Amsterdam, Netherlands. - 0263-5046 .- 1365-2397. ; 35:8, s. 41-47
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • It is estimated that urban life will be the norm for around 60% of the world’s population by 2040, leading to a more centralized distribution of people and making the city as the main place of residence (Whiteley, 2009). This population centralization inherently implies rapidly expanding cities and imposes the need for more infrastructure within, around and between the present city boundaries. However, infrastructure projects nowadays have to follow strict civil engineering standards that require detailed knowledge of subsurface conditions during different stages of the construction processes. Since direct methods conventionally used for site characterization (e.g., drilling and/or core testing) are still relatively expensive the focus in the last two decades has been on non-invasive, geophysical methods. However, geophysical site characterization in urban areas is not an easy task owing to numerous challenges and various types of noise sources. Challenges such as electric/electromagnetic (EM) noise, pipelines and other subsurface objects (sometimes even unknown or undocumented), the inability to properly couple sensors because of pavement, traffic noises and limited space are common in urban environment. Since geophysical surveys need to be done with the least amount of disturbances to the environment, residents and traffic, new geophysical techniques for fast, non-invasive and high-resolution site characterization are needed. To overcome some of these challenges, a nationwide joint industry-academia project was launched in 2012 TUST GeoInfra, www.trust-geoinfra.se). As a component in the project, Uppsala University developed two new data acquisition systems. These are a fully digital MEMS-based (Micro-machined Electro-Mechanical Sensor) three component (3C) seismic landstreamer and a boat-towed radio-magnetotelluric (RMT) acquisition system. Both systems were specifically designed to address urban environments with the RMT system particularly aiming at efficient and cost-effective geophysical surveying on shallow-water bodies, which constitute 7% of Scandinavia. In this article, we will describe the two systems and present two case studies illustrating their potential. A number of published accounts are now available from the two systems showing what type of problems they can address (e.g., Bastani et al., 2015; Brodic et al., 2015; Malehmir et al., 2015a, 2015b, 2016a, 2016b, 2017; Dehghannejad et al., 2017; Maries et al., 2017; Mehta et al., 2017; Brodic et al., 2017).
  •  
21.
  • Bruckman, Viktor J., et al. (författare)
  • Preface to the special issue of the Division Energy, Resources and the Environment at the EGU General Assembly EGU22
  • 2022
  • Ingår i: Advances in Geosciences. - : Copernicus Publications. - 1680-7340 .- 1680-7359. ; 58, s. 87-91
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The European Geosciences Union (EGU) is one of the leading global bottom-up societies that promotes earth, planetary and space sciences. In its annual general assemblies, EGU brings together experts from all over the world to discuss cutting-edge research and implementation of findings in their respective disciplines and beyond via its inter-and transdisciplinary sessions, and thus offers a unique forum for scientific exchange, science-policy interaction, and joint development of strategies for future research endeavours. Within that framework the Energy, Resources and the Environment (ERE) Programme Group provides the platform for discussion about adequate and reliable supplies of affordable energy and other georesources in environmentally sustainable ways. This special issue in Advances in Geosciences comprises a collection of contributions from the ERE Programme Group, which were presented at the General Assembly 2022. It was held in hybrid mode for the first time from 23-27 May 2022, after two virtual assemblies in 2020 and 2021.
  •  
22.
  • Bruckman, Viktor J., et al. (författare)
  • Preface to the special issue of the Division Energy, Resources and the Environment at vEGU2021 : Gather online
  • 2021
  • Ingår i: Advances in Geosciences. - : Copernicus Publications. - 1680-7340 .- 1680-7359. ; 56, s. 13-18
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The European Geosciences Union (EGU) is one of the leading global bottom-up societies that promotes earth, planetary and space sciences. In its annual general assemblies, EGU brings together experts from all over the world to discuss cutting-edge research and implementation of findings in its respective disciplines and thus offers a unique forum for scientific exchange, science-policy interaction, and joint development of strategies for future research endeavours.This special issue in Advances in Geosciences comprises a collection of contributions from the Division Energy, Resources and the Environment (ERE) of the EGU, which were presented at the General Assembly 2021, vEGU2021: Gather online. It was held entirely online for the second time after EGU2020 from 19 to 30 April 2021.
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23.
  • Buntin, Sebastian, et al. (författare)
  • Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
  • 2019
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
  • Tidskriftsartikel (refereegranskat)abstract
    • Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.
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24.
  • Buntin, Sebastian, 1990- (författare)
  • Seismic structure of the central Svecofennian lithosphere
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lithospheric structures in the Fennoscandian Shield in Sweden have been studied by a number of large-scale wide-angle seismic reflection/refraction (WARR) and normal-incidence reflection profiles since the 1960s. Among these were the over 2000 km long Fennoscandian Long Range (FENNOLORA) project in 1979 and the Baltic and Bothnian Echoes from the Lithosphere (BABEL) in 1989, which provided valuable images of the subsurface down to over 60 km depth including the Moho. Additionally, the 550 km long WARR profile, UPPLAND, was acquired in 2017, transecting across the Uppland and Ljusdal Batholiths from south to north. Due to the computational progress in the last 25 years, improved seismic images and velocity models could be obtained by reprocessing the recovered BABEL data set. The main finding of the reprocessed BABEL profiles is the presence of large-scale saucer-shaped intrusions of around 100 km diameter connected to an up-domed lower crust and sub-Moho reflectors. These interpreted offshore saucer-shaped intrusions together with those observed onshore suggest a nested interconnected emplacement model, implying that the deeper saucer-shaped intrusions fed the shallower ones.Ray tracing forward modelling of the UPPLAND data revealed a unique velocity structure below the Uppland Batholith with high velocities in both the lowermost crust (~7.3 km/s) and uppermost mantle (~8.5 km/s). Such a velocity structure has not been observed anywhere else to this extent and robustness. It is interpreted to represent the presence of eclogitized material in the lowermost crust and complicates further the difference between the seismological and petrological crust-mantle boundary.The recovery and reprocessing of the FENNOLRA data set provided new insights into the lower crust and upper mantle. Consistent with the results of the UPPLAND velocity profile where collocated, it also reveals a high-velocity lowermost crustal structure in the Fennoscandian Shield and a heterogenous upper mantle with different average velocities (8.2-8.5 km/s) across various geological terranes. Additionally, a zone with lower velocities (8.0-8.2 km/s) is detected in 70-90 km depth in the mantle.Overall, the studies in this thesis demonstrate the potential of reprocessing legacy data, but also of acquiring new high-resolution deep seismic sounding profiles for the investigation of the crust and upper mantle structures. Aside from recovering fully digital reusable BABEL and FENNOLORA data, new and refined geophysical and geological models can be tested and provide key information for cratonic setting studies.
  •  
25.
  • Dehghannejad, Mahdieh, et al. (författare)
  • Crustal geometry of the central Skellefte district, northern Sweden : constraints from reflection seismic investigations
  • 2012
  • Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 524-525, s. 87-99
  • Tidskriftsartikel (refereegranskat)abstract
    • The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting north-dipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.
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26.
  • Dehghannejad, M., et al. (författare)
  • High-resolution reflection seismic imaging in the Kristineberg mining area, Northern Sweden
  • 2010
  • Ingår i: Society of Petroleum Engineers - 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010 - Incorporating SPE EUROPEC 2010. - Barcelona : Curran Associates, Inc.. - 9781617386671 ; , s. 5368-5371
  • Konferensbidrag (refereegranskat)abstract
    • The Kristineberg mining area is located in the western part of the Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, two new reflection seismic profiles were acquired. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Reflection modeling was carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.
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27.
  • Doughty, Christine, et al. (författare)
  • Flowing fluid electrical conductivity logging of a deep borehole during and following drilling : estimation of transmissivity, water salinity and hydraulic head of conductive zones
  • 2017
  • Ingår i: Hydrogeology Journal. - : SPRINGER. - 1431-2174 .- 1435-0157. ; 25:2, s. 501-517
  • Tidskriftsartikel (refereegranskat)abstract
    • Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at re, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of information for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped conditions. The challenges accompanying 1-day FFEC logging are summarized, along with lessons learned in addressing them.
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28.
  • Elger, Judith, et al. (författare)
  • Core‐log‐seismic integration in metamorphic rocks and its implication for the regional geology : A case study for the ICDP drilling project COSC‐1, Sweden
  • 2021
  • Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 22:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Continental collision causes deformation in the crust along shear zones. However, the physical and chemical conditions at which these zones operate and the deformation processes that enable up to hundreds of km of tectonic transport are still unclear because of the depth at which they occur and the challenges in imaging them. Ancient exhumed collision zones allow us to investigate these processes much better, for example at the COSC‐1 borehole in the central Scandinavian Caledonides. This study combines data from the COSC‐1 borehole with different seismic measurements to provide constraints on the spatial lithological and textural configuration of the Seve Nappe Complex. This is one of the few studies that shows that core‐log‐seismic integration in metamorphic rocks allows to identify the spatial distribution of major lithological units. Especially gamma ray logs in combination with density data are powerful tools to distinguish between mafic and felsic lithologies in log‐core correlation. Our results indicate that reflections along the borehole are primarily caused by compositional rather than textural changes. Reflections in the Seve Nappe Complex are not as distinct as in greater depths but continuous and several of them can be linked to magmatic intrusions, which have been metamorphically overprinted. Their setting indicates that the Seve Nappe Complex consists of the remnants of a volcanic continental margin. Our results suggest that ductile‐deformed middle crustal reflectivity is primarily a function of pre‐orogenic lithological variations which has to be considered when deciphering mountain building processes.Plain Language SummaryAreas where continents collide experience different kind of deformation. However, these processes and the conditions at which they take place are difficult to study because of the great depth at which they occur. Former collision zones that are closer to the surface these days allow the investigation of these processes much better, for example at the COSC‐1 borehole in the central Scandinavian Caledonides. The challenge remains to image the remnant of these processes in high detail but at the same time over a large area. This study combines data from the COSC‐1 borehole with different geophysical measurements to better understand the lithology and structure of the Seve Nappe Complex. We show that the combination of these data allows us to distinguish between rocks from mafic and sedimentary origin. Our results indicate that the geophysical data along the borehole image the change of the composition of the rocks which probably originates from magmatic intrusions and have been overprinted by geological processes, rather than from fracture zones.
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29.
  • Foerster, A., et al. (författare)
  • The Geology of the CO2SINK Site : From Regional Scale to Laboratory Scale
  • 2009
  • Ingår i: GREENHOUSE GAS CONTROL TECHNOLOGIES 9. - : Elsevier BV. ; , s. 2911-2918
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Here we report on the framework of geological site exploration, which encompassed investigations at different scales prior to and after the drilling of the three CO2SINK boreholes. Past and new exploration data are integrated to delineate at regional scale (1) the geological structure of CO2 storage formation and its overburden, including fault systems as potential fluid pathways and (2) the shallow hydrogeology and the groundwater flow directions for an assessment of effects in case of CO2 leakage and migration. The poro-perm facies and mineralogical composition of the CO2 reservoir rock and the top seal formation were studied by routine and special core analyses, including the measurement of porosity, gas and brine permeability, and by XRD analysis. (C) 2009 Elsevier Ltd. All rights reserved.
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30.
  • Frenje, L, et al. (författare)
  • Scattering attenuation: 2-D and 3-D finite difference simulations vs. theory
  • 2000
  • Ingår i: Journal of Applied Geophysics. - : Elsevier. - 0926-9851 .- 1879-1859. ; 44:1, s. 33-46
  • Tidskriftsartikel (refereegranskat)abstract
    • Scattering of seismic waves is studied by producing synthetic vertical seismic profiling (VSP) seismograms with 2-D and 3-D finite difference modelling in random media. The random models used are Gaussian and band-limited self-similar, or fractal random media. The modelling is performed acoustically, but we believe that, considering the geometry of this study, the results obtained will hold for the elastic case as well.Properties of the random media are discussed, in particular the difference between discrete and continuous media, and the importance of this difference. We show that when using the band-limited Von Karman correlation function when generating the random medium, the size of the model should be greater than 2πa, where a is the correlation distance, and the grid spacing should be less then a. If not, the medium will not have the proper characteristics.Analytical expressions for scattering attenuation, derived from single scattering theory, can be used to estimate scattering Q from borehole velocity logs, if it is known what minimum scattering angle, θmin, to use. θmin, the minimum angle energy, must be scattered to be regarded as not contributing to the propagating wave. We estimate θmin by comparing Q values estimated from our synthetic VSP seismograms with the analytical expressions. The comparison also shows when the assumption of single scattering is valid. Previous studies in 2-D give a θmin of ∼30°. In this paper, we make a comparison for both the 2-D and 3-D cases, and show that the Q estimate is highly sensitive to how the analysis is done. We show that single scattering theory agrees well with finite difference simulations for self-similar media with low Hurst numbers, but with a somewhat lower θmin of 10–20°. This holds for a range of correlation lengths, a, including the case of infinite, or absence of, a. For Gaussian and exponential media, simulations and theory agree as well with θmin of 10–20°, but only for ka<5, where k is the wave number of the source. For ka>5, simulations and theory diverge, and single scattering theory cannot explain the amplitude attenuation observed in the scattering simulations for these types of media, indicating that it may be difficult to estimate the fractal properties of a medium from seismic data alone.With the difficulties of characterizing the scattering medium, and to estimate the scattering attenuation in the simple case of synthetic data with pure scattering, we conclude that it may be difficult to separate scattering and intrinsic attenuation from real data.
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31.
  • Friberg, M, et al. (författare)
  • Europrobe seismic reflection profiling across the eastern Middle Urals and West Siberian Basin
  • 2001
  • Ingår i: Terra Nova. - : Blackwell Publishing. - 0954-4879 .- 1365-3121. ; 12:6, s. 252-257
  • Tidskriftsartikel (refereegranskat)abstract
    • New deep seismic reflection data provide images of the crust and uppermost mantle underlying the eastern Middle Urals and adjacent West Siberian Basin. Distinct truncations of reflections delineate the late-orogenic strike-slip Sisert Fault extending vertically to ∼28 km depth, and two gently E-dipping reflection zones, traceable to 15–18 km depth, probably represent normal faults associated with the opening of the West Siberian Basin. A possible remnant Palaeozoic subduction zone in the lower crust under the West Siberian Basin is visible as a gently SW-dipping zone of pronounced reflectivity truncated by the Moho. Continuity of shallow to intermediate-depth reflections suggest that Palaeozoic accreted island-arc terranes and overlying molasse sequences exposed in the hinterland of the Urals form the basement for Triassic and younger deposits in the West Siberian Basin. A highly reflective lower crust overlies a transparent mantle at about 43 km depth along the entire 100 km long seismic reflection section, suggesting that the lower crust and Moho below the eastern Middle Urals and West Siberian Basin have the same origin.
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32.
  • García Juanatey, María de los Angeles, et al. (författare)
  • 2D and 3D MT in the central Skellefte Ore District, northern Sweden
  • 2019
  • Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 764, s. 124-138
  • Tidskriftsartikel (refereegranskat)abstract
    • New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.
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33.
  • Ghosal, D., et al. (författare)
  • Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea
  • 2018
  • Ingår i: Journal of Geophysics and Engineering. - : Oxford University Press (OUP). - 1742-2132 .- 1742-2140. ; 15:5, s. 1799-1810
  • Tidskriftsartikel (refereegranskat)abstract
    • Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1-100 Hz) dispersion maxima appear at similar to 5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity (V-p) dispersion is estimated similar to 5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on the angle dependent seismic migrated sections is carried out by inverting spectrally decomposed isofrequency sections using a least squares algorithm. The inverted results show that the top of the reservoir is more clearly demarcated at low frequency (similar to 7Hz) than at higher frequencies.
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34.
  • Giese, R., et al. (författare)
  • Monitoring at the CO2SINK Site : A Concept Integrating Geophysics, Geochemistry and Microbiology
  • 2009
  • Ingår i: Proceedings of the 9th International Conference on Greenhouse Gas Control Technologies (GHGT-9), 16–20 November 2008, Washington DC, USAGREENHOUSE GAS CONTROL TECHNOLOGIES 9. - : Elsevier BV. ; , s. 2251-2259
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • At the CO2SINK site (Ketzin, near Berlin, Germany), the pilot study for onshore CO2 storage in saline aquifers includes monitoring of the storage reservoir and the structures above using physical, chemical, and microbial observations. Seismic and geoelectric measurements have delivered the structural framework and monitor CO2 propagation between two observation wells. Borehole temperature data serves to derive information about in-situ formation temperatures and to detect processes related to the injection and movement of CO2 in the subsurface. Pressure measurements aim at ensuring safe operations and characterization of the reservoir. For a complete characterization of the CO2 storage process, the physical observations have to be complemented by chemical and biological probing, as fluid/fluid and fluid/rock interactions and microbial processes play an important role possibly affecting the stability of the reservoir and caprock. A newly developed Gas Membrane Sensor detected the CO2 breakthrough on the first monitoring well. Microbial investigations contributed in optimizing the injection borehole after recognizing organisms reducing its injectivity.
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35.
  •  
36.
  • Hedin, Peter, 1981-, et al. (författare)
  • 3D interpretation by integrating seismic and potential field data in the vicinity of the proposed COSC-1 drill site, central Swedish Caledonides
  • 2014
  • Ingår i: Geological Society Special Report. - : Geological Society. - 0309-670X. ; 390, s. 301-319
  • Tidskriftsartikel (refereegranskat)abstract
    • The scientific drilling project COSC (Collisional Orogeny in the Scandinavian Caledonides), designed to study key questions concerning orogenic processes, aims to drill two fully cored boreholes to depths of c. 2.5 km each at carefully selected locations in west-central Sweden. The first of these, COSC-1, is scheduled for start late spring 2014 and will target the Seve Nappe Complex, characterized by inverted metamorphism and with parts that have evidently been subjected to hot ductile extrusion. In this study available seismic sections have been combined with surface geology to produce a 3D interpretation of the tectonic structures in the vicinity of the COSC-1 borehole. Constrained 3D inverse gravity modelling over the same area supports the interpretation, and the high-density Seve Nappe Complex stands out clearly in the model. Interpretation and models show that the maximum depth extent of the Seve Nappe Complex is less than 2.5 km, consistent with reflection seismic data. The gravity modelling also requires underlying units to comprise low-density material, consistent with the Lower Allochthon, but the modelling is unable to discern the décollement separating the allochthons from the crystalline Precambrian basement.
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37.
  • Holliger, K, et al. (författare)
  • Stochastic analysis of sonic logs from the upper crystalline crust: Methodology
  • 1996
  • Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 264:1-4, s. 341-356
  • Tidskriftsartikel (refereegranskat)abstract
    • To relate local fluctuations observed in sonic logs to small-scale velocity fabric along boreholes, both filtering effects and noise introduced by the logging procedure must be taken into account. Sonic log velocities are represented as a time series consisting of a large-scale deterministic and a small-scale stochastic component. The deterministic trend, approximated by a low-order polynomial best-fit, contains information on the average velocity structure, whereas the small-scale stochastic variations consist of noise plus in situ velocity variations convolved with the logging system response. The velocity fluctuations of the sonic data considered here are zero-mean and have quasi-Gaussian probability density functions. Therefore, they are well characterised by their second statistical moment, i.e. their autocovariance function. Tests on synthetic data indicate that the autocovariance function corresponding to this data model may be used to extract information on the second-order statistics of the in situ velocity variations along the borehole and to constrain the level of white noise in sonic logs. Ignoring the presence of filtering effects and noise in sonic logs may result in seriously flawed estimates of the second-order statistics of the actual velocity structure. Assuming a von Kármán autocovariance function for the in situ velocity variations, this model provides a good match to the autocovariance functions of sonic log data from the Siljan Ring (Sweden) and Sudbury areas (Canada). Although differing significantly in their noise content, these two data sets yield similar results for the small-scale velocity structure, which is modelled as a bandlimited self-affine time series. For the Siljan Ring borehole we found a close relation between small-scale variations of the borehole diameter as determined from caliper logs and the level of uncorrelated noise present in the sonic log data.
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38.
  • Huang, Fei, et al. (författare)
  • Feasibility of utilizing wavelet phase to map the CO2 plume at the Ketzin pilot site, Germany
  • 2017
  • Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 65:2, s. 523-543
  • Tidskriftsartikel (refereegranskat)abstract
    • Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time‐lapse three‐dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero‐offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal‐to‐noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site.
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39.
  • Huang, Fei, 1987-, et al. (författare)
  • The first post-injection seismic monitor survey at the Ketzin pilot CO2 storage site : results from time-lapse analysis
  • 2018
  • Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 66:1, s. 62-84
  • Tidskriftsartikel (refereegranskat)abstract
    • The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 diffusion, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 being dissolved and diffused was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.
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40.
  • Ivandic, Monika, et al. (författare)
  • Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany
  • 2018
  • Ingår i: Geophysical Prospecting. - : WILEY. - 0016-8025 .- 1365-2478. ; 66:8, s. 1568-1585
  • Tidskriftsartikel (refereegranskat)abstract
    • The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630-650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post-injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time-lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post-injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%-60% are similar to those obtained earlier from pulsed neutron-gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.
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41.
  • Ivandic, Monika, et al. (författare)
  • Subsurface seismic imaging with a hammer drilling source at an exploration drilling test center in Örebro, Sweden
  • 2022
  • Ingår i: Advances in Geosciences. - : European Geosciences Union (EGU). - 1680-7340 .- 1680-7359. ; 56, s. 163-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Seismic imaging while drilling (SWD) technology offers possibilities of imaging ahead of the drill-bit, which could be useful for determining when to go from hammer drilling to core drilling. Also, seismic images of the surrounding rock can improve geological models which could be then used to guide drilling programs.An SWD field test was carried out in August 2020 at an exploration drilling test site in Örebro, Sweden, with the aim to determine if the signals from hammer drilling can be used for seismic imaging around the drill-bit in a hard-rock environment where the strong drill-rig noise interference is one of the main challenges. The test site had previously been investigated with various geophysical methods, geological mapping and diamond core drilling, and it therefore represented an ideal location to perform this feasibility study.After data pre-processing and cross-correlation with the trace from the geophone closest to the rig, the shot-gathers were vertically stacked over the length of a drill pipe to achieve further signal improvement. A comparison with the active seismic data shows reasonable agreement, in spite of the fact that the noise level is significant even after careful processing. However, the lack of clear reflections in the active seismic data, indicating no detectable changes in the bedrock lithology in the near surface, hinders the full assessment of the seismic signal generated with hammer drilling at this site.
  •  
42.
  • Ivandic, Monika, et al. (författare)
  • Subsurface seismic imaging with a hammer drilling source at an exploration drilling test center in Örebro, Sweden
  • 2021
  • Ingår i: EGU General Assembly 2021. - : Copernicus GmbH.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • &lt;p&gt;Seismic imaging while drilling technology offers possibilities of imaging ahead of the drill-bit, which could be useful for determining when to go from hammer drilling to core drilling. Moreover, seismic images of the surrounding rock can improve geological models which could be then used to guide drilling programs.&lt;/p&gt;&lt;p&gt;A seismic imaging while drilling field test was carried out in August 2020 at the I-EDDA Test Center next to the Epiroc factory in &amp;#214;rebro, which is an outcome of the EIT Raw Materials funded project &amp;#8220;Innovative Exploration Drilling and Data Acquisition (I-EDDA)&amp;#8221;. The purpose of the test presented here was to determine if the signals from hammer drilling can be used for seismic imaging around the drill-bit. The I-EDDA test site has been extensively investigated with geophysical investigations, geological mapping and diamond core drilling, and it therefore represents an ideal location to perform the proposed feasibility study.&lt;/p&gt;&lt;p&gt;The data were recorded along a west-east oriented line consisting of 45 active 1C vertical geophones with a spacing of about 2 m and the rig located approximately in the middle of the profile. A reference signal, which is usually recorded by the pilot sensor fixed to the top of the drill string to be used to convert geophone recordings to impulsive-like seismic data, was not available. The passive recordings on the surface were thus correlated with the trace from the geophone closest to the rig.&lt;/p&gt;&lt;p&gt;After data pre-processing and cross-correlation, the shot-gathers were vertically stacked over the length of a drill pipe to achieve further signal improvement. A comparison with the results of a modelling study shows certain agreement. However, it has to be noted that the velocity model obtained from earlier studies and used to generate the synthetic data set here is rather a simple one and the noise level in the real data set is still significant, in spite of careful processing. Besides the strong contamination by the rig noise, more typical for data with smaller offsets, the mono-frequency waveform footprints present in the cross-correlograms, which have been observed in similar experiments where a trace from the nearest geophone was used to approximate the bit signal, could also play a role. The recent results from the active seismic studies conducted at the site have not detected any clear reflections within the bedrock, which further hinders the quality assessment of the seismic signal.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;This work was partly supported by VINNOVA with the project 2019-04832 titled Integrated Smart Test environment for the mining industry - SMIG. We gratefully acknowledge this financial support.&lt;/p&gt;
  •  
43.
  • Ivanova, Alexandra, et al. (författare)
  • Seismic modeling of the AVO/AVA response to CO2 injection at the Ketzin site, Germany
  • 2013
  • Konferensbidrag (refereegranskat)abstract
    • Over 64 kilotons of CO2 have been injected (May, 2013) into a heterogeneous sandstone reservoir (saline aquifer) at 630-650 m depth. 4D seismics have been applied to monitor CO2 at the Ketzin site. However, the obtained time-lapse seismic signals have been so far interpreted as being caused by fluid saturation changes only. Modeling of the AVO/AVA response allows us to study two kinds of effects: CO2-saturation- and pore-pressure-related effects. Our results indicate that it is rather infeasible to discriminate between both these effects at the Ketzin site dealing with the real seismic data with limited signal/noise ratios.
  •  
44.
  • Juhlin, Christopher, 1956-, et al. (författare)
  • Reflection seismic imaging of the end-glacial Pärvie Fault system, northern Sweden
  • 2010
  • Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 70:4, s. 307-316
  • Tidskriftsartikel (refereegranskat)abstract
    • Reflection seismic data were acquired along a c. 23 km long profile over the Pärvie Fault system with a nominal receiver and source spacing of 20 m. An hydraulic breaking hammer was used as a source, generating signals with a penetration depth of about 5–6 km. Steeply dipping reflections from the end-glacial faults are observed, as well as sub-horizontal reflections. The location and orientation of the reflections from the faults agree well with surface geological observations of fault geometries. Reflections from a potential fourth end-glacial fault is observed further to the east along the profile. The more sub-horizontal reflections may originate from gabbroic bodies within the granitic basement or from deeper lying greenstones. Our results indicate that the end-glacial faults dip at moderate to steep dips down to at least 2–3 km depth, and possibly continue at this dip to depths of 6 km. This result has significant implications for determining the state of stress required to activate the faults in the past and in the future.
  •  
45.
  • Juhlin, Christopher, 1956-, et al. (författare)
  • Reflection seismic studies over the end-glacial Burträsk fault, Skellefteå, Sweden
  • 2010
  • Ingår i: Solid Earth Discussions. - : Copernicus GmbH. - 1869-9537. ; 2, s. 307-329
  • Tidskriftsartikel (refereegranskat)abstract
    • Reflection seismic data were acquired along a ca. 22 km long profile over the end-glacial Burträsk Fault with a nominal receiver and source spacing of 20 m. A steeply dipping reflection can be correlated to the Burträsk Fault, indicating that the fault dips at about 55° to the southeast near the surface. The reflection from the fault is rather poorly imaged, probably due to a jump in the fault and the crookedness of the seismic profile in the vicinity of the fault. A more pronounced steeply dipping reflection is observed about 4 km southeast of the Burträsk Fault. Based on its correlation with a topographic low at the surface this reflection is interpreted to originate from a fracture zone. There are no signs of large displacements along this fault as the glacial ice receded, but it may be active today. Other reflections on the processed seismic section may originate from changes in lithological variations in the supra-crustal rocks or from intrusions of more mafic rock. Constraints on the fault geometry provided by the reflection seismic data will help determine what stresses were required to activate the fault when the major rupture along it occurred.
  •  
46.
  • Juhlin, Christopher, 1956-, et al. (författare)
  • Seismic and Electrical Resistivity Tomography 3D Monitoring at the Ketzin Pilot Storage Site in Germany
  • 2019
  • Ingår i: Geophysics and Geosequestration. - : Cambridge University Press. - 9781316480724
  • Bokkapitel (refereegranskat)abstract
    • Geosequestration involves the deep geological storage of carbon dioxide from major industrial sources, providing a potential solution for reducing the rate of increase of atmospheric concentrations of carbon dioxide and mitigating climate change. This volume provides an overview of the major geophysical techniques and analysis methods for monitoring the movement and predictability of carbon dioxide plumes underground. Comprising chapters from eminent researchers, the book is illustrated with practical examples and case studies of active projects and government initiatives, and discusses their successes and remaining challenges. A key case study from Norway demonstrates how governments and other stake-holders could estimate storage capacity and design storage projects that meet the requirements of regulatory authorities. Presenting reasons for embracing geosequestration, technical best practice for carbon management, and outlooks for the future, this volume provides a key reference for academic researchers, industry practitioners and graduate students looking to gain insight into subsurface carbon management.
  •  
47.
  •  
48.
  • Karabetoglu, Sevan, et al. (författare)
  • Effect of layered geological structures on borehole heat transfer
  • 2021
  • Ingår i: Geothermics. - : Elsevier BV. - 0375-6505 .- 1879-3576. ; 91
  • Tidskriftsartikel (refereegranskat)abstract
    • Borehole heat exchangers, especially deep ones, are usually drilled through different geological layers havingvarying properties. Homogeneous and layered models can be used for borehole performance predictions. Thehomogeneous model considers all layers as a single layer having effective properties while the layered modelconsiders all layers separately and gives better accuracy, although it is more complicated and time consuming tocalculate. In this study, by considering real geological structures, thermal performance predictions of a deepborehole are made using both homogeneous and layered models and the results are compared to examine howpredictions differ from each other depending on the statistical characteristics of geological structures. Ananalytical expression is derived for the relation between statistical characteristics and deviations from the predictionsof the homogeneous model. The magnitudes of deviations are very small and essentially depend on thevariance of the difference for the thermal properties of the layers and a time decaying function. The results helpto understand how horizontally layered geological structures influence borehole performance and when we needa layered model.
  •  
49.
  • Kruachanta, Mingkhwan, et al. (författare)
  • Estimation of Anisotropy Parameters, delta and epsilon : An Application to Borehole and Seismic Data from Ketzin, Germany
  • 2016
  • Ingår i: CHIANG MAI JOURNAL OF SCIENCE. - : CHIANG MAI UNIV. - 0125-2526. ; 43:6, s. 1299-1305
  • Tidskriftsartikel (refereegranskat)abstract
    • Weak anisotropy was indicated in a previous investigation of the 3D baseline seismic data acquired through the EU funded CO2 SINK project at the Ketzin pilot site for CO2 storage, Germany. Fourth order velocity analysis yielded the Alkhalifah anellipticity factor, or eta (eta), ranging from -0.2399 to 0.1341 for the whole study area. Although application of the simple eta term in the moveout correction allowed reflections to be flattened at far offsets, resulting in an improved seismic stacked section, the Thomsen parameters, delta (delta) and epsilon (epsilon) are of greater interest from a rock physics perspective. Borehole data from Ketzin were introduced to estimate delta and epsilon using known relationships between sonic wave velocity, NMO velocity, eta,delta and epsilon. In this paper, delta and epsilon estimations were performed using data from three wells; the CO2 injection well and two observation wells. Preliminary estimates of the Thomsen parameters give delta ranging from -0.2658 to -0.1270, while epsilon ranges from -0.2611 to -0.1141. These delta and epsilon values also indicate the presence of weak vertical transverse isotropy at the site, which is consistent with the previous study.
  •  
50.
  • Kühn, Michael, et al. (författare)
  • Energy, Resources & the Environment-Some Future Challenges
  • 2013
  • Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 40, s. 1-5
  • Tidskriftsartikel (refereegranskat)abstract
    • The European Geosciences Union brings together geoscientists from all over Europe and the rest of the world, covering all disciplines of the earth sciences. This geoscientific inter- and multidisciplinarity is needed to tackle the challenges of the future. A major challenge for humankind is to provide adequate and reliable supplies of affordable energy and other resources. These should be obtained in environmentally sustainable ways, which is essential for economic prosperity, environmental quality and political stability around the world. This issue gives a general overview of contributions during the General Assembly 2013 in the division for Energy, Resources & the Environment.
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