Pore-scale tomography and imaging: applications, techniques and recommended practice

[No abstract available

Zero-Offset VSP Monitoring of CO2Storage: Impedance Inversion and Wedge Modelling at the Ketzin Pilot Site

At the CO2 storage pilot site near the town of Ketzin (35 km west of Berlin, Germany) the sandstone reservoir at 630 m–650 m depth is thin and heterogeneous. The time-lapse analysis of zero-offset VSP measurements shows that CO2-induced amplitude changes can be observed on near-well corridor stacks. Further, we investigate whether CO2-induced amplitude changes in the monitoring data can be used to derive geometrical and petrophysical parameters governing the migration of CO2 within a brine saturated sandstone aquifer. 2D seismic-elastic modelling is done to test the processing workflow and to perform a wedge modelling study for estimation of the vertical expansion of the CO2 plume. When using the NRMS error as a measure for the similarity between the modelled and recorded repeat traces, the best match is achieved for a plume thickness of 6-7 m within the reservoir sandstone of 8 m thickness. With band limited impedance inversion a velocity reduction at the top of the reservoir of 30%, influenced by casing reverberations as well as CO2 injection, is found. The relation of seismic amplitude to CO2 saturated layer thickness and CO2-induced changes in P-wave velocities are important parameters for the quantification of the injected CO2 volume

Near‐surface fault detection using high‐resolution shear wave reflection seismics at the CO2CRC Otway Project site, Australia

High‐resolution, near‐surface, shear wave reflection seismic measurements were carried out in November 2013 at the CO2CRC Otway Project site, Victoria, Australia, with the aim to determine whether and, if so, where deeper faults reach the near subsurface. From a previous P wave 3‐D reflection seismic data set that was concentrated on a reservoir at 2 km depth, we can only interpret faults up to 400 m below sea level. For the future monitoring in the overburden of the CO2 reservoir it is important to know whether and how the faults continue in the subsurface. We prove that two regional fault zones do in fact reach the surface instead of dying out at depth. Individual first‐break signatures in the shot gathers along the profiles support this interpretation. However, this finding does not imply perforce communication between the reservoir and the surface in the framework of CO2 injection. The shear wave seismic sections are complementary to existing P wave volumes. They image with high resolution (better than 3 m vertically) different tectonic structures. Similar structures also outcrop on the southern coast of the Otway Basin. Both the seismic and the outcrops evidence the complex youngest structural history of the area.BMBF, 03G0797A, Verbundprojekt UR VI: PROTECT; Vorhersage von Deformation für eine abgesicherte Speicherung von Kohlenstoff (PRediction Of deformation To Ensure Carbon Traps); Vorhaben: Subseismische Deformationsvorhersage potentieller Wegsamkeiten und ihre seismische Validierung - Sonderprogramm GEOTECHNOLOGIE

Fault‐controlled lithospheric detachment of the volcanic southern South Atlantic rift

© 2016. American Geophysical Union.We present structural models of two exemplary conjugate seismic lines of the southernmost South Atlantic margins to examine their initial evolution, especially the seaward‐dipping reflectors (SDRs). Modeling illustrates the different structure and inclination angles of the SDRs, which therefore require different subsidence histories. Since typical symmetrical subsidence models are not applicable, we suggest a model with a westward‐dipping detachment fault that offsets the SDRs on the South American margin and we speculate on passively subsided SDRs on the South African margin. We propose a simple‐shear rifting mechanism to explain the initial break‐up of the South Atlantic.DFG, 61089689, SPP 1375: SAMPLE: South Atlantic Margin Processes and Links with onshore Evolutio

Coherent diffraction imaging for enhanced fault and fracture network characterization

Faults and fractures represent unique features of the solid Earth and are especially pervasive in the shallow crust. Aside from directly relating to crustal dynamics and the systematic assessment of associated risk, fault and fracture networks enable the efficient migration of fluids and therefore have a direct impact on concrete topics relevant to society, including climate-change-mitigating measures like CO2 sequestration or geothermal exploration and production. Due to their small-scale complexity, fault zones and fracture networks are typically poorly resolved, and their presence can often only be inferred indirectly in seismic and ground-penetrating radar (GPR) subsurface reconstructions. We suggest a largely data-driven framework for the direct imaging of these features by making use of the faint and still often underexplored diffracted portion of the wave field. Finding inspiration in the fields of optics and visual perception, we introduce two different conceptual pathways for coherent diffraction imaging and discuss respective advantages and disadvantages in different contexts of application. At the heart of both of these strategies lies the assessment of data coherence, for which a range of quantitative measures is introduced. To illustrate the versatility and effectiveness of the approach for high-resolution geophysical imaging, several seismic and GPR field data examples are presented, in which the diffracted wave field sheds new light on crustal features like fluvial channels, erosional surfaces, and intricate fault and fracture networks on land and in the marine environment

Structural analysis of S-wave seismics around an urban sinkhole: evidence of enhanced dissolution in a strike-slip fault zone

In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the dissolution, we carried out several shear-wave reflection-seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks ( < 100 m in size), around which steep-dipping normal faults, reverse faults and a dense fracture network serve as fluid pathways for the artesian-confined groundwater. The faults also acted as barriers for horizontal groundwater flow perpendicular to the fault planes. Instead groundwater flows along the faults which serve as conduits and forms cavities in the Permian deposits below ca. 60 m depth. Mass movements and the resulting cavities lead to the formation of sinkholes and dissolution-induced depressions. Since the processes are still ongoing, the occurrence of a new sinkhole cannot be ruled out. This case study demonstrates how S-wave seismics can characterize a sinkhole and, together with geological information, can be used to study the processes that result in sinkhole formation, such as a near-surface fault zone located in soluble rocks. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence

Structural investigation and strain analysis of a polyphase flower structure in the Lower Saxony Basin, Germany

The Lower Saxony Basin (LSB) is a part of the post-Variscan Central European Basin System. We used a 3-D reflection seismic dataset in the northern LSB, provided by RWE-DEA AG, Hamburg (c.f. Lohr et al. submitted) for our investigation, which is concerned with the detailed structural and kinematic analysis of a flower structure within Mesozoic strata. This data is used in turn to determine input parameters for further 3-D geometrical retro-deformation. The retro-deformation verifies our assumptions about the structure and tectonic processes, and gives further information about sub-seismic strain distribution with respect to the branch faults of the flower structure.conferenc

Combined seismic and borehole investigation of the deep granite weathering structure—Santa Gracia Reserve case in Chile

Imaging the critical zone at depth, where intact bedrock transforms into regolith, is critical in understanding the interaction between geological and biological processes. We acquired a 500 m‐long near‐surface seismic profile to investigate the weathering structure in the Santa Gracia National Reserve, Chile, which is located in a granitic environment in an arid climate. Data processing comprised the combination of two seismic approaches: (1) body wave tomography and (2) multichannel analysis of surface wave (MASW) with Bayesian inversion. This allowed us to derive P‐wave and S‐wave velocity models down to 90 and 70 m depth, respectively. By calibrating the seismic results with those from an 87 m‐deep borehole that is crossed by the profile. We identified the boundaries of saprolite, weathered bedrock, and bedrock. These divisions are indicated in the seismic velocity variations and refer to weathering effects at depth. The thereby determined weathering front in the borehole location can be traced down to 30 m depth. The modelled lateral extent of the weathering front, however, cannot be described by an established weathering front model. The discrepancies suggest a more complex interaction between different aspects such as precipitation and topography in controlling the weathering front depth

Wavelet transform‐based seismic facies classification and modelling: application to a geothermal target horizon in the NE German Basin

At the geothermal test site near Groß Schönebeck (NE German Basin), a new 3D seismic reflection survey was conducted to study geothermal target layers at around 4 km depth and 150°C. We present a workflow for seismic facies classification and modelling which is applied to a prospective sandstone horizon within the Rotliegend formation. Signal attributes are calculated along the horizon using the continuous Morlet wavelet transform. We use a short mother wavelet to allow for the temporal resolution of the relatively short reflection signals to be analysed. Time‐frequency domain data patterns form the input of a neural network clustering using self‐organizing maps. Neural model patterns are adopted during iterative learning to simulate the information inherent in the input data. After training we determine a gradient function across the self‐organizing maps and apply an image processing technique called watershed segmentation. The result is a pattern clustering based on similarities in wavelet transform characteristics. Three different types of wavelet transform patterns were found for the sandstone horizon. We apply seismic waveform modelling to improve the understanding of the classification results. The modelling tests indicate that thickness variations have a much stronger influence on the wavelet transform response of the sandstone horizon compared with reasonable variations of seismic attenuation. In our interpretation, the assumed thickness variations could be a result of variable paleo‐topography during deposition of predominantly fluvial sediments. A distinct seismic facies distribution is interpreted as a system of thicker paleo‐channels deposited within a deepened landscape. The results provide constraints for the ongoing development of the geothermal test site.BMWi, 0324065 TIB, Rissdominierte Erschließung eines tiefen geothermischen Reservoirs zur Stromerzeugung im Norddeutschen Becken - seismische Erkundung, Konzeption und bohrtechnische Planung am Standort Groß Schönebec