scholarly journals Sparse 3D reflection seismic survey for deep-targeting iron-oxide deposits and their host rocks, Ludvika Mines-Sweden

2020 ◽  
Author(s):  
Alireza Malehmir ◽  
Magdalena Markovic ◽  
Paul Marsden ◽  
Alba Gil ◽  
Stefan Buske ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Collaborative Work ◽  
Energy Transition ◽  
Seismic Survey ◽  
Quality Data ◽  
Normal Faults ◽  
3D Seismic ◽  
Near Surface ◽  
Reflection Seismic ◽  
Static Corrections

Abstract. Many metallic mineral deposits have sufficient contrasts, particularly density, to be detectable using seismic methods. These deposits are sometimes significant for our society, economic growth and can help to accelerate the energy transition towards decarbonization. However, their exploration at depth requires high-resolution and sensitive methods. Following a series of 2D seismic trials, a sparse, narrow source-receiver azimuth, 3D seismic survey was conducted in the Blötberget mine, in central Sweden, covering an area of approximately 6 km2 for deep targeting iron-oxide deposits and their host rock structures. The survey benefited from a collaborative work by putting together 1266 seismic recorders and a 32t vibrator generating 1056 shot points in a fixed geometry setup. A linear sweep ranging from 10–160 Hz and 20 s long was generated three times per shot point. Shots were fired at every 10 m where possible and receivers placed at every 10–20 m. Notable quality data were acquired although the area is dominated by swampy places as well as by built-up roads and historical tailings. The data processing had to overcome these challenges in particular for the static corrections and strong surface-waves. A tailored for hardrock-setting-processing workflow was developed for handling such a dataset, where the use of mixed 2D and 3D refraction static corrections were relevant. The resulting seismic volume is rich in terms of reflectivity with clear southeast dipping reflections originated from iron-oxide deposits extending vertically and laterally at least 300 m beyond what was known from boreholes. We estimate potential additional resources from the 3D reflection seismic experiment on the order of 10 Mt worth drilling for detailed assessments. The mineralization is crosscut by at least two major sets of northwest dipping reflections interpreted to be dominantly normal faults and responsible for much of the lowland in the Blötberget area. Moreover, these post-mineralization faults likely control the current 3D geometry of the deposits. Curved and submerged reflections interpreted from folds or later intrusions are also observed showing the geological complexity of the study area. The seismic survey also delineates the near-surface expression of a historical tailing as a by-product of refraction static corrections demonstrating why 3D seismic data. The sparse 3D survey illustrates that performing cost-effective reflection surveys for mineral exploration is achievable if they are conducted and planned carefully, systematically and based on earlier experiences.

scholarly journals Sparse 3D reflection seismic survey for deep-targeting iron oxide deposits and their host rocks, Ludvika Mines, Sweden

Solid Earth ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 483-502
Author(s):  
Alireza Malehmir ◽  
Magdalena Markovic ◽  
Paul Marsden ◽  
Alba Gil ◽  
Stefan Buske ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Collaborative Work ◽  
Mine Planning ◽  
Seismic Survey ◽  
Quality Data ◽  
Normal Faults ◽  
3D Seismic ◽  
Near Surface ◽  
Reflection Seismic ◽  
Static Corrections

Abstract. Many metallic mineral deposits have sufficient physical property contrasts, particularly density, to be detectable using seismic methods. These deposits are sometimes significant for our society and economic growth and can help to accelerate the energy transition towards decarbonization. However, their exploration at depth requires high-resolution and sensitive methods. Following a series of 2D seismic trials, a sparse, narrow source–receiver azimuth, 3D seismic survey was conducted in the Blötberget mine, in central Sweden, covering an area of approximately 6 km2 for deep-targeting iron oxide deposits and their host rock structures. The survey benefited from a collaborative work by putting together 1266 seismic recorders and a 32 t vibrator, generating 1056 shot points in a fixed geometry setup. Shots were fired at every 10 m where possible, and receivers were placed at every 10–20 m. Notable quality data were acquired despite the area being dominated by swampy places as well as by built-up roads and historical tailings. The data processing had to overcome these challenges for the static corrections and strong surface waves in particular. A tailored for hardrock setting and processing workflow was developed for handling such a dataset, where the use of mixed 2D and 3D refraction static corrections was relevant. The resulting seismic volume is rich in terms of reflectivity, with clear southeast-dipping reflections originating from the iron oxide deposits extending vertically and laterally at least 300 m beyond what was known from available boreholes. As a result, we estimate potential additional resources from the 3D reflection seismic experiment on the order of 10 Mt to be worth drilling for detailed assessments. The mineralization is crosscut by at least two major sets of northwest-dipping reflections interpreted to dominantly be normal faults and to be responsible for much of the lowland in the Blötberget area. Moreover, these post-mineralization faults likely control the current 3D geometry of the deposits. Curved and submerged reflections interpreted from folds or later intrusions are also observed, showing the geological complexity of the study area. The seismic survey also delineates the near-surface expression of a historical tailing as a by-product of refraction static corrections, demonstrating why 3D seismic data are so valuable for both mineral exploration and mine planning applications.

Sand curve facelift: Empirical to polynomial model and the effect on the tomogram

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. U37-U48 ◽  
Author(s):  
Ralph Bridle
Keyword(s):  
Saudi Arabia ◽  
Seismic Survey ◽  
Theoretical Curve ◽  
3D Seismic ◽  
Near Surface ◽  
Direct Measurements ◽  
Curve Model ◽  
Variable Success ◽  
Static Corrections ◽  
The Relationship

An empirical thickness versus time relationship sand curve has been established in the Rub’ al-Khali desert and verified by a theoretical curve from the direct measurements of sand. The empirical sand curve has variable success in other areas of Saudi Arabia. We established a theoretical sand curve model to determine the single-way time in dry sand. Tomographic modeling of a higher resolution 3D seismic survey contributes more data to refine the relationship. Polynomial curves were used in the calculation of near-surface static corrections to improve the solution for low-relief structures.

3D seismic traveltime tomography imaging of the shallow subsurface at the C O2 SINK project site, Ketzin, Germany

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. G1-G15 ◽  
Author(s):  
Sawasdee Yordkayhun ◽  
Ari Tryggvason ◽  
Ben Norden ◽  
Christopher Juhlin ◽  
Björn Bergman
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
Geological Structure ◽  
Seismic Survey ◽  
Storage Site ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Traveltime Tomography ◽  
Reflection Seismic ◽  
Reflection Data

A 3D reflection seismic survey was performed in 2005 at the Ketzin carbon dioxide [Formula: see text] pilot geological-storage site (the [Formula: see text] project) near Berlin, Germany, to image the geological structure of the site to depths of about [Formula: see text]. Because of the acquisition geometry, frequency limitations of the source, and artefacts of the data processing, detailed structures shallower than about [Formula: see text] were unclear. To obtain structural images of the shallow subsurface, we applied 3D traveltime tomography to data near the top of the Ketzin anticline, where faulting is present. Understanding the shallow subsurface structure is important for long-term monitoring aspects of the project after [Formula: see text] has been injected into a saline aquifer at about [Formula: see text] depth. We used a 3D traveltime tomography algorithm based on a combination ofsolving for 3D velocity structure and static corrections in the inversion process to account for artefacts in the velocity structure because of smearing effects from the unconsolidated cover. The resulting velocity model shows low velocities of [Formula: see text] in the uppermost shallow subsurface of the study area. The velocity reaches about [Formula: see text] at a depth of [Formula: see text]. This coincides approximately with the boundary between Quaternary units, which contain the near-surface freshwater reservoir and the Tertiary clay aquitard. Correlation of tomographic images with a similarity attribute slice at [Formula: see text] (about [Formula: see text] depth) indicates that at least one east-west striking fault zone observed in the reflection data might extend into the Tertiary unit. The more detailed images of the shallow subsurface from this study provided valuable information on this potentially risky area.

3‐D tomographic static correction

Geophysics ◽  
2002 ◽  
Vol 67 (4) ◽  
pp. 1275-1285 ◽  
Author(s):  
Xu Chang ◽  
Yike Liu ◽  
Hui Wang ◽  
Fuzhong Li ◽  
Jing Chen
Keyword(s):  
Computation Time ◽  
Matrix Decomposition ◽  
Velocity Model ◽  
Seismic Survey ◽  
Surface Model ◽  
Low Velocity ◽  
Near Surface ◽  
Model Inversion ◽  
Static Corrections ◽  
Refracted Waves

A 3‐D tomographic inversion approach based on a surface‐consistent model for static corrections is presented in this paper. Direct, reflected, and refracted waves are used simultaneously to update the near‐surface model. We analyze the characteristics of the first‐break traveltime in complicated low‐velocity layers. To improve the accuracy for the velocity model, the various first‐break times from direct, reflected, and refracted waves are considered for model inversion. A fractal algorithm which overcomes the error caused by wavelet shape differences is applied to pick first breaks. It also overcomes the leg jump of refractions. The method can pick a large number of first breaks automatically. The raypaths and traveltimes are calculated with a 3‐D ray tracer that does not increase computation time for complicated geological models. Our method can determine the raypath associated with minimum traveltimes regardless of wave mode (direct, refracted, or reflected). We use a least‐squares approach in conjunction with a matrix decomposition to reconstruct a 3‐D velocity model from the actual first‐break times obtained from 3‐D data. Finally, long‐ and short‐wavelength static corrections are calculated concurrently, based on the reconstructed velocity profile. The method can be applied to wide‐line profiles, crooked lines, and 2‐D and 3‐D seismic survey geometries. The results applied to a real 3‐D data example indicate that the 3‐D tomographic static corrections are effective for field data.

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

2017 ◽  
Vol 17 (12) ◽  
pp. 2335-2350 ◽  
Author(s):  
Sonja H. Wadas ◽  
David C. Tanner ◽  
Ulrich Polom ◽  
Charlotte M. Krawczyk
Keyword(s):  
Fault Zone ◽  
Fracture Network ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Normal Faults ◽  
S Wave ◽  
Seismic Profiles ◽  
Near Surface ◽  
Reflection Seismic ◽  
Enhanced Dissolution

Abstract. 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.

Offset Dependent Static Corrections on a Continental Shelf Edge 3D Seismic Survey

1991 ◽  
Vol 22 (1) ◽  
pp. 75-80
Author(s):  
M. G. Cousins ◽  
P. M. Whiting ◽  
A. M. Allen
Keyword(s):  
Continental Shelf ◽  
Seismic Survey ◽  
Shelf Edge ◽  
3D Seismic ◽  
Static Corrections

High‐resolution seismic traveltime tomography incorporating static corrections applied to a till‐covered bedrock environment

Geophysics ◽  
2004 ◽  
Vol 69 (4) ◽  
pp. 1082-1090 ◽  
Author(s):  
Björn Bergman ◽  
Ari Tryggvason ◽  
Christopher Juhlin
Keyword(s):  
High Resolution ◽  
Velocity Model ◽  
Surface Velocity ◽  
Data Set ◽  
Near Surface ◽  
Seismic Processing ◽  
Simultaneous Inversion ◽  
Reflection Seismic ◽  
Static Corrections ◽  
Velocity Variations

A major obstacle in tomographic inversion is near‐surface velocity variations. Such shallow velocity variations need to be known and correctly accounted for to obtain images of deeper structures with high resolution and quality. Bedrock cover in many areas consists of unconsolidated sediments and glacial till. To handle the problems associated with this cover, we present a tomographic method that solves for the 3D velocity structure and receiver static corrections simultaneously. We test the method on first‐arrival picks from deep seismic reflection data acquired in the mid‐ late to 1980s in the Siljan Ring area, central Sweden. To use this data set successfully, one needs to handle a number of problems, including time‐varying, near‐surface velocities from data recorded in winter and summer, several sources and receivers within each inversion cell, varying thickness of the cover layer in each inversion cell, and complex 3D geology. Simultaneous inversion for static corrections and velocity produces a much better image than standard tomography without statics. The velocity model from the simultaneous inversion is superior to the velocity model produced using refraction statics obtained from standard reflection seismic processing prior to inversion. Best results using the simultaneous inversion are obtained when the initial top velocity layer is set to the near‐surface bedrock velocity rather than the velocity of the cover. The resulting static calculations may, in the future, be compared to refraction static corrections in standard reflection seismic processing. The preferred final model shows a good correlation with the mapped geology and the airborne magneticmap.

Evaluation of the 2D reflection seismic method toward the exploration of thrust-controlled mineral deposits in southwestern Fujian Province, China

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. B209-B220 ◽  
Author(s):  
Guofeng Liu ◽  
Xiaohong Meng ◽  
Jianhui Ni ◽  
Zhaoxi Chen ◽  
Da Zhang
Keyword(s):  
Forward Modeling ◽  
Seismic Survey ◽  
Mineral Deposits ◽  
Reflection Seismology ◽  
Fujian Province ◽  
Lower Velocity ◽  
Near Surface ◽  
Reflection Seismic ◽  
Mineral Deposition ◽  
Wide Range

The southwestern region of the Fujian Province is one of the major ore districts in China. The current model states that mineral deposition is highly controlled by thrust structure, which means that there may be concealed deposits located deep within overlapping thrust areas. Reflection seismology, which has great depth penetration and higher resolution than other geophysical methods, has great potential to delineate complex structures and give some clues to mineralization. In 2015, an experimental 2D reflection seismic survey called “Fujian 2D” was conducted in this region. Data were acquired along a 13.8 km length, with a source interval of 60 m, and 691 identical receivers with an equal spacing of 20 m were used to record data for each source. Due to topographical restrictions caused by the source environment, the mass or position of some shots was changed. Despite the restrictions, the average fold number reached 64 for a 10 km distance along the middle of the survey line. During the data processing procedure, conventional technologies involving static correction, noise elimination, deconvolution, and iterative velocity analyses were applied. After the prestack time migration failed to obtain a high-quality imaging result, rugged prestack depth migration (PSDM) was introduced that resulted in a better quality image of the subsurface structure and which included near-surface parts of the thrusts. In addition, P- and S-wave velocities and density data were determined from two borehole cores. Forward modeling and imaging found that the Permian marble hosting the mineral deposits has lower velocity than the surrounding rocks, where contacts give rise to strong reflections. The final rugged PSDM also clearly delineated the thrust bodies and magma intrusion zones. Combining this forward modeling with the known geology of the investigated site, the Fujian 2D reflection seismic experiment demonstrates great potential for unveiling the main elements controlling mineral deposition, such as tectonic structure, stratigraphic contacts, and lithology. Our experimental results demonstrate that reflection seismology has a wide range of applications for future mineral exploration at greater depths.

scholarly journals On Including Near-surface Zone Anisotropy for Static Corrections Computation—Polish Carpathians 3D Seismic Processing Case Study

Geosciences ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 66
Author(s):  
Mateusz Zaręba ◽  
Tomasz Danek ◽  
Jerzy Zając
Keyword(s):  
Seismic Data ◽  
Three Dimensional ◽  
Seismic Signal ◽  
Surface Zone ◽  
3D Seismic ◽  
Near Surface ◽  
Seismic Surveys ◽  
Geological Interpretation ◽  
Geological Conditions ◽  
Static Corrections

Obtaining the most accurate and detailed subsurface information from seismic surveys is one of the main challenges for seismic data processing, especially in the context of complex geological conditions (e.g., mountainous areas). The correct calculation of static corrections allows for the reliable processing of seismic data. This, in turn, leads to better geological interpretation. A seismic signal passing through a near-surface zone (NSZ) is adversely affected by the high heterogeneity of this zone. As a result of this, observed travel times often show anisotropy. The application of refractive waves and the time delay solution without taking into account the effects caused by the complex anisotropy of an NSZ does not meet the standards of modern seismic surveys. The construction of the NSZ model in mountain regions with the use of refraction may be extremely difficult, as the vertical layers can be observed very close to the surface. It is not sufficient to apply regular isotropic refractive solutions in such conditions. The presented studies show the results of taking into account the anisotropy of an NSZ in the calculations of static corrections. The presented results show that this step is critical for the detailed processing of three-dimensional (3D) seismic data collected in the difficult region of the Carpathians in Southern Poland.

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