Preliminary results for a near surface 3‐D seismic survey of a geothermal system in Colorado

Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.

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ADAPTATION OF THE METHOD OF CHROMATOGRAPHIC ANALYSIS OF GASOLINE TO ACHIEVE PURPOSES OF GEOCHEMICAL PROSPECTING FOR OIL AND GAS

Oil and Gas Studies ◽

10.31660/0445-0108-2018-6-16-23 ◽

2019 ◽

pp. 16-23

Author(s):

A. R. Kurchikov ◽

R. I. Timshanov ◽

E. A. Ustimenko

Keyword(s):

Chromatographic Analysis ◽

Oil And Gas ◽

Seismic Survey ◽

Near Surface ◽

Petroleum Potential ◽

Geological Interpretation ◽

Gasoline Hydrocarbons ◽

Snow Water ◽

Individual Hydrocarbons ◽

Background Content

Geochemical survey is commonly applied during geological exploration to predict petroleum potential of large areas and to estimate the content of traps identified by the results of seismic survey. C1-C6 hydrocarbon concentrations in samples of surface and subsurface air, soil, snow, water, etc. are used as predictive indicators. At the exploration stage the capabilities of geochemical methods can be significantly expanded by comparing the content of gasoline hydrocarbons in samples of formation fluids and in samples of near-surface sediments. The method of chromatographic analysis of gasolines Chromatec Gazolin has been adapted for sample analysis. The taken measures to increase the sensitivity allowed us to register individual hydrocarbons C1-C10 in concentrations up to 0,01 ppb, which is obviously lower than their background content in the oil prospect areas. The revealed patterns are used in the geological interpretation of geochemical distributions based on theoretical ideas about the subvertical migration of hydrocarbons from the reservoir to the surface.

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Near-surface glaciotectonic structures in the sediments of an overdeepened glacial valley revealed by a shallow 3D seismic survey

10.5194/egusphere-egu21-8195 ◽

2021 ◽

Author(s):

David Tanner ◽

Hermann Buness ◽

Thomas Burschil

Keyword(s):

Seismic Reflection ◽

P Wave ◽

Seismic Survey ◽

Small Scale ◽

Academic Press ◽

Near Surface ◽

Glacial Sediments ◽

Area Source ◽

Terminal Moraine ◽

Rhine Valley

Glaciotectonic structures commonly include thrusting and folding, often as multiphase deformation. Here we present the results of a small-scale 3-D P-wave seismic reflection survey of glacial sediments within an overdeepened glacial valley in which we recognise unusual folding structures in front of push-moraine. The study area is in the Tannwald Basin, in southern Germany, about 50 km north of Lake Constance, where the basin is part of the glacial overdeepened Rhine Valley. The basin was excavated out of Tertiary Molasse sediments during the Hosskirchian stage, and infilled by 200 m of Hosskirchian and Rissian glacioclastics (Dietmanns Fm.). After an unconformity in the Rissian, a ca. 7 m-thick till (matrix-supported diamicton) was deposited, followed by up to 30 m of Rissian/W&#252;rmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last W&#252;rmian glaciation overlies these deposits to the SW, not 200 m away.We conducted a 3-D, 120 x 120 m&#178;, P-wave seismic reflection survey around a prospective borehole site in the study area. Source/receiver points and lines were spaced at 3 m and 9 m, respectively. A 10 s sweep of 20-200 Hz was excited by a small electrodynamic, wheelbarrow-borne vibrator twice at every of the 1004 realized shot positions. We recognised that the top layer of coarse gravel above the till is folded, but not in the conventional buckling sense, rather as cuspate-lobate folding. The fold axes are parallel to the terminal moraine front. The wavelength of the folding varies between 40 and 80 m, and the thickness of the folded layer is on average about 20 m. Cuspate-lobate folding is typical for deformation of layers of differing mechanical competence (after Ramsay and Huber 1987; &#181;1/&#181;2 less than 10), so this tell us something about the relative competence (or stiffness) of the till layer compared to the coarse clastics above. We also detected small thrust faults that are also parallel to the push-moraine, but these have very little offset and most of the deformation was achieved by folding.Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.

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Preliminary results of pore pressure profiling on theTęgoborze-Just landslide

E3S Web of Conferences ◽

10.1051/e3sconf/20186602001 ◽

2018 ◽

Vol 66 ◽

pp. 02001 ◽

Cited By ~ 3

Author(s):

Jacek Stanisz ◽

Zenon Pilecki

Keyword(s):

Pore Pressure ◽

Degree Of Saturation ◽

Flow Paths ◽

Near Surface ◽

Preliminary Results ◽

Water Conditions ◽

Landslide Processes ◽

Pressure Changes ◽

Variable Water ◽

Weak Zones

In this study, we present the preliminary results of deep profiling of pore pressure in the near surface formations of the Carpathian flysch, on the Tęgoborze-Just landslide near Nowy Sącz in Southern Poland. The aim of the study is to identify zones with significant changes in pore pressure influenced landslide processes. These pore pressure changes correspond to a greater change in the degree of saturation or water flow paths. Profiling was performed in four series using a CPTU static probe with a NOVA Acoustic cone. The measurement of pore pressure in flysch formations is very complicated due to the strong heterogeneity of the medium properties and variable water conditions, which are strongly influenced by the intensity of precipitation. The tests were carried out in a colluvium to a depth of approx. 5.0 m, i.e. to the border of a less weathered bedrock, under varying water conditions. The results obtained indicate the presence of four zones of significant changes in pore pressure. The location of these zone is consistent with the location of the greater displacement measured with the inclinometer. There is a greater probability that these weak zones may form a rupture surface.

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Near-surface investigation using additional seismic survey lines: A field experiment

10.1190/segam2017-17723313.1 ◽

2017 ◽

Author(s):

Min Li ◽

Miaoyu Chen ◽

Wei Liu ◽

Meng Zhang ◽

Jiangli Chen ◽

...

Keyword(s):

Surface Investigation ◽

Field Experiment ◽

Seismic Survey ◽

Near Surface

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

Geophysics ◽

10.1190/1.3026553 ◽

2009 ◽

Vol 74 (1) ◽

pp. G1-G15 ◽

Cited By ~ 35

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.

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3‐D tomographic static correction

Geophysics ◽

10.1190/1.1500390 ◽

2002 ◽

Vol 67 (4) ◽

pp. 1275-1285 ◽

Cited By ~ 35

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.

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Seismic imaging and velocity analysis for an Alberta Foothills seismic survey

Geophysics ◽

10.1190/1.1444962 ◽

2001 ◽

Vol 66 (3) ◽

pp. 721-732 ◽

Cited By ~ 18

Author(s):

Lanlan Yan ◽

Larry R. Lines

Keyword(s):

Seismic Imaging ◽

Migration Velocity ◽

Surface Velocity ◽

Seismic Survey ◽

Velocity Analysis ◽

Prestack Depth Migration ◽

Near Surface ◽

Depth Migration ◽

Migration Velocity Analysis ◽

Imaging Results

Seismic imaging of complex structures from the western Canadian Foothills can be achieved by applying the closely coupled processes of velocity analysis and depth migration. For the purposes of defining these structures in the Shaw Basing area of western Alberta, we performed a series of tests on both synthetic and real data to find optimum imaging procedures for handling large topographic relief, near‐surface velocity variations, and the complex structural geology of steeply dipping formations. To better understand the seismic processing problems, we constructed a typical foothills geological model that included thrust faults and duplex structures, computed the model responses, and then compared the performance of different migration algorithms, including the explicit finite difference (f-x) and Kirchhoff integral methods. When the correct velocity was used in the migration tests, the f-x method was the most effective in migration from topography. In cases where the velocity model was not assumed known, we determined a macrovelocity model by performing migration/velocity analysis by using smiles and frowns in common image gathers and by using depth‐focusing analysis. In applying depth imaging to the seismic survey from the Shaw Basing area, we found that imaging problems were caused partly by near‐surface velocity problems, which were not anticipated in the modeling study. Several comparisons of different migration approaches for these data indicated that prestack depth migration from topography provided the best imaging results when near‐surface velocity information was incorporated. Through iterative and interpretive migration/velocity analysis, we built a macrovelocity model for the final prestack depth migration.

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Preliminary results from the Whitehorse Trough seismic survey, Yukon Territory

10.4095/221662 ◽

2006 ◽

Author(s):

G Buffett ◽

D White ◽

B Roberts ◽

M Colpron

Keyword(s):

Yukon Territory ◽

Seismic Survey ◽

Preliminary Results

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