scholarly journals Application of AVAZ inversion algorithm based on exact formulas to a wide-azimuth seismic survey data

2021 ◽  
Vol 6 (2) ◽  
pp. 12-19
Author(s):  
G. A. Dugarov ◽  
T. V. Nefedkina ◽  
I. Yu. Bogatyrev ◽  
N. A. Goreiavchev ◽  
G. M. Mitrofanov ◽  
...  
Keyword(s):  
Wave Reflection ◽  
P Wave ◽  
Seismic Survey ◽  
Inversion Algorithm ◽  
Hti Media ◽  
Reliable Performance ◽  
The Republic ◽  
Well Data ◽  
Conventional Algorithm ◽  
Anisotropy Degree

Results of applying of nonlinear AVAZ inversion optimization algorithm to data from 3D wide-azimuth seismic survey in the Republic of Serbia are presented. The algorithm is based on exact reflection coefficients formulas for PP reflection from anisotropic medium. We compare it with a conventional algorithm based on Ruger linear approximation of P-wave reflection from a boundary between isotropic and anisotropic (HTI) media. Maps of fracture orientation and anisotropy degree are more detailed in the case of using AVAZ inversion based on exact formulas. The results are in general accordance with the FMI well data, which indicates reliable performance of the algorithm.

scholarly journals S-wave experiments for the exploration of a deep geothermal carbonate reservoir in the German Molasse Basin

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Britta Wawerzinek ◽  
Hermann Buness ◽  
Hartwig von Hartmann ◽  
David C. Tanner
Keyword(s):  
Upper Jurassic ◽  
Carbonate Reservoir ◽  
P Wave ◽  
Seismic Survey ◽  
Seismic Exploration ◽  
Molasse Basin ◽  
S Wave ◽  
Induced Earthquakes ◽  
Conversion Point ◽  
Facies Classification

AbstractThere are many successful geothermal projects that exploit the Upper Jurassic aquifer at 2–3 km depth in the German Molasse Basin. However, up to now, only P-wave seismic exploration has been carried out. In an experiment in the Greater Munich area, we recorded S-waves that were generated by the conventional P-wave seismic survey, using 3C receivers. From this, we built a 3D volume of P- to S-converted (PS) waves using the asymptotic conversion point approach. By combining the P-volume and the resulting PS-seismic volume, we were able to derive the spatial distribution of the vp/vs ratio of both the Molasse overburden and the Upper Jurassic reservoir. We found that the vp/vs ratios for the Molasse units range from 2.0 to 2.3 with a median of 2.15, which is much higher than previously assumed. This raises the depth of hypocenters of induced earthquakes in surrounding geothermal wells. The vp/vs ratios found in the Upper Jurassic vary laterally between 1.5 and 2.2. Since no boreholes are available for verification, we test our results against an independently derived facies classification of the conventional 3D seismic volume and found it correlates well. Furthermore, we see that low vp/vs ratios correlate with high vp and vs velocities. We interpret the latter as dolomitized rocks, which are connected with enhanced permeability in the reservoir. We conclude that 3C registration of conventional P-wave surveys is worthwhile.

scholarly journals The offset-midpoint traveltime pyramid in 3D transversely isotropic media with a horizontal symmetry axis

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. T51-T62 ◽  
Author(s):  
Qi Hao ◽  
Alexey Stovas ◽  
Tariq Alkhalifah
Keyword(s):  
Symmetry Axis ◽  
Transversely Isotropic ◽  
P Wave ◽  
Analytic Representation ◽  
Velocity Inversion ◽  
Transversely Isotropic Media ◽  
Horizontal Symmetry ◽  
Time Domains ◽  
Isotropic Media ◽  
Hti Media

Analytic representation of the offset-midpoint traveltime equation for anisotropy is very important for prestack Kirchhoff migration and velocity inversion in anisotropic media. For transversely isotropic media with a vertical symmetry axis, the offset-midpoint traveltime resembles the shape of a Cheops’ pyramid. This is also valid for homogeneous 3D transversely isotropic media with a horizontal symmetry axis (HTI). We extended the offset-midpoint traveltime pyramid to the case of homogeneous 3D HTI. Under the assumption of weak anellipticity of HTI media, we derived an analytic representation of the P-wave traveltime equation and used Shanks transformation to improve the accuracy of horizontal and vertical slownesses. The traveltime pyramid was derived in the depth and time domains. Numerical examples confirmed the accuracy of the proposed approximation for the traveltime function in 3D HTI media.

scholarly journals Geological evolution of the Chalk Group in the northern Dutch North Sea: inversion, sedimentation and redeposition

2018 ◽  
Vol 156 (07) ◽  
pp. 1265-1284
Author(s):  
EVA VAN DER VOET ◽  
LEONORA HEIJNEN ◽  
JOHN J. G. REIJMER
Keyword(s):  
North Sea ◽  
Late Cretaceous ◽  
Seismic Survey ◽  
Structural Elements ◽  
The North ◽  
Show Evidence ◽  
New Finding ◽  
The North Sea ◽  
Thickness Variations ◽  
Well Data

AbstractIn contrast to the Norwegian and Danish sectors, where significant hydrocarbon reserves were found in chalk reservoirs, limited studies exist analysing the chalk evolution in the Dutch part of the North Sea. To provide a better understanding of this evolution, a tectono-sedimentary study of the Late Cretaceous to Early Palaeogene Chalk Group in the northern Dutch North Sea was performed, facilitated by a relatively new 3D seismic survey. Integrating seismic and biostratigraphic well data, seven chronostratigraphic units were mapped, allowing a reconstruction of intra-chalk geological events.The southwestward thickening of the Turonian sequence is interpreted to result from tilting, and the absence of Coniacian and Santonian sediments in the western part of the study area is probably the result of non-deposition. Seismic truncations show evidence of a widespread inversion phase, the timing of which differs between the structural elements. It started at the end of the Campanian followed by a second pulse during the Maastrichtian, a new finding not reported before. After subsidence during the Maastrichtian and Danian, renewed inversion and erosion occurred at the end of the Danian. Halokinesis processes resulted in thickness variations of chalk units of different ages.In summary, variations in sedimentation patterns in the northern Dutch North Sea relate to the Sub-Hercynian inversion phase during the Campanian and Maastrichtian, the Laramide inversion phase at the end of the Danian, and halokinesis processes. Additionally, the Late Cretaceous sea floor was characterized by erosion through contour bottom currents at different scales and resedimentation by slope failures.

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

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

<p>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/Würmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last Würmian glaciation overlies these deposits to the SW, not 200 m away.</p><p>We conducted a 3-D, 120 x 120 m², 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; µ<sub>1</sub>/µ<sub>2</sub> 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.</p><p>Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.</p>

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