Methodology of prestack amplitude analysis and its application to seismic bright spots in the Po Valley, Italy

1988 ◽  
Author(s):  
AIfred Mazzotti
Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Alfredo Mazzotti

The amplitude‐versus‐offset (AVO) characteristics of three separate bright spots on the same seismic section are analyzed. One of the bright spots results from a water‐bearing gravel layer, and the others correspond to gas‐saturated sandy beds. The amplitude analysis includes reflections from the entire range of incidence angles available from the survey; for the shallower amplitude anomaly, these angles reached values up to 66°. Extension of the analysis to longer offsets is aimed at detecting possible critical‐angle phenomena in order to reduce the uncertainty when the zero‐offset reflection’s polarity is unknown. The reflection from the gravel layer has this property. Its amplitude exhibits an initial decrease followed by a sudden rise in the AVO trend due to critical reflection and head waves. The gas‐related anomalies have a much different AVO characteristic, one in which the amplitude increases with offset distance. Two seismic events located above the bright spots were also investigated to further verify the validity of the seismic amplitude processing. The AVO trends of the three bright spots and of the two reference levels were compared with analogous trends of synthetic seismograms that were computed from models derived from borehole data.


2014 ◽  
Vol 2 (4) ◽  
pp. SP5-SP20 ◽  
Author(s):  
Ram Janma Singh

Seismic amplitude anomalies are attractive exploration targets in the Krishna-Godavari Basin offshore India. These bright spots mostly have very high amplitudes, so confident interpretations have been possible. We distinguished between hydrocarbon-bearing sands, water-bearing sands, and high-impedance nonreservoir bodies. Also, we mapped channel architecture and accurately predicted reservoir thickness. Strong amplitude anomalies, prospective seismic character based on an understanding of data phase and polarity, flat spots, and amplitude versus offset have all provided valuable evidence.


Geophysics ◽  
1986 ◽  
Vol 51 (3) ◽  
pp. 699-709 ◽  
Author(s):  
H. Almoghrabi ◽  
J. Lange

Seismic amplitudes are affected by both geometric and lithologic features of reflecting layers. Observation of “bright spots” is a function of not only pore fluid saturations, but also of layer thickness and surrounding rock type. The numerical model developed uses a finite sum of reflected and mode‐converted waves to evaluate the application of wave analysis in determining pore fluid types. Amplitude analysis alone is not sufficient to define realistically pore fluid type, but when amplitude analysis is combined with phase and mode‐converted shear‐wave behavior, it is possible to differentiate between pore fluid types. Various configurations which lead to bright spots, including coal and limestone layers, are evaluated. An algorithm is developed, based on the numerical examples, which can differentiate gas zones from other bright spot data. Thickness of the plane layer is an important factor in defining the overall reflectivity due to interference of the reflected wave components. Gas saturation of a layer is not a sufficient condition for a bright spot, but can lead to “dull spots” for layers in the right thickness range (relative to the incident wavelength). The lithology of the boundary material determines the extremes in amplitude variation which result when thickness or wavelength is varied. If a priori knowledge of the lithology or thickness of the structure is available, the amplitude‐phase‐converted wave algorithm can be applied to other than bright spot data to characterize the structure. This indicates there are important applications of the amplitude‐phase‐converted wave algorithm to field development and to bright spot analysis for exploration.


Author(s):  
J. M. Cowley

Recently a number of authors have reported detail in dark-field images obtained from diffuse-scattering regions of electron diffraction patterns. Bright spots in images from short-range order diffuse peaks of disordered binary alloys have been interpreted as evidence for the existence of microdomains of ordered lattice or of segragated clusters of one component. Spotty contrast in dark field images of near-amorphous materials has been interpreted as evidence for the existense of microcrystals. Without a careful analysis of the imaging conditions such conclusions may be invalid. Usually the conditions of the experiment have not been specified in sufficient detail to allow evaluation of the conclusions.Elementary considerations show that even for a completely random arrangement of atoms the statistical fluctuations of density will give a spotty contrast with spots of minimum diameter determined by the dark field aperture size and other factors influencing the minimum resolvable distance under darkfield imaging conditions, including fluctuations and drift over long exposure times (resolution usually 10Å or more).


ARCHALP ◽  
2020 ◽  
Vol 2020 (N. 4 / 2020) ◽  
Author(s):  
Antonio De Rossi ◽  
Laura Mascino

It hasn’t even been half a century since, in 1977, the famous book by Nuto Revelli entitled Il mondo dei vinti was published. A symbolic image, which summed up with powerful evocative efficacy the dramatic process of depopulation and dissolution of traditional Alpine societies during the twentieth century. A phenomenon that found its epicenter in the valleys of Carnia and in the south-east of France, and especially in the Piedmont’s valleys of the Cuneo area, with drop-out rates that will reach even 80-90% of the population. A little over forty years have passed by since Nuto Revelli’s book was published and since then a lot seemed to have changed. Today many prestigious and successful tourist and winter centers are experiencing a growing crisis of image and public, while the once neglected Valades ousitanes live an unprecedented season, focused on enhancing the trinomial of natural, historical, and cultural heritage. Maira Valley, Ostana in the Po Valley, Paraloup and Rittana in the Stura Valley, the upper Varaita Valley, the phenomena of rebirth are affecting all the Occitan valleys, with interesting resettlement processes that have their engine in who are defined «the new mountaineers». This renaissance of the Occitan valleys is accompanied by new forms of architecture that focus on the theme of the recovery and reuse of heritage, of dialectical confrontation with environmental and historical contexts, but without forgetting the contemporary and technological innovation.


2016 ◽  
Author(s):  
Jennifer E.C. Scully ◽  
◽  
Debra L. Buczkowski ◽  
Paul M. Schenk ◽  
Adrian Neesemann ◽  
...  
Keyword(s):  

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 851
Author(s):  
Xiaorong Ren ◽  
Xiangyu Zeng ◽  
Chunxiang Liu ◽  
Chuanfu Cheng ◽  
Ruirui Zhang ◽  
...  

We investigated the optical spin Hall effect (OSHE) of the light field from a closed elliptical metallic curvilinear nanoslit instead of the usual truncated curvilinear nanoslit. By making use of the characteristic bright spots in the light field formed by the noncircular symmetry of the elliptical slit and by introducing a method to separate the incident spin component (ISC) and converted spin component (CSC) of the output field, the OSHE manifested in the spot shifts in the CSC was more clearly observable and easily measurable. The slope of the elliptical slit, which was inverse along the principal axes, provided a geometric phase gradient to yield the opposite shifts of the characteristic spots in centrosymmetry, with a double shift achieved between the spots. Regarding the mechanism of this phenomenon, the flip of the spin angular momentum (SAM) of CSC gave rise to an extrinsic orbital angular momentum corresponding to the shifts of the wavelet profiles of slit elements in the same rotational direction to satisfy the conservation law. The analytical calculation and simulation of finite-difference time domain were performed for both the slit element and the whole slit ellipse, and the evolutions of the spot shifts as well as the underlying OSHE with the parameters of the ellipse were achieved. Experimental demonstrations were conducted and had consistent results. This study could be of great significance for subjects related to the applications of the OSHE.


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