- Home
- A-Z Publications
- Geophysical Prospecting
- Previous Issues
- Volume 71, Issue 5, 2023
Geophysical Prospecting - Volume 71, Issue 5, 2023
Volume 71, Issue 5, 2023
- ISSUE INFORMATION
-
- ORIGINAL ARTICLES
-
-
-
Attenuating pseudo S‐wave splitting caused by vector infidelity
Authors Moacyr de Souza Bezerra, James E. Gaiser and James L. SimmonsAbstractShear wave (S‐wave) splitting analysis can provide knowledge about, among other properties, principal stress directions and fracture orientation. It is an essential step in multi‐component, converted wave processing. Caution must be taken, however, when performing such analysis on ocean bottom cable seismic data, which is highly susceptible to different coupling of the two horizontal components with the seafloor. Receiver coupling correction methods attempt to balance the seismic response on all components and seek to minimize spurious resonance effects. We show on field data from an ocean bottom cable seismic dataset how these coupling effects that simulate S‐wave splitting behaviour can be attenuated to significantly improve PS‐wave stack images of the shallow seabed. Furthermore, corrected pre‐stack data of all azimuths may reveal true splitting effects for stress and fracture information.
-
-
-
-
Dual‐sensor wavefield separation in a compressed domain using parabolic dictionary learning
AbstractIn the marine seismic industry, the size of the recorded and processed seismic data is continuously increasing and tends to become very large. Hence, applying compression algorithms specifically designed for seismic data at an early stage of the seismic processing sequence helps to save cost on storage and data transfer. Dictionary learning methods have been shown to provide state‐of‐the‐art results for seismic data compression. These methods capture similar events from the seismic data and store them in a dictionary of atoms that can be used to represent the data in a sparse manner. However, as with conventional compression algorithms, these methods still require the data to be decompressed before a processing or imaging step is carried out. Parabolic dictionary learning is a dictionary learning method where the learned atoms follow a parabolic travel time move out and are characterized by kinematic parameters such as the slope and the curvature. In this paper, we present a novel method where such kinematic parameters are used to allow the dual‐sensor (or two‐components) wavefield separation processing step directly in the dictionary learning compressed domain for 2D seismic data. Based on a synthetic seismic data set, we demonstrate that our method achieves similar results as an industry‐standard FK‐based method for wavefield separation, with the advantage of being robust to spatial aliasing without the need for data preconditioning such as interpolation and reaching a compression rate around 13. Using a field data set of marine seismic acquisition, we observe insignificant differences on a 2D stacked seismic section between the two methods, whereas reaching a compression ratio higher than 15 when our method is used. Such a method could allow full bandwidth data transfer from vessels to onshore processing centres, where the compressed data could be used to reconstruct not only the recorded data sets, but also the up‐ and down‐going parts of the wavefield.
-
-
-
Selecting velocity models using Bayesian Information Criterion
More LessABSTRACTWe present a strategy for selecting the values of model parameters by comparing walkaway vertical seismic profiling data with a multilayered model in the context of Bayesian information criterion. We consider P‐wave traveltimes and assume elliptical polar velocity dependence. A model with different propagation speeds, depending on the angle of propagation, can be a good approximation for a medium composed of thin layers. While elliptical anisotropy in a one‐layer model yields good results, an efficient tool for multilayer modelling would provide improved inversion results. To obtain the proper set of velocity values for specific parameterizations, we require two steps of optimization. In the first step, we find the signal trajectory; in the second step, we obtain parameter values by minimizing the misfit between the model and the data. By comparing models and data, we choose the best model in the sense of the Bayesian information criterion.
-
-
-
Ground force analysis of a portable electromagnetic seismic vibrator for different surface environments and driving voltages
Authors Yuda Chen, Jun Lin, Yuanjie Jiang and Xuefeng XingAbstractKnowing the actual ground force is important for seismic data processing and seismic vibrator control. However, the weighted‐sum method is widely used to estimate the actual ground force in seismic vibrator exploration. Due to the nonideal body of the baseplate and the nonlinear coupling between the baseplate and the ground, the weighted‐sum method suffers from estimation error. It is feasible to obtain the actual ground force by using load cells. In previous studies, the effects of different surface environments and driving voltages on the actual ground force were rarely analysed. In this paper, a field experiment was conducted to study the actual ground force of a portable electromagnetic seismic vibrator for different surface environments and driving voltages. The fundamental wave, multiple harmonics, phase distortion, response delay, weighted‐sum method estimation error and ground impedance were analysed. The experimental results show that there are obvious second‐to‐fifth harmonics in the actual ground force. An increase in the driving voltage will enhance the energy ratio of the fundamental wave, suppress the phase distortion and increase the response time of the actual ground force. In a soft soil environment, there are obvious amplitude and phase differences between the weighted‐sum ground force and the actual ground force. The phase difference is affected by the driving voltage, which causes a time delay in the cross‐correlated wavelet between the weighted‐sum ground force and the actual ground force. The ground impedance beneath the baseplate is highly non‐linear. As the vibration frequency increases, the viscosity and stiffness of the coupled ground tend to be stable.
-
-
-
2D seismic design on frontier basins using potential field data, a case study in the south of the eastern arm of the East African Rift System
Authors Mussa Nalogwa, Gehrig Schultz, Kevin Laws and Richard ThompsonAbstractThe 2D seismic design for a frontier basin was conducted from potential field data and available geological information using a case of a Block within the East African Rift System. The Block forms part of a southern extension of the eastern branch of the East African Rift System. The most significant structural features of the Block within this part of the rift were mapped using Airborne Gravity Gradiometry data along A, B and C sub‐basin boundaries. The Block covers a total area of more than 10,107 km2 in the central north of Tanzania. The 2D seismic lines were planned to intersect the major structures within the Block, in which a total of 1074 line kilometres from 18 seismic lines were proposed. The spatial sampling interval of 12.5 m with a minimum of two samples per wavelength was deemed adequate for a frontier basin, as would record dips well above 15° limit from the minimum target of 2000 m. The relevant source spacing may be suitable if tested, and the required energy has been recorded. These parameters, though may need refining depending on the field, are proposed for a good resolution imaging and wide bandwidth recording of complex geology for a frontier basin. The seismic design provided the basis for the economic evaluation of the possible survey to be undertaken for a frontier basin. The suggested parameters allow for the flexibility of inclusion or improvement in any subsequent study related to the seismic acquisition in a Block with similar characteristics.
-
-
-
Ensemble scenario‐based inversion: A new approach for estimating the uncertainty of resistivity models derived from 3D controlled source electromagnetic data
More LessAbstractNon‐linear inversion of controlled source electromagnetic data is non‐unique. Inversion ambiguity and uncertainty grow with model complexity and limitations in sensitivity, for example when imaging deep targets. Uncertainties should be estimated. The best way to do that is by statistical inversion techniques. Because of the large number of parameters of 3D models, these methods are too costly for 3D applications. But neglecting or underestimating uncertainties often leads to erroneous interpretation and poor exploration decisions. The number of inversion parameters can be dramatically reduced while still being able to describe a complex 3D subsurface. To obtain that, I represent prior information by an input ensemble of geologically reasonable prior models. The model space is defined by the principal directions of this ensemble, where the inversion parameters are the coefficients of the different components. In this model space, inversion becomes much more efficient and can produce an updated ensemble of posterior models at the same computational cost as a controlled‐source electromagnetic inversion project using conventional non‐linear inversion techniques. I present examples where unique Gauss–Newton inversions lead to difficult interpretations and poor conclusions about hydrocarbon presence and saturation. The new approach provides a quantitative estimation of resistivity ambiguities and uncertainties leading to better interpretation and safer decisions. The examples use 2D synthetic controlled‐source electromagnetic data and 3D controlled‐source electromagnetic field data.
-
-
-
Two‐dimensional inversion of airborne radiometric data for source concentrations: Application to Cu–Au targeting at Mara Rosa Magmatic Arc, Brazil
AbstractAirborne radiometrics (radiometric surveying) has been used in many applications, such as geological mapping, environmental studies, mineral exploration and lithology mapping. The standard processing of gamma‐ray spectrometry data provides good results when the acquisition conditions such as the flight and sensor orientation are constant. In practice, abrupt changes in flight height when flying in mountainous terrain are common, and standard processing neglecting this factor can lead to erroneous interpretation. The primary cause is the fact that the successive corrections applied to radiometric data in standard processing do not consider the effective sampled area of a survey (i.e. the field of view), which can have significant and variable overlaps between adjacent samples due to changing observation height. For this reason, standard height and sensitivity corrections may lead to incorrect estimates of the concentrations of the radioelements on the ground. To ameliorate this problem, we have developed a two‐dimensional inversion‐based processing method that incorporates the aircraft height, replaces the sensitivity correction and accounts for a positivity condition using a logarithmic barrier. Some minerals associated with potassium, uranium and thorium allow the mapping of hydrothermal alteration, especially potassium which is an important constituent of hydrothermal fluids. We demonstrate the new methods by comparing the standard processing results with the inversion‐based processing of airborne gamma‐ray spectrometry data in the gold deposit‐rich area of Mara Rosa Magmatic Arc, Brazil. The inversion‐based processing results enhance the anomalies and suppress the interpolation artefacts as well as increase the signal‐to‐noise ratio. The application of airborne radiometric transformed maps also improved the footprint knowledge around Cu–Au mineralization and highlighted potential areas for further studies.
-
Volumes & issues
-
Volume 72 (2023 - 2024)
-
Volume 71 (2022 - 2023)
-
Volume 70 (2021 - 2022)
-
Volume 69 (2021)
-
Volume 68 (2020)
-
Volume 67 (2019)
-
Volume 66 (2018)
-
Volume 65 (2017)
-
Volume 64 (2015 - 2016)
-
Volume 63 (2015)
-
Volume 62 (2014)
-
Volume 61 (2013)
-
Volume 60 (2012)
-
Volume 59 (2011)
-
Volume 58 (2010)
-
Volume 57 (2009)
-
Volume 56 (2008)
-
Volume 55 (2007)
-
Volume 54 (2006)
-
Volume 53 (2005)
-
Volume 52 (2004)
-
Volume 51 (2003)
-
Volume 50 (2002)
-
Volume 49 (2001)
-
Volume 48 (2000)
-
Volume 47 (1999)
-
Volume 46 (1998)
-
Volume 45 (1997)
-
Volume 44 (1996)
-
Volume 43 (1995)
-
Volume 42 (1994)
-
Volume 41 (1993)
-
Volume 40 (1992)
-
Volume 39 (1991)
-
Volume 38 (1990)
-
Volume 37 (1989)
-
Volume 36 (1988)
-
Volume 35 (1987)
-
Volume 34 (1986)
-
Volume 33 (1985)
-
Volume 32 (1984)
-
Volume 31 (1983)
-
Volume 30 (1982)
-
Volume 29 (1981)
-
Volume 28 (1980)
-
Volume 27 (1979)
-
Volume 26 (1978)
-
Volume 25 (1977)
-
Volume 24 (1976)
-
Volume 23 (1975)
-
Volume 22 (1974)
-
Volume 21 (1973)
-
Volume 20 (1972)
-
Volume 19 (1971)
-
Volume 18 (1970)
-
Volume 17 (1969)
-
Volume 16 (1968)
-
Volume 15 (1967)
-
Volume 14 (1966)
-
Volume 13 (1965)
-
Volume 12 (1964)
-
Volume 11 (1963)
-
Volume 10 (1962)
-
Volume 9 (1961)
-
Volume 8 (1960)
-
Volume 7 (1959)
-
Volume 6 (1958)
-
Volume 5 (1957)
-
Volume 4 (1956)
-
Volume 3 (1955)
-
Volume 2 (1954)
-
Volume 1 (1953)