Sub-basalt seismic imaging using optical-to-acoustic model building and wave equation datuming processing

Bean, Christopher J.; Martini, Francesca

doi:10.1016/j.marpetgeo.2009.09.007

Cited by 6 publications

(3 citation statements)

References 22 publications

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“…The modelling of interfaces as flat and layers as homogenous does not reflect the expected structure of flows and flow interfaces (e.g., Waagstein and Andersen 2003; Passey 2007; Shaw et al . 2008; Bean and Martini 2010). These properties are indeed considered important for understanding the seismic properties of successive basalt flows but are beyond the scope of this paper, where we focus on seismic traveltimes.…”

Section: Quantitative Correlation To Velocity Well Logsmentioning

confidence: 99%

P‐wave velocity distribution in basalt flows of the Enni Formation in the Faroe Islands from refraction seismic analysis

Petersen

Brown

Andersen

2012

Geophysical Prospecting

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The main objective of this work is to establish the applicability of shallow surface‐seismic traveltime tomography in basalt‐covered areas. A densely sampled ∼1300‐m long surface seismic profile, acquired as part of the SeiFaBa project in 2003 (Japsen et al. 2006) at Glyvursnes in the Faroe Islands, served as the basis to evaluate the performance of the tomographic method in basalt‐covered areas. The profile is centred at a ∼700‐m deep well. VP, VS and density logs, a zero‐offset VSP, downhole‐geophone recordings and geological mapping in the area provided good means of control. The inversion was performed with facilities of the Wide Angle Reflection/Refraction Profiling program package (Ditmar et al. 1999). We tested many inversion sequences while varying the inversion parameters. Modelled traveltimes were verified by full‐waveform modelling. Typically an inversion sequence consists in several iterations that proceed until a satisfactory solution is reached. However, in the present case with high velocity contrasts in the subsurface we obtained the best result with two iterations: first obtaining a smooth starting model with small traveltime residuals by inverting with a high smoothing constraint and then inverting with the lowest possible smoothing constraint to allow the inversion to have the full benefit of the traveltime residuals. The tomogram gives usable velocity information for the near‐surface geology in the area but fails to reproduce the expected velocity distribution of the layered basalt flows. Based on the analysis of the tomogram and geological mapping in the area, a model was defined that correctly models first arrivals from both surface seismic data and downhole‐geophone data.

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Section: Quantitative Correlation To Velocity Well Logsmentioning

confidence: 99%

P‐wave velocity distribution in basalt flows of the Enni Formation in the Faroe Islands from refraction seismic analysis

Petersen

Brown

Andersen

2012

Geophysical Prospecting

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“…Various methods have been proposed to quantify and correct for these static-shift effects, including continuous sampling and filtering of the electric channels (Torres-Verdin and Bostick, 1992), spatial filtering based on mapping of MT data (Berdichevsky, 1989), modelling of parametric homogeneous layers at depth (Jones, 1988), estimation of distortionrelated parameters as unknowns during inversion (Sasaki and Meju, 2006;Miensopust, 2010;Avdeeva et al, 2015;De Groot-Hedlin, 1991;DeGroot-Hedlin, 1995), and finally the use of complementary EM geophysical methods (Sternberg et al, 1988;Pellerin and Hohmann, 1990;Miensopust et al, 2014). These methods can be broadly divided into methods that use intrinsic information from MT data and those that use extrinsic information from other geoscientific data.…”

Section: 4mentioning

confidence: 99%

Correcting for static shift of magnetotelluric data with airborne electromagnetic measurements: a case study from Rathlin Basin, Northern Ireland

et al. 2017

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Abstract. Galvanic distortions of magnetotelluric (MT) data, such as the static-shift effect, are a known problem that can lead to incorrect estimation of resistivities and erroneous modelling of geometries with resulting misinterpretation of subsurface electrical resistivity structure. A wide variety of approaches have been proposed to account for these galvanic distortions, some depending on the target area, with varying degrees of success. The natural laboratory for our study is a hydraulically permeable volume of conductive sediment at depth, the internal resistivity structure of which can be used to estimate reservoir viability for geothermal purposes; however, static-shift correction is required in order to ensure robust and precise modelling accuracy.We present here a possible method to employ frequency–domain electromagnetic data in order to correct static-shift effects, illustrated by a case study from Northern Ireland. In our survey area, airborne frequency domain electromagnetic (FDEM) data are regionally available with high spatial density. The spatial distributions of the derived static-shift corrections are analysed and applied to the uncorrected MT data prior to inversion. Two comparative inversion models are derived, one with and one without static-shift corrections, with instructive results. As expected from the one-dimensional analogy of static-shift correction, at shallow model depths, where the structure is controlled by a single local MT site, the correction of static-shift effects leads to vertical scaling of resistivity–thickness products in the model, with the corrected model showing improved correlation to existing borehole wireline resistivity data. In turn, as these vertical scalings are effectively independent of adjacent sites, lateral resistivity distributions are also affected, with up to half a decade of resistivity variation between the models estimated at depths down to 2000 m. Simple estimation of differences in bulk porosity, derived using Archie's Law, between the two models reinforces our conclusion that the suborder of magnitude resistivity contrasts induced by the correction of static shifts correspond to similar contrasts in estimated porosities, and hence, for purposes of reservoir investigation or similar cases requiring accurate absolute resistivity estimates, galvanic distortion correction, especially static-shift correction, is essential.

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“…This is an important topic, as the presence of interfaces with irregularities leads to complex wave propagation phenomena, such as combination of reflections, scattering and other effects, resulting in difficulties in the reconstruction of the shape of the interfaces (useful for both geologists and geophysicists) and in the estimation of seismic parameters (velocity, density, etc). As an example, the rugged topography of the basaltic surfaces generates severe wave distortion and scattering of seismic energy, and hence has a detrimental effect on seismic imaging quality of underlying geological structures [1,2]. This detrimental effect is even greater than that provided by internal heterogeneities of basalt layers [3].…”

Section: Introductionmentioning

confidence: 99%

On the reflection of time-domain acoustic spherical waves by a sinusoidal diffraction grating

et al. 2021

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This work reports on some results obtained from numerical simulations of time-domain acoustic wave propagation in the presence of a periodically rough interface. Emphasis is put on the structure of the reflected signals in the presence of a sinusoidal grating. More specifically, we investigate the effect of the frequency bandwidth of the emitted signal and the effect of the incident wavefront sphericity on the signals reflected from the rough interface and associated with the different diffraction orders.

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Sub-basalt seismic imaging using optical-to-acoustic model building and wave equation datuming processing

Cited by 6 publications

References 22 publications

P‐wave velocity distribution in basalt flows of the Enni Formation in the Faroe Islands from refraction seismic analysis

P‐wave velocity distribution in basalt flows of the Enni Formation in the Faroe Islands from refraction seismic analysis

Correcting for static shift of magnetotelluric data with airborne electromagnetic measurements: a case study from Rathlin Basin, Northern Ireland

On the reflection of time-domain acoustic spherical waves by a sinusoidal diffraction grating

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