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Collaborating Authors
Results
Summary In an inversion for the subsurface conductivity distribution using frequency-domain Controlled-Source Electromagnetic data, various amounts of horizontal components may be included. We investigate which combination of components are best suited to invert for a vertical transverse isotropic (VTI) subsurface. We do this by probing the solutionspace using a genetic algorithm. We found, by studying a simple horizontally layered medium, that if only electric data are used, either the horizontal or the vertical conductivity of a layer can be estimated properly, but not both. Including the crossline electric field does not add additional information. In contrast, including the two horizontal magnetic components along with the two horizontal electric components allows to retrieve a better estimate of some of the VTI parameters. For an isotropic subsurface, the electric field is sufficient to invert for the subsurface conductivity.
Summary Increasing industrial and societal challenges demand a continuous need for improved imaging methods. In recent years, quite some research has been performed on using seismoelectric phenomena for geophysical exploration and imaging. Like the other methods, the seismoelectric technique also has its drawbacks. Besides the fact that the physical phenomenon is very complex, one of itsmain challenges is the very low signalto- noise ratio of the coupled signals, especially the secondorder interface response fields. From seismics, it is wellknown that anonamously high amplitudes can arise due to amplitude-tuning effects which can occur when a seismic signal travels through a package of thin-layers with appropriate amplifying thickness. Using numerical seismoelectric wave propagation experiments through packages of thin-beds, we show that thin-bed geological settings can improve the signalto- noise ratio of the interface response fields. Whether a certain package of thin-beds results in a net strengthening or weakening of the signal, is determined by the contrast in and the order of the coupling coefficients of the different thin-layer media. Formulated differently, we show that the seismoelectric method is sensitive to the medium parameters of thin-bed geological structures far below the seismic resolution, and that due to natural strengthening of the seismoelectric interface response signal, the method might be already suitable for certain geological settings.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.94)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.93)
Summary The seismoelectric effect can be of importance for hydrocarbon exploration as it is complementary to conventional seismics. Besides enabling seismic resolution and electromagnetic sensitivity at the same time, the seismoelectric method can also provide us with additional, high-value information like porosity and permeability. However, very little is still understood of this complex physical phenomenon. Therefore, it is crucial to be able to perform numerical modeling experiments to carefully investigate the effect and the parameters that play a role. Over the last couple of years, several seismoelectric laboratory experiments have been carried out in an attempt to validate the underlying theory of the phenomenon and to better understand this complex physical phenomenon. We have recently extended our analytically based, numerical seismoelectric modeling code ’ESSEMOD’ to be able to model seismoelectric wave propagation in arbitrarily layered Earth geometries with fluid / porous medium / (fluid) interfaces. In this way, we are capable of effectively simulating full seismoelectric wave propagation, i.e. all existing seismoelectric and electroseismic source-receiver combinations, in typical laboratory configurations. We present the underlying theory that is required for the extension towards arbitrary fluid / porous medium / (fluid) geometries and an effective way to incorporate this in a general seismoelectric layered Earth modeling code. We then validate the underlying global reflection scheme by comparing it with an independently developed layered Earth modeling code for purely electromagnetic fields. The results show a perfect match in both amplitude and phase, indicating that ESSEMOD is correctly modeling the electromagnetic parts of the seismoelectric wave propagation in horizontally layered media with fluid / porous medium / fluid transitions. We finalize with a seismoelectric reciprocal modeling experiment, proving that also the full seismoelectric wave propagation through fluid / porous medium transitions is modeled consistently.
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Electromagnetic Surveying (1.00)
Summary Interferometric methods are well known for retrieving the reflection response of a virtual source at a physical receivers location. The position of the sources does not have to be known for this. Interferometry by multidimensional deconvolution can even be used in dissipative media, and is therefore of interest for GPR applications. It gives an accurate estimation, both spatially and temporally, of the reflection response, and can especially be useful in monitoring applications and in cases where it is not possible to place a source for GPR measurements. The reflection response due to a virtual source at a receiver position can be retrieved using band-limited synthetic noise with a centrum frequency around the mobile phone frequency.