Multiwave imaging of the Earth's subsurface : a laboratory scale feasibility study (original) (raw)
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Geophysical Journal International Non-linear interaction of elastic waves in rocks
We study theoretically the interaction of elastic waves caused by non-linearities of rock elastic moduli, and assess the possibility to use this phenomenon in hydrocarbon exploration and in the analysis of rock samples. In our calculations we use the five-constant model by Gol'dberg. It is shown that the interaction of plane waves in isotropic solids is completely described by five coupling coefficients, which have the same order of magnitude. By considering scattering of compressional waves generated by controlled sources at the Earth surface from a non-linear layer at the subsurface, we conclude that non-linear signals from deep formations are unlikely to be measured with the current level of technology. Our analysis of field tests where non-linear signals were measured, suggests that these signals are generated either in the shallow subsurface or in the vicinity of sources. Non-linear wave interaction might be observable in lab tests with focused ultrasonic beams. In this case, the non-linear response is generated in the secondary parametric array formed by linear beams scattered from inclusions. Although the strength of this response is controlled by non-linearity of the surrounding medium rather than by non-linearity of inclusions, its measurement can help to obtain better images of rock samples.
The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 2
Journal of Geophysical Research, 1961
The velocity of compressional waves has been determined by measurement of travel time of pulses in specimens of rock at pressures to 10 kilobars a•d room temperature. Most of the samples, mainly igneous and metamorphic rocks, furnished three specimens oriented at right angles to one another. The present paper gives experimental details, modal analyses, and numerical tables of velocity as function of direction of propagation, initial density, and pressure. Discussion of various aspects of the mea•mrements is reserved for part 2. Introduction. Laboratory measurements of elastic constants or of the velocities of elastic waves in rocks are needed for the interpretation of seismic velocities in terms of materials. The first useful measurements were of compressibility: extended to 10 or 12 kilobars by Adams and his collaborators and by Bridgman, they have guided inferences about crust and substratum and, by extrapolation, still deeper levels. In later investigations [Birch and Bancroit, 1938, 1940], the velocity Vs of shear waves was measured to 4 and then 10 kilobars, with temperatures reaching about 600øC [Birch, 1943, 1955]. This velocity may be found with good precision from the resonant frequency of vibration in the torsional mode of cylindrical bars. Attempts to measure elastic constants entering in the frequency equation of other modes of vibration (extensional, flexural) encountered difficulties x Published under the auspices of the Committee on Experimental Geology and Geophysics and the Division of Geological Sciences at Harvard University. ' Editors' note: Professor Birch is to be the recipient of the Twenty-Second Award of the William Bowie Medal during the 1960 Annual Meeting of the American Geophysical Union. associated with the reaction of the pressure medium upon the motion of the specimen. An effort to determine velocity by observation of the travel times of pulses, made in the late 1930's with the aid of Dr. Dennison Bancroft, was hampered by the inadequacy of the oscilloscopes and other electronic devices of that period; a primitive time-measuring device was constructed, however [Bancro]t, 1940], which showed a degree of promise. This situation was transformed by the wartime development of pulse circuitry, fast-writing oscilloscopes, and many other useful components; it then became relatively easy to accomplish what had previously seemed virtually impossible. Responding to these new possibilities, a number of investigators have published measurements of wave velocities in rocks, as well as in many other materials. Among those especially interesting for geophysical problems are the papers by Hughes and others, showing effects of both pressure and temperature [Hughes approaches (E/p) TM for wavelengths long with respect to the bar diameter. A large number of papers have been devoted to the discussion of wave propagation in cylindrical bars, but there seems to be no complete theoretical solution for the propagation of pulses in short bars. (For a recent review, see, for example, Mason, 1958, p. 40 et seq.) It can be demonstrated experimentally, however, that the first motion does travel with the velocity Vr in materials for which the elastic constants can be determined independently, such as glass, steel, or aluminum, and, by observing with samples of different sizes, that this velocity is independent of length and diameter of sample and of transducer frequency within certain ranges of dimensions and of experimental accuracy. This has been done in the course of the present study, and earlier by students of ultrasonic delay lines and others [for example, Mason and McSkimin, 1947; Roth, 1948; Hughes, Pondtom, and Mims, 1949]. Probably the most comprehensive investigation, though of relatively low precision, is that of ilaevaandilaeva and ilaevaandhamina [1958]. Even for so nearly ideal a medium as silica glass, the first motion arrives gradually, with a 'foot' which recedes toward shorter times as the amplification is increased. This is discussed in more detail below; the principal limitation on accuracy comes from this circumstance. The first motion is followed by a long train of disturbances which have not been much utilized in the present work. Hughes and others (1949 VELOCITY OF COMPRESSIONAL WAVES IN ROCKS 1085 WAVES IN ROCKS
Imaging above an extended-reach horizontal well using converted shear waves and a rig source
GEOPHYSICS, 2013
ABSTRACT We evaluated a method for using 3C vertical seismic profile data to image acoustic interfaces located between the surface source and a downhole receiver array. The approach was based on simple concepts adapted from whole-earth seismology, in which observed compressional and shear wavefields are traced back to a common origin. However, unlike whole-earth and passive seismology, in which physical sources are imaged, we used the observed compressional and shear wavefields to image secondary sources (scatterers) situated between the surface source and the downhole receiver array. The algorithm consisted of the following steps: first, estimating the receiver compressional wavefield; second, using polarization to estimating the shear wavefield; third, deconvolving the shear wavefield using estimates of the source wavelet obtained from the direct compressional wave; fourth, the compressional and shear wavefields were back projected into the volume between the source and receivers; where, finally, an imaging condition was applied. When applied to rig-source VSP data acquired in an extended-reach horizontal well, this process was demonstrated to give images of formation features in the overburden, consistent with surface-seismic images obtained from the same area.
Earth, Planets and Space, 2009
We analyzed temporal changes in the velocity and amplitude of P waves transmitted through a granite sample during a triaxial compression test, with the goal of monitoring the fault formation process associated with open and shear cracking. We used newly developed transducer assemblies for the broadband recording, and we continued to record transmitting waves even after the peak stress occurred. For transmitting P waves with paths parallel to the maximum compressive axis, we found that both the first wave amplitude and the velocity decreased after dilatancy started, and they kept decreasing even after the peak stress. In addition, the large nonlinear decrease in amplitude was associated with a rapid decrease in differential stress, whereas the rate of decrease in velocity remained almost constant. Thus, before the rapid decrease of differential stress, when both the amplitude and the velocity gradually decreased, open cracking was indicated to be dominant. Thereafter, shear cracking was indicated to become dominant in synchronization with the rapid decrease in differential stress. It is suggested that a main fault started to grow around the sample surface and then progressed into the sample interior; this corresponded to the rapid stress decrease. This fault acts as a strong scatterer for P waves that are parallel to the maximum compressive axis.
International Journal of Geophysics, 2012
As organized and intelligible displays of data, seismic images constitute invaluable tools for gaining and conveying information on structural and material properties of the Earth. The present special issue on “Seismic imaging” aims to explore basic and/or applied aspects of seismic data that are relevant to meet today's challenges in subsurface imaging. It comprises 13 articles, covering a wide variety of state-of-the-art topics on seismology and seismics, on both theoretical, and practical issues. ... H. Kern examines, in the form of a review, the interdependence of ...
2014
Near surface seismic imaging bears a high potential to enhance geotechnical site characterization.We highlight recent advances made in S-wave tomography for characterizing near surface unconsolidated sediments. This comprises progress in experimental setup and acquisition technology for local scale S-wave tomography. We discuss the development of mobile seismic crosshole tomography solely building on temporary installations realized by direct push technology as well as a modular borehole geophone chain suitable for operation in shallow and slim near surface boreholes. These technical developments are accompanied by progress in geophysical model generation, i.e., fully non-linear inversion strategies suitable for routine application and model uncertainty appraisal. We link S-wave and P-wave tomographic models to geotechnical target parameters and evaluate recent develop- ments made for high resolution ground-truthing using direct push technology for geotechnical and stratigraphic analyses. To be able to provide improved regional scale seismic properties we advanced the Rayleigh wave based imaging of S-wave velocity variations using diffusivewavefield theory for modeling the full microtremor H/V spectral ratio for receivers at the surface and in depth. full citation: Paasche, H., Rumpf, M., Lontsi, A., Hausmann, J., Hannemann, K., Fechner, T., Ohrnberger, M., Werban, U., Tronicke, J., Krüger, F., Dietrich, P., 2014. MuSaWa: Multi-Scale S-wave Tomography for Exploration and Risk Assessment of Development Sites. In: M. Weber, U. Münch (Eds.), Tomography of the Earth’s Crust: From Geophysical Sounding to Real-Time Monitoring. Advanced Technologies in Earth Sciences. Springer Int. Pub. 95-114.