1,721,057 research outputs found
Nonlinear Wave Mixing as a Function of Applied Load
No full textThis is a dataset for experiments that look at the change in arrival time of P- and S-waves (the probes) caused by the passage of a lower frequency, higher-amplitude wave (the PUMP). The experiments were done on 2 samples of Crab Orchard Sandstone at a number of applied loads. The load was applied using a hydraulic press
A field expansions method for scattering by periodic multilayered media
No full textThe interaction of acoustic and electromagnetic waves with periodic structures plays an important role
in a wide range of problems of scientific and technological interest. This contribution focuses upon the
robust and high-order numerical simulation of a model for the interaction of pressure waves generated
within the earth incident upon layers of sediment near the surface. Herein is described a Boundary
Perturbation Method for the numerical simulation of scattering returns from irregularly shaped periodic
layered media. The method requires only the discretization of the layer interfaces (so that the number of
unknowns is an order of magnitude smaller than Finite Difference and Finite Element simulations), while
it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic
of Boundary Integral/Element Methods. The approach is a generalization to multiple layers of Bruno &
Reitich's "Method of Field Expansions" for dielectric structures with two layers. By simply considering
the entire structure simultaneously, rather than solving in individual layers separately, the full field can
be recovered in time proportional to the number of interfaces. As with the original Field Expansions
method, this approach is extremely efficient and spectrally accurate.National Science Foundation (U.S.) (grant No. DMS–0810958)United States. Dept. of Energy (Award No. DE–SC0001549)Massachusetts Institute of Technology. Earth Resources Laborator
Interferometric imaging of multiples in an RTM approach
No full textIt is well known that reverse-time migration is capable of correctly
imaging multiply scattered energy. To do this, one of the interfaces
from which the waves scatter must be included in the background velocity
model. In a one-way framework this requirement is avoided
by iteratively forming images of higher-order scattered waves. These
techniques use an image made with singly scattered waves to estimate
the locations of some of the reflection points in a multiply-scattered
wave, from which the location of an additional scattering point is
determined through standard imaging techniques. This removes the
requirement that a single multiple-generating interface be identified.
Here we extend this technique to reverse-time migration using results
from several recent studies linking standard and extended imaging
conditions to interferometry. This results in a method to generate images
with multiply-scattered waves using the full-waveform imaging
techniques of reverse-time migration and the iterative imaging formulations
of scattering series in a one-way framework.Geo-Mathematical Imaging GroupTOTAL (Firm)Massachusetts Institute of Technology. Earth Resources Laborator
A boundary perturbation method for recovering interface shapes in layered media
No full textThe scattering of linear acoustic radiation by a periodic layered structure is a fundamental model in the geosciences as it closely approximates the propagation of pressure waves in the earth's crust. In this contribution, the authors describe new algorithms for (1) the forward problem of prescribing incident radiation and, given the known structure, determining the scattered field, and (2) the inverse problem of approximating the form of the structure given prescribed incident radiation and measured scattered data. Each of these algorithms is based upon a novel statement of the problem in terms of boundary integral operators (Dirichlet–Neumann operators), and a boundary perturbation algorithm (the method of operator expansions) for their evaluation. Detailed formulas and numerical simulations are presented to demonstrate the utility of these new approaches.National Science Foundation (U.S.) (DMS-0810958)United States. Dept. of Energy (award no DE-SC0001549)Massachusetts Institute of Technology. Earth Resources Laborator
Detecting medium changes from coda by interferometry
No full textIn many applications, sequestering CO[subscript 2] underground for example,
determining whether or not the medium has changed is
of primary importance, with secondary goals of locating and
quantifying that change. We consider an acoustic model of the
Earth as a sum of a smooth background velocity, isolated velocity
jumps and random small scale fluctuations. Although
the first two parts of the model can be determined precisely,
the random fluctuations are never known exactly and are thus
modeled as a realization of a random process with assumed
statistical properties. We exploit the so-called coda of multiply
scattered energy recorded in such models to monitor for
change and to localize and quantify that change, by examining
the shape and frequency content of correlations of the coda
produced by different parts in the medium. These ideas build
upon past work in time-reversal detection methods that have
often been limited to theoretical regimes in which the scales
of scattering and reflection are strictly separated. This results
in an application of time-reversal detection methods to non-theoretical
regimes in which the separation of scales is not
strictly satisfied, opening up the possibility, discussed here, of
using such techniques to monitor CO[subscript 2] sequestration sites for
leakage.Massachusetts Institute of Technology. Earth Resources Laborator
Recursive Imaging with Multiply-Scattered Waves Using Partial Image Regularization: A North Sea Case Study
No full textAs more resources are directed toward reverse-time migration an accurate velocity
model, including strong reflectors, is necessary to form a clear image of the subsurface.
This is of particular importance in the vicinity of salt, where singly-scattered waves are
often not ideal for imaging the salt flanks. This has led to interest in processing doubly-scattered
waves (also called duplex or prismatic waves) for imaging salt flanks and thus
improving the location of salt boundaries in a velocity model. We present a case study in
which we use doubly-scattered waves in a two-pass one-way method to image salt flanks
in a North Sea data set. By working in the one-way framework we are able to separately
construct images with singly, doubly, and triply scattered waves. We illustrate a multi-step
imaging process that includes multiply-scattered waves by using an imaged reflector to fix
one (or more) of the scattering points, allowing for multiply-scattered energy from several
reflectors, potentially with poor continuity, to be included without picking each reflector
individually. With this method we are able to image the flank of a North Sea salt body.Norwegian State Oil CompanyNorwegian Research CouncilGeo-Mathematical Imaging GroupTOTAL (Firm)Massachusetts Institute of Technology. Earth Resources Laborator
What moved where?: The impact of velocity uncertainty on microseismic location and moment-tensor inversion
Get PDFWith the rise of unconventional resources, microseismic monitoring is becoming increasingly important because of its cost-effectiveness. This has led to significant research activity on how best to locate events and characterize their moment tensors. Locations tell us where fracturing is occurring, allow the tracking of fluid movement, and fracture propagation. Moment tensors help to determine the type of failure occurring, which is beneficial in planning and interpreting the results of hydraulic-fracturing jobs and in monitoring production. The rising number of methods to determine parameters raises important questions about how uncertainties in the input parameters are translated into uncertainties in the final locations and moment tensors. We present a framework for assessing these uncertainties and use it to demonstrate how velocity uncertainty — as well as uncertainties in arrival times and amplitudes — translates into uncertainties on the recovered quantities of location and moment-tensor parameters
Tomographic errors from wavefront healing: more than just a fast bias
Get PDFWave front healing, in which diffractions interfere with directly travelling waves causing a reduction in recorded traveltime delays, has been postulated to cause a bias towards faster estimated earth models. This paper reviews the theory from the mathematical physics community that explains the properties of diffractions and applies it to a suite of increasingly complicated numerical examples. We focus in particular on the elastic case and on the differences between P and S healing. We find that rather than introducing a systemic fast bias, wave front healing gives a more complicated bias in the results of traveltime tomography, with fast anomalies even manifesting themselves as slow anomalies in some situations. Of particular interest, we find that a negative correlation between the bulk and shear or compressional velocities may result to a large extend from healing.Netherlands Organization for Scientific Research (NWO:VICI865.03.007
Time-lapse full-waveform inversion with ocean-bottom-cable data: Application on Valhall field
No full textKnowledge of changes in reservoir properties resulting from extracting hydrocarbons or injecting fluid is critical to future production planning. Full-waveform inversion (FWI) of time-lapse seismic data provides a quantitative approach to characterize the changes by taking the difference of the inverted baseline and monitor models. The baseline and monitor data sets can be inverted either independently or jointly. Time-lapse seismic data collected by ocean-bottom cables (OBCs) in the Valhall field in the North Sea are suitable for such time-lapse FWI practice because the acquisitions are of a long offset, and the surveys are well-repeated. We have applied independent and joint FWI schemes to two time-lapse Valhall OBC data sets, which were acquired 28 months apart. The joint FWI scheme is double-difference waveform inversion (DDWI), which inverts differenced data (the monitor survey subtracted by the baseline survey) for model changes. We have found that DDWI gave a cleaner and more easily interpreted image of the reservoir changes compared with that obtained with the independent FWI schemes. A synthetic example is used to demonstrate the advantage of DDWI in mitigating spurious estimates of property changes and to provide cross validations for the Valhall data results.Hess CorporationMassachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Consortium
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