Marine magnetotellurics for petroleum exploration, Part II: Numerical analysis of subsalt resolution

Geophysics ◽  
1998 ◽  
Vol 63 (3) ◽  
pp. 826-840 ◽  
Author(s):  
G. Michael Hoversten ◽  
H. Frank Morrison ◽  
Steven C. Constable
Keyword(s):  
Structural Information ◽  
Numerical Models ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Lateral Position ◽  
Petroleum Exploration ◽  
Vertical Position ◽  
Velocity Anisotropy ◽  
Position Errors ◽  
Marine Magnetotellurics

In areas where seismic imaging of the base of salt structures is difficult, seaborne electromagnetic techniques offer complementary as well as independent structural information. Numerical models of 2-D and 3-D salt structures demonstrate the capability of the marine magnetotelluric (MT) technique to map the base of the salt structures with an average depth accuracy of better than 10%. The mapping of the base of the salt with marine MT is virtually unaffected by internal variation within the salt. Three‐dimensional anticlinal structures with a horizontal aspect ratio greater than two can be interpreted adequately via two‐dimensional inversions. Marine MT can distinguish between salt structures which possess deep vertical roots and those which do not. One measure of the relative accuracy of MT and seismic methods can be made by considering the vertical and lateral position errors in the locations of interfaces caused by neglecting velocity anisotropy in migration. For the shallow part of the section where two‐way travel times are on the order of 1 s, the vertical and lateral position errors in the locations of salt‐sediment interfaces from 2-D MT inversion is more than twice the expected migration error in reflectors in transversely isotropic sediments, such as those in the Gulf of Mexico. Deeper in the section where two‐way times are on the order of 4 s, lateral position errors in migration become comparable to those of the MT inverse, whereas seismic vertical position errors remain more than a factor of two smaller than MT errors. This analysis shows that structural mapping accuracy would be improved using MT and seismic together.

On Constitutive Relations and Finite Deformations of Passive Cardiac Tissue: I. A Pseudostrain-Energy Function

1987 ◽  
Vol 109 (4) ◽  
pp. 298-304 ◽  
Author(s):  
J. D. Humphrey ◽  
F. C. P. Yin
Keyword(s):  
Energy Function ◽  
Cardiac Tissue ◽  
Functional Form ◽  
Structural Information ◽  
Constitutive Relations ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Limited Range ◽  
Material Parameters ◽  
Data Result

A three-dimensional constitutive relation for passive cardiac tissue is formulated in terms of a structurally motivated pseudostrain-energy function, W, while the mathematical simplicity of phenomenological approaches is preserved. A specific functional form of W is proposed on the basis of limited structural information and multiaxial experimental data. The material parameters are determined in a least-squared sense from both uniaxial and biaxial data. Our results suggest that (1) multiaxially-loaded cardiac tissue is nearly transversely-isotropic with respect to local muscle fiber directions, at least for a limited range of strain histories, (2) material parameters determined from uniaxial papillary muscle data result in gross underestimates of the stresses in multiaxially-loaded specimens, and (3) material parameters determined from equibiaxial tests predict the behavior of the tissue under various nonequibiaxial stretching protocols reasonably well.

scholarly journals Migration error in transversely isotropic media with linear velocity variation in depth

Geophysics ◽  
1993 ◽  
Vol 58 (10) ◽  
pp. 1454-1467 ◽  
Author(s):  
Ken L. Larner ◽  
Jack K. Cohen
Keyword(s):  
Transversely Isotropic ◽  
Lateral Position ◽  
Inhomogeneous Media ◽  
Velocity Variation ◽  
Position Errors ◽  
Time Migration ◽  
Reflection Time ◽  
Transversely Isotropic Media ◽  
Isotropic Media ◽  
Axis Of Symmetry

Given the sensitivity of imaging accuracy to the velocity used in migration, migration founded (as in practice) on the erroneous assumption that a medium is isotropic can be expected to be inaccurate for steep reflectors. Here, we estimate errors in interpreted reflection time and lateral position as a function of reflector dip for transversely isotropic models in which the axis of symmetry is vertical and the medium velocity varies linearly with depth. We limit consideration to media in which ratios of the various elastic moduli are independent of depth. Tests with reflector dips up to 120 degrees on a variety of anisotropic media show errors that are tens of wavelengths for dips beyond 90 degrees when the medium (unrealistically) is homogeneous. For a given anisotropy, the errors are smaller for inhomogeneous media; the larger the velocity gradient, the smaller the errors. For gradients that are representative of the subsurface, lateral‐position errors tend to be minor for dips less than about 60 degrees, growing to two to five wavelengths as dip passes beyond 90 degrees. These errors depend on reflector depth and average velocity to the reflector only through their ratio, i.e., migrated reflection time. Migration error, which is found to be unrelated to the ratio of horizontal to vertical velocity, is such that reflections with later migrated reflection times tend to be more severely overmigrated than are those with earlier times. Over a large range of dips, migration errors that arise when anisotropy is ignored but inhomogeneity is honored tend to be considerably smaller than those encountered when inhomogeneity is ignored in migrating data from isotropic, inhomogeneous media.

Mapping Complex Geological Surface Morphology During Landing Operations Using 3-D Inversion of Ultra-Deep Electromagnetic LWD Data

2021 ◽  
Author(s):  
Nigel Mark Clegg ◽  
Ana Beatriz Domingues ◽  
Rosamary Ameneiro Paredes ◽  
Nicki Gardner ◽  
Vanessa Mendoza Barrón ◽  
...  
Keyword(s):  
Surface Morphology ◽  
Real Time ◽  
Three Dimensional ◽  
Lateral Position ◽  
Geological Structure ◽  
High Resistivity ◽  
Vertical Position ◽  
Well Placement ◽  
Azimuthal Position ◽  
The Impact

Abstract Ultra-deep azimuthal electromagnetic (EM) logging-while-drilling (LWD) tools are frequently used during landing operations for early detection of the reservoir top. This enables alterations to the well plan before the reservoir is penetrated. To date, this approach has relied on one-dimensional (1-D) inversions that accounts only for changes in resistivity above or below the wellbore. When geology is complex, resulting in lateral changes in resistivity, 3-D inversion of EM data is required to provide increased reservoir understanding. This paper presents a case study from offshore Brazil, targeting a turbidite deposit. A complex reservoir surface was expected, as defined by seismic data for the area. Although top structure rugosity and lateral position uncertainty had been incorporated into the prognosis, the impact of surface topography on inversion results while landing was not anticipated. During real-time operations, 1-D EM inversion was used along with correlation of shallow LWD data to map the reservoir top. It was clear the geology was more complicated than depicted by the 2-D geological model constructed from the 1-D inversion and that lateral changes in surface morphology may be occurring. Post well a 3-D inversion of the EM data revealed the 3-D geological structure. During the initial approach, the 1-D inversion indicated that relief of the reservoir top was more exaggerated than expected; the well intersected a sharp peak prior to approaching the target zone. The misfit on the 1-D inversion indicated there was potential for lateral variation in resistivity, influencing the 1-D results; lateral changes can produce artefacts that obscure the subsurface structure. This was confirmed after drilling with analysis of ultra-deep azimuthal resistivity images, indicating significant changes in resistivity to the left and right of the borehole. A 3-D EM inversion was run to depict these complex subsurface geometries. The 1-D inversion results were better understood post-drill with the 3-D inversion results, which show a high point in the reservoir top to the side of the wellbore that was drilled past, but not penetrated by, the well. This high-resistivity zone had a negative effect on the 1-D inversion results and made delineation of the reservoir top difficult. Understanding lateral variations in formation and fluid boundaries can improve well placement and reservoir understanding. This knowledge can impact landing scenarios and well placement within the reservoir. Three-dimensional inversion of ultra-deep azimuthal EM LWD data in real time will provide a clearer picture of the position of resistivity changes while drilling. This will enable decisions to be made that affect the azimuthal position of a well, as well as its vertical position during drilling, thereby facilitating optimal well placement, even in complex geological environments or for infill wells requiring precise well placement.

Two-Dimensional Crystallization of Tetanus Toxin

1985 ◽  
Vol 43 ◽  
pp. 528-529
Author(s):  
Jeffry A. Reidler ◽  
John P. Robinson
Keyword(s):  
Electron Microscopy ◽  
Tetanus Toxin ◽  
Structural Information ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Membrane Interface ◽  
3D Reconstructions ◽  
Cellular Receptors ◽  
Computer Reconstruction ◽  
2D Crystals

We have prepared two-dimensional (2D) crystals of tetanus toxin using procedures developed by Uzgiris and Kornberg for the directed production of 2D crystals of monoclonal antibodies at an antigen-phospholipid monolayer interface. The tetanus toxin crystals were formed using a small mole fraction of the natural receptor, GT1, incorporated into phosphatidyl choline monolayers. The crystals formed at low concentration overnight. Two dimensional crystals of this type are particularly useful for structure determination using electron microscopy and computer image refinement. Three dimensional (3D) structural information can be derived from these crystals by computer reconstruction of photographs of toxin crystals taken at different tilt angles. Such 3D reconstructions may help elucidate the mechanism of entry of the enzymatic subunit of toxins into cells, particularly since these crystals form directly on a membrane interface at similar concentrations of ganglioside GT1 to the natural cellular receptors.

EMCAT: An automatic image-processing system for electron-microscopic tomography

1994 ◽  
Vol 52 ◽  
pp. 418-419
Author(s):  
Weiping Liu ◽  
John W. Sedat ◽  
David A. Agard
Keyword(s):  
Image Processing ◽  
Structural Information ◽  
Imaging Technique ◽  
Three Dimensional ◽  
Processing System ◽  
Electron Microscopic ◽  
Data Set ◽  
Ordered Structures ◽  
Automatic Image Processing ◽  
Em Tomography

Any real world object is three-dimensional. The principle of tomography, which reconstructs the 3-D structure of an object from its 2-D projections of different view angles has found application in many disciplines. Electron Microscopic (EM) tomography on non-ordered structures (e.g., subcellular structures in biology and non-crystalline structures in material science) has been exercised sporadically in the last twenty years or so. As vital as is the 3-D structural information and with no existing alternative 3-D imaging technique to compete in its high resolution range, the technique to date remains the kingdom of a brave few. Its tedious tasks have been preventing it from being a routine tool. One keyword in promoting its popularity is automation: The data collection has been automated in our lab, which can routinely yield a data set of over 100 projections in the matter of a few hours. Now the image processing part is also automated. Such automations finish the job easier, faster and better.

Pushing the Envelope

2018 ◽  
Author(s):  
Eaton E. Lattman ◽  
Thomas D. Grant ◽  
Edward H. Snell
Keyword(s):  
High Resolution ◽  
Electron Density ◽  
Structural Information ◽  
Hydration Shell ◽  
Three Dimensional ◽  
Scattering Data ◽  
Saxs Data ◽  
Electron Density Function ◽  
Angle Scattering ◽  
Iterative Structure

Direct electron density determination from SAXS data opens up new opportunities. The ability to model density at high resolution and the implicit direct estimation of solvent terms such as the hydration shell may enable high-resolution wide angle scattering data to be used to calculate density when combined with additional structural information. Other diffraction methods that do not measure three-dimensional intensities, such as fiber diffraction, may also be able to take advantage of iterative structure factor retrieval. While the ability to reconstruct electron density ab initio is a major breakthrough in the field of solution scattering, the potential of the technique has yet to be fully uncovered. Additional structural information from techniques such as crystallography, NMR, and electron microscopy and density modification procedures can now be integrated to perform advanced modeling of the electron density function at high resolution, pushing the boundaries of solution scattering further than ever before.

scholarly journals Experimental and Numerical Investigation of 3D Dam-Break Wave Propagation in an Enclosed Domain with Dry and Wet Bottom

2021 ◽  
Vol 11 (12) ◽  
pp. 5638
Author(s):  
Selahattin Kocaman ◽  
Stefania Evangelista ◽  
Hasan Guzel ◽  
Kaan Dal ◽  
Ada Yilmaz ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Dam Break ◽  
Dam Failure ◽  
Navier Stokes ◽  
Negative Wave ◽  
Through Flow ◽  
Instantaneous Removal ◽  
Surface Patterns

Dam-break flood waves represent a severe threat to people and properties located in downstream regions. Although dam failure has been among the main subjects investigated in academia, little effort has been made toward investigating wave propagation under the influence of tailwater depth. This work presents three-dimensional (3D) numerical simulations of laboratory experiments of dam-breaks with tailwater performed at the Laboratory of Hydraulics of Iskenderun Technical University, Turkey. The dam-break wave was generated by the instantaneous removal of a sluice gate positioned at the center of a transversal wall forming the reservoir. Specifically, in order to understand the influence of tailwater level on wave propagation, three tests were conducted under the conditions of dry and wet downstream bottom with two different tailwater depths, respectively. The present research analyzes the propagation of the positive and negative wave originated by the dam-break, as well as the wave reflection against the channel’s downstream closed boundary. Digital image processing was used to track water surface patterns, and ultrasonic sensors were positioned at five different locations along the channel in order to obtain water stage hydrographs. Laboratory measurements were compared against the numerical results obtained through FLOW-3D commercial software, solving the 3D Reynolds-Averaged Navier–Stokes (RANS) with the k-ε turbulence model for closure, and Shallow Water Equations (SWEs). The comparison achieved a reasonable agreement with both numerical models, although the RANS showed in general, as expected, a better performance.

Ice-Phase Precipitation

2017 ◽  
Vol 58 ◽  
pp. 6.1-6.36 ◽  
Author(s):  
I. Gultepe ◽  
A. J. Heymsfield ◽  
P. R. Field ◽  
D. Axisa
Keyword(s):  
Collection Efficiency ◽  
Numerical Models ◽  
Mass Density ◽  
Three Dimensional ◽  
Phase Precipitation ◽  
Microphysical Parameters ◽  
Mass Size ◽  
Ice Water ◽  
Ice Phase

AbstractIce-phase precipitation occurs at Earth’s surface and may include various types of pristine crystals, rimed crystals, freezing droplets, secondary crystals, aggregates, graupel, hail, or combinations of any of these. Formation of ice-phase precipitation is directly related to environmental and cloud meteorological parameters that include available moisture, temperature, and three-dimensional wind speed and turbulence, as well as processes related to nucleation, cooling rate, and microphysics. Cloud microphysical parameters in the numerical models are resolved based on various processes such as nucleation, mixing, collision and coalescence, accretion, riming, secondary ice particle generation, turbulence, and cooling processes. These processes are usually parameterized based on assumed particle size distributions and ice crystal microphysical parameters such as mass, size, and number and mass density. Microphysical algorithms in the numerical models are developed based on their need for applications. Observations of ice-phase precipitation are performed using in situ and remote sensing platforms, including radars and satellite-based systems. Because of the low density of snow particles with small ice water content, their measurements and predictions at the surface can include large uncertainties. Wind and turbulence affecting collection efficiency of the sensors, calibration issues, and sensitivity of ground-based in situ observations of snow are important challenges to assessing the snow precipitation. This chapter’s goals are to provide an overview for accurately measuring and predicting ice-phase precipitation. The processes within and below cloud that affect falling snow, as well as the known sources of error that affect understanding and prediction of these processes, are discussed.

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