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- X M Tang, C H Cheng, M N Toksoz
- 2012

Stoneley waves in permeable boreholes are diagnostic of formation permeability because their propagation is affected by the dynamic fluid flow at the borehole wall. We characterize this flow using the concept of dynamic permeability. We examined the applicability of the dynamic permeability to porous media by applying it to a single fracture case and found… (More)

- r B Beydoun, C H Cheng, M N Toksoz
- 2012

In Vertical Seismic Profiling surveys tube waves are generated by compressional waves impinging on subsurface fractures or permeable zones. The problem of generation of these waves by a non-normal incident P wave for an inclined borehole intersecting a tilted parallel wall fracture is formulated theoretically. The amplitude of tube waves depends on the… (More)

- Zhenya Zhu, C H Cheng, M N Toksoz
- 2012

Flexural waves generated by a dipole source have been studied theoretically and used to estimate the shear parameters of a formation. The basic principles and main properties of flexural waves propagating in a borehole are reviewed in this paper. A mono/dipole transducer made of a PZT piezoelectric tube is used for laboratory experiments in borehole models.… (More)

- K J Ellefsen, C H Cheng, M N Toksoz
- 2012

The effects of anisotropy upon elastic wave propagation along a fluid-filled cylindrical borehole are determined. The wave equation is solved in the frequency-wavenumber domain with a variational method, and the solution yields the phase velocities, group velocities, pressures, and displacements for the normal modes. These properties are studied for two… (More)

- C H Cheng
- 2012

A commonly used model for a transversely anisotropic crack rock is that by Hudson (1980, 1981). This model is based on a simplified analysis of a thin circular crack, with displacement and stress conditions specified on the boundary. These papers have a second order correction in addition to the first order term in porosity/crack density. In this paper we… (More)

- R A Stephen, F Pardo-Casas, C H Cheng
- 2012

Synthetic seismograms of elastic wave propagation in a fluid-filled borehole were generated using both the finite difference technique and the discrete wavenumber summation technique. The latter is known to be accurate for both body and surface (gUided) waves. The finite difference grid has absorbing boundaries on two sides and axes of symmetry on the… (More)

There are many potential medical applications in which it is desirable to noninvasively induce electric fields. One such application that serves as the backdrop of this work is that of stimulating neurons in the brain. The magnetic fields necessary must be quite high in magnitude, and fluctuate rapidly in time to induce the internal electric fields… (More)

- K J Ellefsen, C H Cheng, K M Tubman
- 2012

Phase velocity and attenuation of guided waves have been estimated from acoustic logging data recorded by a receiving array. The method uses data from multiple sources and successive depths yielding more accurate estimates than could be obtained with data from one source and one depth. The inversion requires two steps: (1) all traces are transformed into… (More)

- C H Cheng, Y Nan Toksoz
- 2012

Direct determination of formation shear wave travel time is impossible in "slow" formations where the shear wave velocity is lower than the borehole fluid (mud) velocity. However, the Stoneley waves in these formations are very sensitive to changes in formation shear wave properties and can be used to indirectly determine the formation shear velocity, In… (More)