Rock Static Moduli From Borehole Sonic Data in Stress-Dependent Formations.

This article describes a novel technique to estimate static Young's modulus of stress-sensitive rocks using dynamic linear and nonlinear constants estimated from borehole sonic data. Two linear and three nonlinear constants are estimated from the transit time of compressional headwaves and inversion of borehole-guided Stoneley and crossdipole dispersions in tectonically stressed formations. A major advantage of this technique is that the rock static Young's modulus is determined from the dynamic elastic constants measured at a chosen reference state that is rather close to the in situ conditions.

Radial Profiles of Formation Mass Density, Bulk and Shear Moduli From Borehole Flexural and Stoneley Dispersions.

Exploration wells are liquid-filled boreholes drilled into formations with different geophysical and petrophysical properties. These boreholes support axisymmetric, flexural, and quadrupole family of guided modes that can probe radially varying formation properties at different frequencies. Radially varying formation properties are caused by drilling-induced fractures or near-wellbore stress concentrations.

Stress- and temperature-compensated orientations for thickness-shear langasite resonators for high-temperature and high-pressure environment.

This paper describes an exhaustive study of the variations of the mean force sensitivity coefficients in the entire region of crystalline langasite (LGS). We also study the variation of temperature coefficients in the entire region of the crystalline LGS and its isomorphs. The computational results have been obtained from a procedure that has been successfully employed in the study of the planar and temperature stressinduced frequency shifts in thickness-mode resonators.

Applications of piezoelectric materials in oilfield services.

Piezoelectric materials are used in many applications in the oilfield services industry. Four illustrative examples are given in this paper: marine seismic survey, precision pressure measurement, sonic logging-while-drilling, and ultrasonic bore-hole imaging. In marine seismics, piezoelectric hydrophones are deployed on a massive scale in a relatively benign environment.

Analysis of noncircular fluid-filled boreholes in elastic formations using a perturbation model.

This paper presents a perturbation model to obtain flexural mode dispersions of noncircular fluid-filled boreholes in homogeneous elastic formations. The perturbation model is based on Hamilton's principle with a modified procedure for the reference state selection in order to handle the directional sensitivity of the flexural modes. The accuracy of the perturbation model has been confirmed by comparison to boundary integral solutions.

Inversion of guided-wave dispersion data with application to borehole acoustics.

The problem of inferring unknown geometry and material parameters of a waveguide model from noisy samples of the associated modal dispersion curves is considered. In a significant reduction of the complexity of a common inversion methodology, the inner of two nested iterations is eliminated: The approach described does not employ explicit fitting of the data to computed dispersion curves. Instead, the unknown parameters are adjusted to minimize a cost function derived directly from the determinant of the boundary condition system matrix.