Experimental Verification of Acoustic Waveform and VSP Seismic Tube Wave Measurements of Fracture Permeability

A variety of established and experimental geophysical techniques was used to measure the vertical distribution of fracture permeability in a 229-meter deep borehole penetrating schist and quartz monzonite near Mirror Lake, New Hampshire. The distribution of fractures in the borehole was determined by acoustic borehole televiewer and other geophysical logs. Fracture permeability was estimated by application of two experimental methods: (1) Analysis of tube-wave-amplitude attenuation in acoustic full-waveform logs; and (2) interpretation of tube waves generated in vertical seismic profiles. Independent information on fracture permeability was obtained by means of packer-isolation flow tests and flowmeter measurement of vertical velocity distributions during pumping in the same borehole. Both experimental methods and packer-isolation-flow tests and flowmeter data indicated a single, near horizontal zone of permeability intersecting the borehole at a depth of about 45 meters. Smaller values of transmissivity were indicated for other fractures at deeper depths, with details of fracture response related to the apparent volume of rock represented by the individual measurements. Tube-wave amplitude attenuation in full-waveform acoustic logs, packer-isolation flow tests, and flowmeter measurements during pumping indicated transmissivity values for the upper permeability zone within the range of 0.6 to 10.0 centimeters squared per second. Vertical seismic-profile data indicated a relative distribution of fracture permeability in agreement with the other methods; however, the calculated values of transmissivity appeared to be too small. This disagreement is attributed to oversimplification of the model for fracture-zone compressibility used in the analysis of vertical seismic-profile data

Acoustic Waveform Logging - Advances In Theory And Application

Full-waveform acoustic logging has made significant advances in both theory and application in recent years, and these advances have greatly increased the capability of log analysts to measure the physical properties of formations. Advances in theory provide the analytical tools required to understand the properties of measured seismic waves, and to relate those properties to such quantities as shear and compressional velocity and attenuation, and primary and fracture porosity and permeability of potential reservoir rocks. The theory demonstrates that all parts of recorded waveforms are related to various modes of propagation, even in the case of dipole and quadrupole source logging. However, the theory also indicates that these mode properties can be used to design velocity and attenuation picking schemes, and shows how source frequency spectra can be selected to optimize results in specific applications. Synthetic microseismogram computations are an effective tool in waveform interpretation theory; they demonstrate how shear arrival picks and mode attenuation can be used to compute shear velocity and intrinsic attenuation, and formation permeability for monopole, dipole and quadrupole sources. Array processing of multi-receiver data offers the opportunity to apply even more sophisticated analysis techniques. Synthetic microseismogram data is used to illustrate the application of the maximum-likelihood method, semblance cross-correlation, and Prony's method analysis techniques to determine seismic velocities and attenuations. The interpretation of acoustic waveform logs is illustrated by reviews of various practical applications, including synthetic seismogram generation, lithology determination, estimation of geomechanical properties in situ, permeability estimation, and design of hydraulic fracture operations

Theoretical Models Relating Acoustic Tube-Wave Attenuation To Fracture Permeability - Reconciling Model Results With Field Data

Several recent investigations indicate that tube-wave amplitude attenuation in acoustic full-waveform logs is correlated with permeability in fractured rocks. However, there are significant differences between predictions based on theoretical models for tubewave propagation and experimental waveform amplitude data. This investigation reviews the results of existing theoretical models for tube-wave attenuation in fractured rock and compares model predictions with acoustic full-waveform data where extensive independent fracture-permeability data are available from straddle-packer permeability tests. None of the tube-wave models presented in the literature predicts attenuation at fracture apertures as small as those producing attenuation in the field; and most models predict tube-wave reflections, which are rarely measured at frequencies greater then 5 kHz. Even the unrealistic assumption that all of the tube-wave energy loss is caused by viscous dissipation in fracture openings does not result in predicted apertures being as small as those indicated by packer permeability measurements in most situations. On the basis of these results, it is concluded that plane-fracture models cannot account for the measured tube-wave attenuation where natural fractures intersect fluidfilled boreholes. However, natural fractures are fundamentally different from plane parallel passages. This difference appears to explain the small equivalent flow apertures and lack of reflections associated with fractures in waveform-log data. Permeable fracture openings modeled as irregular tubes embedded between asperities along the fracture face are predicted to produce significant tube-wave attenuation when tube diameters exceed 1.0 cm, but arrays of such tubes conduct fluid flow equivalent to that through plane fractures less than 2 mm in effective flow aperture. Although the theory predicts some reflection from simple cylindrical passages, scattering from irregular distributions of natural fracture openings probably accounts for the infrequency with which coherent tube-wave reflections occur in field data.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636

Phonon Linewidths and Electron Phonon Coupling in Nanotubes

We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G- peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G- linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G- peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G+ and G- peaks to TO (tangential) and LO (axial) modes.Comment: 5 pages, 4 figures (correction in label of fig 3

Modeling Borehole Stoneley Wave Propagation Across Permeable In-Situ Fractures

The characterization of hydraulic transmissivity of permeable fracture reservoirs is a very important task in the exploration of water resources and hydrocarbons. Previous studies that model the permeable structure as a single fluid-filled fracture failed to explain the observed significant Stoneley wave attenuation across the permeable structure. In this paper, the structure is modeled as a permeable fracture zone and synthetic Stoneley wave seismograms in the vicinity of the structure are calculated. The results show that Stoneley waves can be strongly attenuated or even eliminated without significant reflection, because of the dissipation of wave energy into the permeable zone. Several field cases are also modeled and the theoretical results are compared with the field data. It is shown that low- and medium-frequency Stoneley waves (1 kHz data from Moodus, Conneticut, and 5 kHz data from Monitoba, Canada) are very sensitive to the permeability of the fractures and can be used to assess permeability from in-situ logging data, if the fracture porosity and zone thickness can be measured. At high frequencies, however, Stoneley waves are not very sensitive to permeability but are mainly affected by the sum of the fracture openings expressed as the product of fracture zone thickness and porosity in the fracture zone. This finding is demonstrated by a logging data set (Monitoba, Canada) obtained using high-frequency Stoneley waves at 34 kHz.United States. Dept. of Energy (Grant DE-FG0286ER13636)Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu

Raman-modes of index-identified free-standing single-walled carbon nanotubes

Using electron diffraction on free-standing single-walled carbon nanotubes we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3nm. On the same free-standing tubes we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7nm) these measurements confirm previously established radial breathing mode frequency versus diameter relations, and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.Comment: 4 pages, 4 figures, +additional materials (select PostScript to obtain it

Laboratory Studies Of The Acoustic Properties Of Samples From The Salton Sea Scientific Drilling Project And Their Relation To Microstructure And Field Measurements

Compressional and shear wave velocities were measured at confining pressures up to 200 MPa for twelve core samples from the depth interval of 600 to 2600 m in the California State 2-14 borehole. Samples were selected to represent the various lithologies, including clean, heavily cemented sandstones, altered, impermeable claystones, and several intermediate siltstones. Velocities measured at ultrasonic frequencies in the laboratory correspond closely with velocities determined from acoustic waveform logs and vertical seismic profiles. The samples exhibit P-wave velocities around 3.5 km/sec at depths above 1250 m, but increase to nearly 5.0 km/sec at 1300 m in depth. Further increases with depth result in compressional wave velocity increasing to nearly 6.0 km/sec. These increases in velocities are related to systematic variations in lithology, microstructure and hydrothermal alteration of originally clay-rich sediments. Scanning electron microscope observations of core samples confirm that local core velocities are determined by the combined effects of pore size distributions, and the proportion of clays and alteration minerals such as epidote present in the form of pore fillings and veins.United States. Dept. of the Interior. Geological Survey (Grant 14-08-001A-0328)Elf-Aquitaine (Postdoctoral Fellowship

Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure

Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added - water, hexane, sulphuric acid - and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris