Sonic Data Research Articles

Improvements in Modeling 90-degree Bleed Holes for Supersonic Inlets

The modeling of porous bleed regions as boundary conditions in computational fluid dynamics (CFD) simulations of supersonic inlet flows has been improved through a scaling of sonic flow coefficient data for 90deg bleed holes. The scaling removed the Mach number as a factor in computing the sonic flow coefficient and allowed the data to be fitted with a quadratic equation, with the only factor being the ratio of the plenum static pressure to the surface static pressure. The implementation of the bleed model into the Wind-US CFD flow solver was simplified by no longer requiring the evaluation of the flow properties at the boundary-layer edge. The quadratic equation can be extrapolated to allow the modeling of small amounts of blowing, which can exist when recirculation of the bleed flow occurs within the bleed region. The improved accuracy of the bleed model was demonstrated through CFD simulations of bleed regions on a flat plate in supersonic flow with and without an impinging oblique shock. The bleed model demonstrated good agreement with experimental data and three-dimensional CFD simulations of bleed holes.

Precise inversion of logged slownesses for elastic parameters in a gas shale formation

Dipole sonic log data recorded in a vertical pilot well and the associated production well are analyzed over a [Formula: see text]-ft section of a North American gas shale formation. The combination of these two wells enables angular sampling in the vertical direction and over a range of inclination angles from 54° to 90°. Dipole sonic logs from these wells show that the formation’s average properties are, to a very good approximation, explained by a transversely isotropic medium with a vertical symmetry axis and with elastic parameters satisfying [Formula: see text], but inconsistent with the additional ANNIE relation ([Formula: see text]). More importantly, these data clearly show that, at least for fast anisotropic formations such as this gas shale, sonic logs measure group slownesses for propagation with the group angle equal to the borehole inclination angle. Conversely, the data are inconsistent with an interpretation that they measure phase slownesses for propagation with the phase angle equal to the borehole inclination angle.

Estimation of horizontal stress magnitudes and stress coefficients of velocities using borehole sonic data

We described a nondestructive method to estimate the maximum and minimum horizontal stresses and formation nonlinear elastic constants using sonic data from a vertical wellbore. This method for the estimation of horizontal stress magnitudes consists of using radial profiles of the three shear moduli obtained from the Stoneley and cross-dipole sonic data in a vertical wellbore. These shear moduli change as a function of formation stresses, which in turn change as a function of the radial position away from the wellbore. Two difference equations were constructed from the three far-field shear moduli and the other two were constructed from differences in the shear moduli at radial positions with different stresses in the presence of near-wellbore stress concentrations. Outputs from this inversion algorithm included the maximum and minimum horizontal stress magnitudes, and two rock nonlinear constants referred to a local hydrostatically loaded reference state. The underlying acoustoelastic theory behind this inversion algorithm assumes that differences in the three shear moduli are caused by differences in the formation principal stresses. Additionally, the orientation of the maximum horizontal stress direction was identified from the fast-shear azimuth in the presence of a dipole dispersion crossover. Hence, the principal horizontal stress state was fully determined. Good agreement was obtained between the predicted minimum horizontal stress magnitude and that measured from an extended leak-off test in a vertical offshore wellbore in Malaysia. One of the nonlinear constants was obtained from differences between compressional velocity at two depths caused by differences in the overburden stress and the maximum and minimum horizontal stresses. Estimates were obtained for the stress coefficients of the compressional, fast-shear, and slow-shear velocities referred to a local reference state. These stress coefficients of velocities helped in the interpretation of observed time-lapse changes in seismic traveltimes caused by fluid saturation and reservoir stress changes.

A theoretical study on formation shear radial profiling in well-bonded cased boreholes using sonic dispersion data based on a parameterized perturbation model

Interpretation of sonic data can be challenging in the presence of a steel casing that has a strong influence on elastic waves propagating along a borehole. The cement annulus behind the casing together with drilling-induced near-wellbore alteration causes radial heterogeneity in the propagating medium. It is necessary to study the influence of such heterogeneities on borehole waves and estimate the radial extent of near-wellbore alteration in terms of radial variation of velocities away from the casing. To this end, we based our study on the model of a fluid-filled well-bonded cased borehole surrounded by a cylindrically layered formation. The formation is isotropic and purely elastic, and can be either fast or slow. Borehole monopole and dipole dispersions for this kind of model can be obtained from a root finding mode-search routine. A modified perturbation model based on Hamilton’s principle is used to predict changes in borehole dispersions caused by formation heterogeneities. A two-layer formation model as the reference state is introduced, which always provides normal dispersive reference dispersion for calculations of perturbation integrals for fast and slow formations. Radial variations of the formation shear velocity can be expressed in terms of a parametric exponential profile. Consequently, estimation of these parameters in the assumed profile yields the radial variation of the formation shear slowness away from the casing. Numerical results using synthetic examples are presented to demonstrate the validity of this radial profiling methodology.

Static and dynamic effective stress coefficient of chalk

Deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it. The effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction (effective stress coefficient) of the pore pressure. The effective stress coefficient is thus relevant for studying reservoir deformation and for evaluating 4D seismic for the correct pore pressure prediction. The static effective stress coefficient [Formula: see text] is estimated from mechanical tests and is highly relevant for effective stress prediction because it is directly related to mechanical strain in the elastic stress regime. The corresponding dynamic effective stress coefficient [Formula: see text] is easy to estimate from density and velocity of acoustic (elastic) waves. We studied [Formula: see text] and [Formula: see text] of chalk from the reservoir zone of the Valhall field, North Sea, and found that [Formula: see text] and [Formula: see text] vary with differential stress (overburden stress-pore pressure). For Valhall reservoir chalk with 40% porosity, [Formula: see text] ranges between 0.98 and 0.85 and decreases by 10% if the differential stress is increased by 25 MPa. In contrast, for chalk with 15% porosity from the same reservoir, [Formula: see text] ranges between 0.85 and 0.70 and decreases by 5% due to a similar increase in differential stress. Our data indicate that [Formula: see text] measured from sonic velocity data falls in the same range as for [Formula: see text], and that [Formula: see text] is always below unity. Stress-dependent behavior of [Formula: see text] is similar (decrease with increasing differential stress) to that of [Formula: see text] during elastic deformation caused by pore pressure buildup, for example, during waterflooding. By contrast, during the increase in differential stress, as in the case of pore pressure depletion due to production, [Formula: see text] increases with stress while [Formula: see text] decreases.

Does the Viscosity Exponent Derive from Ultrasonic Attenuation Spectra?

Based on a representation of the sound velocity of critical liquids in terms of a frequency-dependent complex specific heat at constant pressure, a simple relation between the low-frequency normalized sonic attenuation coefficient and the correlation length of fluctuations is derived. This relation provides a promising alternative for the determination of the dynamics exponent and thus the critical exponent of the shear viscosity. Sonic attenuation data from the literature, measured at frequencies down to 50 kHz, are re-evaluated with a view of the viscosity exponent determination. It is found that only in a small temperature range, the major requirement of the approach is fulfilled with the available data. Close to the critical temperature, the frequencies of measurement are still insufficiently small as compared to the inverse relaxation time of order parameter fluctuations. Criteria for future experiments are discussed briefly.

Historical population structure of White Sturgeon in the Upper Columbia River detected with combined analysis of capture, telemetry and genetics

Summary A combined analysis of capture/recapture, sonic tracking, and genetics was carried out to examine population structure of White Sturgeon of the Kootenay and Upper Columbia rivers. Analysis of capture/recapture and sonic telemetry data identified spatial patterns in habitat use, with individuals showing a preference for one of four high-use zones. Mitochondrial DNA analysis of groups of fish defined by zonal preference and age suggests there is genetic population structure across this region, even between groups frequenting different zones in the contiguous river system. This population structure likely has its origin in patterns of habitat use established prior to the impacts of human development when White Sturgeon in the region existed as assemblage of semi-reproductively isolated populations. Identification of this historical population structure reveals unrecognized complexity regarding the spatial extent of historic habitat use and breeding structure of White Sturgeon in the region, which must be considered in further research and recovery efforts.

Geostatistical traveltime tomography in elliptically anisotropic media

ABSTRACTIn geological materials, anisotropy may arise due to different mechanisms and can be found at different scales. Neglecting anisotropy in traveltime tomographic reconstruction leads to artefacts that can obscure important subsurface features. In this paper, a geostatistical tomography algorithm to invert cross‐hole traveltime data in elliptically anisotropic media is presented. The advantages of geostatistical tomography are that the solution is regularized by the covariance of the model parameters, that known model parameters can be used as constraints and fitted exactly or within a prescribed variance and that stochastic simulations can be performed to appraise the variability of the solution space. The benefits of the algorithm to image anisotropic media are illustrated by two examples using synthetic georadar data and real seismic data. The first example confirms suspected electromagnetic anisotropy in the vadose zone caused by relatively rapid water content variations with respect to wavelength at georadar frequencies. The second presents how sonic log data can be used to constrain the inversion of cross‐well seismic data and how geostatistical simulations can be used to infer parameter uncertainty. Results of both examples show that considering anisotropy yields a better fit to the data at high ray angles and reduces reconstruction artefacts.

Elastic anisotropy in the Haynesville Shale from dipole sonic data

Worldwide interest in shales as hydrocarbon resources has increased in recent years, driven mostly by the successful develop- ment of gas shales in North America. One of these gas shale plays is the Haynesville Shale located in Texas and Louisiana. In this paper we analyse dipole sonic log data acquired over the build section of a deviated well and show how these data can be used to estimate the elastic anisotropy of the formation. In this case the formation is relatively homogeneous over the build section and so the deviated well allows the sampling of well deviations from approximately 50° to horizontal. Using the compressional, fast-shear, and slow-shear data as a function of the well deviation angle, we estimated the anisotropy for the gas shale. These anisotropy estimates were then used to remove the anisotropy effects observed in the deviated well. Comparison of these 'corrected' sonic logs to sonic logs acquired in the vertical pilot well shows good agreement.

Frequency-dependent velocity prediction theory with implication for better reservoir fluid prediction

A series of experiments have shown that the elastic wave velocities and attenuation are dependent on frequency (Jones, 1986; Sams et al., 1997; Batzle et al., 2006). Velocity dispersion and attenuation may make it difficult to match different frequency bands of geophysical data such as surface seismic and VSP (∼5 to 300 Hz), sonic log (1 kHz to 20 kHz), and ultrasonic core survey (>[Formula: see text] Hz). For example, sonic log data are often used to constrain seismic inversion on the assumption that log velocity equals to seismic velocity at well locations. However, these two sets of velocities are different due to the effect of velocity dispersion, especially in reservoirs. Therefore, if we could develop a proper frequency-dependent rock physics model to correct the data at the sonic frequency band to that at the seismic frequency band, it would be useful for the solution to the data-matching problem.

Lasers get groovy

Laser turntables make light work of playing gramophone records without the need for scratchy styli, and claim to beam into hidden areas of sonic data, reports James Hayes. Audio digital recovery and restoration technologies have, in recent years, attracted interest from music labels keen to tap into the commercial opportunities of releasing archive recordings for a new generation of consumers. At the same time sound preservationists and recording engineers are intrigued by new ways to 'release' sounds locked into old-fashioned recording media. In recent decades the necessity to preserve historic archive recordings for national cultural history has become a matter of great importance whether they be records of statesmen making historically-important broadcasts or legendary poets reading their own work, shellac, like silver nitrate film stock, is a fragile base medium. Moreover, aged recordings have been damaged by mishandling and over-play down the years.

High-Resolution Fibre-Optic Temperature Sensing: A New Tool to Study the Two-Dimensional Structure of Atmospheric Surface-Layer Flow

We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal structure of the surface layer at high resolution (0.25 m, ≈0.5 Hz). Air temperature observations obtained from a vertically-oriented fibre-optics array of approximate dimensions 8 m × 8 m and sonic anemometer data from two levels were collected over a short grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric stability, and to analyze the space–time dynamics of transient cold-air pools in the calm boundary layer. The time response and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity variance and the Brunt–Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange.

Estimation of formation shear and borehole-fluid slownesses using sonic dispersion data in well-bonded cased boreholes

New inversion algorithms have been developed for estimating the formation shear and borehole-fluid slownesses, using either the borehole Stoneley or dipole flexural dispersion in well-bonded cased boreholes surrounded by a fast or slow isotropic and purely elastic formation. Two inversion algorithms have been developed for each type of formation. The first algorithm inverts either the measured borehole Stoneley or flexural dispersion at select frequencies for the formation shear slowness when all other model parameters are known. The second algorithm inverts either the borehole Stoneley or flexural dispersion for both the formation shear and borehole-fluid compressional slownesses. Optimal bandwidths for the inversion of the Stoneley and dipole flexural dispersions for the formation shear slowness range from about 5 to 8 kHz. The well-bonded cased borehole dispersion sensitivity to formation shear slowness becomes larger at these higher frequencies than in an open-hole. Moreover, the Stoneley dispersion sensitivity to the borehole-fluid compressional slowness is so large that it becomes necessary to input an extremely accurate estimate of fluid compressional slowness in the inversion algorithm. Inverted formation shear slowness from the Stoneley data in a fast formation exhibits an uncertainty of about 3%, whereas the input borehole-fluid slowness has an uncertainty of 0.5%. Given a certain amount of uncertainty in the borehole-fluid slowness, one can then estimate possible variances in the inverted formation shear slowness. In contrast, inversion of the flexural dispersion for formation shear slowness is less sensitive to the input borehole-fluid compressional slowness in the preferred frequency band of 5 to 8 kHz. Inverted formation shear slownesses in slow formations that use either the Stoneley or flexural dispersion are also far less sensitive to uncertainties in the borehole-fluid compressional slowness.

P-wave and S-wave velocity structure of northern Cascadia margin gas hydrates

SUMMARY Single-channel seismic and wide-angle reflection data collected in September 2005 were analysed along a 2-D profile of 10 ocean bottom seismometers (OBSs) on the continental slope region off Vancouver Island, near ODP Site 889 and IODP Site U1327. The objectives were to determine the shallow P-wave and S-wave velocity structure associated with marine gas hydrates and to estimate the hydrate concentration and distribution in the sediment pore space. Combined traveltime inversion of single-channel and OBS data produced a P-wave velocity model down to the depth of the bottom-simulating reflector (BSR) at 230(±5) m below the seafloor (mbsf). Mean velocities, which increased from 1.50 km s−1 at the seafloor to 1.88 km s−1 at the BSR, are in good agreement with the sonic log data from Sites 889 and U1327. The increase in P-wave velocity of the hydrate-bearing sediments relative to a background no-hydrate velocity was utilized to estimate the hydrate concentration by using effective medium theory. An average concentration of 13 per cent in the interval from 120–230 mbsf was estimated from the P-wave velocity model. Lateral continuity of the model data confirms that these average hydrate concentrations are also found around the drillsites out to distances of a few kilometres. Forward modelling of S-waves was carried out using the data from the OBS horizontal components. Above the BSR, S-wave velocities are higher than a background velocity profile based on a rock physics model and on global averages for unconsolidated sediments. This increase in velocity suggests that the hydrate is distributed as part of the load-bearing matrix to increase the rigidity of the sediment.

Estimating Sand–Shale Formation Pore Pressure

This article presents a comprehensive evaluation method of estimating sand–shale formation pore pressure by using sonic velocity and other logging data. The method takes the influence of porosity, density, shale content, effective stress, and some other physical properties of sand–shale formation on sonic velocity into account. The influence and related logging data are combined to estimate the effective stress, and then pore pressure can be obtained by the effective stress principle. Using this method, software was developed and it applied in the well site. Its applications indicate that this method can accurately estimate the abnormal pressure of a sand–shale formation.

Atmospheric stability and turbulence fluxes at Horns Rev—an intercomparison of sonic, bulk and WRF model data

ABSTRACTDirect estimations of turbulent fluxes and atmospheric stability were performed from a sonic anemometer at 50 m height on a meteorological mast at the Horns Rev wind farm in the North Sea. The stability and flux estimations from the sonic measurements are compared with bulk results from a cup anemometer at 15 m height and potential temperature differences between the water and the air above. Surface flux estimations from the advanced weather research and forecast (WRF) model are also validated against the sonic and bulk data. The correlation between the sonic and bulk estimates of friction velocity is high and the highest among all velocity comparisons. From the sonic–bulk–WRF inter‐comparison, it is found that the atmospheric stability measures at the sonic height tend to be closer to the neutral value than the WRF and bulk estimates, which are performed within an air layer closer to the surface, not only from a systematic bulk and WRF under‐prediction of the friction velocity when compared with the sonic value but also because of the lower magnitude of the sonic heat flux compared with that from the WRF simulations. Although they are not measured but parameterized or estimated, the bulk–WRF comparisons of friction velocity and 10 m wind speed show good agreement. It is also shown that on a long‐term basis, the WRF and bulk estimates of stability are nearly equal and that a correction towards a slightly stable atmospheric condition has to be applied to the long‐term wind profile at Horns Rev and at other locations over the North Sea, the correction being larger for points close to the coast. Copyright © 2011 John Wiley & Sons, Ltd.

Multiparameter joint tomography for TTI model building

Model building for tilted transversely isotropic media has commonly been performed by a single parameter tomography that updates the velocity in the symmetry direction, while the orientation of the symmetry axis and Thomsen parameters [Formula: see text] and [Formula: see text] are typically estimated from the migration stack and well data. Unfortunately, well data are often not available. In addition, when they are available, their lateral sampling is typically very sparse and their vertical sampling usually spans only a limited range of depths. In order to obtain spatially varying anisotropic models, with or without well data, we developed a multiparameter joint tomographic approach that simultaneously inverts for the velocity in the symmetry axis direction, [Formula: see text] and [Formula: see text]. We derived a set of reflection tomography equations for slowness in the symmetry axis direction and Thomsen parameters [Formula: see text] and [Formula: see text]. In order to address the nonuniqueness of the tomography, we developed a regularization strategy that uses an independent regularization operator and regularization factor for each individual anisotropy parameter. Synthetic tests found that ambiguity exists between the anisotropy parameters and that velocity has a better resolution than [Formula: see text] and [Formula: see text]. They also confirmed that joint tomography provides a better data fit than single parameter tomography. The field example was used to test a way to incorporate the sonic data in the model building process and limit the tomographic updates on certain anisotropy parameters by adjusting the regularization.

Estimation of azimuthal anisotropy from VSP data using multicomponent S-wave velocity analysis

Observation of azimuthal shear wave anisotropy can be useful for characterization of fractures or stress fields. Shear wave anisotropy is often estimated by measuring splitting of individual shear wave events in vertical seismic profile (VSP) data. However, this method may become unreliable for zero-offset (marine) VSP where the seismogram often contains no strong individual shear events, such as direct downgoing shear wave, but often contains many low-amplitude PS mode converted waves. We have developed a new approach for estimation of the fast and slow shear wave velocities and orientation of polarization planes based on the multicomponent linear traveltime moveout velocity analysis. This technique is applicable to zero-offset VSP data, and should take advantage of the presence of a large number of shear wave events with the same apparent velocity (which, for a horizontally layered medium, should be close to the interval velocity). The approach assumes that the VSP data are acquired in a vertical well drilled in an orthorhombic medium with a horizontal symmetry plane (including horizontal transverse isotropy). The main idea is to estimate the dominant apparent velocity for a given polarization direction by measuring the coherency of the seismic signal of a large number of events as a function of the apparent velocity. The algorithm was tested on marine three-component (3C) VSP acquired in the North West Shelf of Australia, and on land 3C VSP acquired with different sources in the same borehole located in Otway Basin, Victoria. These tests show good agreement between anisotropy parameters (magnitude and orientation) derived from the VSP and cross-dipole sonic log data.

Integrated seismic analysis of the Chalk Group in eastern Denmark—Implications for estimates of maximum palaeo-burial in southwest Scandinavia

The origin of the topography of southwest Scandinavia is subject to discussion. Analysis of borehole seismic velocity has formed the basis for interpretation of several hundred metres of Neogene uplift in parts of Denmark. Here, refraction seismic data constrain a 7.5 km long P-wave velocity model of the Chalk Group below the Stevns peninsula, eastern part of the Danish Basin. The model contains four layers in the ~ 860 m thick Chalk Group with mean velocities of 2.2 km/s, 2.4 km/s, 3.1 km/s, and 3.9–4.3 km/s. Sonic and gamma wireline log data from two cored boreholes represent the upper ~ 450 m of the Chalk Group. The sonic velocities are consistent with the overall seismic layering, although they show additional fine-scale layering. Integration of gamma and sonic log with porosity data shows that seismic velocity is sensitive to clay content. In intervals near boundaries of the refraction model, moderate increases in clay content correlate with reduction of porosity and increase in velocity. Higher clay contents do not further increase velocity. The reduction of porosity and increase in velocity are interpreted as clay causing increased pressure dissolution and cementation. The interpreted velocities are systematically higher than values of a chalk velocity curve determined in previous studies, and it is estimated that a significant part of the velocity anomaly may be explained by the presence of clay. The remaining velocity anomaly can be explained by 450–500 m palaeo-burial of the Chalk Group. The burial anomaly will be over-estimated by ~ 150–200 m if the analysis is based on the average Chalk Group velocity and clay content is disregarded. Burial anomaly values of ~ 450–600 m result if the strongest velocity contrast at ~ 600–650 m depth is interpreted to be a result of diagenetic effects, consistent with the clay-corrected estimates within uncertainty.

Relationships of sonification to music and sound art

The definition of sonification has been reframed in recent years but remains somewhat in flux; the basic concepts and procedural flows have remained relatively unchanged. Recent definitions have focused on the objective the important uses of sonification in terms of scientific method. The full realization of the potential of the field must also include the craft and art of music composition. The author proposes examining techniques of sonification in a two-order framework: direct and procedural. The impact of new technologies and historical roots of that work argues that framing this broad topic should be in terms inclusive of scientific method and craftsmanship and art. The expressive use of sonic time-based data flows needs to be refined and expanded. The unexamined territory of how a broad-based population of listeners on a subjective, as well as objective level needs, have to be included in this new field.