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Nonlinear interaction of plane elastic waves

Description: The paper presents basic first order results of nonlinear elastic theory by Murnaghan for elastic wave propagation in isotropic solids. The authors especially address the problem of resonant scattering of two collimated beams and present analytical solutions for amplitudes of all possible types of resonant interactions for elastic plane waves. For estimation of nonlinear scattered waves they use measured elastic parameters for sandstone. The most profound nonlinear effect is expected for interactions of two SH waves generating compressional P wave at sum frequency. Estimations show that nonlinear phenomena is likely to be observed in seismic data. Basic equations of nonlinear five-constant theory by Murnaghan are also presented.
Date: June 1, 1998
Creator: Korneev, V.A.; Nihei, K.T. & Myer, L.R.
Partner: UNT Libraries Government Documents Department

Evaluation of Cross-Hole Seismic Tomography for Imaging Low Resistance Intervals and Associated Carbonate Sediments in Coastal Plain Sequences on the Savannah River Site, South Carolina

Description: The objectives of the pilot study were to investigate the limitations of the technique for imaging the presence, extent, and boundaries of the low-resistance intervals and associated carbonate sediments.
Date: January 5, 1999
Creator: Cumbest, R. J.
Partner: UNT Libraries Government Documents Department

Computational methods for improving the resolution of subsurface seismic images. Final report

Description: The original goal is to devise computational methods for improving the resolution of subsurface seismic images. Initially the research emphasis was primarily on developing methods for efficient ray- theoretic modeling of acoustic waves in triangulated representations of media and on efficient means of modeling waves that travel sub- horizontally in horizontally layered media. Subsequent directions included new efficient methods for imaging the Earth`s subsurface (specifically, 3-D migration via the McClellan transformation, and squeezing dip movement (DMO) for depth-variable velocity), demonstrations of the importance of taking P-wave anisotrophy into account in migration and DMO, the development of algorithms for doing migration and DMO in heterogeneous, anisotropic media, and the development of a methodology for the all-important step of deriving the anisotrophy parameters necessary for imaging of P-wave data.
Date: December 31, 1994
Creator: Larner, K.L.
Partner: UNT Libraries Government Documents Department


Description: During this period, the principal investigator wrote an abstract and research accomplishments which was published in the journal of the historically black colleges and universities and other minority institutions contract review meeting of June 2003. Interpretations and analysis of data from the study area shows that incident full-elastic seismic wavefield reflected four different wave modes, P, fast-S (SH) , slow-S (SV) and C. These four wave modes image unique geologic stratigraphy and facies and at the same time reflect independent stratal surfaces. It was also observed that P-wave and S-wave do not always reflect from the same stratal boundaries. At inline coordinate 2100 and crossline coordinates of 10,380, 10430, 10480 and 10,520 the P-wave stratigraphy shows coherency at time slice 796 m/s and C-wave stratigraphy shows coherency at time slice 1964 m/s at the same inline coordinate and crossline coordinates of 10,400 to 10470. At inline coordinate 2800 and crossline coordinate 10,650, P-wave stratigraphy shows coherency at time slice 792 m/s and C-wave stratigraphy shows coherency at time slice 1968 m/s.
Date: January 12, 2004
Creator: Aluka, Innocent J.
Partner: UNT Libraries Government Documents Department

Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

Description: The focus of elastic-wavefield seismic stratigraphy research shifted from onshore prospects to marine environments during this report period. Four-component ocean-bottom-cable (4-C OBC) seismic data acquired in water depths of 2400 to 2500 feet across Green Canyon Block 237 in the Gulf of Mexico were processed and analyzed. The P-P and P-SV images of strata immediately below the seafloor exhibit amazing differences in P-P and P-SV seismic facies. These data may be one of the classic examples of the basic concepts of elastic-wavefield seismic stratigraphy.
Date: May 6, 2004
Creator: Hardage, Bob A.
Partner: UNT Libraries Government Documents Department

Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

Description: We have developed a numerical technique that will adjust 3-D S-wave seismic images so that they are depth equivalent to 3-D P-wave seismic images. The ability to make this type of P-SV to P-P depth registration is critical to our elastic wavefield seismic stratigraphy research because we now have higher confidence that depth-equivalent data windows are being used in the P-SV to P-P comparisons that we are making.
Date: July 31, 2005
Creator: Hardage, Bob A.
Partner: UNT Libraries Government Documents Department

Deep Structure Of Long Valley, California, Based On Deep Reflections From Earthquakes

Description: Knowledge of the deep structure of Long Valley comes primarily from seismic studies. Most of these efforts have focused on delimiting the top of the inferred magma chamber. We present evidence for the location of the bottom of the low velocity layer (LVL). Two other studies have provided similar information. Steeples and Iyer (1976) inferred from teleseismic P-wave delays that low-velocity material extends from 7 km depth to 25 to 40 km, depending on the velocities assumed. Luetgert and Mooney (1985) have examined seismic refraction data from earthquake sources and have identified a reflection that appears to be from the lower boundary of a magma chamber. They detected the reflection with a linear array of single component stations, and assuming it traveled in a vertical plane, matched the travel time and apparent velocity (6.3 km/sec) to deduce that it was a P-P reflection from within a LVL. We recorded a similar phase with a 2-dimensional array of three-component stations, and carried out a similar analysis, but utilized additional information about the travel path, particle motions and amplitudes to constrain our interpretation. Our data comes from a passive seismic refraction experiment conducted during August 1982. Fourteen portable seismograph stations were deployed in a network with approximately 5 km station spacing in the Mono Craters region north of Long Valley (Figure 1). The network recorded earthquakes located south of Long Valley and in the south moat. Three components of motion were recorded at all sites. The data represent one of the few times that three-component data has been collected for raypaths through a magma chamber in the Long Valley area.
Date: January 1, 1987
Creator: Zucca, J. J. & Kasameyer, P. W.
Partner: UNT Libraries Government Documents Department

Characterizing Marine Gas-Hydrate Reservoirs and Determining Mechanical Properties of Marine Gas-Hydrate Strata With 4-Component Ocean-Bottom-Cable Seismic Data

Description: The technical approach taken in this gas-hydrate research is unique because it is based on applying large-scale, 3-D, multi-component seismic surveys to improve the understanding of marine gas-hydrate systems. Other gas-hydrate research uses only single-component seismic technology. In those rare instances when multi-component seismic data have been acquired for gas-hydrate research, the data acquisition has involved only a few receiver stations and a few source stations, sometimes only three or four of each. In contrast, the four-component, 3-D, ocean-bottom-cable (4C3D OBC) data used in this study were acquired at thousands of receiver stations spaced 50 m apart over an area of approximately 1,000 km{sup 2} using wavefields generated at thousands of source stations spaced 75 m apart over this same survey area. The reason for focusing research attention on marine multi-component seismic data is that 4C3D OBC will provide a converted-SV image of gas-hydrate systems in addition to an improved P-wave image. Because P and SV reflectivities differ at some stratal surfaces, P and SV data provide two independent, and different, images of subsurface geology. The existence of these two independent seismic images and the availability of facies-sensitive SV seismic attributes, which can be combined with conventional facies-sensitive, P-wave seismic attributes, means that marine gas-hydrate systems should be better evaluated using multi-component seismic data than using conventional single-component seismic data. Conventional seismic attributes, such as instantaneous reflection amplitude and reflection coherency, have been extracted from the P and SV data volumes created from the 4C3D OBC data used in this research. Comparisons of these attributes and comparisons of P and SV time slices and vertical slices show that SV data provide a more reliable image of stratigraphy and structure associated with gas-invaded strata than do P-wave data. This finding confirms that multi-component seismic data will be more valuable than conventional ...
Date: January 1, 2002
Creator: Hardage, B.A.; Backus, M.M.; DeAngelo, M.V.; Graebner, R.J.; Murray, P. & Rogers, L.J. Wood assisted by K.
Partner: UNT Libraries Government Documents Department

Time-domain solutions for nonlinear elastic 1-D plane wave propagation

Description: Time-domain solutions are obtained for 1-D nonlinear elastic wave propagation problems using a five-constant nonlinear theory. The assumption of weak attenuation was used throughout the development. The strongest nonlinear effects are obtained for the case of single compressional wave propagation, for single compressional or shear wave propagation through a longitudinally pre-stressed elastic material, and for shear wave propagation in a shear pre-stressed elastic material. Estimates of the size of these effects indicate that nonlinear phenomena are likely to be observable in real seismic data. The results may be useful for the measurement of nonlinear constants in elastic materials, for explaining the frequency content of seismograms, and for monitoring strain fields in the earth`s crust.
Date: June 1, 1998
Creator: Korneev, V.A.
Partner: UNT Libraries Government Documents Department

Evaluation of national seismograph network detection capabilities: Final report. Volume 2

Description: This final report presents detection thresholds, detection probabilities, and location error ellipse projections for the US National Seismic Network (USNSN) with and without real-time cooperative stations in the eastern US. Network simulation methods are used with spectral noise levels at stations in the USNSN and other stations to simulate the processes of excitation, propagation, detection, and processing of seismic phases. The USNSN alone should be capable of detecting 4 or more P waves for shallow crustal earthquakes in nearly all of the eastern and central US at the magnitude 3.8 level. When real-time cooperative stations are used in conjunction with the USNSN, the network should be capable of detecting 4 or more P waves from events 0.2 to 0.3 magnitude units lower. The planned expansion of the USNSN and cooperative stations should improve detection levels by an additional 0.2 to 0.3 magnitudes units in many areas. Location uncertainties for the USNSN should be significantly improved by addition of real-time cooperative stations. Median error ellipses for magnitude 4.5 earthquakes in the eastern and central US depend strongly upon location, but uncertainties should be less than 100 square km in the central US and degrade to 200 square km or more offshore and to the south and north of the international boundaries. Close cooperation with the Canadian National Network should substantially improve detection thresholds and location uncertainties along the Canadian border.
Date: October 1, 1997
Creator: McLaughlin, K.L.; Barker, T.G. & Bennett, T.J.
Partner: UNT Libraries Government Documents Department

Acoustic detection of Immiscible Liquids in Sand

Description: Laboratory cross-well P-wave transmission at 90 kHz was measured in a 61 cm diameter by 76 cm tall water-saturated sand pack, before and after introducing a non-aqueous phase organic liquid (NAPL) (n-dodecane). In one experiment NAPL was introduced to form a lens trapped by a low permeability layer; a second experiment considered NAPL residual trapped behind the front of flowing NAPL. The NAPL caused significant changes in the travel time and amplitude of first arrivals, as well as the generation of diffracted waves arriving after the direct wave. The spatial variations in NAPL saturation obtained from excavation at the end of the experiment correlated well with the observed variations in the P-wave amplitudes and travel times. NAPL residual saturation changes from NAPL flow channels of 3 to 4% were detectable and the 40 to 80% NAPL saturation in the NAPL lens was clearly visible at acoustic frequencies. The results of these experiments demonstrate that small NAPL saturations may be more easily detected with amplitude rather than travel time data, but that the relationships between the amplitude changes and NAPL saturation maybe more complex than those for velocity.
Date: March 1, 1999
Creator: Geller, Jil T.; Kowalsky, Michael B.; Seifert, Patricia K. & Nihei, Kurt T.
Partner: UNT Libraries Government Documents Department


Description: Pennsylvanian-age Morrow reservoirs are a key component of a large fluvial-deltaic system that extends across portions of Colorado, Kansas, Oklahoma, and Texas. A problem that operators have to solve in some Morrow plays in this multi-state area is that many of the fluvial channels within the Morrow interval are invisible to seismic compressional (P) waves. This P-wave imaging problem forces operators in such situations to site infill, field-extension, and exploration wells without the aid of 3-D seismic technology. The objective of this project was to develop and demonstrate seismic technology that can improve drilling success in Morrow plays. Current P-wave technology commonly results in 80-percent of Morrow exploration wells not penetrating economic reservoir facies. Studies at Colorado School of Mines have shown that some of the Morrow channels that are elusive as P-wave targets create robust shear (S) wave reflections (Rampton, 1995). These findings caused Visos Energy to conclude that exploration and field development of Morrow prospects should be done by a combination of P-wave and S-wave seismic imaging. To obtain expanded information about the P and S reflectivity of Morrow facies, 9-component vertical seismic profile (9-C VSP) data were recorded at three locations along the Morrow trend. These data were processed to create P and S images of Morrow stratigraphy. These images were then analyzed to determine if S waves offer an alternative to P waves, or perhaps even an advantage over P waves, in imaging Morrow reservoir targets. The study areas where these field demonstrations were done are defined in Figure 1. Well A was in Sherman County, Texas; well B in Clark County, Kansas; and well C in Cheyenne County, Colorado. Technology demonstrated at these sites can be applied over a wide geographical area and influence operators across the multi-state region spanned by Morrow channel plays. The ...
Date: October 19, 2001
Creator: Cottman, Thomas
Partner: UNT Libraries Government Documents Department

An Integrated Multi-component Processing and Interpretation Framework for 3D Borehole Seismic Data

Description: This report covers the April 2004-September 2004 time period. Work has been performed successfully on several tasks 1 through 16. Part of this work has been reported in 15418R03. Most of portions of these tasks have been executed independently. We progressed steadily and completed some of the sub-tasks, while others are still on going. We achieved the goals that we had set up in the task schedule. Reviewing the results of this work period indicates that our plan is solid and we did not encounter any unforeseen problems. The work plan will continue as scheduled. A midyear review will be presented in November or December 2004. Several independent tasks pursuant the statement of project objectives have been executed simultaneously and are still on-going. Use of real seismic test data is augmented by the creation a 3D ray tracing synthetic test data. We used the previously constructed 3D layered model and simulated data acquisition from a set of circular source locations at the surface of the model, while a close to vertical VSP well was used to capture the wave field data. The source pattern was optimized with respect to Fresnel zone width at the target depth. Multi-component particle displacements were recorded every 50 ft down with an array length of 4,000 ft. P-P as well as P-S reflections were specified in the resulting wave field. We ensured a large enough aperture with enough fine sampling to perform advanced processing, imaging and analysis tests in the future during this project. We constantly improved the interfacing of our software libraries with newly designed 3C display classes and mechanisms. We used the previously implemented 3C Work Bench tool as the primary prototyping tool. This work bench allows to load as well as manipulate and display data items in a flexible manner. We continued ...
Date: October 15, 2004
Creator: Karrenbach, M.
Partner: UNT Libraries Government Documents Department

An S to P Converted Phase Recorded Near Long Valley/Mono Craters Region, California

Description: We examine and model the arrival time of a large secondary seismic arrival recorded in the Long Valley/Mono Craters region of east-central California. Zucca et. al. (1987) and Peppin (1987) both previously reported on different features of this same arrival. Using both arrays of sources and receivers we demonstrate that the arrival is an S to P converted phase as first suggested by Lewis and Peppin (1988). Backprojection of the observed travel times allows us to constrain the location of the converting material to a southeast dipping zone between 7 and 16 km depth, and {+-} 5 km on either side of the topographic margin of the caldera. The analysis demonstrates the power of source and receiver array combinations when analyzing seismic arrivals in complicated environments.
Date: January 1, 1989
Creator: Ammon, C. J.; Zucca, J. & Kasameyer, P.
Partner: UNT Libraries Government Documents Department

Geotechnology for low-permeability gas reservoirs, 1995

Description: The permeability, and thus the economics, of tight reservoirs are largely dependent on natural fractures, and on the in situ stresses that both originated fractures and control subsequent fracture permeability. Natural fracture permeability ultimately determines the gas (or oil) producibility from the rock matrix. Therefore, it is desirable to be able to predict, both prior to drilling and during reservoir production, (1) the natural fracture characteristics, (2) the mechanical and transport properties of fractures and the surrounding rock matrix, and (3) the present in situ stress magnitudes and orientations. The combination of activities described in this report extends the earlier work to other Rocky Mountain gas reservoirs. Additionally, it extends the fracture characterizations to attempts of crosswell geophysical fracture detection using shear wave birefringence and to obtaining detailed quantitative models of natural fracture systems for use in improved numerical reservoir simulations. Finally, the project continues collaborative efforts to evaluate and advance cost-effective methods for in situ stress measurements on core.
Date: June 1, 1995
Creator: Brown, S.; Harstad, H.; Lorenz, J.; Warpinski, N.; Boneau, T.; Holcomb, D. et al.
Partner: UNT Libraries Government Documents Department

Seismic methods for resource exploration in enhanced geothermal systems

Description: A finite-difference modeling study of seismic wave propagation was conducted to determine how to best investigate subsurface faults and fracture zones in geothermal areas. The numerical model was created based on results from a previous seismic reflection experiment. A suite of fault models was investigated including blind faults and faults with surface expressions. The seismic data suggest that blind faults can be detected by a sudden attenuation of seismic wave amplitudes, as long the fault is located below the receiver array. Additionally, a conversion from P- to S-waves indicates the reflection and refraction of the P-waves while propagating across the fault. The drop in amplitudes and the excitation of S-waves can be used to estimate the location of the fault at depth. The accuracy of the numerical modeling depends on the availability of a priori in situ information (velocity and density) from borehole experiments in the geothermal area.
Date: June 12, 2002
Creator: Gritto, Roland & Majer, Ernest L.
Partner: UNT Libraries Government Documents Department

Naturally fractured tight gas reservoir detection optimization. Quarterly report, April 1--June 30, 1996

Description: Accomplishments during this quarter are described on the study being done in the Wind River basin. Accomplishments include 3-D P-wave alternate processing, interpretation this alternate processing, P-P and P-S processing, correlation matrix, modeling, and Wind River basin geology, including a geologic history of the Wind River basin, located in the center of the Rocky Mountain foreland.
Date: December 31, 1996
Partner: UNT Libraries Government Documents Department

The use of propagation path corrections to improve regional seismic event location in western China

Description: In an effort to improve the ability to locate seismic events in western China using only regional data, the authors have developed empirical propagation path corrections (PPCs) and applied such corrections using both traditional location routines as well as a nonlinear grid search method. Thus far, the authors have concentrated on corrections to observed P arrival times for shallow events using travel-time observations available from the USGS EDRs, the ISC catalogs, their own travel-tim picks from regional data, and data from other catalogs. They relocate events with the algorithm of Bratt and Bache (1988) from a region encompassing China. For individual stations having sufficient data, they produce a map of the regional travel-time residuals from all well-located teleseismic events. From these maps, interpolated PPC surfaces have been constructed using both surface fitting under tension and modified Bayesian kriging. The latter method offers the advantage of providing well-behaved interpolants, but requires that the authors have adequate error estimates associated with the travel-time residuals. To improve error estimates for kriging and event location, they separate measurement error from modeling error. The modeling error is defined as the travel-time variance of a particular model as a function of distance, while the measurement error is defined as the picking error associated with each phase. They estimate measurement errors for arrivals from the EDRs based on roundoff or truncation, and use signal-to-noise for the travel-time picks from the waveform data set.
Date: March 1, 1999
Creator: Steck, L. K.; Cogbill, A. H. & Velasco, A. A.
Partner: UNT Libraries Government Documents Department

The 16 August 1997 Novaya Zemlya seismic event as viewed from GSN stations KEV and KBS

Description: Using current and historic seismic records from Global Seismic Network stations KEV and KBS, the authors find that S minus P arrival time comparisons between nuclear explosions and the 16 August 1997 seismic event (m{sub b} {approx} 3.6) from near Novaya Zemlya clearly indicate that (relative to KEV) the 16 August event occurred at least 80 km east of the Russian test site. Including S minus P arrival times from KBS constrains the location to beneath the Kara Sea and in good agreement with previously reported locations, over 100 km southeast of the test site. From an analysis of P{sub n}/S{sub n} waveform ratios at frequencies above 4 Hz, they find that the 16 August event falls within the population of regional earthquakes and is distinctly separated from Novaya Zemlya and other northern Eurasian nuclear explosion populations. Thus, given its location and waveform characteristics, they conclude the 16 August event was an earthquake. The 16 August event was not detected at teleseismic distances, and thus, this event provides a good example of the regional detection, location, and identification efforts that will be required to monitor the Comprehensive Test Ban Treaty below m{sub b} {approx} 4.
Date: November 1, 1997
Creator: Hartse, H.E.
Partner: UNT Libraries Government Documents Department


Description: The data used in this study were acquired by nine-component (9C) vertical seismic profile (VSP), using three orthogonal vector sources. The 9C vertical seismic profile is capable of generating P-wave mode and the fundamental S-wave mode (SH-SH and SV-SV) directly at the source station and permits the basic components of elastic wavefield (P, SH-SH and SV-SV) to be separated from one another for the purposes of imaging. Analysis and interpretations of data from the study area show that incident full-elastic seismic wavefield is capable of reflecting four different wave modes, P, SH , SV and C which can be utilized to fully understand the architecture and heterogeneities of geologic sequences. The conventional seismic stratigraphy utilizes only reflected P-wave modes. The notation SH mode is the same as SH-SH; SV mode means SV-SV and C mode which is a converted shear wave is a special SV mode and is the same as P-SV. These four wave modes image unique geologic stratigraphy and facies and at the same time reflect independent stratal surfaces because of the unique orientation of their particle-displacement vectors. As a result of the distinct orientation of individual mode.s particle-displacement vector, one mode may react to a critical subsurface sequence more than the other. It was also observed that P-wave and S-wave do not always reflect from the same stratal boundaries. At inline coordinate 2100 and crossline coordinates of 10,380, 10430, 10480 and 10,520 the P-wave stratigraphy shows coherency at time slice 796 m/s and C-wave stratigraphy shows coherency at time slice 1964 m/s at the same inline coordinate and crossline coordinates of 10,400 to 10470. At inline coordinate 2800 and crossline coordinate 10,650, P-wave stratigraphy shows coherency at time slice 792 m/s and C-wave stratigraphy shows coherency at time slice 1968 m/s. The utilization of full-elastic seismic wavefield ...
Date: December 2004
Creator: Aluka, Innocent J.
Partner: UNT Libraries Government Documents Department

Application of seismic tomographic techniques in the investigation of geothermal systems

Description: The utility of microearthquake data for characterizing the Northwest Geysers geothermal field and the Long Valley Caldera (LVC) was investigated. Three-dimensional (3-D) P- and S-wave seismic velocity models were estimated for the Coldwater Creek Steam Field (CCSF) in the Northwest Geysers region. Hypocenters relocated using these 3-D models appear to be associated with the steam producing zone, with a deeper cluster of hypocenters beneath an active injection well. Spatial and temporal patterns of seismicity exhibit strong correlation with geothermal exploitation. A 3-D differential attenuation model was also developed for the CCSF from spectral ratios corrected for strong site effects. High-velocity anomalies and low attenuation in the near surface correspond to Franciscan metagraywacke and greenstone units. Microearthquakes recorded at seismographic stations located near the metagraywacke unit exhibit high corner frequencies. Low-velocity anomalies and higher attenuation in the near surface are associated with sections of Franciscan melange. Near-surface high attenuation and high Vp/Vs are interpreted to indicate liquid-saturated regions affected by meteoric recharge. High attenuation and low Vp/Vs marks the steam producing zone, suggesting undersaturation of the reservoir rocks. The extent of the high attenuation and low Vp/Vs anomalies suggest that the CCSF steam reservoir may extend northwestward beyond the known producing zone. This study concludes that microearthquake monitoring may be useful as an active reservoir management tool. Seismic velocity and attenuation structures as well as the distribution of microearthquake activity can be used to identify and delineate the geothermal reservoir, while temporal variations in these quantities would be useful in tracking changes during exploitation.
Date: May 1, 1995
Creator: Romero, A.E. Jr.
Partner: UNT Libraries Government Documents Department

Linear and Nonlinear Ultrasonic Properties of Granular Soils

Description: The ultrasonic pulse transmission method (100-500 kHz) was adapted to measure compressional (P) and shear (S) wave velocities for synthetic soils fabricated from quartz-clay and quartz-peat mixtures. Velocities were determined as samples were loaded by small (up to 0.1 MPa) uniaxial stress to determine how stress at grain contacts affects ave amplitudes, velocities, and frequency content. Samples were fabricated from quartz sand mixed with either a swelling clay or peat (natural cellulose). P velocities in these dry synthetic soil samples were low, ranging from about 230 to 430 m/s for pure sand, about 91 to 420 m/s for sand-peat mixtures, and about 230 to 470 m/s for dry sand-clay mixtures. S velocities were about half of the P velocity in most cases, about 130 to 250 m/s for pure sand, about 75-220 m/s for sand-peat mixtures, and about 88-220 m/s for dry sand-clay mixtures. These experiments demonstrate that P and S velocities are sensitive to the amount and type of admixed second phase at low concentrations. They found that dramatic increases in all velocities occur with small uniaxial loads, indicating strong nonlinearity of the acoustic properties. Composition and grain packing contribute to the mechanical response at grain contacts and the nonlinear response at low stresses.
Date: April 20, 2000
Creator: Bonner, B.; Berge, P.A.; Aracne-Ruddle, C.M.; Bertete-Auguirre, H.; Wildenschild, D.; Trombino, C.N. et al.
Partner: UNT Libraries Government Documents Department

Compressional wave character in gassy, near-surface sediments in southern Louisiana determined from variable frequency cross-well, borehole logging, and surface seismic measurements

Description: Velocity and attenuation data were used to test theoretical equations describing the frequency dependence of compressional wave velocity and attenuation through gas-rich sediments in coastal Louisiana. The cross-well data were augmented with velocities derived from a nearby seismic refraction station using a low-frequency source. Energy at 1 and 3 kHz was successfully transmitted over distances from 3.69 to 30 m; the 5 and 7-kHz data were obtained only at distances up to 20 m. Velocity tomograms were constructed for one borehole pair and covered a depth interval of 10--50 m. Results from the tomographic modeling indicate that gas-induced low velocities are present to depths of greater than 40 m. Analysis of the velocity dispersion suggests that gas-bubble resonance must be greater than 7 kHz, which is above the range of frequencies used in the experiment. Washout of the boreholes at depths above 15 m resulted in a degassed zone containing velocities higher than those indicated in both nearby refraction and reflection surveys. Velocity and attenuation information were obtained for a low-velocity zone centered at a depth of approximately 18 m. Measured attenuations of 1.57, 2.95, and 3.24 dB/m for the 3-, 5-, and 7-kHz signals, respectively, were modeled along with the velocity data using a silt-clay sediment type. Density and porosity data for the model were obtained from the geophysical logs; the bulk and shear moduli were estimated from published relationships. Modeling results indicate that gas bubbles measuring 1 mm in diameter occupy at least 25% to 35% of the pore space.
Date: June 1995
Creator: Thompson, M. D.; McGinnis, L. D.; Wilkey, P. L. & Fasnacht, T.
Partner: UNT Libraries Government Documents Department