scholarly journals Estimation of Compressional Wave Speed in Marine Sediments using Biot Stoll Model and Buckinghams Grain shearing Model

2020 ◽  
Vol 70 (3) ◽  
pp. 336-341
Author(s):  
A.P. Anu ◽  
P. Velayudhan Nair ◽  
C.P. Uthaman ◽  
T. Pradeep Kumar
Keyword(s):  
Wave Speed ◽  
Theoretical Models ◽  
Compressional Wave ◽  
Acoustic Properties ◽  
Coefficient Of Determination ◽  
Elastic Model ◽  
Experimental Assessment ◽  
Empirical Relations ◽  
Indian Waters ◽  
Seafloor Sediments

Acoustic properties of seafloor sediments can be estimated using theoretical models by giving geophysical properties of sediments as inputs to the respective models. Empirical relations connecting the geophysical and geoacoustic properties are available in literature. In this study an experimental assessment of two such theoretical models viz., Biot-Stoll model (BSM), a poro-elastic model and the Buckingham’s grain shearing (GS) model, a visco-elastic model is done by estimating the compressional wave speed. Compressional wave speed is measured using in-house developed sediment velocimeter and is compared with the speed estimated using both the models and a regression analysis was done. It was observed that the Coefficient of determination R2 for BSM and GS model are 0.769 and 0.729, respectively. It shows that once the constants used in GS model are evaluated for the Indian waters, then it can be used to estimate the acoustic properties of sediments.

scholarly journals A New Compressional Wave Speed Inversion Method Based on Granularity Parameters

IEEE Access ◽  
2019 ◽  
Vol 7 ◽  
pp. 185849-185856 ◽  
Author(s):  
Jingqiang Wang ◽  
Zhengyu Hou ◽  
Guanbao Li ◽  
Guangming Kan ◽  
Xiangmei Meng ◽  
...  
Keyword(s):  
Wave Speed ◽  
Compressional Wave ◽  
Inversion Method

scholarly journals A Comparison of Three Sediment Acoustic Models Using Bayesian Inversion and Model Selection Techniques

2019 ◽  
Vol 11 (5) ◽  
pp. 562 ◽  
Author(s):  
Bo Zou ◽  
Jingsheng Zhai ◽  
Zhanfeng Qi ◽  
Zhaoxing Li
Keyword(s):  
Model Selection ◽  
Model Comparison ◽  
Fluid Model ◽  
Probability Distributions ◽  
Acoustic Properties ◽  
Effective Density ◽  
Bayesian Inversion ◽  
Elastic Model ◽  
Poroelastic Model ◽  
Sandy Sediments

Many geoacoustic models are used to establish the relationship between the physical and acoustic properties of sediments. In this work, Bayesian inversion and model selection techniques are applied to compare combinations of three geoacoustic models and corresponding scattering models—the fluid model with the effective density fluid model (EDFM), the grain-shearing elastic model with the viscosity grain-shearing (VGS(λ)) model, and the poroelastic model with the corrected and reparametrized extended Biot–Stoll (CREB) model. First, the resolution and correlation of parameters for the three models are compared based on estimates of the posterior probability distributions (PPDs), which are obtained by Bayesian inversion using the backscattering strength data. Then, model comparison and selection techniques are utilized to assess the matching degree of model predictions and measurements qualitatively and to ascertain the Bayes factors in favor of each quantitatively. These studies indicate that the fluid and poroelastic models outperform the grain-shearing elastic model, in terms of both parameter resolution and the ability to produce predictions in agreement with measurements for sandy sediments. The poroelastic model is considered to be the best, as the inversion based on it can provide more highly resolved information of sandy sediments. Finally, the attempt to implement geoacoustic inversion with different models provides a relatively feasible remote sensing scheme for various types of sediments under unknown conditions, which needs further validation.

Estimation of gas hydrate and free gas saturation, concentration, and distribution from seismic data

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 582-593 ◽  
Author(s):  
Shaoming Lu ◽  
George A. McMechan
Keyword(s):  
Gas Hydrate ◽  
Seismic Data ◽  
Acoustic Impedance ◽  
Single Channel ◽  
Pore Space ◽  
Theoretical Models ◽  
Free Gas ◽  
Bottom Simulating Reflector ◽  
Saturation Concentration ◽  
Empirical Relations

Gas hydrates contain a major untapped source of energy and are of potential economic importance. The theoretical models to estimate gas hydrate saturation from seismic data predict significantly different acoustic/elastic properties of sediments containing gas hydrate; we do not know which to use. Thus, we develop a new approach based on empirical relations. The water‐filled porosity is calibrated (using well‐log data) to acoustic impedance twice: one calibration where gas hydrate is present and the other where free gas is present. The water‐filled porosity is used in a combination of Archie equations (with corresponding parameters for either gas hydrate or free gas) to estimate gas hydrate or free gas saturations. The method is applied to single‐channel seismic data and well logs from Ocean Drilling Program leg 164 from the Blake Ridge area off the east coast of North America. The gas hydrate above the bottom simulating reflector (BSR) is estimated to occupy ∼3–8% of the pore space (∼2–6% by volume). Free gas is interpreted to be present in three main layers beneath the BSR, with average gas saturations of 11–14%, 7–11%, and 1–5% of the pore space (6–8%, 4–6%, and 1–3% by volume), respectively. The estimated saturations of gas hydrate are very similar to those estimated from vertical seismic profile data and generally agree with those from independent, indirect estimates obtained from resistivity and chloride measurements. The estimated free gas saturations agree with measurements from a pressure core sampler. These results suggest that locally derived empirical relations between porosity and acoustic impedance can provide cost‐effective estimates of the saturation, concentration, and distribution of gas hydrate and free gas away from control wells.

Seismic velocities of unconsolidated sands: Part 1 — Pressure trends from 0.1 to 20 MPa

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. E1-E13 ◽  
Author(s):  
Michael A. Zimmer ◽  
Manika Prasad ◽  
Gary Mavko ◽  
Amos Nur
Keyword(s):  
Shear Wave ◽  
Pressure Dependence ◽  
Glass Bead ◽  
Theoretical Models ◽  
Compressional Wave ◽  
P Wave ◽  
Seismic Velocities ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Shear Wave Velocities

Knowledge of the pressure dependences of seismic velocities in unconsolidated sands is necessary for the remote prediction of effective pressures and for the projection of velocities to unsampled locations within shallow sand layers. We have measured the compressional- and shear-wave velocities and bulk, shear, and P-wave moduli at pressures from [Formula: see text] in a series of unconsolidated granular samples including dry and water-saturated natural sands and dry synthetic sand and glass-bead samples. The shear-wave velocities in these samples demonstrate an average pressure dependence approximately proportional to the fourth root of the effective pressure [Formula: see text], as commonly observed at lower pressures. For the compressional-wave velocities, theexponent in the pressure dependence of individual dry samples is consistently less than the exponent for the shear-wave velocity of the same sample, averaging 0.23 for the dry sands and 0.20 for the glass-bead samples. These pressure dependences are generally consistent over the entire pressure range measured. A comparison of the empirical results to theoretical predictions based on Hertz-Mindlin effective-medium models demonstrates that the theoretical models vastly overpredict the shear moduli of the dry granular frame unless the contacts are assumed to have no tangential stiffness. The models also predict a lower pressure exponent for the moduli and velocities [Formula: see text] than is generally observed in the data. We attribute this discrepancy in part to the inability of the models to account for decreases in the amount of slip or grain rotation occurring at grain-to-grain contacts with increasing pressure.

scholarly journals Role of Horizontal Eddy Diffusivity within the Canopy on Fire Spread

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 672
Author(s):  
Yana Bebieva ◽  
Julia Oliveto ◽  
Bryan Quaife ◽  
Nicholas S. Skowronski ◽  
Warren E. Heilman ◽  
...  
Keyword(s):  
Theoretical Models ◽  
Eddy Diffusivity ◽  
Fire Spread ◽  
Fire Intensity ◽  
Mean Flow ◽  
Canopy Layer ◽  
Fuel Layer ◽  
Empirical Relations ◽  
Southeast Us ◽  
Eddy Dynamics

Wind profile observations are used to estimate turbulent mixing in the atmospheric boundary layer from 1 m up to 300 m height in two locations of pine forests characteristic of the southeast US region, and to 30 m height at one location in the northeast. Basic turbulence characteristics of the boundary layers above and within the canopy were measured near prescribed fires for time periods spanning the burns. Together with theoretical models for the mean horizontal velocity and empirical relations between mean flow and variance, we derive the lateral diffusivity using Taylor’s frozen turbulence hypothesis in the thin surface-fuel layer. This parameter is used in a simple 1D model to predict the spread of surface fires in different wind conditions. Initial assessments of sensitivity of the fire spread rates to the lateral diffusivity are made. The lateral diffusivity with and without fire-induced wind is estimated and associated fire spread rates are explored. Our results support the conceptual framework that eddy dynamics in the fuel layer is set by larger eddies developed in the canopy layer aloft. The presence of fire modifies the wind, hence spread rate, depending on the fire intensity.

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