Inversion of dry and saturated P- and S-wave velocities for the pore-aspect-ratio spectrum using a cracked porous medium elastic wave theory

Geophysics ◽  
2021 ◽  
Vol 86 (6) ◽  
pp. A57-A62
Author(s):  
He-Ming Wang ◽  
Xiao-Ming Tang
Keyword(s):  
Porous Medium ◽  
Aspect Ratio ◽  
Elastic Wave ◽  
Research Work ◽  
Wave Theory ◽  
Wave Dispersion ◽  
Velocity Data ◽  
S Wave ◽  
Ratio Spectrum ◽  
Aspect Ratios

Subsurface rocks contain pores and cracks of various sizes. The cracked porous medium elastic wave theory that describes wave propagation characteristics due to the pore-crack interaction is extended to include cracks of different aspect ratios. The extended theory is applied to model P- and S-wave velocity data of dry and fluid-saturated rock under pressure loading conditions, so as to determine the pore-aspect-ratio spectrum through an inversion procedure. The inversion result is consistent with that from the scanning electron microscope analysis, showing significant improvement versus previous inversion. The inverted pore-aspect-ratio spectrum is input into the wave theory to predict the velocity dispersion of the rock in the full frequency range. The predicted dispersion and its variation trend with pressure agree with the data measured in the (2–200, 106) Hz range at various differential pressures, whereas the modeling using a single-aspect-ratio theory has difficulty matching the data. This research work provides not only a method for analyzing the pore structure characteristics of rocks from the laboratory ultrasonic velocity data, but also a way to predict the seismic wave dispersion from the data.

scholarly journals Indentation of an S2 Floating Ice Sheet in the Brittle Range

1983 ◽  
Vol 4 ◽  
pp. 180-187 ◽  
Author(s):  
B. Michel ◽  
D. Blanchet
Keyword(s):  
Aspect Ratio ◽  
Research Work ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Theory Of Elasticity ◽  
Maximum Pressure ◽  
Shear Cracks ◽  
Aspect Ratios ◽  
Two Parameters ◽  
The Impact

The problem of a floating ice sheet hitting a structure with a vertical face appears to be a simple one but, in fact, has only been solved for a limited number of cases. Research work on this question usually reports on an indentation coefficient which relates the average pressure on the indenter to the uniaxial crushing strength of the ice. Very few tests have been made in the brittle range of ice failure. In this particular area of study, this paper reports on 27 tests that were conducted in a cold-room water basin where controlled S2floating ice sheets were produced with a surface area of 4 × 4 m, three sides being fully restrained and the other, freely float! no, being submitted to the impact of the moving indenter. All tests were carried out at computed indentation rates varying from 0.017 to 0.34 s-1. In this range this ice would normally be considered to act as a brittle material. The thickness of the ice sheets varied from 1.2 to 9.0 cm and the indenter width from 5 cm to 1 m. Overall, the aspect ratio relating these two parameters could be varied from 0.5 to 83.Results have shown that for aspect ratios <5, there was an important oscillatory effect which caused the formation of pi asti fi ed triangles in front of the indenter, increasing its resistance as it would under ductile conditions. Because of this plastification, an extrusion effect appeared in front of the indenter as the broken ice crystals were blown up and down in front of the fast-moving indenter. The theory of plasticity which gives an indentation coefficient of 2.97 seems to apply in this case. Another mode of failure which occurred with aspect ratios 5 was cleavage in the plane of the ice sheet which also gives a higher indentation coefficient for S2ice, but of the same order of magnitude as previously.For intermediate values of the aspect ratio, between 5 and 20, the theory of elasticity used by Michel (1978) seems to apply well. Shear cracks are first formed on both sides of the square indenter and control the maximum pressure when they propagate inside forming big triangles in front of it.Finally, for aspect ratios ~>20, buckling of the ice occurs, either after or at the same time as the formation of wedges, together with a reduction in the indentation coefficient to a value close to that given by the theory of buckling of a truncated 45° wedge with a hinged edge.

scholarly journals AN INVESTIGATION ON THE SHRINKAGE CHARACTERISTICS OF HYBRID FIBER REINFORCED CONCRETE PRODUCED BY USING FIBERS OF DIFFERENT ASPECT RATIO

2020 ◽  
Author(s):  
Rudraswamy M P ◽  
B.R Patagundi ◽  
K.B Prakash
Keyword(s):  
Reinforced Concrete ◽  
Aspect Ratio ◽  
Research Work ◽  
Fiber Reinforced Concrete ◽  
Future Research ◽  
Bench Mark ◽  
Fiber Reinforced ◽  
Aspect Ratios ◽  
Fiber Materials ◽  
Reinforcing Fiber

In the present paper, effects of shrinkage in fiber reinforced concrete are studied.Here, in the current research work, an attempt is made to study the effects onshrinkage of concrete when five different fiber materials are used for reinforcing plainconcrete. Three configurations of each reinforcing fiber material is studied. Fiberaspect ratios of 40 and 100 and a combination of the fibers of the two aspect ratios inequal proportion (hybrid) make up the three configurations for one individual fibermaterial reinforcement. Shrinkage values are indicated in terms of total length ofcrack and the total area of the crack. On-field measurement of crack dimensions atperiodic time intervals ranging from 0 minutes to 28 days after casting of concrete hasbeen undertaken to determine the accurate values of shrinkage cracks in the fifteenscenarios i.e. five reinforcing fiber materials with three configurations each usingaspect ratio of fibers 40, 100 and the hybrid (40 +100) case. It is seen that,irrespective of the material of fiber used for reinforcing concrete, hybridized concreteconsistently shows better results relative to single aspect ratio fiber reinforcement.This research also aims to provide a bench mark for future research works onshrinkage characteristics of hybridized fiber reinforced concrete

scholarly journals Indentation of an S2 Floating Ice Sheet in the Brittle Range

1983 ◽  
Vol 4 ◽  
pp. 180-187 ◽  
Author(s):  
B. Michel ◽  
D. Blanchet
Keyword(s):  
Aspect Ratio ◽  
Research Work ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Theory Of Elasticity ◽  
Maximum Pressure ◽  
Shear Cracks ◽  
Aspect Ratios ◽  
Two Parameters ◽  
The Impact

The problem of a floating ice sheet hitting a structure with a vertical face appears to be a simple one but, in fact, has only been solved for a limited number of cases. Research work on this question usually reports on an indentation coefficient which relates the average pressure on the indenter to the uniaxial crushing strength of the ice. Very few tests have been made in the brittle range of ice failure. In this particular area of study, this paper reports on 27 tests that were conducted in a cold-room water basin where controlled S2 floating ice sheets were produced with a surface area of 4 × 4 m, three sides being fully restrained and the other, freely float! no, being submitted to the impact of the moving indenter. All tests were carried out at computed indentation rates varying from 0.017 to 0.34 s-1. In this range this ice would normally be considered to act as a brittle material. The thickness of the ice sheets varied from 1.2 to 9.0 cm and the indenter width from 5 cm to 1 m. Overall, the aspect ratio relating these two parameters could be varied from 0.5 to 83.Results have shown that for aspect ratios <5, there was an important oscillatory effect which caused the formation of pi asti fi ed triangles in front of the indenter, increasing its resistance as it would under ductile conditions. Because of this plastification, an extrusion effect appeared in front of the indenter as the broken ice crystals were blown up and down in front of the fast-moving indenter. The theory of plasticity which gives an indentation coefficient of 2.97 seems to apply in this case. Another mode of failure which occurred with aspect ratios 5 was cleavage in the plane of the ice sheet which also gives a higher indentation coefficient for S2 ice, but of the same order of magnitude as previously.For intermediate values of the aspect ratio, between 5 and 20, the theory of elasticity used by Michel (1978) seems to apply well. Shear cracks are first formed on both sides of the square indenter and control the maximum pressure when they propagate inside forming big triangles in front of it.Finally, for aspect ratios ~>20, buckling of the ice occurs, either after or at the same time as the formation of wedges, together with a reduction in the indentation coefficient to a value close to that given by the theory of buckling of a truncated 45° wedge with a hinged edge.

Are self-consistent models capable of jointly modeling elastic velocity and electrical conductivity of reservoir sandstones?

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. D377-D382 ◽  
Author(s):  
Tongcheng Han ◽  
Michael Ben Clennell ◽  
Arthur C. H. Cheng ◽  
Marina Pervukhina
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Aspect Ratio ◽  
Physical Property ◽  
S Waves ◽  
Ratio Spectrum ◽  
Aspect Ratios ◽  
Self Consistent ◽  
Spectrum Distribution ◽  
Reservoir Sandstones

Self-consistent (SC) models are commonly used for simulating elastic and electrical properties of reservoir rocks. We have developed a technique to test the capability of SC models to jointly model elastic velocity and electrical conductivity of porous media using a database of measurements of these properties on reservoir sandstones. The pores were represented by randomly oriented spheroidal shapes with a spectrum distribution of aspect ratios, and elasticity theory was used to compute the variation of aspect ratios and volume fractions of the pores subject to varying differential pressures. Using this method, the pore aspect ratio spectra of a reservoir sandstone were obtained separately from the measured elastic (P- and S-waves) velocity and electrical conductivity under loading. We have determined that when the SC formalism is used, there is a systematic discrepancy in the estimated pore structure predicted by the two measurements. Despite the supposed applicability of the SC method to this class of problem, the pore aspect ratio spectrum inverted from one physical property (e.g., velocity or conductivity) failed in practice to predict the other physical property (e.g., conductivity or velocity), at least for porous sandstones. Our results suggested the requirement of a new model to link the elastic and electrical properties to a unified pore aspect ratio spectrum of rocks.

Pore Aspect Ratio Spectrum Inversion from Ultrasonic Measurements and Its Application

2015 ◽  
Vol 23 (04) ◽  
pp. 1540009 ◽  
Author(s):  
Fuyong Yan ◽  
De-Hua Han ◽  
Xue-Lian Chen
Keyword(s):  
Aspect Ratio ◽  
Carbonate Rock ◽  
Velocity Dispersion ◽  
Rock Sample ◽  
Wave Dispersion ◽  
Ratio Spectrum ◽  
Poroelastic Media ◽  
Ultrasonic Measurements ◽  
Dispersion And Attenuation ◽  
Spectrum Inversion

We have conducted simultaneous ultrasonic velocity and pore volume change measurements on a carbonate rock sample. By including of pressure dependent porosity data, we have improved Cheng’s pore aspect ratio spectrum inversion methodology and made the inverted pore aspect ratio spectrum more realistic. Tang’s unified velocity dispersion and attenuation model is modified and extended to poroelastic media with complex pore structure under undrained condition. Using improved pore aspect ratio spectra inversion methodology and modified Tang’s model, we have explored the potential application of pore aspect ratio spectrum in prediction of seismic wave dispersion and attenuation.

Effect of Buoyancy Driven Stream Loop Numbers on Heat Transfer and Entropy Generation

2009 ◽  
Author(s):  
H. Heidary ◽  
M. Davoudi ◽  
M. J. Kermani
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Aspect Ratio ◽  
Free Convection ◽  
Entropy Generation ◽  
Saturated Porous Medium ◽  
Numerical Procedure ◽  
Bottom Wall ◽  
Bejan Number ◽  
Aspect Ratios

Free convection in a cavity filled with a fluid-saturated porous medium is from prime importance in many technological applications. Transient free convection in a rectangular cavity filled with a porous medium is numerically studied in this paper. Uniformly and non-uniformly sinusoidal heated bottom wall and adiabatic side walls maintaining constant temperature of cold top wall has been performed. Investigation of problems with this boundary condition is very complicated, as there are a limited number of studies available in the literature dealing with this problem. The finite volume numerical method is used to solve the non-dimensional governing equations. The numerical procedure has been done over a range of Rayleigh number, Ra, 10 ≤ Ra ≤ 103 and Prandtl number, Pr, 0.71 and Aspect ratio, AR, 0.25≤ AR ≤8 and effect of them is investigated on heat transfer and entropy generation. For uniform heating of the bottom wall, the heat transfer rate or Nub is high at the edges of the bottom wall due to the discontinuities present in the temperature boundary conditions at the edges and reduces towards the center of the bottom wall with the minimum value at the center. Effect of streamline loop numbers on heat transfer is shown for various aspect ratios in this study. The present paper analyzes entropy generation induced by free convection and effect of different parameters on entropy generation is studied. Relation of Nusselt number and Bejan number with aspect ratio is given that is due to effect of stream loops number. In lower Ra, because of weak stream, entropy generation is more due to heat transfer irreversibility (HHI).

Laboratory measurements of porosity, permeability, resistivity, and velocity on Fontainebleau sandstones

Geophysics ◽  
2010 ◽  
Vol 75 (6) ◽  
pp. E191-E204 ◽  
Author(s):  
Carmen T. Gomez ◽  
Jack Dvorkin ◽  
Tiziana Vanorio
Keyword(s):  
Aspect Ratio ◽  
Elastic Wave ◽  
Wave Velocity ◽  
Water Saturation ◽  
Confining Pressure ◽  
Elastic Wave Velocity ◽  
P Wave ◽  
Aspect Ratios ◽  
P Wave Velocity ◽  
Grain Aspect Ratio

The relations among the resistivity, elastic-wave velocity, porosity, and permeability in Fontainebleau sandstone samples from the Ile de France region, around Paris, France were experimentally revisited. These samples followed a permeability-porosity relation given by Kozeny-Carman’s equation. For the resistivity measurements, the samples were partially saturated with brine. Archie’s equation was used to estimate resistivity at 100% water saturation, assuming a saturation exponent, [Formula: see text]. Using self-consistent (SC) approximations modeling with grain aspect ratio 1, and pore aspect ratio between 0.02 and 0.10, the experimental data fall into this theoretical range. The SC curve with the pore aspect ratio 0.05 appears to be close to the values measured in the entire porosity range. The elastic-wave velocity was mea-sured on these dry samples for confining pressure between 0 and [Formula: see text]. A loading and unloading cycle was used and did not produce any significant hysteresis in the velocity-pressure behavior. For the velocity data, using the SC model with a grain aspect ratio 1 and pore aspect ratios 0.2, 0.1, and 0.05 fit the data at [Formula: see text]; pore aspect ratios ranging between 0.1, 0.05, and 0.02 were a better fit for the data at [Formula: see text]. Both velocity and resistivity in clean sandstones can be modeled using the SC approximation. In addition, a linear fit was found between the P-wave velocity and the decimal logarithm of the normalized resistivity, with deviations that correlate with differences in permeability. Combining the stiff sand model and Archie for cementation exponents between 1.6 and 2.1, resistivity was modeled as a function of P-wave velocity for these clean sandstones.

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