Laboratory velocities and attenuation of P‐waves in limestones during freeze‐thaw cycles

Geophysics ◽  
1994 ◽  
Vol 59 (2) ◽  
pp. 245-251 ◽  
Author(s):  
Jean‐Michel Remy ◽  
Michel Bellanger ◽  
Françoise Homand‐Etienne
Keyword(s):  
Hydrostatic Compression ◽  
P Wave ◽  
Compression Tests ◽  
Freezing And Thawing ◽  
P Waves ◽  
Freeze Thaw ◽  
Rock Samples ◽  
Wave Velocities ◽  
P Wave Velocities ◽  
Freezing And Thawing Cycles

The velocity and the attenuation of compressional P‐waves, measured in the laboratory at ultrasonic frequencies during a series of freezing and thawing cycles, are used as a method for predicting frost damage in a bedded limestone. Pulse transmission and spectral ratio techniques are used to determine the P‐wave velocities and the attenuation values relative to an aluminum reference sample with very low attenuation. Limestone samples were water saturated under vacuum conditions, jacketed with rubber sleeves, and immersed in an antifreeze bath (50 percent methanol solution). They were submitted to repeated 24-hour freezing and thawing cycles simulating natural environment conditions. During the freeze/thaw cycles, P‐wave velocities and quality factor Q diminished rapidly in thawed rock samples, indicating modification of the pore space. Measurements of crack porosity were conducted by hydrostatic compression tests on cubic rock samples that had been submitted to these freeze/thaw cycles. These measurements are used as an index of crack formation. The hydrostatic compression tests confirmed the phases of rock damage that were shown by changes in the value of Q. Furthermore, comparisons between Q values and crack porosity demonstrated that the variations of P‐wave attenuation are caused by the creation of new cracks and not by the enlargement of pre‐existing cracks.

Laboratory ultrasonic measurements: Shear transducers for compressional waves

2019 ◽  
Vol 38 (5) ◽  
pp. 392-399 ◽  
Author(s):  
Alexey Yurikov ◽  
Nazanin Nourifard ◽  
Marina Pervukhina ◽  
Maxim Lebedev
Keyword(s):  
Elastic Properties ◽  
Elastic Waves ◽  
High Energy ◽  
P Wave ◽  
P Waves ◽  
S Waves ◽  
Wave Velocities ◽  
Dipole Structure ◽  
Ultrasonic Measurements ◽  
P Wave Velocities

The ultrasonic measurements technique is well established to measure the elastic properties of rocks in the laboratory for seismic and well-log data interpretation. The key components of every laboratory ultrasonic setup are piezoelectric transducers, which generate and register elastic waves in rock samples. The elastic properties of rocks are determined through the velocities of elastic waves, which are measured by the times of the waves' travel from the source to the receiver transducer. Transducers can be specifically designed to generate P-waves (P-transducers) or S-waves (S-transducers). In limited studies, the measurement of P-wave velocities with S-transducers is mentioned. Such measurement is possible due to specific aspects of the operation of S-transducers. Namely, S-transducers are known to emit parasitic low-energy P-waves, which travel faster than high-energy S-waves and hence can be registered. However, no justification or elaboration of this method of measuring P-wave velocities was reported. To fill this gap, we first compare P-wave velocities measured with S-transducers against P-wave velocities measured with P-transducers in different rocks and materials. We show that the discrepancy between velocities measured with the two methods in homogeneous materials is less than 1% and can be up to 4% for natural rocks. Second, we numerically simulate the operation of S-transducers, show that parasitic P-waves have a dipole structure, and explain how the receiver transducer can register this compressional dipole. Finally, we use laser doppler interferometry to measure the displacement of the free surface of a sample caused by elastic waves emitted by the source S-transducer. We observed the dipole structure of the sample's surface displacement upon P-wave arrival on the surface.

ANALYSIS OF ACOUSTIC PROPERTIES OF RESERVOIR ROCKS FROM RUNOVSCHYNSKA FIELD ON THE BASIS OF PETROPHYSICAL STUDIES IN VARIOUS PRESSURE CONDITIONS

2019 ◽  
pp. 21-26
Author(s):  
I. Bezrodna ◽  
S. Vyzhva
Keyword(s):  
Wave Velocity ◽  
Acoustic Properties ◽  
P Wave ◽  
Variable Pressure ◽  
Atmospheric Conditions ◽  
Void Space ◽  
Correlation Dependence ◽  
P Waves ◽  
Wave Velocities ◽  
P Wave Velocities

The results of rock physics study of 68 core samples from well No. 110 of the Runovshchynska field of the Dnipro-Donets depression in Ukraine are presented. Investigation of the P-waves on samples under different pressure conditions with the use of 'Kern-4' and high pressure VSC-1000 was performed. Analysis of the obtained data and calculated reservoir values of P-waves was performed. The character of the change in velocity of P- and S-waves for atmospheric conditions is considered. It is shown that the predominant amount of water saturated samples has a velocity of P-waves 3200–3500 m/s (dry samples 2100–2550 m/s), and the S-wave velocity for saturated samples is 2100–2550 m/s (dry specimens 1400–1500 m/s). For a collection of samples, which were measured in atmospheric conditions, the correlation dependence between velocities of P-waves and their density with a close correlation was established. Correlation dependences between elastic wave velocities and the connected porosity of saturated samples were investigated. The dependences of type Vð = f (Kð) with high correlation coefficient for three separate picks of the homotypic sandstones were established. During the analysis of the acoustic studies results under conditions of variable pressure for the majority of samples from the studied intervals, the authors obtained the following common factors. The values of the P-wave velocity, measured in atmospheric conditions, are always smaller than the values obtained after the removal of the pressure; however, there are sometimes quite noticeable fluctuations in their difference, which can be explained by a sharp (possibly hopping) closure of microcracks in the rock with increasing pressure and their delayed opening or non-disclosure when it is reduced. The most contrasting changes in the behavior of the P-wave velocities are haracteristic for several samples (Nos. 27, 48, 50, 53/1), which is most likely due to the void space structure in the rocks, possibly with an increased number of microcracks compared with other samples. On the basis of a priori data and the results of researches of samples at variable pressures, the authors calculated the P-wave velocities in reservoir conditions, conducted their comparative analysis with velocities that are characteristic for samples in atmospheric conditions, built a tight (R² = 0,85) correlation dependence of the investigated parameters.

scholarly journals Verification of the seismic P-wave velocities under Moho boundary: Central Poland case study, LUMP profile

2018 ◽  
Vol 67 (1) ◽  
pp. 41-57
Author(s):  
Monika Dec ◽  
Marcin Polkowski ◽  
Tomasz Janik ◽  
Krystyna Stec ◽  
Marek Grad
Keyword(s):  
P Wave ◽  
Wave Velocities ◽  
Central Poland ◽  
Moho Boundary ◽  
P Wave Velocities

Permeability and volume changes in till due to cyclic freeze/thaw

1998 ◽  
Vol 35 (3) ◽  
pp. 471-477 ◽  
Author(s):  
Peter Viklander
Keyword(s):  
Soil Structure ◽  
Void Ratio ◽  
Vertical Direction ◽  
Rigid Wall ◽  
Freezing And Thawing ◽  
Volume Changes ◽  
Freeze Thaw ◽  
Fine Grained ◽  
Loose Soil ◽  
Freezing And Thawing Cycles

A fine-grained nonplastic till was compacted in the laboratory in three types of rigid wall permeameters, having a volume of 0.4, 1.5, and 25 dm3, respectively, and, was thereafter exposed to a maximum of 18 freezing and thawing cycles. The permeabilities in the vertical direction of saturated samples were measured in unfrozen soil as well as in thawed soil. The results show that the permeabilities changed after freezing and thawing. The magnitude of the changes in this study were in the range 0.02-10 times after freeze/thaw compared with the unfrozen soil. Soil exhibited volume changes subsequent to freeze/thaw. The volume typically decreased for an initially loose soil and increased for a dense soil. Independent of whether the initial soil structure was loose or dense, a constant "residual" void ratio, eres, was obtained after 1-3 cycles. For the soil investigated, the residual void ratio ranged from 0.31 to 0.40.Key words: till, fine-grained, non plastic, permeability, freeze/thaw, residual void ratio.

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